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Sample records for pulsatile flow

  1. Pulsatile prosthetic valve flows.

    PubMed

    Phillips, W M; Snyder, A; Alchas, P; Rosenberg, G; Pierce, W S

    1980-01-01

    The laser Doppler system has been established as a useful tool for eliciting the properties of simulated cardiovascular flows, and thus for comparative studies of flow properties of prosthetic valves. Significant differences among valve types and between models of one type have been documented. The complex variations of velocity profiles with time show that comparisons must be made for unsteady pulsatile rather than steady flow, despite the volume and complexity of the data required. Future studies will include methods of compacting the data presentation and improving the details of the experimental stimulation.

  2. Transition in Pulsatile Pipe Flow

    NASA Astrophysics Data System (ADS)

    Vlachos, Pavlos; Brindise, Melissa

    2016-11-01

    Transition has been observed to occur in the aorta, and stenotic vessels, where pulsatile flow exists. However, few studies have investigated the characteristics and effects of transition in oscillating or pulsatile flow and none have utilized a physiological waveform. In this work, we explore transition in pipe flow using three pulsatile waveforms which all maintain the same mean and maximum flow rates and range to zero flow, as is physiologically typical. Velocity fields were obtained using planar particle image velocimetry for each pulsatile waveform at six mean Reynolds numbers ranging between 500 and 4000. Turbulent statistics including turbulent kinetic energy (TKE) and Reynolds stresses were computed. Quadrant analysis was used to identify characteristics of the production and dissipation of turbulence. Coherent structures were identified using the λci method. We developed a wavelet-Hilbert time-frequency analysis method to identify high frequency structures and compared these to the coherent structures. The results of this study demonstrate that the different pulsatile waveforms induce different levels of TKE and high frequency structures, suggesting that the rates of acceleration and deceleration influence the onset and development of transition.

  3. Surface obstacles in pulsatile flow

    NASA Astrophysics Data System (ADS)

    Carr, Ian A.; Plesniak, Michael W.

    2016-11-01

    Flows past obstacles mounted on flat surfaces have been widely studied due to their ubiquity in nature and engineering. For nearly all of these studies, the freestream flow over the obstacle was steady, i.e. constant velocity unidirectional flow. Unsteady, pulsatile flows occur frequently in biology, geophysics, biomedical engineering, etc. Our study is aimed at extending the comprehensive knowledge base that exists for steady flows to considerably more complex pulsatile flows. Beyond the important practical applications, characterizing the vortex and wake dynamics of flows around surface obstacles embedded in pulsatile flows can provide insights into the underlying physics in all wake and junction flows. In this study, we experimentally investigated the wake of four canonical surface obstacles: hemisphere, cube, and circular cylinders with aspect ratio of 1:1 and 2:1. Phase-averaged PIV and hot-wire anemometry are used to characterize the dynamics of coherent structures in the wake and at the windward junction of the obstacles. Complex physics occur during the deceleration phase of the pulsatile inflow. We propose a framework for understanding these physics based on self-induced vortex propagation, similar to the phenomena exhibited by vortex rings. This material is based in part upon work supported by the National Science Foundation under Grant Number CBET-1236351, and GW Centeor Biomimetics and Bioinspired Engineering (COBRE).

  4. 21 CFR 870.4320 - Cardiopulmonary bypass pulsatile flow generator.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Cardiopulmonary bypass pulsatile flow generator... Cardiopulmonary bypass pulsatile flow generator. (a) Identification. A cardiopulmonary bypass pulsatile flow generator is an electrically and pneumatically operated device used to create pulsatile blood flow. The...

  5. 21 CFR 870.4320 - Cardiopulmonary bypass pulsatile flow generator.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Cardiopulmonary bypass pulsatile flow generator... Cardiopulmonary bypass pulsatile flow generator. (a) Identification. A cardiopulmonary bypass pulsatile flow generator is an electrically and pneumatically operated device used to create pulsatile blood flow. The...

  6. 21 CFR 870.4320 - Cardiopulmonary bypass pulsatile flow generator.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Cardiopulmonary bypass pulsatile flow generator... Cardiopulmonary bypass pulsatile flow generator. (a) Identification. A cardiopulmonary bypass pulsatile flow generator is an electrically and pneumatically operated device used to create pulsatile blood flow. The...

  7. 21 CFR 870.4320 - Cardiopulmonary bypass pulsatile flow generator.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Cardiopulmonary bypass pulsatile flow generator... Cardiopulmonary bypass pulsatile flow generator. (a) Identification. A cardiopulmonary bypass pulsatile flow generator is an electrically and pneumatically operated device used to create pulsatile blood flow. The...

  8. 21 CFR 870.4320 - Cardiopulmonary bypass pulsatile flow generator.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Cardiopulmonary bypass pulsatile flow generator... Cardiopulmonary bypass pulsatile flow generator. (a) Identification. A cardiopulmonary bypass pulsatile flow generator is an electrically and pneumatically operated device used to create pulsatile blood flow. The...

  9. Pulsatile Flow Studies in Atherosclerotic Carotid Bifurcations

    NASA Astrophysics Data System (ADS)

    Bale-Glickman, Jocelyn; Selby, Kathy; Saloner, David; Savas, Omer

    2001-11-01

    Particle image velocimetry and flow visualization techniques are used to study flows in models of atherosclerotic carotid bifurcations. The flow models exactly replicate the interior geometry of plaque excised from patients. The input flows are physiological wave forms derived from Doppler Ultrasound scans done on patients before surgery. The systolic and diastolic Reynolds numbers are 300 and 900. The complex internal geometry of the diseased artery combined with the pulsatile input flow results in exceedingly complex flow patterns. These flow patterns include internal jets, three-dimensional shear layers, stagnation lines, and multiple recirculation and separation regions. The physiological input flows are compared to flows when the wave form is sinusoidal.

  10. Study on the effect of steady, simple pulsatile and physiological pulsatile flows through a stenosed artery

    NASA Astrophysics Data System (ADS)

    Goswami, P.; Mandal, D. K.; Manna, N. K.; Chakrabarti, S.

    2014-10-01

    In the present paper, the comparison of steady, simple pulsatile flow and physiological pulsatile flow on flow reversal zone and hemodynamic wall parameters [wall shear stress (WSS) and oscillatory shear index (OSI)] for the progression of the disease, atherosclerosis has been investigated numerically. The governing equations have been solved by finite volume method. For the numerical analysis, Womersley number, Reynolds number and percentage of restriction are taken as 10, 100 and 50 % respectively. From this study it is revealed that the separated flow from the stenosis strongly depends on inlet flow situations, the maximum chance of deposition of plaque material due to streamline contour is higher at time step t* = 0.75 for simple pulsatile flow and at time step t* = 0 for physiological pulsatile flow and this chance is lower in case of steady flow. The effect of WSS on the disease is higher in physiological pulsatile flow compared to steady as well as simple pulsatile flow. The maximum possibility of initiation as well as progression for atherosclerosis in arterial wall due to high WSS takes place at t* = 0.25 for physiological pulsatile flow. OSI indicates same length of separation for two cases of transient flow, but the rate of cyclic departure of WSS is higher in case of physiological pulsatile flow.

  11. Pulsatile Flow Studies in Atherosclerotic Carotid Bifurcation

    NASA Astrophysics Data System (ADS)

    Bale-Glickman, Jocelyn; Selby, Kathy; Saloner, David; Savas, Omer

    2002-11-01

    Particle image velocimetry and flow visualization techniques are used to study flow in models of atherosclerotic carotid bifurcations. The models exactly replicate the interior geometry of plaque excised from patients. The input flow is a physiological waveform derived from Doppler Ultrasound scans done on the patients before surgery. The systolic and diastolic Reynolds numbers are 200 and 900 respectively. The complex internal geometry of the diseased artery combined with the pulsatile input flows give exceedingly complex flow patterns. These flow patterns include internal jets, three-dimensional shear layers, stagnation lines, and multiple recirculation and separation regions. Ensemble averaged and instantaneous flow fields are compared. Wall shear stresses at the stenoses are estimated to be on the order of 10 PA. The physiological input flows are also compared to flows when the waveform is sinusoidal.

  12. How to produce a pulsatile flow with low haemolysis?

    PubMed

    Qian, K X; Zeng, P; Ru, W M; Yuan, H Y; Feng, Z G; Li, I

    2000-01-01

    It is evident that a pulsatile flow is important for blood circulation because the flow pulsatility can reduce the resistance of peripheral vessels. It is difficult, however, to produce a pulsatile flow with an impeller pump, since blood damage will occur when a pulsatile flow is produced. Further investigation has revealed that the main factor for blood damage is turbulence shear, which tears the membranes of red blood cells, resulting in free release of haemoglobin into the plasma, and consequently leads to haemolysis. Therefore, the question for developing a pulsatile impeller blood pump is: how to produce a pulsatile flow with low haemolysis? The authors have successively developed a pulsatile axial pump and a pulsatile centrifugal pump. In the pulsatile axial pump, the impeller reciprocates axially and rotates simultaneously. The reciprocation is driven by a pneumatic device and the rotation by a dc motor. For a pressure of 40 mm Hg pulsatility, about 50 mm axial reciprocating amplitude of the impeller is desirable. In order to reduce the axial amplitude, the pump inlet and the impeller both have cone-shaped heads, and the gap between the impeller and the inlet pipe changes by only 2 mm, that is the impeller reciprocates up to 2 mm and a pressure pulsatility of 40 mm Hg can be produced. As the impeller rotates with a constant speed, low turbulence in the pump may be expected. In the centrifugal pulsatile pump, the impeller changes its rotating speed periodically; the turbulence is reduced by designing an impeller with twisted vanes which enable the blood flow to change its direction rather than its magnitude during the periodic change of the rotating speed. In this way, a pulsatile flow is produced and the turbulence is minimized. Compared to the axial pulsatile pump, the centrifugal pulsatile pump needs only one driver and thus has more application possibilities. The centrifugal pulsatile pump has been used in animal experiments. The pump assisted the

  13. Pulsatile flow in ventricular catheters for hydrocephalus

    NASA Astrophysics Data System (ADS)

    Giménez, Á.; Galarza, M.; Thomale, U.; Schuhmann, M. U.; Valero, J.; Amigó, J. M.

    2017-05-01

    The obstruction of ventricular catheters (VCs) is a major problem in the standard treatment of hydrocephalus, the flow pattern of the cerebrospinal fluid (CSF) being one important factor thereof. As a first approach to this problem, some of the authors studied previously the CSF flow through VCs under time-independent boundary conditions by means of computational fluid dynamics in three-dimensional models. This allowed us to derive a few basic principles which led to designs with improved flow patterns regarding the obstruction problem. However, the flow of the CSF has actually a pulsatile nature because of the heart beating and blood flow. To address this fact, here we extend our previous computational study to models with oscillatory boundary conditions. The new results will be compared with the results for constant flows and discussed. It turns out that the corrections due to the pulsatility of the CSF are quantitatively small, which reinforces our previous findings and conclusions. This article is part of the themed issue `Mathematical methods in medicine: neuroscience, cardiology and pathology'.

  14. Pulsatile flow past an oscillating cylinder

    NASA Astrophysics Data System (ADS)

    Qamar, Adnan; Seda, Robinson; Bull, Joseph L.

    2011-04-01

    A fundamental study to characterize the flow around an oscillating cylinder in a pulsatile flow environment is investigated. This work is motivated by a new proposed design of the total artificial lung (TAL), which is envisioned to provide better gas exchange. The Navier-Stokes computations in a moving frame of reference were performed to compute the dynamic flow field surrounding the cylinder. Cylinder oscillations and pulsatile free-stream velocity were represented by two sinusoidal waves with amplitudes A and B and frequencies ωc and ω, respectively. The Keulegan-Carpenter number (Kc=Uo/Dωc) was used to describe the frequency of the oscillating cylinder while the pulsatile free-stream velocity was fixed by imposing ω /Kc=1 for all cases investigated. The parameters of interest and their values were amplitude (0.5D

  15. Pulsatile flow past an oscillating cylinder

    PubMed Central

    Qamar, Adnan; Seda, Robinson; Bull, Joseph L.

    2011-01-01

    A fundamental study to characterize the flow around an oscillating cylinder in a pulsatile flow environment is investigated. This work is motivated by a new proposed design of the total artificial lung (TAL), which is envisioned to provide better gas exchange. The Navier–Stokes computations in a moving frame of reference were performed to compute the dynamic flow field surrounding the cylinder. Cylinder oscillations and pulsatile free-stream velocity were represented by two sinusoidal waves with amplitudes A and B and frequencies ωc and ω, respectively. The Keulegan–Carpenter number (Kc=Uo∕Dωc) was used to describe the frequency of the oscillating cylinder while the pulsatile free-stream velocity was fixed by imposing ω∕Kc=1 for all cases investigated. The parameters of interest and their values were amplitude (0.5D

  16. Pulsatile flow past a single oscillating cylinder

    NASA Astrophysics Data System (ADS)

    Seda, Robinson; Qamar, Adnan; Bull, Joseph

    2010-11-01

    The potential for oscillating fibers to modify flow within a new artificial lung design is first examined in the present fundamental fluid mechanics study of flow past a single oscillating cylinder. This new design is intended to provide better gas exchange through vorticity enhancement by oscillating microfibers (cylinders) in a pulsatile flow environment. The Keulegan-Carpenter number (Kc=Uo/Dφc) was used to describe the frequency of the oscillating cylinder (φc) while the pulsatile free stream velocity was fixed by imposing φ/Kc=1 for all cases investigated. The parameters investigated in this study were amplitude of oscillation (0.5D

  17. Blood flow in abdominal aortic aneurysms: pulsatile flow hemodynamics.

    PubMed

    Finol, E A; Amon, C H

    2001-10-01

    Numerical predictions of blood flow patterns and hemodynamic stresses in Abdominal Aortic Aneurysms (AAAs) are performed in a two-aneurysm, axisymmetric, rigid wall model using the spectral element method. Physiologically realistic aortic blood flow is simulated under pulsatile conditions for the range of time-averaged Reynolds numbers 50< or =Re(m)< or =300, corresponding to a range of peak Reynolds numbers 262.5< or =Re(peak) < or = 1575. The vortex dynamics induced by pulsatile flow in AAAs is characterized by a sequence of five different flow phases in one period of the flow cycle. Hemodynamic disturbance is evaluated for a modified set of indicator functions, which include wall pressure (p(w)), wall shear stress (tau(w)), and Wall Shear Stress Gradient (WSSG). At peak flow, the highest shear stress and WSSG levels are obtained downstream of both aneurysms, in a pattern similar to that of steady flow. Maximum values of wall shear stresses and wall shear stress gradients obtained at peak flow are evaluated as a function of the time-average Reynolds number resulting in a fourth order polynomial correlation. A comparison between predictions for steady and pulsatile flow is presented, illustrating the importance of considering time-dependent flow for the evaluation of hemodynamic indicators.

  18. Effects of the pulsatile flow settings on pulsatile waveforms and hemodynamic energy in a PediVAS centrifugal pump.

    PubMed

    Wang, Shigang; Rider, Alan R; Kunselman, Allen R; Richardson, J Scott; Dasse, Kurt A; Undar, Akif

    2009-01-01

    The objective of this study was to test different pulsatile flow settings of the PediVAS centrifugal pump to seek an optimum setting for pulsatile flow to achieve better pulsatile energy and minimal backflow. The PediVAS centrifugal pump and the conventional pediatric clinical circuit, including a pediatric membrane oxygenator, arterial filter, arterial cannula, and 1/4 in circuit tubing were used. The circuit was primed with 40% glycerin water mixture. Postcannula pressure was maintained at 40 mm Hg by a Hoffman clamp. The experiment was conducted at 800 ml/min of pump flow with a modified pulsatile flow setting at room temperature. Pump flow and pressure readings at preoxygenator and precannula sites were simultaneously recorded by a data acquisition system. The results showed that backflows appeared at flow rates of 200-800 ml/min (200 ml/min increments) with the default pulsatile flow setting and only at 200 ml/min with the modified pulsatile flow setting. With an increased rotational speed difference ratio and a decreased pulsatile width, the pulsatility increased in terms of surplus hemodynamic energy and total hemodynamic energy at preoxygenator and precannula sites. Backflows seemed at preoxygenator and precannula sites at a 70% of rotational speed difference ratio. The modified pulsatile flow setting was better than the default pulsatile flow setting in respect to pulsatile energy and backflow. The pulsatile width and the rotational speed difference ratio significantly affected pulsatility. The parameter of the rotational speed difference ratio can automatically increase pulsatility with increased rotational speeds. Further studies will be conducted to optimize the pulsatile flow setting of the centrifugal pump.

  19. Improved cerebral oxygen saturation and blood flow pulsatility with pulsatile perfusion during pediatric cardiopulmonary bypass.

    PubMed

    Su, Xiaowei W; Guan, Yulong; Barnes, Mollie; Clark, J Brian; Myers, John L; Undar, Akif

    2011-08-01

    Brain monitoring techniques near-infrared spectroscopy (NIRS) and transcranial Doppler (TCD) ultrasound were used in pediatric patients undergoing cardiopulmonary bypass for congenital heart defect (CHD) repair to analyze the effect of pulsatile or nonpulsatile flow on brain protection. Regional cerebral oxygen saturation (rSO2) and cerebrovascular pulsatility index (PI) were measured by NIRS and TCD, respectively, in 111 pediatric patients undergoing bypass for CHD repair randomized to pulsatile (n = 77) or nonpulsatile (n = 34) perfusion. No significant differences in demographic and intraoperative data, including surgical risk stratification, existed between groups. Patients undergoing pulsatile perfusion had numerically lower decreases in rSO2 from baseline for all time points analyzed compared with the nonpulsatile group, with significant ∼12% lower decreases at 40 and 60 min after crossclamp. Patients undergoing pulsatile perfusion had numerically lower decreases in PI from baseline for the majority of time points compared with the nonpulsatile group, with significant ∼30% lower decreases between 5 and 40 min after crossclamp. Pulsatile flow has advantages over nonpulsatile flow as measured by NIRS and TCD, especially at advanced time points, which may improve postoperative neurodevelopmental outcomes.

  20. A turbulence model for pulsatile arterial flows.

    PubMed

    Younis, B A; Berger, S A

    2004-10-01

    Difficulties in predicting the behavior of some high Reynolds number flows in the circulatory system stem in part from the severe requirements placed on the turbulence model chosen to close the time-averaged equations of fluid motion. In particular, the successful turbulence model is required to (a) correctly capture the "nonequilibrium" effects wrought by the interactions of the organized mean-flow unsteadiness with the random turbulence, (b) correctly reproduce the effects of the laminar-turbulent transitional behavior that occurs at various phases of the cardiac cycle, and (c) yield good predictions of the near-wall flow behavior in conditions where the universal logarithmic law of the wall is known to be not valid. These requirements are not immediately met by standard models of turbulence that have been developed largely with reference to data from steady, fully turbulent flows in approximate local equilibrium. The purpose of this paper is to report on the development of a turbulence model suited for use in arterial flows. The model is of the two-equation eddy-viscosity variety with dependent variables that are zero-valued at a solid wall and vary linearly with distance from it. The effects of transition are introduced by coupling this model to the local value of the intermittency and obtaining the latter from the solution of a modeled transport equation. Comparisons with measurements obtained in oscillatory transitional flows in circular tubes show that the model produces substantial improvements over existing closures. Further pulsatile-flow predictions, driven by a mean-flow wave form obtained in a diseased human carotid artery, indicate that the intermittency-modified model yields much reduced levels of wall shear stress compared to the original, unmodified model. This result, which is attributed to the rapid growth in the thickness of the viscous sublayer arising from the severe acceleration of systole, argues in favor of the use of the model for the

  1. A Novel Rotary Pulsatile Flow Pump for Cardiopulmonary Bypass

    PubMed Central

    Teman, Nicholas R.; Mazur, Daniel E.; Toomasian, John; Jahangir, Emilia; Alghanem, Fares; Goudie, Marcus; Rojas-Peña, Alvaro; Haft, Jonathan W.

    2014-01-01

    It has been suggested that pulsatile blood flow is superior to continuous flow in cardiopulmonary bypass (CPB). However, adoption of pulsatile flow (PF) technology has been limited due to practically and complexity of creating a consistent physiologic pulse. A pediatric pulsatile rotary ventricular pump (PRVP) was designed to address this problem. We evaluated the PRVP in an animal model, and determined its ability to generate PF during CPB. The PRVP (modified peristaltic pump, with tapering of the outlet of the pump chamber) was tested in 4 piglets (10-12kg). Cannulation was performed with right atrial and aortic cannulae, and pressure sensors were inserted into the femoral arteries. Pressure curves were obtained at different levels of flow and compared with both the animal's baseline physiologic function and a continuous flow (CF) roller pump. Pressure and flow waveforms demonstrated significant pulsatility in the PRVP setup compared to CF at all tested conditions. Measurement of hemodynamic energy data, including the percent pulsatile energy and the surplus hydraulic energy, also revealed a significant increase in pulsatility with the PRVP (p <0.001). PRVP creates physiologically significant PF, similar to the pulsatility of a native heart, and has the potential to be easily implemented in pediatric CPB. PMID:24625536

  2. Pulsatile blood flow in Abdominal Aortic Aneurysms

    NASA Astrophysics Data System (ADS)

    Salsac, Anne-Virginie; Lasheras, Juan C.; Singel, Soeren; Varga, Chris

    2001-11-01

    We discuss the results of combined in-vitro laboratory measurements and clinical observations aimed at determining the effect that the unsteady wall shear stresses and the pressure may have on the growth and eventual rupturing of an Abdominal Aortic Aneurysm (AAA), a permanent bulging-like dilatation occurring near the aortic bifurcation. In recent years, new non-invasive techniques, such as stenting, have been used to treat these AAAs. However, the development of these implants, aimed at stopping the growth of the aneurysm, has been hampered by the lack of understanding of the effect that the hemodynamic forces have on the growth mechanism. Since current in-vivo measuring techniques lack the precision and the necessary resolution, we have performed measurements of the pressure and shear stresses in laboratory models. The models of the AAA were obtained from high resolution three-dimensional CAT/SCANS performed in patients at early stages of the disease. Preliminary DPIV measurements show that the pulsatile blood flow discharging into the cavity of the aneurysm leads to large spikes of pressure and wall shear stresses near and around its distal end, indicating a possible correlation between the regions of high wall shear stresses and the observed location of the growth of the aneurysm.

  3. Pulsatile Ocular Blood Flow in Healthy Koreans

    PubMed Central

    Kim, Seung Kab; Cho, Byung Joo; Hong, Samin; Kang, Sung Yong; Kim, Jae Sung; Kim, Chan Yun

    2008-01-01

    Purpose To determine the normal reference range of pulsatile ocular blood flow (POBF) values in healthy Korean subjects and to find out the factors that may affect them. Methods A total of 280 eyes of 280 normal subjects were included in this study. Best corrected visual acuity (BCVA), intraocular pressure (IOP), axial length, POBF, systemic blood pressure, and pulse rate were measured. The mean, standard deviation, range, and the 5th and 95th percentiles of POBF were calculated, and the influences of various parameters to POBF were determined by multiple regression analyses. Results The mean POBF value was 766.0±221.6 µl/min in men and 1021.1±249.5 µl/min in women. The 5th and 95th percentiles for POBF values were 486.0 µl/min and 1140.0 µl/min in men and 672.0 µl/min and 1458.0 µl/min in women. The POBF values were significantly influenced by gender, mean blood pressure, pulse rate, and axial length. Conclusions Even though the POBF values were influenced by gender, BP, and axial length, we could define the normal reference range of POBF in healthy Koreans. PMID:18323699

  4. Brain damage in dogs immediately following pulsatile and non-pulsatile blood flows in extracorporeal circulation

    PubMed Central

    Sanderson, J. M.; Wright, G.; Sims, F. W.

    1972-01-01

    The brains of dogs subjected to total cardiac bypass were examined for early signs of ischaemic nerve cell changes. Diffuse nerve cell changes were found immediately following two- and three-hour non-pulsatile perfusions but not following pulsatile perfusions of the same durations. The nerve cell changes found in the brains were acute cell swelling and early ischaemic cell change. Acute cell swelling was found only in the cerebellar Purkinje cells. Ischaemic cell change was found in several regions of the brain but the cerebral cortex and cerebellar Purkinje cells were most frequently affected. Diffuse nerve cell changes are attributed to non-pulsatile blood flow but some complicating factors are recognized. Focal lesions found in three brains may have been due to embolism by blood cell aggregates and/or gas microbubbles. Images PMID:5039442

  5. Flush-mounted hot film anemometer accuracy in pulsatile flow.

    PubMed

    Nandy, S; Tarbell, J M

    1986-08-01

    The accuracy of a flush-mounted hot film anemometer probe for wall shear stress measurements in physiological pulsatile flows was evaluated in fully developed pulsatile flow in a rigid straight tube. Measured wall shear stress waveform based on steady flow anemometer probe calibrations were compared to theoretical wall shear stress waveforms based on well-established theory and measured flow rate waveforms. The measured and theoretical waveforms were in close agreement during systole (average deviation of 14 percent at peak systole). As expected, agreement was poor during diastole because of flow reversal and diminished frequency response at low shear rate.

  6. Entrainment and thrust augmentation in pulsatile ejector flows

    NASA Technical Reports Server (NTRS)

    Sarohia, V.; Bernal, L.; Bui, T.

    1981-01-01

    This study comprised direct thrust measurements, flow visualization by use of a spark shadowgraph technique, and mean and fluctuating velocity measurements with a pitot tube and linearized constant temperature hot-wire anemometry respectively. A gain in thrust of as much as 10 to 15% was observed for the pulsatile ejector flow as compared to the steady flow configuration. From the velocity profile measurements, it is concluded that this enhanced augmentation for pulsatile flow as compared to a nonpulsatile one was accomplished by a corresponding increased entrainment by the primary jet flow. It is also concluded that the augmentation and total entrainment by a constant area ejector critically depends upon the inlet geometry of the ejector. Experiments were performed to evaluate the influence of primary jet to ejector area ratio, ejector length, and presence of a diffuser on pulsatile ejector performance.

  7. Effects of non-pulsatile flow on thrombogenesis

    NASA Astrophysics Data System (ADS)

    Metcalfe, Ralph; Harting, Matthew; Delgado, Reynolds; Frazier, O. Howard

    2002-11-01

    Congestive heart failure afflicts 4.5 million people in the US alone, with an average 5-year mortality of more than 50%. Among the most promising treatments for this condition are VADs (ventricular assist devices). While conventional pulsatile flow VADs are large and introduce some significant complications such as thrombosis, non-pulsatile axial flow VADs have potentially significant advantages in being smaller, with smaller thrombogenic surfaces. However, the long term effects of non-pulsatile flow on the vascular system are not well understood. We have investigated the effects of pulsatility of blood flow in the stenotic human carotid artery using unsteady, three-dimensional computational fluid dynamic simulations. We have found that permanent, low shear stagnation zones can develop distal to stenoses with non-pulsatile flow, potentially leading to thrombus formation. In contrast, systolic peak flow tends to flush out such stagnation zones. These results are consistent with observed thrombus formation in two patients who underwent implantation of a Jarvik 2000 LVAD.

  8. Numerical simulation of pulsatile flow in rough pipes

    NASA Astrophysics Data System (ADS)

    Chin, Cheng; Monty, Jason; Ooi, Andrew; Illingworth, Simon; Marusic, Ivan; Skvortsov, Alex

    2016-11-01

    Direct numerical simulation (DNS) of pulsatile turbulent pipe flow is carried out over three-dimensional sinusoidal surfaces mimicking surface roughness. The simulations are performed at a mean Reynolds number of Reτ 540 (based on friction velocity, uτ, and pipe radii, δ) and at various roughness profiles following the study of Chan et al., where the size of the roughness (roughness semi-amplitude height h+ and wavelength λ+) is increased geometrically while maintaining the height-to-wavelength ratio of the sinusoidal roughness element. Results from the pulsatile simulations are compared with non-pulsatile simulations to investigate the effects of pulsation on the Hama roughness function, ΔU+ . Other turbulence statistics including mean turbulence intensities, Reynolds stresses and energy spectra are analysed. In addition, instantaneous phase (eg. at maximum and minimum flow velocities) and phase-averaged flow structures are presented and discussed.

  9. Microbubble transport through a bifurcating vessel network with pulsatile flow.

    PubMed

    Valassis, Doug T; Dodde, Robert E; Esphuniyani, Brijesh; Fowlkes, J Brian; Bull, Joseph L

    2012-02-01

    Motivated by two-phase microfluidics and by the clinical applications of air embolism and a developmental gas embolotherapy technique, experimental and theoretical models of microbubble transport in pulsatile flow are presented. The one-dimensional time-dependent theoretical model is developed from an unsteady Bernoulli equation that has been modified to include viscous and unsteady effects. Results of both experiments and theory show that roll angle (the angle the plane of the bifurcating network makes with the horizontal) is an important contributor to bubble splitting ratio at each bifurcation within the bifurcating network. When compared to corresponding constant flow, pulsatile flow was shown to produce insignificant changes to the overall splitting ratio of the bubble despite the order one Womersley numbers, suggesting that bubble splitting through the vasculature could be modeled adequately with a more modest constant flow model. However, bubble lodging was affected by the flow pulsatility, and the effects of pulsatile flow were evident in the dependence of splitting ratio of bubble length. The ability of bubbles to remain lodged after reaching a steady state in the bifurcations is promising for the effectiveness of gas embolotherapy to occlude blood flow to tumors, and indicates the importance of understanding where lodging will occur in air embolism. The ability to accurately predict the bubble dynamics in unsteady flow within a bifurcating network is demonstrated and suggests the potential for bubbles in microfluidics devices to encode information in both steady and unsteady aspects of their dynamics.

  10. Noninvasive pulsatile flow estimation for an implantable rotary blood pump.

    PubMed

    Karantonis, Dean M; Cloherty, Shaun L; Mason, David G; Ayre, Peter J; Lovell, Nigel H

    2007-01-01

    A noninvasive approach to the task of pulsatile flow estimation in an implantable rotary blood pump (iRBP) has been proposed. Employing six fluid solutions representing a range of viscosities equivalent to 20-50% blood hematocrit (HCT), pulsatile flow data was acquired from an in vitro mock circulatory loop. The entire operating range of the pump was examined, including flows from -2 to 12 L/min. Taking the pump feedback signals of speed and power, together with the HCT level, as input parameters, several flow estimate models were developed via system identification methods. Three autoregressive with exogenous input (ARX) model structures were evaluated: structures I and II used the input parameters directly; structure II incorporated additional terms for HCT; and the third structure employed as input a non-pulsatile flow estimate equation. Optimal model orders were determined, and the associated models yielded minimum mean flow errors of 5.49% and 0.258 L/min for structure II, and 5.77% and 0.270 L/min for structure III, when validated on unseen data. The models developed in this study present a practical method of accurately estimating iRBP flow in a pulsatile environment.

  11. A pulsatile developing flow in a bend

    NASA Astrophysics Data System (ADS)

    Thiriet, M.; Graham, J. M. R.; Issa, R. I.

    1992-06-01

    Low frequency pulsatile flow of an incompressible viscous fluid has been numerically investigated in a rigid 90° bend of circular cross-section, using the finite-volume method. The governing parameters are as follows : amplitude ratio of 1.25, Womersley parameter of 4, peak Reynolds number of 358, peak Dean number of 113, Strouhal number ranging from 0.05 to 0.45. With this set of input data, no flow reversal is observed and a single axial vortex occurs in the half cross-section. Upstream and downstream effects of the bend are mainly characterized by an inward shift of the peak axial velocity in the upstream straight tube and the persistency of the secondary motions several diameters down the exit straight pipe. Secondary motions, present in steady flow, weaken greatly when the unsteady axial component of the flow (W) is lower than the mean flow bar{W}. The axial shear stress tau_a, whose maximum is more often located at the outer part of the bend, increases and remains nearly constant about 8 diameters downstream from the bend inlet. The circumferential shear stress tau_c maximum, located slightly towards the outer bend, is 28% of tau_a maximum, and 20% when W < bar{W}. The magnitude of both tau_a and tau_c increases during the accelerative phase. The low shear region is more often located near the inner tube wall. However, the existence of bends in a tube network might increase the deposit of solid particles, with respect to straight pipes, only when W (t)>W, and locally at the inner edge. Un écoulement pulsé à basse fréquence d'un fluide incompressible visqueux a été étudié numériquement dans un coude, à 90°, de parois rigides et de section droite circulaire et constante, par la méthode des volumes finis. Les valeurs des paramètres adimensionnels gouvernant l'écoulement sont: un rapport d'amplitude de 1,25, un paramètre de Womersley de 4, un nombre de Reynolds crête de 358, un nombre de Dean crête de 113; le nombre de Strouhal varie entre 0

  12. Direct measurement of mixing quality in a pulsatile flow micromixer

    NASA Astrophysics Data System (ADS)

    Truesdell, Richard A.; Bartsch, J. W.; Buranda, T.; Sklar, L. A.; Mammoli, A. A.

    2005-11-01

    Pulsatile action can be used to mix two streams entering a tube from two separate branches of a bifurcation at low Reynolds numbers. The pulsatile action is provided by two pinch valves, which deform flexible tubing immediately upstream of the connection. The pinch valve action is controlled using a master-slave pulse generator setup. The quality of mixing is evaluated directly by measuring the fluorescence that results from the chemical reaction of species transported in the two streams, one containing native biotin and the other, fluorescein biotin bound to streptavidin. The reaction kinetics are accounted for by normalization using fluorescence measurements on well mixed solutions at the same residence time. The results show that the pulsatile micromixer provides almost complete mixing. Furthermore, the present measurements match results obtained in a previous experiment where flow visualization and image analysis were used to measure mixing quality in a scaled-up model.

  13. The Use of Pulsatile Flow to Separate Species

    NASA Astrophysics Data System (ADS)

    Narayanan, R.; Thomas, Aaron M.

    2002-11-01

    The removal of carbon dioxide from air is important in producing a habitable environment for the self-supporting space stations of the space program. Pulsatile flow is a novel way to help in the partial separation of different species from air by using a purely mechanical method. The advantage of this is that no chemicals are needed. Pulsatile flow also has the advantage that it can handle large volumes. While it is not expected that this process will replace existing methods of separation, it can surely be used as a means to assist in the overall separation process, possibly as a precursor to conventional methods. This work specifically focuses on the physics of pulsatile flow and its effect on the mass transfer of species and the separation that can be achieved. From the theoretical model that predicts the mass transfer and separation of species, we provide a physical explanation of the phenomena predicted by the models. If two dilute species are present in a carrier, the mass transfer of the faster diffusing species may be higher, lower, or the same as the slow diffusing species. This depends on the time constants associated with the system and the ability of a species to remain in the fast moving portion of the flow field. The difference in the mass transfer of each species can lead to a separation that can be used in a number of processes including the removal of carbon dioxide from the air. This phenomenon is modeled in an open tube geometry and in the annular space between two concentric cylinders. Further, in annular pulsatile flow, the effect of the inner cylinder being off center from the outer cylinder on the mass transfer and separation is also analyzed. Experiments were also conducted to verify the validity of the models and the viability of pulsatile flows as a separations procedure.

  14. A new method of providing pulsatile flow in a centrifugal pump: assessment of pulsatility using a mock circulatory system.

    PubMed

    Herreros, Jesús; Berjano, Enrique J; Sales-Nebot, Laura; Más, Pedro; Calvo, Irene; Mastrobuoni, Stefano; Mercé, Salvador

    2008-06-01

    Previous studies have demonstrated the potential advantages of pulsatile flow as compared with continuous flow. However, to date, physiologic pumps have been technically complex and their application has therefore remained in the experimental field. We have developed a new type of centrifugal pump, which can provide pulsatile as well as continuous flow. The inner wall of a centrifugal pump is pulsed by means of a flexible membrane, which can be accurately controlled by means of either a hydraulic or pneumatic driver. The aim of this study was to assess the hydraulic behavior of the new pump in terms of surplus hemodynamic energy (SHE). We conducted experiments using a mock circulatory system including a membrane oxygenator. No differences were found in the pressure-flow characteristics between the new pump and a conventional centrifugal pump, suggesting that the inclusion of the flexible membrane does not alter hydraulic performance. The value of SHE rose when systolic volume was increased. However, SHE dropped when the percentage of ejection time was reduced and also when the continuous flow (programmed by the centrifugal console) increased. Mean flow matched well with the continuous flow set by the centrifugal console, that is, the pulsatile component of the flow was exclusively controlled by the pulsatile console, and was therefore independent of the continuous flow programmed by the centrifugal console. The pulsatility of the new pump was approximately 25% of that created with a truly pulsatile pump.

  15. Numerical modeling of pulsatile turbulent flow in stenotic vessels.

    PubMed

    Varghese, Sonu S; Frankel, Steven H

    2003-08-01

    Pulsatile turbulent flow in stenotic vessels has been numerically modeled using the Reynolds-averaged Navier-Stokes equation approach. The commercially available computational fluid dynamics code (CFD), FLUENT, has been used for these studies. Two different experiments were modeled involving pulsatile flow through axisymmetric stenoses. Four different turbulence models were employed to study their influence on the results. It was found that the low Reynolds number k-omega turbulence model was in much better agreement with previous experimental measurements than both the low and high Reynolds number versions of the RNG (renormalization-group theory) k-epsilon turbulence model and the standard k-epsilon model, with regard to predicting the mean flow distal to the stenosis including aspects of the vortex shedding process and the turbulent flow field. All models predicted a wall shear stress peak at the throat of the stenosis with minimum values observed distal to the stenosis where flow separation occurred.

  16. Large-Eddy simulation of pulsatile blood flow.

    PubMed

    Paul, Manosh C; Mamun Molla, Md; Roditi, Giles

    2009-01-01

    Large-Eddy simulation (LES) is performed to study pulsatile blood flow through a 3D model of arterial stenosis. The model is chosen as a simple channel with a biological type stenosis formed on the top wall. A sinusoidal non-additive type pulsation is assumed at the inlet of the model to generate time dependent oscillating flow in the channel and the Reynolds number of 1200, based on the channel height and the bulk velocity, is chosen in the simulations. We investigate in detail the transition-to-turbulent phenomena of the non-additive pulsatile blood flow downstream of the stenosis. Results show that the high level of flow recirculation associated with complex patterns of transient blood flow have a significant contribution to the generation of the turbulent fluctuations found in the post-stenosis region. The importance of using LES in modelling pulsatile blood flow is also assessed in the paper through the prediction of its sub-grid scale contributions. In addition, some important results of the flow physics are achieved from the simulations, these are presented in the paper in terms of blood flow velocity, pressure distribution, vortices, shear stress, turbulent fluctuations and energy spectra, along with their importance to the relevant medical pathophysiology.

  17. Visualization of pulsatile flow for magnetic nanoparticle based therapies

    NASA Astrophysics Data System (ADS)

    Wentzel, Andrew; Yecko, Philip

    2015-11-01

    Pulsatile flow of blood through branched, curved, stenosed, dilated or otherwise perturbed vessels is more complex than flow through a straight, uniform and rigid tube. In some magnetic hyperthermia and magnetic chemo-therapies, localized regions of magnetic nanoparticle laden fluid are deliberately formed in blood vessels and held in place by magnetic fields. The effect of localized magnetic fluid regions on blood flow and the effect of the pulsatile blood flow on such magnetic fluid regions are poorly understood and difficult to examine in vivo or by numerical simulation. We present a laboratory model that facilitates both dye tracer and particle imaging velocimetry (PIV) studies of pulsatile flow of water through semi-flexible tubes in the presence of localized magnetic fluid regions. Results on the visualization of flows over a range of Reynolds and Womersley numbers and for several different (water-based) ferrofluids are compared for straight and curved vessels and for different magnetic localization strategies. These results can guide the design of improved magnetic cancer therapies. Support from the William H. Sandholm Program of Cooper Union's Kanbar Center for Biomedical Engineering is gratefully acknowledged.

  18. Quantification of Pressure-Flow Waveforms and Selection of Components for the Pulsatile Extracorporeal Circuit

    PubMed Central

    Wang, Shigang; Haines, Nikkole; Ündar, Akif

    2009-01-01

    Abstract: The debate on pulsatile flow during cardiopulmonary bypass (CPB) has continued for more than half a century. This longstanding debate stems from imprecise quantification methods for arterial pressure and pump flow waveforms and the inability to determine which waveforms accurately depict pulsatile flow. The differences in in vitro and in vivo research outcomes for pulsatile and non-pulsatile flow experiments compounds these issues. The concepts of energy equivalent pressure (EEP) and surplus hemodynamic energy (SHE) have been introduced in studies using pulsatile and nonpulsatile flow. Their main advantage lies in their focus on energy gradients rather than pressure gradients as the driving force of blood flow. These formulas can precisely quantify different levels of pulsatility and non-pulsatility, allowing direct and meaningful comparisons. In clinical practice, before using pulsatile flow during CPB, all components of CPB circuits, including the roller pump, membrane oxygenator, arterial filter, aortic cannula, and circuit tubing, should be carefully selected to ensure maximal pulsatility. In addition, it is necessary to select appropriate patients and durations for pulsatile perfusion to obtain better clinical effects. We hope results from our previous experiments can be used as a source of reference when using pulsatile flow in pediatric cardiac surgery. PMID:19361036

  19. Pulsatility role in cylinder flow dynamics at low Reynolds number

    NASA Astrophysics Data System (ADS)

    Qamar, Adnan; Samtaney, Ravi; Bull, Joseph L.

    2012-08-01

    We present dynamics of pulsatile flow past a stationary cylinder characterized by three non-dimensional parameters: the Reynolds number (Re), non-dimensional amplitude (A) of the pulsatile flow velocity, and Keulegan-Carpenter number (KC = Uo/Dωc). This work is motivated by the development of total artificial lungs (TAL) device, which is envisioned to provide ambulatory support to patients. Results are presented for 0.2 ≤ A ≤ 0.6 and 0.57 ≤ KC ≤ 2 at Re = 5 and 10, which correspond to the operating range of TAL. Two distinct fluid regimes are identified. In both regimes, the size of the separated zone is much greater than the uniform flow case, the onset of separation is function of KC, and the separation vortex collapses rapidly during the last fraction of the pulsatile cycle. The vortex size is independent of KC, but with an exponential dependency on A. In regime I, the separation point remains attached to the cylinder surface. In regime II, the separation point migrates upstream of the cylinder. Two distinct vortex collapse mechanisms are observed. For A < 0.4 and all KC and Re values, collapse occurs on the cylinder surface, whereas for A > 0.4 the separation vortex detaches from the cylinder surface and collapses at a certain distance downstream of the cylinder. The average drag coefficient is found to be independent of A and KC, and depends only on Re. However, for A > 0.4, for a fraction of the pulsatile cycle, the instantaneous drag coefficient is negative indicating a thrust production.

  20. A Experimental Investigation of Pulsatile Flow Through Modelled Arterial Stenoses.

    NASA Astrophysics Data System (ADS)

    Ojha, Mathadyal

    The effects of pulsatile flow through constricted tubes were investigated using an existing computer controlled photochromic tracer method. The system was modified and the major improvements in the resolution of the method for the measurement of the instantaneous velocity profiles are described. In addition, a split-beam measurement method developed for the first time allows the velocity profiles at three different positions along a flow vessel to be measured simultaneously. This new feature facilitated the determination of the relative position of the reattachment point, it resulted in a more efficient data acquisition and it provided a detailed description of the instantaneous spatial relationship of the flow field. Intense studies were conducted using a 2.9 Hz sinusoidal flow with a frequency parameter of 7.5 and with mean and modulation Reynolds numbers of 575 and 350 respectively. For flow through mild occlusions, a 45% axisymmetric and a 38% asymmetric stenoses, the flow separation pattern displayed oscillation of both the separation boundary and the reattachment point with some non-periodic components. Additional flow patterns such as irregular radial distribution of the velocities and isolated areas of high shear rates were seen mostly during the deceleration phase and in the regions closer to the vessel wall. The effects of the 38% constriction were more severe when compared to the 45% constriction, thereby indicating the importance of considering asymmetry in the modelling of pulsatile flow through mild arterial stenoses. With more moderate occlusions, a 65% and a 75% axisymmetric stenoses, transition to turbulence through the formation and breakdown of streamwise vortices was seen just before peak flow. During this turbulent phase of the flow cycle, the wall shear stress near the reattachment point fluctuated quite intensely, the magnitude of the instantaneous values increased at least by a factor of eight. These shear stresses are much higher than the

  1. A model of pulsatile flow in a uniform deformable vessel.

    PubMed

    Johnson, G A; Borovetz, H S; Anderson, J L

    1992-01-01

    Simulations of blood flow in natural and artificial conduits usually require large computers for numerical solution of the Navier-Stokes equations. Often, physical insight into the fluid dynamics is lost when the solution is purely numerical. An alternative to solving the most general form of the Navier-Stokes equations is described here, wherein a functional form of the solution is assumed in order to simplify the required computations. The assumed forms for the axial pressure gradient and velocity profile are chosen such that conservation of mass is satisfied for fully established pulsatile flow in a straight, deformable vessel. The resulting equations are cast in finite-difference form and solved explicitly. Results for the limiting cases of rigid wall and zero applied pressure are found to be in good agreement with analytical solutions. Comparison with the experimental results of Klanchar et al. [Circ. Res. 66, 1624-1635 (1990]) also shows good agreement. Application of the model to realistic physiological parameter values provides insight as to the influence of the pulsatile nature of the flow field on wall shear development in the presence of a moving wall boundary. Specifically, the model illustrates the dependence of flow rate and shear rate on the amplitude of the vessel wall motion and the phase difference between the applied pressure difference and the oscillations of the vessel radius. The present model can serve as a useful tool for experimentalists interested in quantifying the magnitude and character of velocity profiles and shearing forces in natural and artificial biologic conduits.

  2. Ordered and random structures in pulsatile flow through constricted tubes

    NASA Astrophysics Data System (ADS)

    Lieber, B. B.

    The poststenotic flow field in a rigid tube was investigated under pulsatile conditions. The waveform employed in the present experiment was sinusoidal and three contoured constrictions with 50, 75, and 90% area reduction were investigated. The fluid dynamic similarity parameters were chosen to represent conditions found in large arteries of humans and of experimental animals, using a Reynolds number range of 200 to 1000 and a frequency parameter value of 5.3. The analysis techniques of autoregressive modeling, correlation methods, and phase-shift averaging were employed in order to extract the maximum information about flow behavior. Analysis focuses on identification and representation of coherent flow disturbances, and examination of the influence of core flow behavior on the cyclic wall shear stress.

  3. Pulsatility flow around a single cylinder - an experimental model of flow inside an artificial lung

    NASA Astrophysics Data System (ADS)

    Lin, Yu-Chun; Bull, Joseph L.

    2004-11-01

    Pulsatile flow past a single cylinder is experimentally investigated using particle image velocimetry. This study aims to elucidate the effects of pulstility on the velocity field, which influences the convection-dominated transport within the fluid. The artificial lung device can be connected in parallel or series with the native lungs and may potentially be used as a bridge to transplant or for pulmonary replacement. The artificial lung consists of hollow microfibers through which gas flows and blood flows around. Blood flow through the device is pulsatile because it is driven entirely by the right heart. Steady flow over bluff bodies has been investigated in many contexts, such as heat exchangers. However, few studies have been investigated the effect of pulsatility. The effects of frequency, amplitude of pulsatility, and average flow rate on the formation of vortices after a cylinder are examined. Vortices near the cylinder are found to develop at lower Reynolds number in pulsatile flow than in steady flow. This work is supported by NIH grant R01 HL69420-01.

  4. Mechanics of pulsatile transpyloric flow in the pig.

    PubMed

    Anvari, M; Dent, J; Malbert, C; Jamieson, G G

    1995-10-01

    1. In eight conscious pigs equipped with gastric and duodenal cannulae, the relationship of transpyloric flow to gastro-duodenal motor events was evaluated during gastric emptying of 1000 ml of saline. Rates of liquid gastric emptying were correlated with pressures at the antrum, pylorus and duodenum, recorded by a sleeve sensor and multiple perfused side-holes. Transpyloric flow was recorded concurrently by continuous collection and weighing of the duodenal effluent. 2. In three pigs the above measurements were repeated during concurrent videofluoroscopy of gastric emptying after adding 100 ml of liquid barium to the gastric instillate. 3. The mean volume of saline emptied in 30 min was 627 +/- 51.2 ml. Pulsatile flow accounted for 71% of total emptying. Pulses had a mean flow rate of 3.9 +/- 0.44 ml s-1. Most flow pulses (59%) occurred during the first 5 min of emptying. 4. Distinctive, low-amplitude (4.8 +/- 0.33 mmHg), relatively long-lasting (15.8 +/- 0.46 s) antral pressure waves were associated with 58% of flow pulses. In all antral pressure recording points, the first and longest duration component of these pressure waves had an identical timing, amplitude and waveform consistent with pressurization of the entire antrum-gastric cavity. 5. Videofluoroscopy and concurrent manometry showed that these antral common cavity pressure waves were associated with non-lumen-occlusive contractions of the gastric wall, initially observed at the corpus which propagated down to the pylorus; 93% of these contractions became lumen occlusive in the terminal antrum and pylorus when pressure waves of a unique pattern for each recording point were recorded at this level. 6. The onset of 68% of the flow pulses which accounted for 62% of pulsatile emptying occurred in the interval (mean 7.9 +/- 0.65 s) between the onset of the common cavity wave and the onset of localized, lumen-occlusive distal antral-pyloric pressure waves. 7. These findings indicate that in the pig, pulsatile

  5. [Five years experience with non-pulsatile flow].

    PubMed

    Grinda, J M; Bricourt, M O; Salvi, S; Jouan, J; Guillemain, R; Deloche, A; Fabiani, J N

    2005-10-01

    Mechanical circulatory assistances now belong to the therapeutic stock in case of advanced heart failure. Their mainspring lays on the substitution of the failing left and/or right ventricle function with a pump. The goal being to maintain or restore the system main functions. Their main indication is a bridge to transplant mechanical circulatory assistance, allowing the patient to await transplantation. However, indications for definitive implantation appear in case of transplantation counter indication, mechanical circulatory assistances already emerging as a possible alternative to transplantation. For over 10 years, we have used pulsatile flow assistances, either with pneumatic ventricles or electro-mechanic implantable left ventricles. We henceforth observe the development of a new generation of implantable assistance providing a non-pulsatile flow. These are axial pumps. We evaluated the first model, the DeBakey axial pump which became the most used axial pump worldwide. We now observe the development of other axial pumps as well as the development of new implantable centrifugal pumps.

  6. Quantitative flow and velocity measurements of pulsatile blood flow with 4D-DSA

    NASA Astrophysics Data System (ADS)

    Shaughnessy, Gabe; Hoffman, Carson; Schafer, Sebastian; Mistretta, Charles A.; Strother, Charles M.

    2017-03-01

    Time resolved 3D angiographic data from 4D DSA provides a unique environment to explore physical properties of blood flow. Utilizing the pulsatility of the contrast waveform, the Fourier components can be used to track the waveform motion through vessels. Areas of strong pulsatility are determined through the FFT power spectrum. Using this method, we find an accuracy from 4D-DSA flow measurements within 7.6% and 6.8% RMSE of ICA PCVIPR and phantom flow probe validation measurements, respectively. The availability of velocity and flow information with fast acquisition could provide a more quantitative approach to treatment planning and evaluation in interventional radiology.

  7. Pulsatile flow and mass transport past a circular cylinder

    NASA Astrophysics Data System (ADS)

    Zierenberg, Jennifer R.; Fujioka, Hideki; Suresh, Vinod; Bartlett, Robert H.; Hirschl, Ronald B.; Grotberg, James B.

    2006-01-01

    The mass transport of a pulsatile free-stream flow past a single circular cylinder is investigated as a building block for an artificial lung device. The free stream far from the cylinder is represented by a time-periodic (sinusoidal) component superimposed on a steady velocity. The dimensionless parameters of interest are the steady Reynolds number (Re), Womersley parameter (α), sinusoidal amplitude (A), and the Schmidt number (Sc). The ranges investigated in this study are 5⩽Re⩽40, 0.25⩽α⩽4, 0.25⩽A⩽0.75, and Sc =1000. A pair of vortices downstream of the cylinder is observed in almost all cases investigated. These vortices oscillate in size and strength as α and A are varied. For α <αc, where αc=0.005A-1.13Re1.33, the vortex is always attached to the cylinder (persistent); while for α >αc, the vortex is attached to the cylinder only during part of a time cycle (intermittent). The time-averaged Sherwood number, Sh̿, is found to be largely influenced by the steady Reynolds number, increasing approximately as Re1/2. For α =0.25, Sh̿ is less than the steady (α =0, A =0) value and decreases with increasing A. For α =2 and α =4, Sh̿ is greater than the steady value and increases with increasing A. These qualitatively opposite effects of pulsatility are discussed in terms of quasisteady versus unsteady transport. The maximum increase over steady transport due to pulsatility varies between 14.4% and 20.9% for Re =10-40, α =4, and A =0.75.

  8. Direct Numerical Simulations of transitional pulsatile flow through stenotic vessels

    NASA Astrophysics Data System (ADS)

    Beratlis, Nikolaos; Balaras, Elias

    2006-11-01

    A series of direct numerical simulations of pulsatile flows in pipes with a constriction are presented here. Results capture the flow features reported in earlier experiments in the literature and confirm a qualitatively similar multi-step process to transition to turbulence observed in planar configurations. In particular, an instability of the shear layer leads to the formation of an array of vortices rings. Transition to turbulence takes place as these vortex rings undergo three-dimensional instabilities. We will present a systematic study of the effects of: 1. geometry of the constriction; 2. percent occlusion; 3. inflow conditions, to the above transition process. In addition, the effects of blood rheology on the results will be explored via numerical experiments with a variety of non-Newtonian models.

  9. Cinematics and sticking of heart valves in pulsatile flow test.

    PubMed

    Köhler, J; Wirtz, R

    1991-05-01

    The aim of the project was to develop laboratory test devices for studies of the cinematics and sticking behaviour of technical valve protheses. The second step includes testing technical valves of different types and sizes under static and dynamic conditions. A force-deflection balance was developed in order to load valve rims by static radial forces until sticking or loss of a disc (sticking- and clamping-mould point) with computer-controlled force deflection curves. A second deflection device was developed and used for prosthetic valves in the aortic position of a pulsatile mock circulation loop with simultaneous video-cinematography. The stiffness of technical valve rims varied between 0.20 (St. Jude) and about 1.0 N/micron (metal rim valves). The stiffness decreased significantly with increasing valve size. Sticking under pulsatile flow conditions was in good agreement with the static deflection measurements. Hence, valve sticking with increasing danger of thrombus formation is more likely with a less stiff valve rim. In the case of forces acting perpendicularly to the pendulum axis, the clamping mould-point of the valve can be reached, followed by disc dislodgement.

  10. An experimental study of pulsatile flow through compliant tubes

    NASA Astrophysics Data System (ADS)

    Sturgeon, Victoria; Savas, Omer; Saloner, David

    2006-11-01

    An experimental investigation is made into transitional behaviors and instability of oscillatory input flows through elastic tubes, a problem with applications to hemodynamics and flows in the pulmonary system. Sinusoidal input flow is driven through a compliant silicone model in a series of experiments to investigate the effects of wall motion. A novel mechanism allows active control and feedback over the pressure on the tube exterior. By comparing the pressure within and outside of the tube and modifying the exterior pressure accordingly, the tube is inflated in a controlled manner without altering the input flow. In these experiments, the tube wall is deformed sinusoidally with an amplitude of approximately ten percent of its radius. Experiments are conducted using varying values of the parameters α= a √φν and β= δx √φν where a is the tube radius, φ the angular velocity of the input flow, ν the kinematic viscosity, and δx the cross-stream averaged periodic displacement of a fluid particle undergoing pulsatile motion. For a given α, it is found that indications of conditional turbulence appear in this flow through elastic tubes at far lower values of β - and thus at lower amplitudes of oscillation - than are reported in the literature for flows through rigid tubing.

  11. Numerical investigations of pulsatile flow in stenosed artery.

    PubMed

    Bit, Arindam; Chattopadhyay, Himadri

    2014-01-01

    Abnormalities in blood vessels by virtue of complex blood flow dynamics is being supported by non-Newtonian behavior of blood. Thus it becomes a focus of research to most of the researchers. Additionally, consideration of real life patient specific model of vessel as well as patient specific inlet flow boundary condition implementation was limited in literature. Thus a thorough implementation of these considerations was done here. In this work, a numerical investigation of hemodynamic flow in stenosed artery has been carried out with realistic pulsating profile at the inlet. Flow has been considered to be laminar due to arresting condition of cardiovascular state of the subject. Two non- Newtonian rheological models namely, Power Law viscosity model and Quemada viscosity model have been used. Two different patient- specific pulsatile profiles are considered at the inlet of a long stenosed artery with varying degree of stenoses from 25% to 80%. Transient form of Navier-Stokes equation is solved in an axi-symmetric domain to calculate the detailed flow structure of the flow field. From the simulation data, temporal and time averaged wall shear stress, oscillatory shear index and pressure drop are calculated. The results demonstrate that oscillatory shear index and wall shear stresses are extensively governed by the degree of stenoses. The position and movement of recirculation bubbles are found to vary with flow Reynolds number.

  12. Pulsatile flow during cardiopulmonary bypass. Evaluation of a new pulsatile pump.

    PubMed

    Waaben, J; Andersen, K; Husum, B

    1985-01-01

    Pulsatile cardiopulmonary bypass (CPB) has been suggested to be superior to nonpulsatile CPB. This report concerns a newly developed pulsatile pump for clinical use. It is designed as a positive displacement pump, with blood allowed to collect in a valved cavity from which it is ejected by the reciprocating action of a piston. Using a uniform procedure of anaesthesia and surgery, 14 pigs were subjected to CPB at 37 degrees C for 3 hours. The pulsatile pump was used in seven pigs and a conventional roller pump in the other seven. The wave-form of the pulse during pulsatile CPB was similar to that recorded in the pigs before bypass. The values for rate of pressure change with respect to time (dp/dt) obtained in the aorta were close to the pre-CPB values. No difference was found between the two groups with respect to platelet count or haemolysis. The investigated pulsatile device appeared to be reliable and easy to handle, and the pulsation it produced closely resembled the physiologic pulse-wave form.

  13. The importance of flow pulsatility for the rate of transvascular fluid filtration in lungs.

    PubMed

    Hauge, A; Nicolaysen, G

    1979-05-01

    1. The rate of transvascular fluid filtration has been studied with a gravimetric technique in isolated perfused rabbit lungs during periods of elevated left atrial pressure (PLA). 2. Fluid filtration was expressed as the filtration coefficient, Kf (g/min x 100 g bloodless lung x mmHg PLA) and determined during alternately pulsatile and non-pulsatile perfusion in six zone III and three zone II/I lung preparations. Perfusion pattern was changed without interruption of flow. Mean in- and outflow pressures were kept constant. 3. In all the lungs it was found that Kf was higher during pulsatile than during non-pulsatile flow (P less than 0.01). Mean Kf (+/- S.E. of mean) for the zone III preparations was 0.42 (+/- 0.089) and 0.27 (+/- 0.057) for pulsatile and non-pulsatile perfusion, respectively. The corresponding figures for the zone II/I preparations were 0.11 (+/- 0.035) and 0.04 (+/- 0.030). 4. We suggest that the difference is due to a larger filtration area and/or a higher mean microvascular hydrostatic pressure during pulsatile than during non-pulsatile flow and not to a rise in hydraulic conductivity due to pressure pulsations ('stretched pores'). 5. When the water-exchange function of the lung is considered, flow pattern should be taken into account as an entity in its own right in addition to the steady state or the mean component of blood flow.

  14. Study of erythrocyte aggregation at pulsatile flow conditions with backscattering analysis.

    PubMed

    Nam, Jeong-Hun; Xue, Shubin; Lim, Hyunjung; Shin, Sehyun

    2012-01-01

    In vivo red blood cell aggregation will vary under pulsatile flow but few studies have been reported due to various difficulties in generating physiological flow conditions and detecting RBC aggregation. The present study developed a microfluidic system that generates cyclic pulsatile flow through a microchannel. Backscattered light signals from human blood were recorded over time and analyzed for RBC aggregation in pulsatile flow. Four different blood samples (control, normal RBCs in PBS, hardened RBCs in autologous plasma, and hardened RBCs in PBS) were examined. In a cyclic pulsatile flow condition, light intensity-time curve for the control and hardened RBCs in plasma exhibited apparent critical shear stresses that were similar to the respective values measured at a single pulse flow condition. During entire cycles of pulsatile flow, the measured critical shear stress remained nearly constant. We conclude that the critical shear stress can be observed in cyclic pulsatile flow and would be an important index to represent in-vivo pulsatile blood flow rheology.

  15. In vitro pulsatility analysis of axial-flow and centrifugal-flow left ventricular assist devices.

    PubMed

    Stanfield, J Ryan; Selzman, Craig H

    2013-03-01

    Recently, continuous-flow ventricular assist devices (CF-VADs) have supplanted older, pulsatile-flow pumps, for treating patients with advanced heart failure. Despite the excellent results of the newer generation devices, the effects of long-term loss of pulsatility remain unknown. The aim of this study is to compare the ability of both axial and centrifugal continuous-flow pumps to intrinsically modify pulsatility when placed under physiologically diverse conditions. Four VADs, two axial- and two centrifugal-flow, were evaluated on a mock circulatory flow system. Each VAD was operated at a constant impeller speed over three hypothetical cardiac conditions: normo-tensive, hypertensive, and hypotensive. Pulsatility index (PI) was compared for each device under each condition. Centrifugal-flow devices had a higher PI than that of axial-flow pumps. Under normo-tension, flow PI was 0.98 ± 0.03 and 1.50 ± 0.02 for the axial and centrifugal groups, respectively (p < 0.01). Under hypertension, flow PI was 1.90 ± 0.16 and 4.21 ± 0.29 for the axial and centrifugal pumps, respectively (p = 0.01). Under hypotension, PI was 0.73 ± 0.02 and 0.78 ± 0.02 for the axial and centrifugal groups, respectively (p = 0.13). All tested CF-VADs were capable of maintaining some pulsatile-flow when connected in parallel with our mock ventricle. We conclude that centrifugal-flow devices outperform the axial pumps from the basis of PI under tested conditions.

  16. Fluid-structure interaction for nonlinear response of shells conveying pulsatile flow

    NASA Astrophysics Data System (ADS)

    Tubaldi, Eleonora; Amabili, Marco; Païdoussis, Michael P.

    2016-06-01

    Circular cylindrical shells with flexible boundary conditions conveying pulsatile flow and subjected to pulsatile pressure are investigated. The equations of motion are obtained based on the nonlinear Novozhilov shell theory via Lagrangian approach. The flow is set in motion by a pulsatile pressure gradient. The fluid is modeled as a Newtonian pulsatile flow and it is formulated using a hybrid model that contains the unsteady effects obtained from the linear potential flow theory and the pulsatile viscous effects obtained from the unsteady time-averaged Navier-Stokes equations. A numerical bifurcation analysis employs a refined reduced order model to investigate the dynamic behavior. The case of shells containing quiescent fluid subjected to the action of a pulsatile transmural pressure is also addressed. Geometrically nonlinear vibration response to pulsatile flow and transmural pressure are here presented via frequency-response curves and time histories. The vibrations involving both a driven mode and a companion mode, which appear due to the axial symmetry, are also investigated. This theoretical framework represents a pioneering study that could be of great interest for biomedical applications. In particular, in the future, a more refined model of the one here presented will possibly be applied to reproduce the dynamic behavior of vascular prostheses used for repairing and replacing damaged and diseased thoracic aorta in cases of aneurysm, dissection or coarctation. For this purpose, a pulsatile time-dependent blood flow model is here considered by applying physiological waveforms of velocity and pressure during the heart beating period. This study provides, for the first time in literature, a fully coupled fluid-structure interaction model with deep insights in the nonlinear vibrations of circular cylindrical shells subjected to pulsatile pressure and pulsatile flow.

  17. Association of pulsatile and mean cerebral blood flow velocity with age and neuropsychological performance.

    PubMed

    Pase, Matthew P; Grima, Natalie A; Stough, Con; Scholey, Andrew; Pipingas, Andrew

    2014-05-10

    Low cerebral blood flow velocity is associated with cognitive decline. However, the association between pulsatile brain blood flow velocity and cognition has not been investigated. High pulsatile hemodynamic stress in the brain may impair cognitive function through damage to small cerebral vessels. The current objective was to examine the cross-sectional association of pulsatile and mean cerebral blood flow velocity with age and neuropsychological performance. We also examined whether cerebral blood flow velocity was associated with aortic pulse pressure, a measure of arterial ageing and aortic stiffness. Cerebral blood flow velocity was measured in the middle cerebral artery using Transcranial Doppler Ultrasonography (TDU) while neuropsychological performance was measured using a computerized cognitive test battery. Aortic pulse pressure was non-invasively derived from applanation tonometry of the radial artery. The sample comprised 160 healthy adults aged 50-70 years. Results indicated that increasing age correlated with lower mean (r=-0.23, p<0.01) and higher pulsatile (r=0.27, p<0.01) brain blood flow velocity. In multivariate adjusted models, both peripheral (β=0.28, p<0.05) and aortic (β=0.24, p<0.05) pulse pressure were associated with higher pulsatile flow velocity through the middle cerebral artery. In adjusted models, neither mean nor pulsatile cerebral blood flow velocity was associated with performance on any cognitive task. In conclusion, arterial ageing was associated with increased pulsatile hemodynamic stress in the brain. However, this was not associated with impaired neuropsychological performance.

  18. Measurement of real pulsatile blood flow using X-ray PIV technique with CO2 microbubbles.

    PubMed

    Park, Hanwook; Yeom, Eunseop; Seo, Seung-Jun; Lim, Jae-Hong; Lee, Sang-Joon

    2015-03-06

    Synchrotron X-ray imaging technique has been used to investigate biofluid flows in a non-destructive manner. This study aims to investigate the feasibility of the X-ray PIV technique with CO2 microbubbles as flow tracer for measurement of pulsatile blood flows under in vivo conditions. The traceability of CO2 microbubbles in a pulsatile flow was demonstrated through in vitro experiment. A rat extracorporeal bypass loop was used by connecting a tube between the abdominal aorta and jugular vein of a rat to obtain hemodynamic information of actual pulsatile blood flows without changing the hemorheological properties. The decrease in image contrast of the surrounding tissue was also investigated for in vivo applications of the proposed technique. This technique could be used to accurately measure whole velocity field information of real pulsatile blood flows and has strong potential for hemodynamic diagnosis of cardiovascular diseases.

  19. Measurement of real pulsatile blood flow using X-ray PIV technique with CO2 microbubbles

    PubMed Central

    Park, Hanwook; Yeom, Eunseop; Seo, Seung-Jun; Lim, Jae-Hong; Lee, Sang-Joon

    2015-01-01

    Synchrotron X-ray imaging technique has been used to investigate biofluid flows in a non-destructive manner. This study aims to investigate the feasibility of the X-ray PIV technique with CO2 microbubbles as flow tracer for measurement of pulsatile blood flows under in vivo conditions. The traceability of CO2 microbubbles in a pulsatile flow was demonstrated through in vitro experiment. A rat extracorporeal bypass loop was used by connecting a tube between the abdominal aorta and jugular vein of a rat to obtain hemodynamic information of actual pulsatile blood flows without changing the hemorheological properties. The decrease in image contrast of the surrounding tissue was also investigated for in vivo applications of the proposed technique. This technique could be used to accurately measure whole velocity field information of real pulsatile blood flows and has strong potential for hemodynamic diagnosis of cardiovascular diseases. PMID:25744850

  20. Platelet adhesion to polyurethane urea under pulsatile flow conditions.

    PubMed

    Navitsky, Michael A; Taylor, Joshua O; Smith, Alexander B; Slattery, Margaret J; Deutsch, Steven; Siedlecki, Christopher A; Manning, Keefe B

    2014-12-01

    Platelet adhesion to a polyurethane urea surface is a precursor to thrombus formation within blood-contacting cardiovascular devices, and platelets have been found to adhere strongly to polyurethane surfaces below a shear rate of approximately 500 s(-1). The aim of the current work is to determine the properties of platelet adhesion to the polyurethane urea surface as a function of time-varying shear exposure. A rotating disk system was used to study the influence of steady and pulsatile flow conditions (e.g., cardiac inflow and sawtooth waveforms) for platelet adhesion to the biomaterial surface. All experiments were conducted with the same root mean square angular rotation velocity (29.63 rad/s) and waveform period. The disk was rotated in platelet-rich bovine plasma for 2 h, with adhesion quantified by confocal microscopy measurements of immunofluorescently labeled bovine platelets. Platelet adhesion under pulsating flow was found to decay exponentially with increasing shear rate. Adhesion levels were found to depend upon peak platelet flux and shear rate, regardless of rotational waveform. In combination with flow measurements, these results may be useful for predicting regions susceptible to thrombus formation within ventricular assist devices.

  1. PLATELET ADHESION TO POLYURETHANE UREA UNDER PULSATILE FLOW CONDITIONS

    PubMed Central

    Navitsky, Michael A.; Taylor, Joshua O.; Smith, Alexander B.; Slattery, Margaret J.; Deutsch, Steven; Siedlecki, Christopher A.; Manning, Keefe B.

    2014-01-01

    Platelet adhesion to a polyurethane urea surface is a precursor to thrombus formation within blood-contacting cardiovascular devices, and platelets have been found to adhere strongly to polyurethane surfaces below a shear rate of approximately 500 s−1. The aim of the current work is to determine platelet adhesion properties to the polyurethane urea surface as a function of time varying shear exposure. A rotating disk system is used to study the influence of steady and pulsatile flow conditions (e.g. cardiac inflow and sawtooth waveforms) for platelet adhesion to the biomaterial surface. All experiments retain the same root mean square angular rotation velocity (29.63 rad/s) and waveform period. The disk is rotated in platelet rich bovine plasma for two hours with adhesion quantified by confocal microscopy measurements of immunofluorescently labeled bovine platelets. Platelet adhesion under pulsating flow is found to exponentially decay with increasing shear rate. Adhesion levels are found to depend upon peak platelet flux and shear rate regardless of rotational waveform. In combination with flow measurements, these results may be useful for predicting regions susceptible to thrombus formation within ventricular assist devices. PMID:24721222

  2. Pulsatile Flow Across a Cylinder--An Investigation of Flow in a Total Artificial Lung

    NASA Astrophysics Data System (ADS)

    Lin, Yu-Chun

    2005-11-01

    The effect of pulsatility on flow across a single cylinder has been examined experimentally using particle image velocimetry. This work is motivated by the ongoing development of a total artificial lung (TAL), a device which would serve as a bridge to lung transplant. The prototype TAL consists of hollow microfibers through which oxygen-rich gas flows and blood flows around. Flow through the device is provided entirely by right heart and, therefore, is puslatile. The Peclet number of the flow is large and consequently the development of secondary flow affects the resulting gas exchange. The effects of frequency and average flow rate of pulsatile flow around a cylinder were investigated experimentally in a water tunnel and some of the results were compared with preliminary numerical results. Vortices developed behind the cylinder at lower Reynolds numbers in pulsatile flow than steady flow. The results indicate that there are critical values of the Reynolds number between 3 to 5 and Stokes numbers of 0.22, below which vortices were not observed. The findings suggest that higher Stokes and Reynolds numbers within the device could enhance vortex formation. However, this enhanced gas exchange could be at the expense of higher device resistance and increased likelihood of blood trauma. Intelligent TAL design will require consideration of these effects. This work is supported by NIH grant HL69420.

  3. Numerical study of pulsatile flow in a constricted channel

    NASA Astrophysics Data System (ADS)

    Mittal, R.; Simmons, S. P.; Najjar, F.

    2003-06-01

    Pulsatile flow in a planar channel with a one-sided semicircular constriction has been simulated using direct numerical simulation and large-eddy simulation. This configuration is intended as a simple model for studying blood flow in a constricted artery. Simulations have been carried out over a range of Reynolds numbers (based on channel height and peak bulk velocity) from 750 to 2000 and a fixed non-dimensional pulsation frequency of 0.024. The results indicate that despite the simplicity of the chosen geometry, the simulated flow exhibits a number of features that have been observed in previous experiments carried out in more realistic configurations. It is found that over the entire Reynolds number range studied here, the flow downstream of the constriction is dominated by the complex dynamics associated with two shear-layers, one of which separates from the lip of the constriction and other from the opposite wall. Computed statistics indicate that for Reynolds numbers higher than about 1000, the flow transitions to turbulence downstream of the region where the separated shear layers first reattach to the channel walls. Large fluctuations in wall pressure and shear stress have also been associated with this reattachment phenomenon. Frequency spectra corresponding to velocity and pressure fluctuations have been analysed in detail and these indicate the presence of a characteristic shear-layer frequency which increases monotonically with Reynolds number. For Reynolds numbers greater than 1000, this frequency is found to be associated with the periodic formation of vortex structures in the shear-layers and the impact of this characteristic shear-layer frequency on the dynamics of the flow is described in detail.

  4. Using flow feature to extract pulsatile blood flow from 4D flow MRI images

    NASA Astrophysics Data System (ADS)

    Wang, Zhiqiang; Zhao, Ye; Yu, Whitney; Chen, Xi; Lin, Chen; Kralik, Stephen F.; Hutchins, Gary D.

    2017-02-01

    4D flow MRI images make it possible to measure pulsatile blood flow inside deforming vessel, which is critical in accurate blood flow visualization, simulation, and evaluation. Such data has great potential to overcome problems in existing work, which usually does not reflect the dynamic nature of elastic vessels and blood flows in cardiac cycles. However, the 4D flow MRI data is often low-resolution and with strong noise. Due to these challenges, few efforts have been successfully conducted to extract dynamic blood flow fields and deforming artery over cardiac cycles, especially for small artery like carotid. In this paper, a robust flow feature, particularly the mean flow intensity is used to segment blood flow regions inside vessels from 4D flow MRI images in whole cardiac cycle. To estimate this flow feature more accurately, adaptive weights are added to the raw velocity vectors based on the noise strength of MRI imaging. Then, based on this feature, target arteries are tracked in at different time steps in a cardiac cycle. This method is applied to the clinical 4D flow MRI data in neck area. Dynamic vessel walls and blood flows are effectively generated in a cardiac cycle in the relatively small carotid arteries. Good image segmentation results on 2D slices are presented, together with the visualization of 3D arteries and blood flows. Evaluation of the method was performed by clinical doctors and by checking flow volume rates in the vertebral and carotid arteries.

  5. Micro-PIV Measurements of Pulsatile Flow Over Endothelial Cells.

    NASA Astrophysics Data System (ADS)

    Leong, Chiamin; Nackman, Gary; Wei, Timothy

    2007-11-01

    In both humans and mammals, endothelial cells remodel themselves according to mechanical loading by changing shape and orientation. Subsequently, these mechanical forces are transduced into chemical signals, mechanotransduction, involving changes in gene and protein expression. Alterations in mechanotransduction by endothelial cells to underlying smooth muscle cells is a key factor in human arterial disease. The goal of this study is to determine the importance of spatially and temporally varying mechanical loading and examine biological response under different flow conditions. In-vitro micro-PIV measurements are made in pulsatile flow over cultured endothelial cells flush mounted in a small rectangular channel. Cells are subjected to peak shear stress of 20 dynes/cm^2 corresponding to peak Re of 1000 and Womersley number of 1.4. Using multiple measurement planes, local surface height, surface pressure, and wall shear stress are extracted from the measurements. Simultaneous Raman spectroscopy is also being explored to investigate the bio-chemical response of live cultured human and bovine cells.

  6. High pulsatility flow stimulates smooth muscle cell hypertrophy and contractile protein expression

    PubMed Central

    Scott, Devon; Tan, Yan; Shandas, Robin; Stenmark, Kurt R.

    2013-01-01

    Proximal arterial stiffening is an important predictor of events in systemic and pulmonary hypertension, partly through its contribution to downstream vascular abnormalities. However, much remains undetermined regarding the mechanisms involved in the vascular changes induced by arterial stiffening. We therefore addressed the hypothesis that high pulsatility flow, caused by proximal arterial stiffening, induces downstream pulmonary artery endothelial cell (EC) dysfunction that in turn leads to phenotypic change of smooth muscle cells (SMCs). To test the hypothesis, we employed a model pulmonary circulation in which upstream compliance regulates the pulsatility of flow waves imposed onto a downstream vascular mimetic coculture composed of pulmonary ECs and SMCs. The effects of high pulsatility flow on SMCs were determined both in the presence and absence of ECs. In the presence of ECs, high pulsatility flow increased SMC size and expression of the contractile proteins, smooth muscle α-actin (SMA) and smooth muscle myosin heavy chain (SM-MHC), without affecting proliferation. In the absence of ECs, high pulsatility flow decreased SMC expression of SMA and SM-MHC, without affecting SMC size or proliferation. To identify the molecular signals involved in the EC-mediated SMC responses, mRNA and/or protein expression of vasoconstrictors [angiotensin-converting enzyme (ACE) and endothelin (ET)-1], vasodilator (eNOS), and growth factor (TGF-β1) in EC were examined. Results showed high pulsatility flow decreased eNOS and increased ACE, ET-1, and TGF-β1 expression. ACE inhibition with ramiprilat, ET-1 receptor inhibition with bosentan, and treatment with the vasodilator bradykinin prevented flow-induced, EC-dependent SMC changes. In conclusion, high pulsatility flow stimulated SMC hypertrophy and contractile protein expression by altering EC production of vasoactive mediators and cytokines, supporting the idea of a coupling between proximal vascular stiffening, flow

  7. Pulsatile flow and gas transfer over arrays of cylinders

    NASA Astrophysics Data System (ADS)

    Chan, Kit Yan; Fujioka, Hideki; Grotberg, James B.

    2004-11-01

    In an artificial lung device, blood passes through arrays of porous microfibers and the gas transfer occurring across the fiber surfaces strongly depends on the flow field. Pulsatile flow distribution and gas transfer over arrays of porous microfibers (modeled as cylinders) are numerically simulated for both Newtonian and Casson fluids using Finite Volume method. Different arrangements of the cylinders: square array, rectangular array, staggered array are considered in this study. For some of the studies, the average x-velocity U(t) is described by U(t) = U0 ( 1 +A sin ( ω t) ) [1], where U0 is the time-average x-velocity, A is the amplitude of the oscillation, and ω is the frequency. For other studies, half of a cycle is described by [1] and half of the cycle U(t) = 0. The inclusion of a zero average velocity period in U(t) is physiologically a better description of the time-average velocity of blood exiting the heart. Interestingly, gas transfer increases when U(t) is described this way, due to the appearance of large vortices that enhance mixing. The existence, the size and the location of the recirculation zones are found to be controlled by array geometry and flow parameters. In general, conditions that enhance the gas transfer also at the same time increase the maximum flow resistance; such as the increase of the Reynolds number, the Womersley number, A, and cylinder density, with the exception of the increase of the yield stress for a Casson fluid. This work is supported by NIH: HL 69420.

  8. Pulsatile flow into the aqueous veins: Manifestations in normal and glaucomatous eyes

    PubMed Central

    Johnstone, Murray; Martin, Elizabeth; Jamil, Annisa

    2015-01-01

    The aqueous outflow system is unique because nowhere else can the pattern of flow of an extravascular fluid be directly observed as it returns to the vascular system. Such observations reveal that aqueous flow both from Schlemm’s canal into the aqueous veins and from the aqueous veins into the episcleral veins is pulsatile. Pulsatile aqueous flow mechanisms are observable in vivo not only in normal and but also in glaucomatous eyes. A series of specific patterns accompany the pulsatile mixing of aqueous with blood in the episcleral veins. These directly observable patterns of pulsatile flow are synchronous with intraocular pressure (IOP) transients induced by the cardiac pulse, blinking and eye movement. Patterns of pulsatile flow are altered by events that increase IOP such as pressure on the side of the eye, tonography and water drinking. Pulsatile flow stops when IOP is reduced below its resting level, but begins again when IOP returns to the resting level. Pulsatile flow reduction probably results from the intrinsic reduction of pulse amplitude at a lower IOP, and may thus provide a passive mechanism to maintain short-term homeostasis. Thus modulation of the pulsatile flow phenomenon appears to maintain a homeostatic IOP setpoint. Visible pulsatile flow abnormalities develop in glaucoma patients. Medications that reduce IOP through improvement in outflow do so through pulsatile flow mechanisms. Laboratory studies have demonstrated that cyclic stresses in outflow tissues alter signaling pathways, cytoskeletal responses, extracellular matrix composition and cytokine secretion. How physiologic pulse transients orchestrate cellular responses and how cellular responses identified in the laboratory may in turn regulate pulsatile aqueous outflow is unknown. Linkage of laboratory and in vivo observations await an improved understanding of how cellular and extracellular structures within the outflow system are able to generate an aqueous pulse wave. The purpose of the

  9. Relationship between velocity profile and ultrasound echogenicity in pulsatile blood flows.

    PubMed

    Yeom, Eunseop; Lee, Sang Joon

    2015-01-01

    Pulsatile blood flows are easily found in the vessels of living organisms. Under pulsatile flow conditions, red blood cells (RBCs) are aggregated and dispersed repetitively. The phenomenon of RBC aggregation is an influential factor in hemorheological and hemodynamic properties. This study aims to investigate the relationship between velocity profile and RBC aggregation in pulsatile blood flows. A rat extracorporeal bypass model was adopted to generate a real pulsatile flow without changing the rheological properties. To check the stability of the experimental model, variations of the hemodynamic parameters were measured consecutively for 2 h. Ultrasound speckle images of the blood flow in the extracorporeal bypass loop were acquired using a 35-MHz ultrasound scanner. The velocity fields were measured by the speckle image velocimetry (SIV) method, in which the cross-correlation algorithm is applied to the speckle images. In addition, the RBC aggregation was estimated by analyzing the echogenicity distribution of the speckle images. The shape of the velocity profile was cyclically varied according to the cardiac cycle. This variation may be closely related to the variation of the echogenicity distribution in pulsatile flows. The simultaneous measurement of velocity and RBC aggregation would be useful for understanding the effects of the hemorheological features on the hemodynamic characteristics of pulsatile blood flows.

  10. Flow-induced wall shear stress in abdominal aortic aneurysms: Part II--pulsatile flow hemodynamics.

    PubMed

    Finol, Ender A; Amon, Cristina H

    2002-08-01

    In continuing the investigation of AAA hemodynamics, unsteady flow-induced stresses are presented for pulsatile blood flow through the double-aneurysm model described in Part I. Physiologically realistic aortic blood flow is simulated under pulsatile conditions for the range of time-average Reynolds numbers 50< or =Re(m) < or =300. Hemodynamic disturbance is evaluated for a modified set of indicator functions which include wall pressure (p(w)), wall shear stress (tau(w)), Wall Shear Stress Gradient (WSSG), time-average wall shear stress (tau(w)*), and time-average Wall Shear Stress Gradient WSSG*. At peak flow, the highest shear stress and WSSG levels are obtained at the distal end of both aneurysms, in a pattern similar to that of steady flow. The maximum values of wall shear stresses and wall shear stress gradients are evaluated as a function of the time-average Reynolds number resulting in a fourth order polynomial correlation. A comparison between numerical predictions for steady and pulsatile flow is presented, illustrating the importance of considering time-dependent flow for the evaluation of hemodynamic indicators.

  11. Easy Pulsatile Phantom for Teaching and Validation of Flow Measurements in Ultrasound

    PubMed Central

    Rominger, M. B.; Müller-Stuler, E.-M.; Pinto, M.; Becker, A. S.; Martini, K.; Frauenfelder, T.; Klingmüller, V.

    2016-01-01

    Purpose: To build a simple model to teach and validate non-pulsatile and pulsatile flow quantification in ultrasound. Materials and Methods: The setting consists of the following connected components: (1) medical syringe pump producing an adjustable constant flow (ml/min), (2) modulator modifying constant flow to a reproducible pulsatile flow, (3) water tank containing a diagonal running silicone tube (0.5 mm inner diameter), and (4) a fixated ultrasound probe (L9 Linear Array 9 MHz, GE Logiq E9) measuring the flow inside the tube. Commercially available microbubbles suspended with physiological saline solution were used for ultrasonic visibility. Spectral Doppler of different flow profiles is performed. Results: The syringe pump produces an adjustable, constant flow and serves as the reference standard. The filling volume of the tube system is 1.2 ml. Microbubbles are very well detected by ultrasound and can be used as an easy and clean blood mimicking substance. The modulator generates different physiological and pathological flow profiles. Velocities are similar to those found within human blood vessels. Thus, it is possible to train and validate flow measurements in ultrasound. Conclusion: The model produces non-pulsatile and various pulsatile flow profiles and allows validation of flow measurements. The compact size permits easy and economic setup for flow measurements in research, skills lab and continuing education. PMID:27689183

  12. A one-dimensional mathematical model for studying the pulsatile flow in microvascular networks.

    PubMed

    Pan, Qing; Wang, Ruofan; Reglin, Bettina; Cai, Guolong; Yan, Jing; Pries, Axel R; Ning, Gangmin

    2014-01-01

    Techniques that model microvascular hemodynamics have been developed for decades. While the physiological significance of pressure pulsatility is acknowledged, most of the microcirculatory models use steady flow approaches. To theoretically study the extent and transmission of pulsatility in microcirculation, dynamic models need to be developed. In this paper, we present a one-dimensional model to describe the dynamic behavior of microvascular blood flow. The model is applied to a microvascular network from a rat mesentery. Intravital microscopy was used to record the morphology and flow velocities in individual vessel segments, and boundaries are defined according to the experimental data. The system of governing equations constituting the model is solved numerically using the discontinuous Galerkin method. An implicit integration scheme is adopted to increase computing efficiency. The model allows the simulation of the dynamic properties of blood flow in microcirculatory networks, including the pressure pulsatility (quantified by a pulsatility index) and pulse wave velocity (PWV). From the main input arteriole to the main output venule, the pulsatility index decreases by 66.7%. PWV obtained along arterioles declines with decreasing diameters, with mean values of 77.16, 25.31, and 8.30 cm/s for diameters of 26.84, 17.46, and 13.33 μm, respectively. These results suggest that the 1D model developed is able to simulate the characteristics of pressure pulsatility and wave propagation in complex microvascular networks.

  13. Application of full field optical studies for pulsatile flow in a carotid artery phantom

    PubMed Central

    Nemati, M.; Loozen, G. B.; van der Wekken, N.; van de Belt, G.; Urbach, H. P.; Bhattacharya, N.; Kenjeres, S.

    2015-01-01

    A preliminary comparative measurement between particle imaging velocimetry (PIV) and laser speckle contrast analysis (LASCA) to study pulsatile flow using ventricular assist device in a patient-specific carotid artery phantom is reported. These full-field optical techniques have both been used to study flow and extract complementary parameters. We use the high spatial resolution of PIV to generate a full velocity map of the flow field and the high temporal resolution of LASCA to extract the detailed frequency spectrum of the fluid pulses. Using this combination of techniques a complete study of complex pulsatile flow in an intricate flow network can be studied. PMID:26504652

  14. Enhancement of Arterial Pressure Pulsatility by Controlling Continuous-Flow Left Ventricular Assist Device Flow Rate in Mock Circulatory System.

    PubMed

    Bozkurt, Selim; van de Vosse, Frans N; Rutten, Marcel C M

    Continuous-flow left ventricular assist devices (CF-LVADs) generally operate at a constant speed, which reduces pulsatility in the arteries and may lead to complications such as functional changes in the vascular system, gastrointestinal bleeding, or both. The purpose of this study is to increase the arterial pulse pressure and pulsatility by controlling the CF-LVAD flow rate. A MicroMed DeBakey pump was used as the CF-LVAD. A model simulating the flow rate through the aortic valve was used as a reference model to drive the pump. A mock circulation containing two synchronized servomotor-operated piston pumps acting as left and right ventricles was used as a circulatory system. Proportional-integral control was used as the control method. First, the CF-LVAD was operated at a constant speed. With pulsatile-speed CF-LVAD assistance, the pump was driven such that the same mean pump output was generated. Continuous and pulsatile-speed CF-LVAD assistance provided the same mean arterial pressure and flow rate, while the index of pulsatility increased significantly for both arterial pressure and pump flow rate signals under pulsatile speed pump support. This study shows the possibility of improving the pulsatility of CF-LVAD support by regulating pump speed over a cardiac cycle without reducing the overall level of support.

  15. Local anaesthetic techniques and pulsatile ocular blood flow

    PubMed Central

    Chang, B.; Hee, W.; Ling, R.; Broadway, D.; Beigi, B.

    2000-01-01

    AIM—To compare pulsatile ocular blood flow (POBF) and intraocular pressure (IOP) between eyes of patients receiving either peribulbar (with and without balloon compression) or subconjunctival local anaesthesia (LA).
METHODS—30 eyes of 30 patients undergoing cataract surgery by phacoemulsification were investigated in a study of parallel group design. Ten patients had peribulbar LA and 10 minutes compression with a Honan's balloon (group A). A further 10 patients who received peribulbar LA alone (group B) acted as controls for the effects of balloon compression. Ten other patients were given subconjunctival LA (group C). POBF and IOP were measured using a modified Langham pneumatonometer. Three measurements were made in each eye, the first recording immediately before LA, the second 1 minute after, and the third 10 minutes after LA.
RESULTS—No significant change in POBF or IOP was recorded in eyes receiving subconjunctival LA. In the peribulbar groups (A and B), there was a drop in median POBF of 252 and 138 µl/min respectively 1 minute after LA, which was statistically significant in both groups (p<0.01). By 10 minutes, POBF tended to return to baseline levels, but remained significantly reduced in group B (p<0.05). In addition, there was a significant (p<0.05) reduction in IOP (mean drop of 4.82 mm Hg) in group A following peribulbar LA with balloon compression.
CONCLUSIONS—POBF was significantly reduced after peribulbar LA but was unchanged after subconjunctival LA. Balloon compression reduced IOP and improved POBF following peribulbar LA. The findings may have clinical implications in patients with compromised ocular circulation or significant glaucomatous optic neuropathy.

 PMID:11049951

  16. Effect of pulsatile blood flow on thrombosis potential with a step wall transition.

    PubMed

    Corbett, Scott C; Ajdari, Amin; Coskun, Ahmet U; Nayeb-Hashemi, Hamid

    2010-01-01

    It is well known that thrombus can be formed at stagnation regions in blood flow. However, studies of thrombus formation have typically focused on steady state flow. We hypothesize that pulsating flow may reduce persistent stagnation at the sites of low shear stress by decreasing exposure time. In this study, a step-wall transition, which is commonly found on implantable devices, is used as a test bed causing a recirculation vortex. Stagnation at such a step is considered using computational fluid dynamics studies and flow visualization experiments. Parametric studies were performed with varying step height, pulsatility, and velocity. The percentage of time along the wall with shear stresses below a threshold for thrombosis and the total length of wall that maintains contact with stagnant flow throughout the cardiac cycle are calculated. Persistent stagnation occurs at the corner of a step-wall transition in all cases and is observed to decrease with a decrease in step height, an increase in mean velocity, and an increase in pulsatility. Under steady flow conditions, a flow reattachment point resulting from recirculation is observed with expanding steps, whereas a flow separation point is observed with contracting steps. Pulsatility decreases persistent stagnation at the flow separation point with contracting steps, whereas it completely eliminates persistent stagnation at the flow reattachment point with expanding steps. The results of this work conclusively show that stagnation can be reduced by increasing pulsatility and flow velocity and by decreasing step height.

  17. Attenuation of hypoxic pulmonary vasoconstriction by pulsatile flow in dog lungs.

    PubMed

    Gregory, T J; Newell, J C; Hakim, T S; Levitzky, M G; Sedransk, N

    1982-12-01

    We measured pulmonary arterial pressure in isolated lower lobes of dog lungs perfused in situ at several flows during ventilation with 95% O2-5% CO2 and with 3% O2-5% CO2. Pulsatile perfusion was provided by a piston pump, and steady perfusion was provided by a roller pump. The slope of the pressure-flow curve was 16.1 +/- 1.6 Torr X 1(-1) X min at all flows between 200 and 800 ml/min during 95-5 ventilation and increased to 19.4 +/- 3.7 in hypoxia. When flow was 600 ml/min, with 95-5 ventilation, mean arterial pressure was 16.2 +/- 1.2 Torr in steady flow and was unchanged at 15.0 +/- 1.0 Torr in pulsatile flow. At the same flow during hypoxic ventilation, mean arterial pressure increased to 27.9 +/- 2.4 Torr (P less than 0.01) when flow was steady but only to 19.3 +/- 1.6 Torr (P less than 0.01) when flow was made pulsatile. Thus hypoxia increased perfusion pressure by a nearly parallel shift of the pressure-flow curve to higher pressures, and this change was smaller in pulsatile than in steady flow.

  18. Computational fluid dynamics-based study of possibility of generating pulsatile blood flow via a continuous-flow VAD.

    PubMed

    Nammakie, Erfan; Niroomand-Oscuii, Hanieh; Koochaki, Mojtaba; Ghalichi, Farzan

    2017-01-01

    Until recent years, it was almost beyond remedy to save the life of end-stage heart failure patients without considering a heart transplant. This is while the need for healthy organs has always far exceeded donations. However, the evolution of VAD technology has certainly changed the management of these patients. Today, blood pumps are designed either pulsatile flow or continuous flow, each of which has its own concerns and limitations. For instance, pulsatile pumps are mostly voluminous and hardly can be used for children. On the other hand, the flow generated by continuous-flow pumps is in contrast with pulsatile flow of the natural heart. In this project, having used computational fluid dynamics, we studied the possibility of generating pulsatile blood flow via a continuous-flow blood pump by adjusting the rotational speed of the pump with two distinct patterns (sinusoidal and trapezoidal), both of which have been proposed and set based on physiological needs and blood flow waveform of the natural heart. An important feature of this study is setting the outlet pressure of the pump similar to the physiological conditions of a patient with heart failure, and since these axial pumps are sensitive to outlet pressures, more secure and reliable results of their performance are achieved. Our results show a slight superiority of a sinusoidal pattern compared to a trapezoidal one with the potential to achieve an adequate pulsatile flow by precisely controlling the rotational speed.

  19. Simulation of a pulsatile non-Newtonian flow past a stenosed 2D artery with atherosclerosis.

    PubMed

    Tian, Fang-Bao; Zhu, Luoding; Fok, Pak-Wing; Lu, Xi-Yun

    2013-09-01

    Atherosclerotic plaque can cause severe stenosis in the artery lumen. Blood flow through a substantially narrowed artery may have different flow characteristics and produce different forces acting on the plaque surface and artery wall. The disturbed flow and force fields in the lumen may have serious implications on vascular endothelial cells, smooth muscle cells, and circulating blood cells. In this work a simplified model is used to simulate a pulsatile non-Newtonian blood flow past a stenosed artery caused by atherosclerotic plaques of different severity. The focus is on a systematic parameter study of the effects of plaque size/geometry, flow Reynolds number, shear-rate dependent viscosity and flow pulsatility on the fluid wall shear stress and its gradient, fluid wall normal stress, and flow shear rate. The computational results obtained from this idealized model may shed light on the flow and force characteristics of more realistic blood flow through an atherosclerotic vessel. Copyright © 2013. Published by Elsevier Ltd.

  20. Impact of flow pulsatility on arterial drug distribution in stent-based therapy

    PubMed Central

    O’Brien, Caroline C.; Kolachalama, Vijaya B.; Barber, Tracie J.; Simmons, Anne; Edelman, Elazer R.

    2013-01-01

    Drug-eluting stents reside in a dynamic fluid environment where the extent to which drugs are distributed within the arterial wall is critically modulated by the blood flowing through the arterial lumen. Yet several factors associated with the pulsatile nature of blood flow and their impact on arterial drug deposition has not been fully investigated. We employed an integrated framework comprising bench-top and computational models to explore the factors governing the time-varying fluid dynamic environment within the vasculature and their effects on arterial drug distribution patterns. A custom-designed bench-top framework comprising a model of a single drug-eluting stent strut and a poly-vinyl alcohol-based hydrogel as a model tissue bed simulated fluid flow and drug transport under fully apposed strut settings. Bench-top experiments revealed a relative independence between drug distribution and the factors governing pulsatile flow and these findings were validated with the in silico model. Interestingly, computational models simulating suboptimal deployment settings revealed a complex interplay between arterial drug distribution, Womersley number and the extent of malapposition. In particular, for a stent strut offset from the wall, total drug deposition was sensitive to changes in the pulsatile flow environment, with this dependence increasing with greater wall displacement. Our results indicate that factors governing pulsatile luminal flow on arterial drug deposition should be carefully considered in conjunction with device deployment settings for better utilization of drug-eluting stent therapy for various arterial flow regimes. PMID:23541929

  1. The response of an elastic splitter plate attached to a cylinder to laminar pulsatile flow

    NASA Astrophysics Data System (ADS)

    Kundu, Anup; Soti, Atul K.; Bhardwaj, Rajneesh; Thompson, Mark C.

    2017-01-01

    The flow-induced deformation of a thin, elastic splitter plate attached to the rear of a circular cylinder and subjected to laminar pulsatile inflow is investigated. The cylinder and elastic splitter plate are contained within a narrow channel and the Reynolds number is mostly restricted to Re = 100, primarily covering the two-dimensional flow regime. An in-house fluid-structure interaction code is employed for simulations, which couples a sharp-interface immersed boundary method for the fluid dynamics with a finite-element method to treat the structural dynamics. The structural solver is implicitly (two-way) coupled with the flow solver using a partitioned approach. This implicit coupling ensures numerical stability at low structure-fluid density ratios. A power spectrum analysis of the time-varying plate displacement shows that the plate oscillates at more than a single frequency for pulsatile inflow, compared to a single frequency observed for steady inflow. The multiple frequencies obtained for the former case can be explained by beating between the applied and plate oscillatory signals. The plate attains a self-sustained time-periodic oscillation with a plateau amplitude in the case of steady flow, while the superimposition of pulsatile inflow with induced plate oscillation affects the plateau amplitude. Lock-in of the plate oscillation with the pulsatile inflow occurs at a forcing frequency that is twice of the plate natural frequency in a particular mode and this mode depends on the plate length. The plate displacement as well as pressure drag increases at the lock-in condition. The percentage change in the maximum plate displacement, and skin-friction and pressure drag coefficients on the plate, due to pulsatile inflow is quantified. The non-linear dynamics of the plate and its coupling with the pulsatile flow are briefly discussed.

  2. Long-term durability test of axial-flow ventricular assist device under pulsatile flow.

    PubMed

    Nishida, Masahiro; Kosaka, Ryo; Maruyama, Osamu; Yamane, Takashi; Shirasu, Akio; Tatsumi, Eisuke; Taenaka, Yoshiyuki

    2017-03-01

    A long-term durability test was conducted on a newly developed axial-flow ventricular assist device (VAD) with hydrodynamic bearings. The mock circulatory loop consisted of a diaphragm pump with a mechanical heart valve, a reservoir, a compliance tank, a resistance valve, and flow paths made of polymer or titanium. The VAD was installed behind the diaphragm pump. The blood analog fluid was a saline solution with added glycerin at a temperature of 37 °C. A pulsatile flow was introduced into the VAD over a range of flow rates to realize a positive flow rate and a positive pressure head at a given impeller rotational speed, yielding a flow rate of 5 L/min and a pressure of 100 mmHg. Pulsatile flow conditions were achieved with the diastolic and systolic flow rates of ~0 and 9.5 L/min, respectively, and an average flow rate of ~5 L/min at a pulse rate of 72 bpm. The VAD operation was judged by not only the rotational speed of the impeller, but also the diastolic, systolic, and average flow rates and the average pressure head of the VAD. The conditions of the mock circulatory loop, including the pulse rate of the diaphragm pump, the fluid temperature, and the fluid viscosity were maintained. Eight VADs were tested with testing periods of 2 years, during which they were continuously in operation. The VAD performance factors, including the power consumption and the vibration characteristics, were kept almost constant. The long-term durability of the developed VAD was successfully demonstrated.

  3. A model to simulate the haemodynamic effects of right heart pulsatile flow after modified Fontan procedure.

    PubMed Central

    Tamaki, S; Kawazoe, K; Yagihara, T; Abe, T

    1992-01-01

    The effect of pulsatile pulmonary flow after the modified Fontan procedure was examined in a model that simulated the right heart. An inlet overflow tank (preload), axial pulsatile pump, Wind-Kessel model (afterload), and an outlet overflow tank were connected in series. The standard conditions were flow 2.00 l/min with 12 mm Hg preload pressure, 3.0 Wood units resistance, and an outlet overflow tank pressure at 6 mm Hg. The pump rate was set at 80 beats/min. The simulated pulmonary arterial pressure and pulmonary flow waves produced by this model closely resembled those obtained from patients who had undergone the modified Fontan procedure. All variables except the preload were fixed and changes in pulmonary flow were examined at preload pressures of 8, 12, 15, and 17 mm Hg. As the peak pulmonary arterial pressure increased so did pulmonary flow, until it was greater than during the non-pulsatile state. Because the afterload of this model was fixed, this result suggests that there was a concomitant decrease in resistance. This model indicates that pulsatile pulmonary blood flow is likely to have a beneficial effect on the pulmonary circulation after the modified Fontan procedure. PMID:1540439

  4. A computer simulation model for Doppler ultrasound signals from pulsatile blood flow in stenosed vessels.

    PubMed

    Gao, Lian; Zhang, Yufeng; Zhang, Kexin; Cai, Guanghui; Zhang, Junhua; Shi, Xinling

    2012-09-01

    A computer simulation model based on an analytic flow velocity distribution is proposed to generate Doppler ultrasound signals from pulsatile blood flow in the vessels with various stenosis degrees. The model takes into account the velocity field from pulsatile blood flow in the stenosed vessels, sample volume shape and acoustic factors that affect the Doppler signals. By analytically solving the Navier-Stokes equations, the velocity distributions of pulsatile blood flow in the vessels with various stenosis degrees are firstly calculated according to the velocity at the axis of the circular tube. Secondly, power spectral density (PSD) of the Doppler signals is estimated by summing the contribution of all scatterers passing through the sample volume grouped into elemental volumes. Finally, Doppler signals are generated using cosine-superposed components that are modulated by the PSD functions that vary over the cardiac cycle. The results show that the model generates Doppler blood flow signals with characteristics similar to those found in practice. It could be concluded that the proposed approach offers the advantages of computational simplicity and practicality for simulating Doppler ultrasound signals from pulsatile blood flow in stenosed vessels. Copyright © 2012 Elsevier Ltd. All rights reserved.

  5. Gaseous micro-emboli activity during cardiopulmonary bypass in adults: pulsatile flow versus nonpulsatile flow.

    PubMed

    Dodonov, Mikhail; Milano, Aldo; Onorati, Francesco; Dal Corso, Bruno; Menon, Tiziano; Ferrarini, Daniele; Tessari, Maddalena; Faggian, Giuseppe; Mazzucco, Alessandro

    2013-04-01

    Cardiopulmonary bypass (CPB) has a risk of cerebral injury, with an important role of gaseous micro-emboli (GME) coming from the CPB circuit. Pulsatile perfusion is supposed to perform specific conditions for supplementary GME activity. We aimed to determine whether pulsatile CPB augments production and delivery of GME and evaluate the role of different events in GME activity during either type of perfusion. Twenty-four patients who underwent on-pump coronary artery bypass grafting surgery at the University of Verona were divided equally into two groups-pulsatile perfusion (PP) group and nonpulsatile perfusion (NP) group. The circuit included a JostraHL-20 roller pump set in pulsatile or nonpulsatile mode, an open Sorin Synthesis membrane oxygenator with integrated screen-type arterial filter, and phosphorylcholine-coated tubes. Hemodynamic flow evaluation was performed in terms of energy equivalent pressure and surplus hemodynamic energy (SHE). GME were counted by means of a GAMPT BCC200 bubble counter (GAMPT, Zappendorf, Germany) with two probes placed at postpump and postarterial filter positions. Results were evaluated in terms of GME number, GME volume, number of over-ranged GME from both probes, and series of filtering indexes. In PP mode, the pump produced and delivered along the circuit significantly higher amounts of SHE than in NP mode. At the venous postpump site, GME number was significantly higher during PP but no difference was found in terms of GME volume or number of over-ranged bubbles. No significant difference in GME number, GME volume, or number of over-ranges was found at the postarterial filter site. Filtering indexes were similar between the two groups. Neither type of perfusion was shown to contribute to excessive GME production during the most important perfusionist manipulation. Pulsatility leads to GME increment by splitting and size diminishing of the existing bubbles but not by additional gas production. PP augmented GME number at the

  6. Vortex generation in pulsatile flow through arterial bifurcation models including the human carotid artery.

    PubMed

    Fukushima, T; Homma, T; Harakawa, K; Sakata, N; Azuma, T

    1988-08-01

    Visualization experiments were performed to elucidate the complicated flow pattern in pulsatile flow through arterial bifurcations. Human common carotid arteries, which were made transparent, and glass-models simulating Y- and T-shaped bifurcations were used. Pulsatile flow with wave forms similar to those of arterial flow was generated with a piston pump, elastic tube, airchamber, and valves controlling the outflow resistance. Helically recirculating flow with a pattern similar to that of the horseshoe vortex produced around wall-based protuberances in circular tubes was observed in pulsatile flow through all the bifurcations used in the present study. This flow type, which we shall refer to as the horseshoe vortex, has also been demonstrated to occur at the human common carotid bifurcation in steady flow with Reynolds numbers above 100. Time-varying flows also produced the horseshoe vortex mostly during the decelerating phase. Fluid particles of dye solution approaching the bifurcation apex diverged, divided into two directions perpendicularly, and then showed helical motion representing the horseshoe vortex formation. While this helical flow was produced, the stagnation points appeared on the wall upstream of the apex. Their position was dependent upon the flow distribution ratio between the branches in the individual arteries. The region affected by the horseshoe vortex was smaller during pulsatile flow than during steady flow. Lowering the Reynolds number together with the Womersley number weakened the intensity of helical flow. A separation bubble, resulting from the divergence or wall roughness, was observed at the outer or inner wall of the branch vessels and made the flow more complicated.

  7. Alkaline phosphatase in osteoblasts is down-regulated by pulsatile fluid flow

    NASA Technical Reports Server (NTRS)

    Hillsley, M. V.; Frangos, J. A.

    1997-01-01

    It is our hypothesis that interstitial fluid flow plays a role in the bone remodeling response to mechanical loading. The fluid flow-induced expression of three proteins (collagen, osteopontin, and alkaline phosphatase) involved in bone remodeling was investigated. Rat calvarial osteoblasts subjected to pulsatile fluid flow at an average shear stress of 5 dyne/cm2 showed decreased alkaline phosphatase (AP) mRNA expression after only 1 hour of flow. After 3 hours of flow, AP mRNA levels had decreased to 30% of stationary control levels and remained at this level for an additional 5 hours of flow. Steady flow (4 dyne/cm2 fluid shear stress), in contrast, resulted in a delayed and less dramatic decrease in AP mRNA expression to 63% of control levels after 8 hours of flow. The reduced AP mRNA expression under pulsatile flow conditions was followed by reduced AP enzyme activity after 24 hours. No changes in collagen or osteopontin mRNA expression were detected over 8 hours of pulsatile flow. This is the first time fluid flow has been shown to affect gene expression in osteoblasts.

  8. Alkaline phosphatase in osteoblasts is down-regulated by pulsatile fluid flow

    NASA Technical Reports Server (NTRS)

    Hillsley, M. V.; Frangos, J. A.

    1997-01-01

    It is our hypothesis that interstitial fluid flow plays a role in the bone remodeling response to mechanical loading. The fluid flow-induced expression of three proteins (collagen, osteopontin, and alkaline phosphatase) involved in bone remodeling was investigated. Rat calvarial osteoblasts subjected to pulsatile fluid flow at an average shear stress of 5 dyne/cm2 showed decreased alkaline phosphatase (AP) mRNA expression after only 1 hour of flow. After 3 hours of flow, AP mRNA levels had decreased to 30% of stationary control levels and remained at this level for an additional 5 hours of flow. Steady flow (4 dyne/cm2 fluid shear stress), in contrast, resulted in a delayed and less dramatic decrease in AP mRNA expression to 63% of control levels after 8 hours of flow. The reduced AP mRNA expression under pulsatile flow conditions was followed by reduced AP enzyme activity after 24 hours. No changes in collagen or osteopontin mRNA expression were detected over 8 hours of pulsatile flow. This is the first time fluid flow has been shown to affect gene expression in osteoblasts.

  9. Pulsatile Flow and Gas Transport of Blood over an Array of Cylinders

    NASA Astrophysics Data System (ADS)

    Chan, Kit Yan

    2005-11-01

    In the artificial lung, blood passes through an array of micro-fibers and the gas transfer is strongly dependent on the flow field. The blood flow is unsteady and pulsatile. We have numerically simulated pulsatile flow and gas transfer of blood (modeled as a Casson fluid) over arrays of cylindrical micro-fibers. Oxygen and carbon dioxide are assumed to be in local equilibrium with hemoglobin in blood; and the carbon dioxide facilitated oxygen transport is incorporated into the model by allowing the coupling of carbon dioxide partial pressure and oxygen saturation. The pulsatile flow inputs considered are the sinusoidal and the cardiac waveforms. The squared and staggered arrays of arrangement of the cylinders are considered in this study. Gas transport can be enhanced by: increasing the oscillation frequency; increasing the Reynolds number; increasing the oscillation amplitude; decreasing the void fraction; the use of the cardiac pulsatile input. The overall gas transport is greatly enhanced by the presence of hemoglobin in blood even though the non-Newtonian effect of blood tends to decrease the size and strength of vortices. The pressure drop is also presented as it is an important design parameter confronting the heart.

  10. An Investigation of Pulsatile Flow Past Two Cylinders as a Model of Blood Flow in an Artificial Lung

    PubMed Central

    Lin, Yu-chun; Khanafer, Khalil M.; Bartlett, Robert H.; Hirschl, Ronald B.; Bull, Joseph L.

    2011-01-01

    Pulsatile flow across two circular cylinders with different geometric arrangements is studied experimentally using the particle image velocimetry method and numerically using the finite element method. This investigation is motivated the need to optimize gas transfer and fluid mechanical impedance for a total artificial lung, in which the right heart pumps blood across a bundle of hollow microfibers. Vortex formation was found to occur at lower Reynolds numbers in pulsatile flow than in steady flow, and the vortex structure depends strongly on the geometric arrangement of the cylinders and on the Reynolds and Stokes numbers. PMID:21701672

  11. Measuring pulsatile flow in cerebral arteries using 4D phase-contrast MR imaging.

    PubMed

    Wåhlin, A; Ambarki, K; Birgander, R; Wieben, O; Johnson, K M; Malm, J; Eklund, A

    2013-09-01

    4D PCMRI can be used to quantify pulsatile hemodynamics in multiple cerebral arteries. The aim of this study was to compare 4D PCMRI and 2D PCMRI for assessments of pulsatile hemodynamics in major cerebral arteries. We scanned the internal carotid artery, the anterior cerebral artery, the basilar artery, and the middle cerebral artery in 10 subjects with a single 4D and multiple 2D PCMRI acquisitions by use of a 3T system and a 32-channel head coil. We assessed the agreement regarding net flow and the volume of arterial pulsatility (ΔV) for all vessels. 2D and 4D PCMRI produced highly correlated results, with r = 0.86 and r = 0.95 for ΔV and net flow, respectively (n = 69 vessels). These values increased to r = 0.93 and r = 0.97, respectively, during investigation of a subset of measurements with <5% variation in heart rate between the 4D and 2D acquisition (n = 31 vessels). Significant differences were found for ICA and MCA net flow (P = .004 and P < .001, respectively) and MCA ΔV (P = .006). However, these differences were attenuated and no longer significant when the subset with stable heart rate (n = 31 vessels) was analyzed. 4D PCMRI provides a powerful methodology to measure pulsatility of the larger cerebral arteries from a single acquisition. A large part of differences between measurements was attributed to physiologic variations. The results were consistent with 2D PCMRI.

  12. Neurocognitive function in destination therapy patients receiving continuous-flow vs pulsatile-flow left ventricular assist device support.

    PubMed

    Petrucci, Ralph J; Rogers, Joseph G; Blue, Laura; Gallagher, Colleen; Russell, Stuart D; Dordunoo, Dzifa; Jaski, Brian E; Chillcott, Suzanne; Sun, Benjamin; Yanssens, Tammy L; Tatooles, Antone; Koundakjian, Lalig; Farrar, David J; Slaughter, Mark S

    2012-01-01

    The HeartMate II (Thoratec Corp, Pleasanton, CA) continuous-flow left ventricular assist device (LVAD) improved survival in destination therapy (DT) patients during a randomized trial compared with pulsatile-flow LVADs. This study documented changes in cognitive performance in DT patients from that trial to determine if there were differences between continuous-flow and pulsatile-flow support. Data were collected in a sub-study from 96 HeartMate II continuous-flow and 30 HeartMate XVE pulsatile-flow LVAD patients from 12 of the 35 trial sites that followed the same serial neurocognitive (NC) testing protocol at 1, 3, 6, 12, and 24 months after LVAD implantation. Spatial perception, memory, language, executive functions, and processing speed were the domains assessed with 10 standard cognitive measures. Differences over time and between LVAD type were evaluated with linear mixed-effects modeling. From 1 to 24 months after LVAD implantation, changes in NC functions were stable or showed improvement in all domains, and there were no differences between the continuous-flow and pulsatile-flow groups. Data at 24 months were only available from patients with the continuous-flow LVAD due to the limited durability of the HeartMate XVE device. There was no decline in any NC domain over the time of LVAD support. Missing data not collected from patients who died could have resulted in a bias toward inflated study results. The NC performance of advanced heart failure patients supported with continuous-flow and pulsatile-flow LVADs shows stabilization or improvement during support for up to 24 months. Copyright © 2012 International Society for Heart and Lung Transplantation. Published by Elsevier Inc. All rights reserved.

  13. Cyclic variations of high-frequency ultrasonic backscattering from blood under pulsatile flow.

    PubMed

    Huang, Chih-Chung

    2009-08-01

    It was shown previously that ultrasonic scattering from whole blood varies during the flow cycle under pulsatile flow both in vitro and in vivo. It has been postulated that the cyclic variations of the backscattering signal are associated with red blood cell (RBC) aggregation in flowing whole blood. To obtain a better understanding of the relationship between blood backscattering and RBC aggregation behavior for pulsatile flowing blood, the present study used high-frequency ultrasound to characterize blood properties. The backscattering signals from both whole blood and an RBC suspension at different peak flow velocities (from 10 to 30 cm/s) and hematocrits (20% and 40%) under pulsatile flow (stroke rate of 20 beats/min) were measured with 3 single-element transducers at frequencies of 10, 35, and 50 MHz in a mock flow loop. To avoid the frequency response problem of a Doppler flowmeter, the integrated backscatter (IB) and flow velocity as functions of time were calculated directly using RF signals from flowing blood. The experimental results showed that cyclic variations of the IB curve were clearly observed at a low flow velocity and a hematocrit of 40% when using 50 MHz ultrasound, and that these variations became weaker as the peak flow velocity increased. However, these cyclic variations were detected only at 10 cm/s when using 10 MHz ultrasound. These results demonstrate that a high flow velocity can stop the formation of rouleaux and that a high hematocrit can promote RBC aggregation to produce cyclic variations of the backscattering signal under pulsatile flow. In addition, slight cyclic variations of the IB curve for an RBC suspension were observed at 35 and 50 MHz. Furthermore, the peak of the IB curve from whole blood led the peak of the velocity waveform when using high-frequency ultrasound, which could be explained by the assumption that a rapid flow can promote RBC aggregation under pulsatile flow. Together, the experimental results showed that the

  14. Computational model for the transition from peristaltic to pulsatile flow in the embryonic heart tube.

    PubMed

    Taber, Larry A; Zhang, Jinmei; Perucchio, Renato

    2007-06-01

    Early in development, the heart is a single muscle-wrapped tube without formed valves. Yet survival of the embryo depends on the ability of this tube to pump blood at steadily increasing rates and pressures. Developmental biologists historically have speculated that the heart tube pumps via a peristaltic mechanism, with a wave of contraction propagating from the inflow to the outflow end. Physiological measurements, however, have shown that the flow becomes pulsatile in character quite early in development, before the valves form. Here, we use a computational model for flow though the embryonic heart to explore the pumping mechanism. Results from the model show that endocardial cushions, which are valve primordia arising near the ends of the tube, induce a transition from peristaltic to pulsatile flow. Comparison of numerical results with published experimental data shows reasonably good agreement for various pressure and flow parameters. This study illustrates the interrelationship between form and function in the early embryonic heart.

  15. Estimation of Several Turbulent Fluctuation Quantities Using an Approximate Pulsatile Flow Model

    SciTech Connect

    Dechant, Lawrence J.

    2015-12-01

    Turbulent fluctuation behavior is approximately modeled using a pulsatile flow model analogy.. This model follows as an extension to the turbulent laminar sublayer model developed by Sternberg (1962) to be valid for a fully turbulent flow domain. Here unsteady turbulent behavior is modeled via a sinusoidal pulsatile approach. While the individual modes of the turbulent flow fluctuation behavior are rather crudely modeled, approximate temporal integration yields plausible estimates for Root Mean Square (RMS) velocity fluctuations. RMS pressure fluctuations and spectra are of particular interest and are estimated via the pressure Poisson expression. Both RMS and Power Spectral Density (PSD), i.e. spectra are developed. Comparison with available measurements suggests reasonable agreement. An additional fluctuating quantity, i.e. RMS wall shear fluctuation is also estimated, yielding reasonable agreement with measurement.

  16. Fluid particle motion and Lagrangian velocities for pulsatile flow through a femoral artery branch model

    NASA Technical Reports Server (NTRS)

    Cho, Y. I.; Crawford, D. W.; Back, L. H.; Back, M. R.

    1987-01-01

    A flow visualization study using selective dye injection and frame by frame analysis of a movie provided qualitative and quantitative data on the motion of marked fluid particles in a 60 degree artery branch model for simulation of physiological femoral artery flow. Physical flow features observed included jetting of the branch flow into the main lumen during the brief reverse flow period, flow separation along the main lumen wall during the near zero flow phase of diastole when the core flow was in the downstream direction, and inference of flow separation conditions along the wall opposite the branch later in systole at higher branch flow ratios. There were many similarities between dye particle motions in pulsatile flow and the comparative steady flow observations.

  17. Precise position control of a helical magnetic robot in pulsatile flow using the rotating frequency of the external magnetic field

    NASA Astrophysics Data System (ADS)

    Kim, Jongyul; Nam, Jaekwang; Lee, Wonseo; Jang, Bongjun; Jang, Gunhee

    2017-05-01

    We propose a position control method for a helical magnetic robot (HMR) that uses the rotating frequency of the external rotating magnetic field (ERMF) to minimize the position fluctuation of the HMR caused by pulsatile flow in human blood vessels. We prototyped the HMR and conducted several experiments in pseudo blood vessel environments with a peristaltic pump. We experimentally obtained the relation between the flow rate and the rotating frequency of the ERMF required to make the HMR stationary in a given pulsatile flow. Then we approximated the pulsatile flow by Fourier series and applied the required ERMF rotating frequency to the HMR in real time. Our proposed position control method drastically reduced the position fluctuation of the HMR under pulsatile flow.

  18. Simulations of pulsatile suspension flow through bileaflet mechanical heart valves to quantify platelet damage

    NASA Astrophysics Data System (ADS)

    Yun, Brian; Aidun, Cyrus; Yoganathan, Ajit

    2012-11-01

    Studies have shown that high shear stress and long exposure times on platelets have a strong impact on thromboembolic complications in bileaflet mechanical heart valves (BMHVs). This numerical study quantifies the platelet damage incurred in pulsatile flow through various BMHV designs. The lattice-Boltzmann method with external boundary force (LBM-EBF) was implemented to simulate pulsatile flow and capture the dynamics and surface shear stresses of modeled platelets with realistic geometry. The platelets are released in key regions of interest in the geometry as well as at various times of the cardiac cycle. The platelet damage is quantified using a linear shear stress-exposure time blood damage index (BDI) model. The multiscale computational method used to quantitatively measure the BDI during the pulsatile flow has been validated as being able to accurately capture bulk BMHV fluid flow and for accurately quantifying platelet damage in BMHV flows. These simulations will further knowledge of the geometric features and cardiac cycle times that most affect platelet damage. This study will ultimately lead to optimization of BMHV design in order to minimize thromboembolic complications.

  19. Fiber-Based Laser Speckle Imaging for the Detection of Pulsatile Flow

    PubMed Central

    Regan, Caitlin; Yang, Bruce Y.; Mayzel, Kent C.; Ramirez-San-Juan, Julio C.; Wilder-Smith, Petra; Choi, Bernard

    2015-01-01

    Background and Objective In endodontics, a major diagnostic challenge is the accurate assessment of pulp status. In this study, we designed and characterized a fiber-based laser speckle imaging system to study pulsatile blood flow in the tooth. Study Design/Materials and Methods To take transilluminated laser speckle images of the teeth, we built a custom fiber-based probe. To assess our ability to detect changes in pulsatile flow, we performed in vitro and preliminary in vivo tests on tissue-simulating phantoms and human teeth. We imaged flow of intralipid in a glass microchannel at simulated heart rates ranging from 40 beats/minute (bpm) to 120 bpm (0.67–2.00 Hz). We also collected in vivo data from the upper front incisors of healthy subjects. From the measured raw speckle data, we calculated temporal speckle contrast versus time. With frequency-domain analysis, we identified the frequency components of the contrast waveforms. Results With our approach, we observed in vitro the presence of pulsatile flow at different simulated heart rates. We characterized simulated heart rate with an accuracy of and >98%. In the in vivo proof-of-principle experiment, we measured heart rates of 69, 90, and 57 bpm, which agreed with measurements of subject heart rate taken with a wearable, commercial pulse oximeter. Conclusions We designed, built, and tested the performance of a dental imaging probe. Data from in vitro and in vivo tests strongly suggest that this probe can detect the presence of pulsatile flow. LSI may enable endodontists to noninvasively assess pulpal vitality via direct measurement of blood flow. PMID:26202900

  20. Clinical effectiveness of centrifugal pump to produce pulsatile flow during cardiopulmonary bypass in patients undergoing cardiac surgery.

    PubMed

    Gu, Y John; van Oeveren, Willem; Mungroop, Hubert E; Epema, Anne H; den Hamer, Inez J; Keizer, Jorrit J; Leuvenink, Ron P; Mariani, Massimo A; Rakhorst, Gerhard

    2011-02-01

    Although the centrifugal pump has been widely used as a nonpulsatile pump for cardiopulmonary bypass (CPB), little is known about its performance as a pulsatile pump for CPB, especially on its efficacy in producing hemodynamic energy and its clinical effectiveness. We performed a study to evaluate whether the Rotaflow centrifugal pump produces effective pulsatile flow during CPB and whether the pulsatile flow in this setting is clinically effective in adult patients undergoing cardiac surgery. Thirty-two patients undergoing CPB for elective coronary artery bypass grafting were randomly allocated to a pulsatile perfusion group (n = 16) or a nonpulsatile perfusion group (n = 16). All patients were perfused with the Rotaflow centrifugal pump. In the pulsatile group, the centrifugal pump was adjusted to the pulsatile mode (60 cycles/min) during aortic cross-clamping, whereas in the nonpulsatile group, the pump was kept in its nonpulsatile mode during the same period of time. Compared with the nonpulsatile group, the pulsatile group had a higher pulse pressure (P < 0.01) and a fraction higher energy equivalent pressure (EEP, P = 0.058). The net gain of pulsatile flow, represented by the surplus hemodynamic energy (SHE), was found much higher in the CPB circuit than in patients (P < 0.01). Clinically, there was no difference between the pulsatile and nonpulsatile groups with regard to postoperative acute kidney injury, endothelial activation, or inflammatory response. Postoperative organ function and the duration of hospital stay were similar in the two patient groups. In conclusion, pulsatile CPB with the Rotaflow centrifugal pump is associated with a small gain of EEP and SHE, which does not seem to be clinically effective in adult cardiac surgical patients.

  1. A pulsatile flow model for in vitro quantitative evaluation of prosthetic valve regurgitation.

    PubMed

    Giuliatti, S; Gallo, L; Almeida-Filho, O C; Schmidt, A; Marin-Neto, J A; Pelá, C A; Maciel, B C

    2000-03-01

    A pulsatile pressure-flow model was developed for in vitro quantitative color Doppler flow mapping studies of valvular regurgitation. The flow through the system was generated by a piston which was driven by stepper motors controlled by a computer. The piston was connected to acrylic chambers designed to simulate "ventricular" and "atrial" heart chambers. Inside the "ventricular" chamber, a prosthetic heart valve was placed at the inflow connection with the "atrial" chamber while another prosthetic valve was positioned at the outflow connection with flexible tubes, elastic balloons and a reservoir arranged to mimic the peripheral circulation. The flow model was filled with a 0.25% corn starch/water suspension to improve Doppler imaging. A continuous flow pump transferred the liquid from the peripheral reservoir to another one connected to the "atrial" chamber. The dimensions of the flow model were designed to permit adequate imaging by Doppler echocardiography. Acoustic windows allowed placement of transducers distal and perpendicular to the valves, so that the ultrasound beam could be positioned parallel to the valvular flow. Strain-gauge and electromagnetic transducers were used for measurements of pressure and flow in different segments of the system. The flow model was also designed to fit different sizes and types of prosthetic valves. This pulsatile flow model was able to generate pressure and flow in the physiological human range, with independent adjustment of pulse duration and rate as well as of stroke volume. This model mimics flow profiles observed in patients with regurgitant prosthetic valves.

  2. Orientation-independent rapid pulsatile flow measurement using dual-angle Doppler OCT

    PubMed Central

    Peterson, Lindsy M; Gu, Shi; Jenkins, Michael W; Rollins, Andrew M

    2014-01-01

    Doppler OCT (DOCT) can provide blood flow velocity information which is valuable for investigation of microvascular structure and function. However, DOCT is only sensitive to motion parallel with the imaging beam, so that knowledge of flow direction is needed for absolute velocity determination. Here, absolute volumetric flow is calculated by integrating velocity components perpendicular to the B-scan plane. These components are acquired using two illumination beams with a predetermined angular separation, produced by a delay encoded technique. This technology enables rapid pulsatile flow measurement from single B-scans without the need for 3-D volumetric data or knowledge of blood vessel orientation. PMID:24575344

  3. Finite element analysis of nonlinear pulsatile suspension flow dynamics in blood vessels with aneurysm.

    PubMed

    Kumar, B V; Naidu, K B

    1995-01-01

    A nonlinear pulsatile suspension flow in a dilated vessel is numerically analysed. Two sets of highly coupled nonlinear partial differential equations governing the suspension flow are numerically solved, to simulate the suspension flow dynamics. A transient velocity-pressure (UVP) finite element method (FEM) and a stable time integration scheme, based on a predictor-corrector strategy, with constant error monitoring are employed in the flow analysis. The pulsatile suspension flow is characterized by analysing the flow, pressure and stress fields. Effects of the nonlinear particulate phase on the nonlinear suspending fluid phase are brought out by comparing the suspension flow results with those of homogeneous flow. Particles are seen to dampen the flow velocity, wall and central axis pressure, pressure gradient and wall shear stress. time-dependent recirculation regions which are sensitive to the presence of particles are seen in the dilated portion of the vessel. These recirculation regions favour thrombogenesis. The nonlinear effects due to the vessel geometry and those due to the convective terms dominate the dampening effect of the particles. These nonlinear effects are depicted through the transverse velocity and pressure plots. Wall shear stresses of suspension flow are not only high but also alternate in direction.

  4. Decreased pulsatile blood flow in the patella in patellofemoral pain syndrome.

    PubMed

    Näslund, Jan; Waldén, Markus; Lindberg, Lars-Göran

    2007-10-01

    Anterior knee pain without clinical and radiologic abnormalities has primarily been explained from a purely structural view. A recently proposed biologic and homeostatic explanation questions the malalignment theory. No objective measurement of the pathophysiology responsible for changes in local homeostasis has been presented. Flexing the knee joint interferes with the perfusion of the patellar bone in patellofemoral pain syndrome. Case control study; Level of evidence, 4. Pulsatile blood flow in the patella was measured continuously and noninvasively using photoplethysmography. Measurements were made with the patient in a resting position with knee flexion of 20 degrees and after passive knee flexion to 90 degrees. In total, 22 patients with patellofemoral pain syndrome were examined bilaterally, and 33 subjects with healthy knees served as controls. The pulsatile blood flow in the patient group decreased after passive knee flexion from 20 degrees to 90 degrees (systematic change in position, or relative position [RP] = -0.32; 95% confidence interval for RP, -0.48 to -0.17), while the response in the control group showed no distinct pattern (RP = 0.17; 95% confidence interval for RP, -0.05 to 0.31). The difference between the groups was significant (P = .0002). The median change in patients was -26% (interquartile range, 37). Pulsatile patellar blood flow in patellofemoral pain syndrome patients is markedly reduced when the knee is being flexed, which supports the previous notion of an ischemic mechanism involved in the pathogenesis of this pain syndrome.

  5. Increased Pulsatile Cerebral Blood Flow, Cerebral Vasodilation, and Post-syncopal Headache in Adolescents

    PubMed Central

    Ocon, Anthony J.; Messer, Zachary; Medow, Marvin S.; Stewart, Julian M.

    2011-01-01

    Objective We hypothesize that following a sudden decrease in cerebral blood flow velocity (CBFV) in adolescents at faint, rapid hyperemic pulsatile CBFV occurs upon the return to the supine position, and is associated with post-syncopal headache. Study design This case-control study involved 16 adolescent subjects with history of fainting and headaches. We induced faint during 70° tilt-table testing and measured mean arterial pressure (MAP), heart rate (HR), end-tidal CO2, and CBFV. Fifteen control subjects were similarly evaluated with a tilt but did not faint, and comparisons with fainters were made at equivalent defined time points. Results Baseline values were similar between groups. Upon fainting, MAP decreased 49% in fainters vs. 6% in controls (P<0.001). HR decreased 15% in fainters and increased 35% in controls (P<0.001). In fainters, cerebrovascular critical closing pressure increased markedly resulting in reduced diastolic (-66%) and mean CBFV (-46%) at faint; systolic CBFV was similar to controls. Pulsatile CBFV (systolic – diastolic CBFV) increased 38% in fainters, driving flow-mediated dilation of cerebral vessels. Returning to supine, fainters’ CBFV exhibited increased systolic and decreased diastolic flows compared with controls (P<0.02). Conclusion Increased pulsatile CBFV during and following faint may cause post-syncopal cerebral vasodilation and headache. PMID:21596391

  6. Simultaneous pulsatile flow and oscillating wall of a non-Newtonian liquid

    NASA Astrophysics Data System (ADS)

    Herrera-Valencia, E. E.; Sánchez-Villavicencio, M. L.; Calderas, F.; Pérez-Camacho, M.; Medina-Torres, L.

    2016-11-01

    In this work, analytical predictions of the rectilinear flow of a non-Newtonian liquid are given. The fluid is subjected to a combined flow: A pulsatile time-dependent pressure gradient and a random longitudinal vibration at the wall acting simultaneously. The fluctuating component of the combined pressure gradient and oscillating flow is assumed to be of small amplitude and can be adequately represented by a weakly stochastic process, for which a quasi-static perturbation solution scheme is suggested, in terms of a small parameter. This flow is analyzed with the Tanner constitutive equation model with the viscosity function represented by the Ellis model. According to the coupled Tanner-Ellis model, the flow enhancement can be separated in two contributions (pulsatile and oscillating mechanisms) and the power requirement is always positive and can be interpreted as the sum of a pulsatile, oscillating, and the coupled systems respectively. Both expressions depend on the amplitude of the oscillations, the perturbation parameter, the exponent of the Ellis model (associated to the shear thinning or thickening mechanisms), and the Reynolds and Deborah numbers. At small wall stress values, the flow enhancement is dominated by the axial wall oscillations whereas at high wall stress values, the system is governed by the pulsating noise perturbation. The flow transition is obtained for a critical shear stress which is a function of the Reynolds number, dimensionless frequency and the ratio of the two amplitudes associated with the pulsating and oscillating perturbations. In addition, the flow enhancement is compared with analytical and numerical predictions of the Reiner-Phillipoff and Carreau models. Finally, the flow enhancement and power requirement are predicted using biological rheometric data of blood with low cholesterol content.

  7. Pulsatile flow in a compliant stenosed asymmetric model

    NASA Astrophysics Data System (ADS)

    Usmani, Abdullah Y.; Muralidhar, K.

    2016-12-01

    Time-varying velocity field in an asymmetric constricted tube is experimentally studied using a two-dimensional particle image velocimetry system. The geometry resembles a vascular disease which is characterized by arterial narrowing due to plaque deposition. The present study compares the nature of flow patterns in rigid and compliant asymmetric constricted tubes for a range of dimensionless parameters appearing in a human artery. A blood analogue fluid is employed along with a pump that mimics cardioflow conditions. The peak Reynolds number range is Re 300-800, while the Womersley number range considered in experiments is Wo 6-8. These values are based on the peak velocity in a straight rigid tube connected to the model, over a pulsation frequency range of 1.2-2.4 Hz. The medial-plane velocity distribution is used to investigate the nature of flow patterns. Temporal distribution of stream traces and hemodynamic factors including WSS, TAWSS and OSI at important phases of the pulsation cycle are discussed. The flow patterns obtained from PIV are compared to a limited extent against numerical simulation. Results show that the region downstream of the constriction is characterized by a high-velocity jet at the throat, while a recirculation zone, attached to the wall, evolves in time. Compliant models reveal large flow disturbances upstream during the retrograde flow. Wall shear stress values are lower in a compliant model as compared to the rigid. Cross-plane flow structures normal to the main flow direction are visible at select phases of the cycle. Positive values of largest Lyapunov exponent are realized for wall movement and are indicative of chaotic motion transferred from the flow to the wall. These exponents increase with Reynolds number as well as compliance. Period doubling is observed in wall displacement of highly compliant models, indicating possible triggering of hemodynamic events in a real artery that may cause fissure in the plaque deposits.

  8. Particulate suspension effect on peristaltically induced unsteady pulsatile flow in a narrow artery: Blood flow model.

    PubMed

    Abdelsalam, Sara I; Vafai, Kambiz

    2017-01-01

    This work is concerned with theoretically investigating the pulsatile flow of a fluid with suspended particles in a flow driven by peristaltic waves that deform the wall of a small blood artery in the shape of traveling sinusoidal waves with constant velocity. The problem formulation in the wave frame of reference is presented and the governing equations are developed up to the second-order in terms of the asymptotic expansion of Womersley number which characterizes the unsteady effect in the wave frame. We suppose that the flow rate imposed, in this frame, is a function versus time. The analytical solution of the problem is achieved using the long wavelength approximation where Reynolds number is considered small with reference to the blood flow in the circulatory system. The present study inspects novelties brought about into the classic peristaltic mechanism by the inclusion of Womersley number, and the critical values of concentration and occlusion on the flow characteristics in a small artery with flexible walls. Momentum and mass equations for the fluid and particle phases are solved by means of a perturbation analysis in which the occlusion is a small parameter. Closed form solutions are obtained for the fluid/particle velocity distributions, stream function, pressure rise, friction force, wall shear stress, instantaneous mechanical efficiency, and time-averaged mechanical efficiency. The physical explanation of the Segré-Silberberg effect is introduced and the trapping phenomenon of plasma for haemodilution and haemoconcentration cases is discussed. It has been deduced that the width of the closed plasma streamlines is increased while their number is minimally reduced in case of haemoconcentration. This mathematical problem has numerous applications in various branches in science including blood flow in small blood vessels. Several results of other models can be deduced as limiting cases of our situation.

  9. Study of laminar-turbulent flow transition under pulsatile conditions in a constricted channel

    NASA Astrophysics Data System (ADS)

    Khair, Abul; Wang, Bing-Chen; Kuhn, David C. S.

    2015-10-01

    In this paper, direct numerical simulation is performed to investigate a pulsatile flow in a constricted channel to gain physical insights into laminar-turbulent-laminar flow transitions. An in-house computer code is used to conduct numerical simulations based on available high-performance shared memory parallel computing facilities. The Womersley number tested is fixed to 10.5 and the Reynolds number varies from 500 to 2000. The influences of the degree of stenosis and pulsatile conditions on flow transitions and structures are investigated. In the region upstream of the stenosis, the flow pattern is primarily laminar. Immediately after the stenosis, the flow recirculates under an adverse streamwise pressure gradient, and the flow pattern transitions from laminar to turbulent. In the region far downstream of the stenosis, the flow becomes re-laminarised. The physical characteristics of the flow field have been thoroughly analysed in terms of the mean streamwise velocity, turbulence kinetic energy, viscous wall shear stresses, wall pressure and turbulence kinetic energy spectra.

  10. [Pulsatile flow model with elastic blood vessels for duplex ultrasound studies].

    PubMed

    Petrick, J; Schlief, R; Zomack, M; Langholz, J; Urbank, A

    1992-12-01

    Using ultrasound duplex technique flow phenomena in patients' circulation can be examined. For the interpretation of these examinations it is necessary to have extensive knowledge on flow influencing parameters. This can be easily obtained from simplified flow models. This article describes the components of a flow model that allows examination of ultrasonic contrast media flowing through an artificial heart and vessel mimicking tubes. The artificial heart is the drive which pumps a water glycerol cellulose mixture through the circulation in a pulsatile manner. The shape of the ventricle, the compliance of the aorta, the viscosity of the flow medium and the wall elasticity of the examination vessel were taken into account. The attenuation caused by the surrounding tissue is simulated by a variable layer of castor oil. The flow model is suitable to produce flow profiles that are very similar to physiological profiles.

  11. [Design and preliminary experiment of an intelligentized physiologic pulsatile flow cardiac support system].

    PubMed

    Wei, Xinchuan; Wang, Daiyuan; Zhou, Ronghua; Dong, Yuchun; Yao, Junyan

    2005-08-01

    A patent cardiac support system which is used as a bridge treatment for acute myocardial infarction has been designed and tested in vitro and in two dogs in vivo. This is an easy-to-use intelligentized pulsatile flow cardiopulmonary bypass device to replace the function of heart. The device consists of two identical pumps and perfusion chambers, a sensing and control system, a gas exchanger between the vein and pump, two one way valves between pump and veins or arteries. Arterial pressure and EKG feedback mechanisms are used for maintaining blood pressure and coordinating the pumping activity with heart contraction. A prototype of the device was built to perform hydraulic in vitro tests with aims of verifying the new device's pumping behavior. Functional evaluation of the device was carried out by using it in a model circuit made with standard CPB components plus a mock hydraulic pipeline. This system demonstrated easy manipulation, good controllability, and provided a 65+/-2ml x beat(-1) flow volume. There was a linear correlation between peak pressure value and pulsatile frequency. In the two in vivo experiments, the primary objective was to determine whether the device could work well in dog, whether physiologic pulsatility could be achieved and whether the blood supply to heart should be sufficient during asystole status by drugs. The results suggest that all the goals have been achieved.

  12. Generating pulsatility by pump speed modulation with continuous-flow total artificial heart in awake calves.

    PubMed

    Fukamachi, Kiyotaka; Karimov, Jamshid H; Sunagawa, Gengo; Horvath, David J; Byram, Nicole; Kuban, Barry D; Dessoffy, Raymond; Sale, Shiva; Golding, Leonard A R; Moazami, Nader

    2017-04-08

    The purpose of this study was to evaluate the effects of sinusoidal pump speed modulation of the Cleveland Clinic continuous-flow total artificial heart (CFTAH) on hemodynamics and pump flow in an awake chronic calf model. The sinusoidal pump speed modulations, performed on the day of elective sacrifice, were set at ±15 and ± 25% of mean pump speed at 80 bpm in four awake calves with a CFTAH. The systemic and pulmonary arterial pulse pressures increased to 12.0 and 12.3 mmHg (±15% modulation) and to 15.9 and 15.7 mmHg (±25% modulation), respectively. The pulsatility index and surplus hemodynamic energy significantly increased, respectively, to 1.05 and 1346 ergs/cm at ±15% speed modulation and to 1.51 and 3381 ergs/cm at ±25% speed modulation. This study showed that it is feasible to generate pressure pulsatility with pump speed modulation; the platform is suitable for evaluating the physiologic impact of pulsatility and allows determination of the best speed modulations in terms of magnitude, frequency, and profiles.

  13. Numerical investigation of pulsatile flow in endovascular stents

    NASA Astrophysics Data System (ADS)

    Rouhi, A.; Piomelli, U.; Vlachos, P.

    2013-09-01

    The flow in a plane channel with two idealized stents (one Λ-shaped, the other X-shaped) is studied numerically. A periodic pressure gradient corresponding to one measured in the left anterior descending coronary artery was used to drive the flow. Two Reynolds numbers were examined, one (Re = 80) corresponding to resting conditions, the other (Re = 200) to exercise. The stents were implemented by an immersed boundary method. The formation and migration of vortices that had been observed experimentally was also seen here. In the previous studies, the compliance mismatch between stent and vessel was conjectured to be the reason for this phenomenon. However, in the present study we demonstrate that the vortices form despite the fact that the walls were rigid. Flow visualization and quantitative analysis lead us to conclude that this process is due to the stent wires that generate small localized recirculation regions that, when they interact with the near-wall flow reversal, result in the formation of these vortical structures. The recirculation regions grow and merge when the imposed waveform produces near-wall flow reversal, forming coherent quasi-spanwise vortices, that migrate away from the wall. The flow behavior due to the stents was compared with an unstented channel. The geometric characteristics of the Λ-stent caused less deviation of the flow from an unstented channel than the X-stent. Investigating the role of advection and diffusion indicated that at Re = 80 advection has negligible contribution in the transport mechanism. Advection plays a role in the generation of streamwise vortices created for both stents at both Reynolds numbers. The effect of these vortices on the near-wall flow behavior is more significant for the Λ-stent compared to the X-stent and at Re = 200 with respect to Re = 80. Finally, it was observed that increasing the Reynolds number leads to early vortex formation and the creation of the vortex in a stented channel is coincident with

  14. A theoretical computerized study for the electrical conductivity of arterial pulsatile blood flow by an elastic tube model.

    PubMed

    Shen, Hua; Zhu, Yong; Qin, Kai-Rong

    2016-12-01

    The electrical conductivity of pulsatile blood flow in arteries is an important factor for the application of the electrical impedance measurement system in clinical settings. The electrical conductivity of pulsatile blood flow depends not only on blood-flow-induced red blood cell (RBC) orientation and deformation but also on artery wall motion. Numerous studies have investigated the conductivity of pulsatile blood based on a rigid tube model, in which the effects of wall motion on blood conductivity are not considered. In this study, integrating Ling and Atabek's local flow theory and Maxwell-Fricke theory, we develop an elastic tube model to explore the effects of wall motion as well as blood flow velocity on blood conductivity. The simulation results suggest that wall motion, rather than blood flow velocity, is the primary factor that affects the conductivity of flowing blood in arteries.

  15. Experiments on Laminar to Turbulence Transition and Relaminarization in Pulsatile Flows

    NASA Astrophysics Data System (ADS)

    Gomez, Joan; Goushcha, Oleg; Andreopoulos, Yiannis

    2016-11-01

    Biological flows display laminar-turbulence-laminar transitions due to the cyclic nature of a beating heart. Addressing the question of how turbulence appears, decays and is suppressed in the cardiovascular system, particularly in the large arteries, is challenging due to flow unsteadiness, very complicated geometry and flow-wall interaction. In the present work we have designed and tested a facility to simulate unsteady pulsatile flows and the onset of transition under varying Reynolds and Womersley numbers. A moving piston is used to generate a flow pulsation and control the velocity amplitude. Time-Resolved Particle Image Velocimetry (TR-PIV) techniques were used to acquire velocity data on the plane of a CW laser illumination. Two different decompositions were applied to analyze the non-stationary and non-linear time-dependent data, the Empirical Mode Decomposition (EMD) and the Trend Removal Method (TRM). Two flow regimes were found, one in which the pulsatile flow exhibits phase-locked turbulence which is associated with the stabilizing effects of longitudinal straining during acceleration and a second where transition occurs very close to the wall while the core remains laminar.

  16. Laser Doppler anemometer measurements of pulsatile flow in a model carotid bifurcation.

    PubMed

    Ku, D N; Giddens, D P

    1987-01-01

    Hemodynamics at the human carotid bifurcation is important to the understanding of atherosclerotic plaque initiation and progression as well as to the diagnosis of clinically important disease. Laser Doppler anemometry was performed in a large scale model of an average human carotid. Pulsatile waveforms and physiologic flow divisions were incorporated. Disturbance levels and shear stresses were computed from ensemble averages of the velocity waveform measurements. Flow in the common carotid was laminar and symmetric. Flow patterns in the sinus, however, were complex and varied considerably during the cycle. Strong helical patterns and outer wall flow separation waxed and waned during each systole. The changing flow patterns resulted in an oscillatory shear stress at the outer wall ranging from -13 to 9 dyn cm-2 during systole with a time-averaged mean of only -0.5 dyn cm-2. This contrasts markedly with an inner wall shear stress range of 17-50, (mean 26) dyn cm-2. The region of transient separation was confined to the carotid sinus outer wall with no reverse velocities detected in the distal internal carotid. Notable disturbance velocities were also time-dependent, occurring only during the deceleration phase of systole and the beginning of diastole. The present pulsatile flow studies have aided in identifying hemodynamic conditions which correlate with early intimal thickening and predict the physiologic level of flow disturbances in the bulb of undiseased internal carotid arteries.

  17. Is Continuous Flow Superior to Pulsatile Flow in Single Ventricle Mechanical Support? Results from a Large Animal Pilot Study.

    PubMed

    Fujii, Yasuhiro; Ferro, Giuseppe; Kagawa, Hiroshi; Centola, Luca; Zhu, Liqun; Ferrier, William T; Talken, Linda; Riemer, R Kirk; Maeda, Katsuhide; Nasirov, Teimour; Hodges, Bill; Amirriazi, Saleh; Lee, Eric; Sheff, Donald; May, Judith; May, Robert; Reinhartz, Olaf

    2015-01-01

    Durable mechanical support in situations of physiologic single ventricle has been met with little success so far, particularly in small children. We created an animal model to investigate whether pulsatile or continuous flow would be superior. Three 1 month old sheep (10-16 kg) were instrumented. Via sternotomy and with cardiopulmonary bypass, a large ventricular septal defect and atrial septal defect were created. The left ventricle was cannulated using a Berlin Heart inflow cannula. This was connected sequentially to a continuous flow device (Thoratec HeartMate X, Pleasanton, CA) and to a pulsatile device (Berlin Heart Excor, The Woodlands, TX). Outflow was via a Y-graft to both aorta and pulmonary artery, striving for equal flow to both. Atrial filling pressures were controlled with volume infusions over a wide range. Under comparable loading conditions, significantly higher maximum flow was obtained by HeartMate X than by Excor (4.95 ± 1.27 L/min [range, 3.84-6.34 L/min] for HeartMate X vs. 1.80 ± 0.85 L/min [range, 1.01-2.7 L/min] for Excor; p < 0.05). Judging from this limited animal study, in single ventricle scenarios, continuous flow devices may achieve higher pump flows than pulsatile devices when provided with similar filling pressures. Their clinical use should be investigated. More extensive experimental studies are needed.

  18. Pulsatile Flow Phantom for Ultrasound Image-Guided HIFU Treatment of Vascular Injuries

    PubMed Central

    Greaby, Robyn; Zderic, Vesna; Vaezy, Shahram

    2009-01-01

    A pulsatile flow phantom was developed for studies of ultrasound image-guided High Intensity Focused Ultrasound (HIFU) application in transcutaneous hemostasis of injured blood vessels. The flow phantom consisted of a pulsatile pump system with instrumented excised porcine carotid artery, which was imbedded in a transparent agarose gel to model structural configuration of in-vivo tissues. Heparinized porcine blood was circulated through the phantom. The artery was injured using an 18 Gauge needle to model a penetrating injury in human peripheral vasculature. A HIFU transducer with the diameter of 7 cm, focal length of 6.3 cm and frequency of 3.4 MHz was used to seal the puncture. Ultrasound imaging was used to localize and target the puncture site, and monitor the HIFU treatment. Triphasic blood flows present in the human arteries were reproduced, with flow rates of 50–500 ml/min, pulse rates of 62–138 beats/min, and peak pressures of 100–250 mmHg. The penetrating injury of an artery was mimicked successfully in the flow phantom setting, and was easily visualized both optically through the transparent gel and with Power Doppler ultrasound imaging. Hemostasis was achieved in 55 ± 31 s (n=9) of HIFU application. Histological observations showed that a HIFU-sealed puncture was filled with clotted blood and covered with a fibrin cap. The pulsatile flow phantom provides a controlled and repeatable environment for studies of transcutaneous image-guided HIFU application in hemostasis of a variety of blood vessel injuries. PMID:17466441

  19. A nonlinear analysis of pulsatile flow in arteries.

    NASA Technical Reports Server (NTRS)

    Ling, S. C.; Atabek, H. B.

    1972-01-01

    An approximate numerical method for calculating flow profiles in arteries is developed. The theory takes into account the nonlinear terms of the Navier-Stokes equations as well as the nonlinear behaviour and large deformations of the arterial wall. Through the locally measured values of the pressure, pressure gradient, and pressure-radius function, the velocity distribution and wall shear at a given location along the artery can be determined. The computed results agree well with the corresponding experimental data.

  20. Impact of the postpump resistance on pressure-flow waveform and hemodynamic energy level in a neonatal pulsatile centrifugal pump.

    PubMed

    Wang, Shigang; Haines, Nikkole; Richardson, J Scott; Dasse, Kurt A; Undar, Akif

    2009-01-01

    This study tested the impact of different postpump resistances on pulsatile pressure-flow waveforms and hemodynamic energy output in a mock extracorporeal system. The circuit was primed with a 40% glycerin-water mixture, and a PediVAS centrifugal pump was used. The pre- and postpump pressures and flow rates were monitored via a data acquisition system. The postpump resistance was adjusted using a Hoffman clamp at the outlet of the pump. Five different postpump resistances and rotational speeds were tested with nonpulsatile (NP: 5000 RPM) and pulsatile (P: 4000 RPM) modes. No backflow was found when using pulsatile flow. With isoresistance, increased arterial resistances decreased pump flow rates (NP: from 1,912 ml/min to 373 ml/min; P: from 1,485 ml/min to 288 ml/min), increased postpump pressures (NP: from 333 mm Hg to 402 mm Hg; P: from 223 mm Hg to 274 mm Hg), and increased hemodynamic energy output with pulsatile mode. Pump flow rate correlated linearly with rotational speed (RPMs) of the pump, whereas postpump pressures and hemodynamic energy outputs showed curvilinear relationships with RPMs. The maximal pump flow rate also increased from 618 ml/min to 4,293 ml/min with pulsatile mode and from 581 ml/min to 5,665 ml/min with nonpulsatile mode. Results showed that higher postpump resistance reduced the pump flow range, and increased postpump pressure and surplus hemodynamic energy output with pulsatile mode. Higher rotational speeds also generated higher pump flow rates, postpump pressures, and increased pulsatility.

  1. A High Performance Pulsatile Pump for Aortic Flow Experiments in 3-Dimensional Models.

    PubMed

    Chaudhury, Rafeed A; Atlasman, Victor; Pathangey, Girish; Pracht, Nicholas; Adrian, Ronald J; Frakes, David H

    2016-06-01

    Aortic pathologies such as coarctation, dissection, and aneurysm represent a particularly emergent class of cardiovascular diseases. Computational simulations of aortic flows are growing increasingly important as tools for gaining understanding of these pathologies, as well as for planning their surgical repair. In vitro experiments are required to validate the simulations against real world data, and the experiments require a pulsatile flow pump system that can provide physiologic flow conditions characteristic of the aorta. We designed a newly capable piston-based pulsatile flow pump system that can generate high volume flow rates (850 mL/s), replicate physiologic waveforms, and pump high viscosity fluids against large impedances. The system is also compatible with a broad range of fluid types, and is operable in magnetic resonance imaging environments. Performance of the system was validated using image processing-based analysis of piston motion as well as particle image velocimetry. The new system represents a more capable pumping solution for aortic flow experiments than other available designs, and can be manufactured at a relatively low cost.

  2. Numerical study of pulsatile channel flows undergoing transition triggered by a modelled stenosis

    NASA Astrophysics Data System (ADS)

    Molla, Md. Mamun; Wang, Bing-Chen; Kuhn, David C. S.

    2012-12-01

    In this research, we numerically investigate the physics of pulsatile flows confined within a 3-dimensional channel with a modelled stenosis formed eccentrically on the upper wall using the method of large-eddy simulation (LES). An advanced dynamic nonlinear subgrid-scale stress model was utilized to conduct numerical simulations and its predictive performance was examined in comparison with that of the conventional dynamic model. The Womersley number tested in the simulation was fixed at 10.5 and the Reynolds numbers tested were set to 750 and 2000, which are characteristics of human blood flows in large arteries. An in-house LES code, based on curvilinear Cartesian coordinates, has been developed to conduct the unsteady numerical simulations using three different grid systems. The physical characteristics of the flow field have been studied in terms of the resolved mean velocity, turbulence kinetic energy, viscous wall shear stress, resolved and subgrid-scale turbulent shear stresses, local kinetic energy fluxes between the filtered and subgrid scales, and turbulence energy spectra along the central streamline of the domain. Triggered by the stenosis, the flow field driven by the pulsatile inlet condition undergoes laminar-turbulent-laminar patterns in the streamwise direction. Correspondingly, the slope of the energy spectra deviates significantly from the well-known -5/3 law for the inertial subrange to reflect the transition in the flow patterns.

  3. Time-resolved X-ray PIV measurements of hemodynamic information of real pulsatile blood flows

    NASA Astrophysics Data System (ADS)

    Park, Hanwook; Yeom, Eunseop; Lee, Sang Joon

    2015-11-01

    X-ray imaging technique has been used to visualize various bio-fluid flow phenomena as a nondestructive manner. To obtain hemodynamic information related with circulatory vascular diseases, a time-resolved X-ray PIV technique with high temporal resolution was developed. In this study, to embody actual pulsatile blood flows in a circular conduit without changes in hemorheological properties, a bypass loop is established by connecting a microtube between the jugular vein and femoral artery of a rat. Biocompatible CO2 microbubbles are used as tracer particles. After mixing with whole blood, CO2 microbubbles are injected into the bypass loop. Particle images of the pulsatile blood flows in the bypass loop are consecutively captured by the time-resolved X-ray PIV system. The velocity field information are obtained with varying flow rate and pulsataility. To verify the feasibility of the use of CO2 microbubbles under in vivo conditions, the effects of the surrounding-tissues are also investigated, because these effects are crucial for deteriorating the image contrast of CO2 microbubbles. Therefore, the velocity information of blood flows in the abdominal aorta are obtained to demonstrate the visibility and usefulness of CO2 microbubbles under ex vivo conditions. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2008-0061991).

  4. The importance of pulsatile and nonpulsatile flow in the design of blood pumps.

    PubMed

    Allen, G S; Murray, K D; Olsen, D B

    1997-08-01

    The traditional approach of total artificial heart (TAH) and ventricular assist device (VAD) development has been the mimicking of the native heart. Nonpulsatile flow using cardiopulmonary bypass has provided evidence of short-term physiologic tolerances. The design of nonpulsatile TAHs and VADs has eliminated the need for valves, flexing diaphragms, and large ventricular volumes. However, these devices require high efficiency power sources and reliable bearing seals or electromagnetic bearings while simultaneously attempting to avoid thromboemboli. The physiologic response to nonpulsatile flow is complex and variable. When compared to a pulsatile device, a nonpulsatile TAH or VAD needs to produce increased flow and higher mean intravascular pressures to maintain normal organ function. Despite its maintaining normal organ function, nonpulsatile flow does cause alterations in biochemical functions and organ specific blood flow. The combination of bioengineering superiority and the maintenance of physiologic homeostasis has directed future TAH and VAD research towards nonpulsatile systems.

  5. Computational analysis of magnetic effects on pulsatile flow of couple stress fluid through a bifurcated artery.

    PubMed

    Srinivasacharya, D; Rao, G Madhava

    2016-12-01

    The objective of the present study is to investigate the magnetic field effect on pulsatile flow of blood through a bifurcated artery with mild stenosis in its parent lumen by taking blood as couple stress fluid. The equations governing the flow are made non-dimensional, and coordinate transformation is employed to convert the irregular boundary to a regular boundary. The resulting system of equations is solved numerically using the finite difference method. The shear stress, flow rate and impedance near the apex with pertinent parameters are obtained numerically and analyzed graphically. It is noticed that physical quantities are changing suddenly with all parameters on both sides of the apex. This occurs because of back flow of the streaming blood at the onset of the lateral junction and secondary flow near the apex in the daughter artery. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

  6. Simulation of pulsatile flow of blood in stenosed coronary artery bypass with graft.

    PubMed

    Wiwatanapataphee, B; Poltem, D; Wu, Y H; Lenbury, Y

    2006-04-01

    In this paper, we investigate the behavior of the pulsatile blood flow in a stenosed right coronary artery with a bypass graft. The human blood is assumed to be a non-Newtonian fluid and its viscous behavior is described by the Carreau model. The transient phenomena of blood flow though the stenosed region and the bypass grafts are simulated by solving the three dimensional unsteady Navier-Stokes equations and continuity equation. The influence of the bypass angle on the flow interaction between the jet flow from the native artery and the flow from the bypass graft is investigated. Distributions of velocity, pressure and wall shear stresses are determined under various conditions. The results show that blood pressure in the stenosed artery drops dramatically in the stenosis area and that high wall shear stresses occur around the stenosis site.

  7. Reducing artifacts in one-dimensional Fourier velocity encoding for fast and pulsatile flow.

    PubMed

    Lee, Daeho; Santos, Juan M; Hu, Bob S; Pauly, John M; Kerr, Adam B

    2012-12-01

    When evaluating the severity of valvular stenosis, the peak velocity of the blood flow is routinely used to estimate the transvalvular pressure gradient. One-dimensional Fourier velocity encoding effectively detects the peak velocity with an ungated time series of spatially resolved velocity spectra in real time. However, measurement accuracy can be degraded by the pulsatile and turbulent nature of stenotic flow and the existence of spatially varying off-resonance. In this work, we investigate the feasibility of improving the peak velocity detection capability of one-dimensional Fourier velocity encoding for stenotic flow using a novel echo-shifted interleaved readout combined with a variable-density circular k-space trajectory. The shorter echo and readout times of the echo-shifted interleaved acquisitions are designed to reduce sensitivity to off-resonance. Preliminary results from limited phantom and in vivo results also indicate that some artifacts from pulsatile flow appear to be suppressed when using this trajectory compared to conventional single-shot readouts, suggesting that peak velocity detection may be improved. The efficiency of the new trajectory improves the temporal and spatial resolutions. To realize the proposed readout, a novel multipoint-traversing algorithm is introduced for flexible and automated gradient-waveform design.

  8. High-order numerical simulations of pulsatile flow in a curved artery model

    NASA Astrophysics Data System (ADS)

    Cox, Christopher; Liang, Chunlei; Plesniak, Michael W.

    2016-11-01

    Cardiovascular flows are pulsatile, incompressible and occur in complex geometries with compliant walls. Together, these factors can produce an environment that can affect the progression of cardiovascular disease by altering wall shear stresses. Unstructured high-order CFD methods are well suited for capturing unsteady vortex-dominated viscous flows, and these methods provide high accuracy for similar cost as low-order methods. We use an in-house three-dimensional flux reconstruction Navier-Stokes solver to simulate secondary flows and vortical structures within a rigid 180-degree curved artery model under pulsatile flow of a Newtonian blood-analog fluid. Our simulations use a physiological flowrate waveform taken from the carotid artery. We are particularly interested in the dynamics during the deceleration phase of the waveform, where we observe the deformed-Dean, Dean, Lyne and Wall vortices. Our numerical results reveal the complex nature of these vortices both in space and time and their effect on overall wall shear stress. Numerical results agree with and complement experimental results obtained in our laboratory using particle image velocimetry. Supported by the GW Center for Biomimetics and Bioinspired Engineering.

  9. Pulsatile flow and oxygen transport past cylindrical fiber arrays for an artificial lung: computational and experimental studies.

    PubMed

    Zierenberg, Jennifer R; Fujioka, Hideki; Cook, Keith E; Grotberg, James B

    2008-06-01

    The influence of time-dependent flows on oxygen transport from hollow fibers was computationally and experimentally investigated. The fluid average pressure drop, a measure of resistance, and the work required by the heart to drive fluid past the hollow fibers were also computationally explored. This study has particular relevance to the development of an artificial lung, which is perfused by blood leaving the right ventricle and in some cases passing through a compliance chamber before entering the device. Computational studies modeled the fiber bundle using cylindrical fiber arrays arranged in in-line and staggered rectangular configurations. The flow leaving the compliance chamber was modeled as dampened pulsatile and consisted of a sinusoidal perturbation superimposed on a steady flow. The right ventricular flow was modeled to depict the period of rapid flow acceleration and then deceleration during systole followed by zero flow during diastole. Experimental studies examined oxygen transfer across a fiber bundle with either steady, dampened pulsatile, or right ventricular flow. It was observed that the dampened pulsatile flow yielded similar oxygen transport efficiency to the steady flow, while the right ventricular flow resulted in smaller oxygen transport efficiency, with the decrease increasing with Re. Both computations and experiments yielded qualitatively similar results. In the computational modeling, the average pressure drop was similar for steady and dampened pulsatile flows and larger for right ventricular flow while the pump work required of the heart was greatest for right ventricular flow followed by dampened pulsatile flow and then steady flow. In conclusion, dampening the artificial lung inlet flow would be expected to maximize oxygen transport, minimize work, and thus improve performance.

  10. Evaluation of tubular poly(trimethylene carbonate) tissue engineering scaffolds in a circulating pulsatile flow system.

    PubMed

    Song, Yan; Wennink, Jos W H; Poot, Andre A; Vermes, Istvan; Feijen, Jan; Grijpma, Dirk W

    2011-02-01

    Tubular scaffolds (internal diameter approximately 3 mm and wall thickness approximately 0.8 mm) with a porosity of approximately 83% and an average pore size of 116 µm were prepared from flexible poly(trimethylene carbonate) (PTMC) polymer by dip-coating and particulate leaching methods. PTMC is a flexible and biocompatible polymer that crosslinks upon irradiation; porous network structures were obtained by irradiating the specimens in vacuum at 25 kGy before leaching soluble salt particles. To assess the suitability of these scaffolds in dynamic cell culturing for cardiovascular tissue engineering, the scaffolds were coated with a thin (0.1 to 0.2 mm) non-porous PTMC layer and its performance was evaluated in a closed pulsatile flow system (PFS). For this, the PFS was operated at physiological conditions at liquid flows of 1.56 ml/s with pressures varying from 80-120 mmHg at a frequency of 70 pulsations per minute. The mechanical properties of these coated porous PTMC scaffolds were not significantly different than non-coated scaffolds. Typical tensile strengths in the radial direction were 0.15 MPa, initial stiffness values were close to 1.4 MPa. Their creep resistance in cyclic deformation experiments was excellent. In the pulsatile flow setup, the distention rates of these flexible and elastic scaffolds were approximately 0.10% per mmHg, which is comparable to that of a porcine carotid artery (0.11% per mmHg). The compliance and stiffness index values were close to those of natural arteries.?In long-term deformation studies, where the scaffolds were subjected to physiological pulsatile pressures for one week, the morphology and mechanical properties of the PTMC scaffolds did not change. This suggests their suitability for application in a dynamic cell culture bioreactor.

  11. Pulsatile flow of blood using a modified second-grade fluid model

    SciTech Connect

    Massoudi, Mehrdad; Tran, P.X.

    2008-07-01

    We study the unsteady pulsatile flow of blood in an artery, where the effects of body acceleration are included. The blood is modeled as a modified second-grade fluid where the viscosity and the normal stress coefficients depend on the shear rate. It is assumed that the blood near the wall behaves as a Newtonian fluid, and in the core as a non-Newtonian fluid. This phenomenon is also known as the Fahraeus–Lindqvist effect. The equations are made dimensionless and solved numerically.

  12. Pulsatile flow with heat transfer of dusty magnetohydrodynamic Ree-Eyring fluid through a channel

    NASA Astrophysics Data System (ADS)

    Shawky, Hameda Mohammed

    2009-08-01

    The flow due to the pulsatile pressure gradient of dusty non-Newtonian fluid with heat transfer in a channel is considered. The system is stressed by an external magnetic field. The non-Newtonian fluid under consideration is obeying the rheological equation of state due to Ree-Eyring’s stress-strain relation. The equations of momentum and energy have been solved by using Lightill method. The velocity and temperature distributions of the two phase of the dusty fluid are obtained. The effects of various physical parameters of distributions the problem on these distributions are discussed and illustrated graphically through a set of figure.

  13. Blood Pressure, Carotid Flow Pulsatility, and the Risk of Stroke: A Community-Based Study.

    PubMed

    Chuang, Shao-Yuan; Cheng, Hao-Min; Bai, Chyi-Huey; Yeh, Wen-Ting; Chen, Jiunn-Rong; Pan, Wen-Harn

    2016-09-01

    High blood pressure is a major cause of cardiovascular events, and carotid flow pulsatility may be associated with cardiovascular events. However, the combined effect of blood pressure and flow pulsatility on the development of stroke remains unclear. Therefore, we investigated the combined influence of central blood pressure and pulsatility index (PI) on the incidence of stroke. Baseline data from 2033 adults (≥30 years) without stroke history in the Cardiovascular Disease Risk Factor Two-Township Study were linked to incident stroke. Common carotid flow PI was calculated by peak systolic velocity, end-diastolic velocity, and mean vessel velocity, which were measured in the common carotid artery. Hazard ratios for the risk of total stroke resulting from high central systolic blood pressure (CSBP) and high PI were calculated with Cox proportional hazard models. Over a median follow-up of 9.81 years, 132 people incurred stroke events. The incidence rates of stroke were 1.3, 6.4, and 13.2 per 1000 person-years for tertile groups of CSBP (P for trend<0.05) and 4.3, 7.0, and 9.4 per 1000 person-years for tertile groups of PI (P for trend<0.05). Compared with the first tertile of CSBP, hazard ratios were 4.88 (95% confidence interval, 2.29-10.43) for the second tertile and 10.42 (5.05-21.53) for the third tertile. Hazard ratios of PI were 2.18 (1.39-3.42; third tertile) and 1.64 (1.02-2.63; second tertile) compared with the first tertile. The individuals with a high CSBP and high PI had a 13-fold higher stroke risk compared with those with low CSBP and low PI (13.2; 1.75-99.71) after adjusting for age, sex, and traditional cardiovascular risk. CSBP and common carotid PI jointly and independently predicted future stroke. Carotid flow pulsatility may play an important role in the development of stroke. © 2016 American Heart Association, Inc.

  14. Acquisition of void fraction of pulsatile gas-liquid two-phase flow in rectangular channel

    NASA Astrophysics Data System (ADS)

    Zhou, Bao; Liu, Jingxing; Tian, Jingda

    2013-07-01

    Experiment on two-phase pulsatile flow in a narrow rectangular visualization channel was carried out and photographed. Every frame was treated and restored as a black-white binary picture with the threshold of both gray-scale and gray-scale gradient. The gas-liquid interface in the binary pictures can be recognized well, including some very obvious interface, which either cannot be distinguished, or introduce big wrong-recognized area with the gray-scale threshold only. Then after such as `dilate', `erode', `fill', `filter' and so on operating, the binary pictures can reflect the twophase distinction situation in the experimental channel well; The instantaneous average void frictions at the length that the camera covered were calculated by counting the black and white pixels from the pictures. The average void fractions in the whole length of the test section were calculated with an iteration method. The average void fractions in the special length covered by camera and the ones in the whole length of the test section are different. The former shows that the void frictions dramatically frequently change, while the later at steady flow almost stay peace, at pulsatile flow change smoothly.

  15. Changes in intracranial venous blood flow and pulsatility in Alzheimer's disease: A 4D flow MRI study.

    PubMed

    Rivera-Rivera, Leonardo A; Schubert, Tilman; Turski, Patrick; Johnson, Kevin M; Berman, Sara E; Rowley, Howard A; Carlsson, Cynthia M; Johnson, Sterling C; Wieben, Oliver

    2016-01-01

    Cerebral blood flow, arterial pulsation, and vasomotion may be important indicators of cerebrovascular health in aging and diseases of aging such as Alzheimer's disease. Noninvasive markers that assess these characteristics may be helpful in the study of co-occurrence of these diseases and potential additive and interacting effects. In this study, 4D flow MRI was used to measure intra-cranial flow features with cardiac-gated phase contrast MRI in cranial arteries and veins. Mean blood flow and pulsatility index as well as the transit time of the peak flow from the middle cerebral artery to the superior sagittal sinus were measured in a total of 104 subjects comprising of four groups: (a) subjects with Alzheimer's disease, (b) age-matched controls, (c) subjects with mild cognitive impairment, and (d) a group of late middle-aged with parental history of sporadic Alzheimer's disease. The Alzheimer's disease group exhibited: a significant decrease in mean blood flow in the superior sagittal sinus, transverse sinus, middle cerebral artery, and internal carotid arteries; a significant decrease of the peak and end diastolic blood flow in the middle cerebral artery and superior sagittal sinus; a faster transmission of peak flow from the middle cerebral artery to the superior sagittal sinus and increased pulsatility index along the carotid siphon.

  16. Pulsatile unsteady flow of blood through porous medium in a stenotic artery under the influence of transverse magnetic field

    NASA Astrophysics Data System (ADS)

    Sharma, Mukesh Kumar; Bansal, Kuldip; Bansal, Seema

    2012-09-01

    The periodic nature of the cardiac cycle induces a pulsatile, unsteady flow within the circulatory system. The pulsatile model of blood flow provides data to analyse the physiological situation in close proximity. The distribution of fatty cholesterol and artery-clogging blood clots in the lumen of the coronary artery is assumed as a porous medium. A mathematical model for pulsatile flow through an stenosed artery filled with porous medium in the presence of transverse static magnetic field has been formulated under the consideration of hematocrit dependent viscosity of blood that governed by Einstein equation. The velocity profile, volume flux, pressure gradient and wall shear stress are obtained and the effects of magnetic number, Darcy number, Womersely number are computed and represented through graphs.

  17. Stability of Carotid Artery Under Steady-State and Pulsatile Blood Flow: A Fluid–Structure Interaction Study

    PubMed Central

    Saeid Khalafvand, Seyed; Han, Hai-Chao

    2015-01-01

    It has been shown that arteries may buckle into tortuous shapes under lumen pressure, which in turn could alter blood flow. However, the mechanisms of artery instability under pulsatile flow have not been fully understood. The objective of this study was to simulate the buckling and post-buckling behaviors of the carotid artery under pulsatile flow using a fully coupled fluid–structure interaction (FSI) method. The artery wall was modeled as a nonlinear material with a two-fiber strain-energy function. FSI simulations were performed under steady-state flow and pulsatile flow conditions with a prescribed flow velocity profile at the inlet and different pressures at the outlet to determine the critical buckling pressure. Simulations were performed for normal (160 ml/min) and high (350 ml/min) flow rates and normal (1.5) and reduced (1.3) axial stretch ratios to determine the effects of flow rate and axial tension on stability. The results showed that an artery buckled when the lumen pressure exceeded a critical value. The critical mean buckling pressure at pulsatile flow was 17–23% smaller than at steady-state flow. For both steady-state and pulsatile flow, the high flow rate had very little effect (<5%) on the critical buckling pressure. The fluid and wall stresses were drastically altered at the location with maximum deflection. The maximum lumen shear stress occurred at the inner side of the bend and maximum tensile wall stresses occurred at the outer side. These findings improve our understanding of artery instability in vivo. PMID:25761257

  18. Stability of carotid artery under steady-state and pulsatile blood flow: a fluid-structure interaction study.

    PubMed

    Saeid Khalafvand, Seyed; Han, Hai-Chao

    2015-06-01

    It has been shown that arteries may buckle into tortuous shapes under lumen pressure, which in turn could alter blood flow. However, the mechanisms of artery instability under pulsatile flow have not been fully understood. The objective of this study was to simulate the buckling and post-buckling behaviors of the carotid artery under pulsatile flow using a fully coupled fluid-structure interaction (FSI) method. The artery wall was modeled as a nonlinear material with a two-fiber strain-energy function. FSI simulations were performed under steady-state flow and pulsatile flow conditions with a prescribed flow velocity profile at the inlet and different pressures at the outlet to determine the critical buckling pressure. Simulations were performed for normal (160 ml/min) and high (350 ml/min) flow rates and normal (1.5) and reduced (1.3) axial stretch ratios to determine the effects of flow rate and axial tension on stability. The results showed that an artery buckled when the lumen pressure exceeded a critical value. The critical mean buckling pressure at pulsatile flow was 17-23% smaller than at steady-state flow. For both steady-state and pulsatile flow, the high flow rate had very little effect (<5%) on the critical buckling pressure. The fluid and wall stresses were drastically altered at the location with maximum deflection. The maximum lumen shear stress occurred at the inner side of the bend and maximum tensile wall stresses occurred at the outer side. These findings improve our understanding of artery instability in vivo.

  19. The impact of deformation of an aneurysm model under pulsatile flow on hemodynamic analysis.

    PubMed

    Kawakami, T; Takao, H; Ichikawa, C; Kamiya, K; Murayama, Y; Motosuke, M

    2016-08-01

    Hemodynamic analysis of cerebral aneurysms has been widely carried out to clarify the mechanisms of their growth and rupture. In several cases, patient-specific aneurysm models made of transparent polymers have been used. Even though periodic changes in aneurysms due to the pulsation of blood flow could be important, the deformation of the model geometry and its effect on hemodynamic evaluation has not been fully investigated. In addition, the fabrication accuracy of aneurysm models has not been evaluated even though it may affect the hemodynamic parameters to be analyzed. In this study, the fabrication accuracy of a silicone aneurysm model was investigated. Additionally, the deformation of the model under pulsatile flow as well as its correlation with flow behavior was evaluated. Consequently, a fabrication method for an aneurysm model with high accuracy was established and the importance of the wall thickness of the model was also specified.

  20. Quantitative photoacoustic assessment of red blood cell aggregation under pulsatile blood flow: experimental and theoretical approaches

    NASA Astrophysics Data System (ADS)

    Bok, Tae-Hoon; Hysi, Eno; Kolios, Michael C.

    2017-03-01

    In the present paper, the optical wavelength dependence on the photoacoustic (PA) assessment of the pulsatile blood flow was investigated by means of the experimental and theoretical approaches analyzing PA radiofrequency spectral parameters such as the spectral slope (SS) and mid-band fit (MBF). For the experimental approach, the pulsatile flow of human whole blood at 60 bpm was imaged using the VevoLAZR system (40-MHz-linear-array probe, 700-900 nm illuminations). For the theoretical approach, a Monte Carlo simulation for the light transmit into a layered tissue phantom and a Green's function based method for the PA wave generation was implemented for illumination wavelengths of 700, 750, 800, 850 and 900 nm. The SS and MBF for the experimental results were compared to theoretical ones as a function of the illumination wavelength. The MBF increased with the optical wavelength in both theory and experiments. This was expected because the MBF is representative of the PA magnitude, and the PA signal from red blood cell (RBC) is dependent on the molar extinction coefficient of oxyhemoglobin. On the other hand, the SS decreased with the wavelength, even though the RBC size (absorber size which is related to the SS) cannot depend on the illumination wavelength. This conflicting result can be interpreted by means of the changes of the fluence pattern for different illumination wavelengths. The SS decrease with the increasing illumination wavelength should be further investigated.

  1. The acute effect of pilocarpine on pulsatile ocular blood flow in ocular hypertension.

    PubMed

    Shaikh, M H; Mars, J S

    2001-02-01

    To determine the acute effects of application of 2% pilocarpine on pulsatile ocular blood flow. In a randomised prospective controlled study of an exploratory nature, 18 subjects with ocular hypertension had pilocarpine 2% eye drops instilled into a randomly chosen eye three times at 10 min intervals. Physiological saline was instilled into the contralateral control eye. Intraocular pressure (IOP) and pulsatile ocular blood flow (POBF) measurements were taken before the first application and 90 min after the last application using the OBF tonometer (OBF Laboratory, Wilts, UK). Statistical analysis was performed using the Wilcoxon signed rank test. Of the 18 patients who entered the trial, 2 were suggested by the OBF system software as having 'poorly reliable' data. The analysis was made on the remaining 16. There was a significant reduction in IOP at 90 min for the treated eye in comparison with the contralateral control eye (p = 0.001; median difference -4.25 mmHg; 95% confidence interval, -5.85 to -2.40). There was a significant increase in POBF at 90 min in the treated eye in comparison with the contralateral control eye (p < 0.001; median difference 4.60 microl/s; 95% confidence interval, 2.35 to 6.75). Acute application of pilocarpine 2% drops increased POBF to a significant extent in untreated ocular hypertension.

  2. Numerical simulation of opening process in a bileaflet mechanical heart valve under pulsatile flow condition.

    PubMed

    Shi, Yubing; Zhao, Yong; Yeo, Tony Joon Hock; Hwang, Ned H C

    2003-03-01

    Most previous computational fluid dynamics (CFD) studies of blood flow in mechanical heart valves (MHVs) have not efficiently addressed the important features of moving leaflet and blood-leaflet interaction. Herein, computationally efficient approaches were developed to study these features and to obtain better insight into the pulsatile flow field in bileaflet MHVs. A simple and effective method to track the moving boundary was proposed, and an efficient method for calculating the blood-leaflet interaction applied. In this way, a CFD code was developed to study the pulsatile flow field around bileaflet MHVs. The CFD code was parallelized on a supercomputer to reduce turn-around time in the simulation. The solver was then used to study the opening process in a St. Jude Medical (SJM) size 29 bileaflet MHV. CFD results showed that, in the opening process, the flow field was consistently partitioned into two side channels and a central channel due to the presence of the two leaflets. In the flow field near the surface of the two leaflets, the fluid velocity followed the local surface velocity of the leaflets, thus showing a strong blood-leaflet interaction effect. Throughout the valve-opening process, peak velocities were always observed near the tips of the valve leaflet. The CFD simulation showed that the opening process took approximately 0.044 s, which compared well with experimental findings. The new computational approaches were efficient and able to address the moving leaflet and blood-leaflet interaction. The flow field in the opening process of a SJM 29 bileaflet MHV was successfully simulated using the developed solver.

  3. Rationale, scope, and 20-year experience of vascular surgical training with lifelike pulsatile flow models.

    PubMed

    Eckstein, Hans-Henning; Schmidli, Jürg; Schumacher, Hardy; Gürke, Lorenz; Klemm, Klaus; Duschek, Nikolaus; Meile, Toni; Assadian, Afshin

    2013-05-01

    Vascular surgical training currently has to cope with various challenges, including restrictions on work hours, significant reduction of open surgical training cases in many countries, an increasing diversity of open and endovascular procedures, and distinct expectations by trainees. Even more important, patients and the public no longer accept a "learning by doing" training philosophy that leaves the learning curve on the patient's side. The Vascular International (VI) Foundation and School aims to overcome these obstacles by training conventional vascular and endovascular techniques before they are applied on patients. To achieve largely realistic training conditions, lifelike pulsatile models with exchangeable synthetic arterial inlays were created to practice carotid endarterectomy and patch plasty, open abdominal aortic aneurysm surgery, and peripheral bypass surgery, as well as for endovascular procedures, including endovascular aneurysm repair, thoracic endovascular aortic repair, peripheral balloon dilatation, and stenting. All models are equipped with a small pressure pump inside to create pulsatile flow conditions with variable peak pressures of ~90 mm Hg. The VI course schedule consists of a series of 2-hour modules teaching different open or endovascular procedures step-by-step in a standardized fashion. Trainees practice in pairs with continuous supervision and intensive advice provided by highly experienced vascular surgical trainers (trainer-to-trainee ratio is 1:4). Several evaluations of these courses show that tutor-assisted training on lifelike models in an educational-centered and motivated environment is associated with a significant increase of general and specific vascular surgical technical competence within a short period of time. Future studies should evaluate whether these benefits positively influence the future learning curve of vascular surgical trainees and clarify to what extent sophisticated models are useful to assess the level of

  4. Impact of Pulsatility and Flow Rates on Hemodynamic Energy Transmission in an Adult Extracorporeal Life Support System.

    PubMed

    Wolfe, Rachel; Strother, Ashton; Wang, Shigang; Kunselman, Allen R; Ündar, Akif

    2015-07-01

    This study investigated the total hemodynamic energy (THE) and surplus hemodynamic energy transmission (SHE) of a novel adult extracorporeal life support (ECLS) system with nonpulsatile and pulsatile settings and varying pulsatility to define the most effective setting for this circuit. The circuit consisted of an i-cor diagonal pump (Xenios AG, Heilbronn, Germany), an XLung membrane oxygenator (Xenios AG), an 18 Fr Medos femoral arterial cannula (Xenios AG), a 23/25 Fr Estech RAP femoral venous cannula (San Ramon, CA, USA), 3/8 in ID × 140 cm arterial tubing, and 3/8 in ID × 160 cm venous tubing. Priming was done with lactated Ringer's solution and packed red blood cells (HCT 36%). The trials were conducted at flow rates 1-4 L/min (1 L/min increments) under nonpulsatile and pulsatile mode, with differential speed values 1000-4000 rpm (1000 rpm increments) at 36°. The pseudo patient's mean arterial pressure was kept at 100 mm Hg using a Hoffman clamp during all trials. Real-time flow and pressure data were collected using a custom-based data acquisition system. Mean pressures across the circuit increased with increasing flow rates, but increased insignificantly with increasing differential speed values. Mean pressure did not change significantly between pulsatile and nonpulsatile modes. Pulsatile flow created more THE than nonpulsatile flow at the preoxygenator site (P < 0.01). Of the different components of the circuit, the arterial cannula created the greatest THE loss. THE loss across the circuit ranged from 24.8 to 71.3%. Still, under pulsatile mode, more THE was delivered to the pseudo patient at low flow rates. No SHE was created with nonpulsatile flow, but SHE was created with pulsatile flow, and increased with increasing differential speed values. At lower flow rates (1-2 L/min), the arterial cannula contributed the most to SHE loss, but at higher flow rates the arterial tubing created the most SHE loss. The circuit

  5. Methicillin Resistant Staphylococcus Aureus Biofilm Formation Over A Separated Flow Region Under Steady And Pulsatile Flow Conditions

    NASA Astrophysics Data System (ADS)

    Salek, M. Mehdi; Martinuzzi, Robert

    2012-02-01

    Several researchers have observed that the formation, morphology and susceptibility of bacterial biofilms are affected by the local hydrodynamic condition and, in particular, shear stresses acting on the fluid-biofilm interface. A backwards facing step (BFS) experimental model has been widely utilized as an in vitro model to examine and characterize the effect of flow separation and recirculation zones comparable to those present within various medical devices as well as those observed in vivo. The specific geometry of BFS covers a vide range of flow features observed in physiological or environmental conditions. The hypothesis of this study is that the flow behavior and structures can effectively contribute to the transport and attachment of cells and affecting the morphology of adhered colonies as well as suspended structures (i.e. biofilm streamers). Hence, the formation of the recirculation region occurring within a backward facing step (BFS) under steady and pulsatile conditions as well as three-dimensional flow structures arising close to the side walls are investigated to correlate to biofilms behavior. This hypothesis is investigated using a backward facing step incorporated into a flow cell under steady and pulsatile flow regimes to study the growth of methicillin resistant Staphylococcus aureus (MRSA) UC18 as the study microorganism.

  6. The hemodynamic and embolizing forces acting on thrombi--II. The effect of pulsatile blood flow.

    PubMed

    Basmadjian, D

    1986-01-01

    A previous analysis (Basmadjian, J. Biomechanics 17, 287-298, 1984) of the embolizing forces acting on thrombi in steady Poiseuille flow has been extended to pulsatile blood flow conditions in the major blood vessels. We show that for incipient and small compact thrombi up to 0.1 mm height, the maximum embolizing stresses can be calculated from the corresponding 'quasi-steady' viscous drag forces and measured maximum wall shear. Their magnitude is from 5 to 30 times (tau w)Max, the maximum wall shear stress during the cardiac cycle in the absence of thrombi. For larger thrombi, inertial and 'history' effects have to be taken into account, leading to embolizing stresses in excess of 100 Pa (1000 dyn cm-2).

  7. Numerical Study of Turbulent Pulsatile Blood Flow through Stenosed Artery Using Fluid-Solid Interaction.

    PubMed

    Jahangiri, Mehdi; Saghafian, Mohsen; Sadeghi, Mahmood Reza

    2015-01-01

    The turbulent pulsatile blood flow through stenosed arteries considering the elastic property of the wall is investigated numerically. During the numerical model validation both standard k-ε model and RNG K-ε model are used. Compared with the RNG K-ε model, the standard K-ε model shows better agreement with previous experimental results and is better able to show the reverse flow region. Also, compared with experimental data, the results show that, up to 70% stenosis, the flow is laminar and for 80% stenosis the flow becomes turbulent. Assuming laminar or turbulent flow and also rigid or elastic walls, the results are compared with each other. The investigation of time-averaged shear stress and the oscillatory shear index for 80% stenosis show that assuming laminar flow will cause more error than assuming a rigid wall. The results also show that, in turbulent flow compared with laminar flow, the importance of assuming a flexible artery wall is more than assuming a rigid artery wall.

  8. Generating a Pulsatile Pulmonary Flow after Fontan Operation by Means of Computational Fluid Dynamics (CFD)

    NASA Astrophysics Data System (ADS)

    Ghoreyshi, Mostafa

    2011-03-01

    This study considers blood flow in total cavopulmonary connection (TCPC) morphology, which is created in Fontan surgical procedure in patients with single ventricle heart disease. Ordinary process of TCPC operation reduces pulmonary blood flow pulsatility; because of right ventricle being bypassed. This phenomenon causes a lot of side effects for patients. A cardiac surgeon has suggested that keeping main pulmonary artery (MPA) partially open, would increase pulmonary flow pulsations. MPA gets closed in ordinary TCPC operation. The purpose of current study is to verify the effects of keeping MPA partially open on pulmonary flow pulsations, by means of computational fluid dynamics (CFD). 3D geometry is reconstructed from CT Angiography (CTA) scan of a patient who has undergone an ordinary TCPC procedure. The stenosed MPA or pulmonary stenosis (PS) is virtually added to the original geometry. Flow field is studied in six different models in which average antegrade flow (AF) -coming through PS- increases gradually. Results show that adding AF increases flow pulsations in both pulmonary arteries. Moreover, power loss increases with respect to average AF. We conclude that adding AF is an impressive way to increase pulsations of pulmonary flow, but energy losses should be considered too.

  9. A Real-Time Programmable Pulsatile Flow Pump for In Vitro Cardiovascular Experimentation.

    PubMed

    Mechoor, Rahul Raj; Schmidt, Tyler; Kung, Ethan

    2016-11-01

    Benchtop in vitro experiments are valuable tools for investigating the cardiovascular system and testing medical devices. Accurate reproduction of the physiologic flow waveforms at various anatomic locations is an important component of these experimental methods. This study discusses the design, construction, and testing of a low-cost and fully programmable pulsatile flow pump capable of continuously producing unlimited cycles of physiologic waveforms. It consists of a gear pump actuated by an AC servomotor and a feedback algorithm to achieve highly accurate reproduction of flow waveforms for flow rates up to 300 ml/s across a range of loading conditions. The iterative feedback algorithm uses the flow error values in one iteration to modify the motor control waveform for the next iteration to better match the desired flow. Within four to seven iterations of feedback, the pump replicated desired physiologic flow waveforms to within 2% normalized RMS error (for flow rates above 20 mL/s) under varying downstream impedances. This pump device is significantly more affordable (∼10% of the cost) than current commercial options. More importantly, the pump can be controlled via common scientific software and thus easily implemented into large automation frameworks.

  10. Numerical Study of Turbulent Pulsatile Blood Flow through Stenosed Artery Using Fluid-Solid Interaction

    PubMed Central

    Jahangiri, Mehdi; Saghafian, Mohsen; Sadeghi, Mahmood Reza

    2015-01-01

    The turbulent pulsatile blood flow through stenosed arteries considering the elastic property of the wall is investigated numerically. During the numerical model validation both standard k-ε model and RNG K-ε model are used. Compared with the RNG K-ε model, the standard K-ε model shows better agreement with previous experimental results and is better able to show the reverse flow region. Also, compared with experimental data, the results show that, up to 70% stenosis, the flow is laminar and for 80% stenosis the flow becomes turbulent. Assuming laminar or turbulent flow and also rigid or elastic walls, the results are compared with each other. The investigation of time-averaged shear stress and the oscillatory shear index for 80% stenosis show that assuming laminar flow will cause more error than assuming a rigid wall. The results also show that, in turbulent flow compared with laminar flow, the importance of assuming a flexible artery wall is more than assuming a rigid artery wall. PMID:26448782

  11. Assessment of blood flow velocity and pulsatility in cerebral perforating arteries with 7-T quantitative flow MRI.

    PubMed

    Bouvy, W H; Geurts, L J; Kuijf, H J; Luijten, P R; Kappelle, L J; Biessels, G J; Zwanenburg, J J M

    2016-09-01

    Thus far, blood flow velocity measurements with MRI have only been feasible in large cerebral blood vessels. High-field-strength MRI may now permit velocity measurements in much smaller arteries. The aim of this proof of principle study was to measure the blood flow velocity and pulsatility of cerebral perforating arteries with 7-T MRI. A two-dimensional (2D), single-slice quantitative flow (Qflow) sequence was used to measure blood flow velocities during the cardiac cycle in perforating arteries in the basal ganglia (BG) and semioval centre (CSO), from which a mean normalised pulsatility index (PI) per region was calculated (n = 6 human subjects, aged 23-29 years). The precision of the measurements was determined by repeated imaging and performance of a Bland-Altman analysis, and confounding effects of partial volume and noise on the measurements were simulated. The median number of arteries included was 14 in CSO and 19 in BG. In CSO, the average velocity per volunteer was in the range 0.5-1.0 cm/s and PI was 0.24-0.39. In BG, the average velocity was in the range 3.9-5.1 cm/s and PI was 0.51-0.62. Between repeated scans, the precision of the average, maximum and minimum velocity per vessel decreased with the size of the arteries, and was relatively low in CSO and BG compared with the M1 segment of the middle cerebral artery. The precision of PI per region was comparable with that of M1. The simulations proved that velocities can be measured in vessels with a diameter of more than 80 µm, but are underestimated as a result of partial volume effects, whilst pulsatility is overestimated. Blood flow velocity and pulsatility in cerebral perforating arteries have been measured directly in vivo for the first time, with moderate to good precision. This may be an interesting metric for the study of haemodynamic changes in aging and cerebral small vessel disease. © 2015 The Authors NMR in Biomedicine Published by John Wiley & Sons Ltd.

  12. Assessment of blood flow velocity and pulsatility in cerebral perforating arteries with 7‐T quantitative flow MRI

    PubMed Central

    Geurts, L. J.; Kuijf, H. J.; Luijten, P. R.; Kappelle, L. J.; Biessels, G. J.; Zwanenburg, J. J. M.

    2015-01-01

    Thus far, blood flow velocity measurements with MRI have only been feasible in large cerebral blood vessels. High‐field‐strength MRI may now permit velocity measurements in much smaller arteries. The aim of this proof of principle study was to measure the blood flow velocity and pulsatility of cerebral perforating arteries with 7‐T MRI. A two‐dimensional (2D), single‐slice quantitative flow (Qflow) sequence was used to measure blood flow velocities during the cardiac cycle in perforating arteries in the basal ganglia (BG) and semioval centre (CSO), from which a mean normalised pulsatility index (PI) per region was calculated (n = 6 human subjects, aged 23–29 years). The precision of the measurements was determined by repeated imaging and performance of a Bland–Altman analysis, and confounding effects of partial volume and noise on the measurements were simulated. The median number of arteries included was 14 in CSO and 19 in BG. In CSO, the average velocity per volunteer was in the range 0.5–1.0 cm/s and PI was 0.24–0.39. In BG, the average velocity was in the range 3.9–5.1 cm/s and PI was 0.51–0.62. Between repeated scans, the precision of the average, maximum and minimum velocity per vessel decreased with the size of the arteries, and was relatively low in CSO and BG compared with the M1 segment of the middle cerebral artery. The precision of PI per region was comparable with that of M1. The simulations proved that velocities can be measured in vessels with a diameter of more than 80 µm, but are underestimated as a result of partial volume effects, whilst pulsatility is overestimated. Blood flow velocity and pulsatility in cerebral perforating arteries have been measured directly in vivo for the first time, with moderate to good precision. This may be an interesting metric for the study of haemodynamic changes in aging and cerebral small vessel disease. © 2015 The Authors NMR in Biomedicine Published by John Wiley & Sons Ltd. PMID:25916399

  13. Effect of pulsatile and continuous flow on yes-associated protein.

    PubMed

    Chitragari, Gautham; Shalaby, Sherif Y; Sumpio, Brandon J; Sumpio, Bauer E

    2014-09-01

    Yes-associated protein (YAP) is a mechanosignaling protein that relays mechanical information to the nucleus by changing its level of phosphorylation. We hypothesize that different flow patterns show differential effect on phosphorylated YAP (pYAP) (S127) and total YAP and could be responsible for flow dependent localization of atherosclerosis. Confluent human umbilical vein endothelial cells (HUVECs) seeded on fibronectin-coated glass slides were exposed to continuous forward flow (CFF) and pulsatile forward flow (PFF) using a parallel plate flow chamber system for 30 minutes. Cell lysates were prepared and immunoblotted to detect the levels of phosphorylated YAP and total YAP. HUVECs exposed to both PFF and CFF showed a mild decrease in the levels of both pYAP (S127) and total YAP. While the levels of pYAP (S127) decreased to 87.85 and 85.21% of static control with PFF and CFF, respectively, the levels of total YAP significantly decreased to 91.31 and 92.27% of static control. No significant difference was seen between CFF and PFF on their effect on pYAP (S127), but both conditions resulted in a significant decrease in total YAP at 30 minutes. The results of this experiment show that the possible effect of different types of flow on YAP is not induced before 30 minutes. Experiments exposing endothelial cells to various types of flow for longer duration of time could help to elucidate the role of YAP in the pathogenesis of atherosclerosis.

  14. The limitation of pulsatile flow through the aqueduct of Sylvius as a cause of hydrocephalus.

    PubMed

    White, D N; Wilson, K C; Curry, G R; Stevenson, R J

    1979-06-01

    The concept is advanced that hydrocephalus results from limitation in the pulsatile flow of CSF downwards through the aqueduct of Sylvius during systole which is necessary to accommodate for the pulsatile pressure and volume increase that accompanies the propagation of the arterial pulse through the brain. Evidence is given to show that flow through the fixed human aqueduct is disturbed and not laminar. Further, with the pressures availalbe, the aqueduct is only just large enough to pass the quantity of fluid which must be vented extracranially during systole. Should the capacity of this systolic venting mechanism be exceeded, physical strain will cause cellular damage in the periventricular and periaqueductal regions which, if prolonged, will lead to tissue destruction and hydrocephalus. There appear to be two main causes for hydrocephalus resulting from this mechanism. Firstly, structural lesions, restricting the lumina of the CSF-venting pathways, especially the aqueduct, will reduce the volume of CSF that can flow through these pathways during systole. The hydrocephalic process will then be continuous and only limited when tissue destruction reduces the systolic volume expansion of the brain such that it can be accomodated by the restricted CSF venting pathways. Secondly, conditions which may increase the amount of the systolic volume expansion of the brain beyond the capacity of the CSF venting pathways. Raised mean intracranial pressure is the most important of these conditions. In such cases the hydrocephalus will be limited by the duration of the causal process and possibly also by the enlargement of the venting pathways, as a result of tissue destruction. This hypothesis also accounts for hydrocephalus resulting from obliteration of the cortical subarachnoid space, obstruction to the cranial venous drainage, deformities in the region of the foramen magnum and arterial encroachment upon the ventricular system.

  15. Completely pulsatile high flow circulatory support with a constant-speed centrifugal blood pump: mechanisms and early clinical observations.

    PubMed

    Yamazaki, Kenji; Saito, Satoshi; Kihara, Shinichiro; Tagusari, Osamu; Kurosawa, Hiromi

    2007-04-01

    Various types of rotary blood pumps (axial flow, centrifugal) have been introduced into clinical use recently. These pumps have different pressure-flow characteristics, and some investigators have noted that a limited pump flow rate and less pulsatility are the problems with the axial flow devices. A new implantable centrifugal blood pump was developed that has an extremely flat pressure-flow curve and is able to produce a significantly high pump flow rate of 20 l/min at a low pressure of 10-30mmHg. When the pressure difference between the left ventricle and aorta decreases during systole, an instant high peak flow is achieved, which results in a higher peak pressure in the aorta (systolic pressure). During the diastolic phase, the left ventricle-aorta pressure difference increases to maximum, and the pump flow rate decreases to minimum. Thus, the pump flow rate becomes completely pulsatile, and the high peak flow provides a higher mean pump flow rate. This pump was applied to two end-stage heart failure patients (dilated cardiomyopathy, New York Heart Association (NYHA) class IV, inotrope-dependent). The pump was observed to provide completely pulsatile high flow assistance of 6-9 l/min with a constant pump speed. Both patients are currently in NYHA class I after 1 year on the device with no major adverse events. The new centrifugal blood pump provides completely pulsatile high-flow circulatory support with a constant pump speed, which solves the current clinical problems with rotary blood pumps.

  16. Pulsatile flow of blood and heat transfer with variable viscosity under magnetic and vibration environment

    NASA Astrophysics Data System (ADS)

    Shit, G. C.; Majee, Sreeparna

    2015-08-01

    Unsteady flow of blood and heat transfer characteristics in the neighborhood of an overlapping constricted artery have been investigated in the presence of magnetic field and whole body vibration. The laminar flow of blood is taken to be incompressible and Newtonian fluid with variable viscosity depending upon temperature with an aim to provide resemblance to the real situation in the physiological system. The unsteady flow mechanism in the constricted artery is subjected to a pulsatile pressure gradient arising from systematic functioning of the heart and from the periodic body acceleration. The numerical computation has been performed using finite difference method by developing Crank-Nicolson scheme. The results show that the volumetric flow rate, skin-friction and the rate of heat transfer at the wall are significantly altered in the downstream of the constricted region. The axial velocity profile, temperature and flow rate increases with increase in temperature dependent viscosity, while the opposite trend is observed in the case of skin-friction and flow impedance.

  17. A study of the pulsatile flow and its interaction with rectangular leaflets

    NASA Astrophysics Data System (ADS)

    Ledesma, Rene; Zenit, Roberto; Pulos, Guillermo

    2009-11-01

    To avoid the complexity and limited understanding of the 3D pulsatile flow field through heart valves, a cardiac-like flow circuit and a test channel were designed to study the behavior of bidimensional leaflets made of hyperelastic materials. We study a simple 2D arrangement to understand the basic physics of the flow-leaflet interaction. Creating a periodic pressure gradient, measurements of leaflet deflection were obtained for different flow conditions, geometries and materials. Using PIV and Phase Locking techniques, we have obtained the leaflet motion and the time-dependent flow velocity fields. The results show that two dimensionless parameters determine the performance of a simple bi-dimensional valve, in accordance with the flow conditions applied: π1=f(sw)^1/2(E/ρ)^1/2 and π2=V/(2slw), where f is the pulsation frequency, V is the stroke volume, s, w and l are the dimensions on the leaftlet and E and ρ are the elastic modulus and density of the material, respectively. Furthermore, we have identified the conditions for which the fluid stresses can be minimized. With these results we propose a new set of parameters to improve the performance of prosthetic heart valves and, in consequence, to reduce blood damage.

  18. The Effect of Pulsatile Versus Nonpulsatile Blood Flow on Viscoelasticity and Red Blood Cell Aggregation in Extracorporeal Circulation

    PubMed Central

    Ahn, Chi Bum; Kang, Yang Jun; Kim, Myoung Gon; Yang, Sung; Lim, Choon Hak; Son, Ho Sung; Kim, Ji Sung; Lee, So Young; Son, Kuk Hui; Sun, Kyung

    2016-01-01

    Background Extracorporeal circulation (ECC) can induce alterations in blood viscoelasticity and cause red blood cell (RBC) aggregation. In this study, the authors evaluated the effects of pump flow pulsatility on blood viscoelasticity and RBC aggregation. Methods Mongrel dogs were randomly assigned to two groups: a nonpulsatile pump group (n=6) or a pulsatile pump group (n=6). After ECC was started at a pump flow rate of 80 mL/kg/min, cardiac fibrillation was induced. Blood sampling was performed before and at 1, 2, and 3 hours after ECC commencement. To eliminate bias induced by hematocrit and plasma, all blood samples were adjusted to a hematocrit of 45% using baseline plasma. Blood viscoelasticity, plasma viscosity, hematocrit, arterial blood gas analysis, central venous O2 saturation, and lactate were measured. Results The blood viscosity and aggregation index decreased abruptly 1 hour after ECC and then remained low during ECC in both groups, but blood elasticity did not change during ECC. Blood viscosity, blood elasticity, plasma viscosity, and the aggregation index were not significantly different in the groups at any time. Hematocrit decreased abruptly 1 hour after ECC in both groups due to dilution by the priming solution used. Conclusion After ECC, blood viscoelasticity and RBC aggregation were not different in the pulsatile and nonpulsatile groups in the adult dog model. Furthermore, pulsatile flow did not have a more harmful effect on blood viscoelasticity or RBC aggregation than nonpulsatile flow. PMID:27298790

  19. Middle cerebral artery blood flow velocities and pulsatility index and the cerebroplacental pulsatility ratio: longitudinal reference ranges and terms for serial measurements.

    PubMed

    Ebbing, C; Rasmussen, S; Kiserud, T

    2007-09-01

    To establish reference ranges suitable for serial assessments of the fetal middle cerebral (MCA) and umbilical (UA) artery blood flow velocities, pulsatility index (PI) and cerebroplacental pulsatility ratio and to provide terms for calculating conditional reference intervals suitable for individual serial measurements. This was a longitudinal study of 161 singleton pregnancies. Using Doppler ultrasound, MCA and UA blood velocities and PI were determined three to five times at 3-5-week intervals over a gestational age range of 19-41 weeks. Polynomial regression lines for the 95th, 50th and 5th percentiles were calculated for the peak systolic velocity (PSV), time-averaged maximum velocity (TAMXV), PI and cerebroplacental ratio. Terms for calculating conditional reference intervals were established. Based on 566 observations our new longitudinal reference ranges for fetal middle cerebral PSV, TAMXV and PI provided terms for calculating conditional reference intervals (i.e. predicting expected 95% confidence limits based on a previous measurement), and correspondingly for the cerebroplacental ratio (n = 550). The reference ranges were at some variance with those of previous cross-sectional studies. The narrow 95% confidence limits for the 5(th) and 95(th) percentiles ensured reliable ranges. We have established longitudinal reference ranges appropriate for the serial assessment of MCA blood velocities and PI and cerebroplacental ratio. Particularly the terms for calculating conditional ranges based on a previous observation make this system more appropriate for longitudinal monitoring than are cross-sectional data. Copyright 2007 ISUOG. Published by John Wiley & Sons, Ltd.

  20. Verification of a computational cardiovascular system model comparing the hemodynamics of a continuous flow to a synchronous valveless pulsatile flow left ventricular assist device

    PubMed Central

    Gohean, Jeffrey R.; George, Mitchell J.; Pate, Thomas D.; Kurusz, Mark; Longoria, Raul G.; Smalling, Richard W.

    2012-01-01

    The purpose of this investigation is to utilize a computational model to compare a synchronized valveless pulsatile left ventricular assist device to continuous flow left ventricular assist devices at the same level of device flow, and to verify the model with in vivo porcine data. A dynamic system model of the human cardiovascular system was developed to simulate support of a healthy or failing native heart from a continuous flow left ventricular assist device or a synchronous, pulsatile, valveless, dual piston positive displacement pump. These results were compared to measurements made during in vivo porcine experiments. Results from the simulation model and from the in vivo counterpart show that the pulsatile pump provides higher cardiac output, left ventricular unloading, cardiac pulsatility, and aortic valve flow as compared to the continuous flow model at the same level of support. The dynamic system model developed for this investigation can effectively simulate human cardiovascular support by a synchronous pulsatile or continuous flow ventricular assist device. PMID:23438771

  1. Verification of a computational cardiovascular system model comparing the hemodynamics of a continuous flow to a synchronous valveless pulsatile flow left ventricular assist device.

    PubMed

    Gohean, Jeffrey R; George, Mitchell J; Pate, Thomas D; Kurusz, Mark; Longoria, Raul G; Smalling, Richard W

    2013-01-01

    The purpose of this investigation is to use a computational model to compare a synchronized valveless pulsatile left ventricular assist device with continuous flow left ventricular assist devices at the same level of device flow, and to verify the model with in vivo porcine data. A dynamic system model of the human cardiovascular system was developed to simulate the support of a healthy or failing native heart from a continuous flow left ventricular assist device or a synchronous pulsatile valveless dual-piston positive displacement pump. These results were compared with measurements made during in vivo porcine experiments. Results from the simulation model and from the in vivo counterpart show that the pulsatile pump provides higher cardiac output, left ventricular unloading, cardiac pulsatility, and aortic valve flow as compared with the continuous flow model at the same level of support. The dynamic system model developed for this investigation can effectively simulate human cardiovascular support by a synchronous pulsatile or continuous flow ventricular assist device.

  2. What is the definition of pulsatile umbilical venous flow in twin-twin transfusion syndrome?

    PubMed

    Russell, Zoi; Quintero, Rubén A; Kontopoulos, Eftichia V

    2008-12-01

    The aim of the study was to derive an objective definition of pulsatile umbilical venous flow (PUVF). Pulsed Doppler waveform analysis of the umbilical vein was performed in stages III and IV twin-twin transfusion syndrome (TTTS) patients. In patients with PUVF, the umbilical vein maximum (Vmax) and the umbilical vein minimum velocity (Vmin) and the resistance index for the umbilical vein (UVRI) = (100 x [Vmax - Vmin]/Vmax) were assessed. PUVF was noted in 130 of 226 stages III and IV TTTS patients. Digital images were available for analysis in 65 of 130 patients (50%). The minimum UVRI associated with PUVF was 16% for stages III and IV TTTS. There was a trend for increasing UVRI with stage (P = .052). Stage IV patients were more likely to have an UVRI greater than 30% (P = .02). PUVF can be defined as an UVRI greater than 15%. A scale definition of PUVF may further facilitate assessment of the degree of fetal hemodynamic compromise.

  3. A numerical and experimental investigation of transitional pulsatile flow in a stenosed channel.

    PubMed

    Beratlis, N; Balaras, E; Parvinian, B; Kiger, K

    2005-12-01

    In the present paper, a closely coupled numerical and experimental investigation of pulsatile flow in a prototypical stenotic site is presented. Detailed laser Doppler velocimetry measurements upstream of the stenosis are used to guide the specification of velocity boundary conditions at the inflow plane in a series of direct numerical simulations (DNSs). Comparisons of the velocity statistics between the experiments and DNS in the post-stenotic area demonstrate the great importance of accurate inflow conditions, and the sensitivity of the post-stenotic flow to the disturbance environment upstream. In general, the results highlight a borderline turbulent flow that sequentially undergoes transition to turbulence and relaminarization. Before the peak mass flow rate, the strong confined jet that forms just downstream of the stenosis becomes unstable, forcing a role-up and subsequent breakdown of the shear layer. In addition, the large-scale structures originating from the shear layer are observed to perturb the near wall flow, creating packets of near wall hairpin vortices.

  4. Pulsatile Flow and Transport of Blood past a Cylinder: Basic Transport for an Artificial Lung.

    NASA Astrophysics Data System (ADS)

    Zierenberg, Jennifer R.

    2005-11-01

    The fluid mechanics and transport for flow of blood past a single cylinder is investigated using CFD. This work refers to an artificial lung in which oxygen travels through fibers oriented perpendicularly to the incoming blood flow. A pulsatile blood flow was considered: Ux=U0[ 1+A( φt ) ], where Ux is the velocity far from the cylinder. The Casson equation was used to describe the shear thinning and yield stress properties of blood. The presence of hemoglobin (i.e. facilitated diffusion) was considered. We examined the effect of A, U0 and φ on the flow and transport by varying the dimensionless parameters: A; Reynolds number, Re; and Womersley parameter, α. Two different feed gases were considered: pure O2 and air. The flow and concentration fields were computed for Re = 5, 10, and 40, 0 <=A<= 0.75, α = 0.25, 0.4, and Schmidt number, Sc = 1000. Vortices attached downstream of the cylinder are found to oscillate in size and strength as α and A are varied. Mass transport is found to primarily depend on Re and to increase with increasing Re, α and decreasing A. The presence of hemoglobin increases mass transport. Supported by NIH HL69420, NSF Fellowship

  5. In vitro Doppler ultrasound investigation of turbulence intensity in pulsatile flow with simulated cardiac variability.

    PubMed

    Thorne, Meghan L; Poepping, Tamie L; Nikolov, Hristo N; Rankin, Richard N; Steinman, David A; Holdsworth, David W

    2009-01-01

    An in vitro investigation of turbulence intensity (TI) associated with a severe carotid stenosis in the presence of physiological cardiac variability is described. The objective of this investigation was to determine if fluctuations due to turbulence could be quantified with conventional Doppler ultrasound (DUS) in the presence of normal physiological cycle-to-cycle cardiac variability. An anthropomorphic model of a 70% stenosed carotid bifurcation was used in combination with a programmable flow pump to generate pulsatile flow with a mean flow rate of 6 mL/s. Utilizing the pump, we studied normal, nonrepetitive cycle-to-cycle cardiac variability (+/-3.9%) in flow, as well as waveform shapes with standard deviations equal to 0, 2 and 3 times the normal variation. Eighty cardiac cycles of Doppler data were acquired at two regions within the model, representing either laminar or turbulent flow; each measurement was repeated six times. Turbulence intensity values were found to be 11 times higher (p < 0.001), on average, in the turbulent region than in the laminar region, with a mean difference of 24 cm/s. Twenty cardiac cycles were required for confidence in TI values. In conclusion, these results indicate that it is possible to quantify TI in vitro, even in the presence of normal and exaggerated cycle-to-cycle cardiac variability.

  6. On the Evolution of Pulsatile Flow Subject to a Transverse Impulse Body Force

    NASA Astrophysics Data System (ADS)

    di Labbio, Giuseppe; Keshavarz-Motamed, Zahra; Kadem, Lyes

    2014-11-01

    In the event of an unexpected abrupt traffic stop or car accident, automotive passengers will experience an abrupt body deceleration. This may lead to tearing or dissection of the aortic wall known as Blunt Traumatic Aortic Rupture (BTAR). BTAR is the second leading cause of death in automotive accidents and, although quite frequent, the mechanisms leading to BTAR are still not clearly identified, particularly the contribution of the flow field. As such, this work is intended to provide a fundamental framework for the investigation of the flow contribution to BTAR. In this fundamental study, pulsatile flow in a three-dimensional, straight pipe of circular cross-section is subjected to a unidirectional, transverse, impulse body force applied on a strictly bounded volume of fluid. These models were simulated using the Computational Fluid Dynamics (CFD) software FLUENT. The evolution of fluid field characteristics was investigated during and after the application of the force. The application of the force significantly modified the flow field. The force induces a transverse pressure gradient causing the development of secondary flow structures that dissipate the energy added by the acceleration. Once the force ceases to act, these structures are carried downstream and gradually dissipate their excess energy.

  7. Photoplethysmography for an independent measure of pulsatile pressure under controlled flow conditions.

    PubMed

    Njoum, Haneen; Kyriacou, Panayiotis A

    2017-02-01

    Noninvasive continuous blood pressure measurements are desirable for patients and clinicians. This work proposes and validates a method for transmural pressure measurement using photoplethysmography (PPG) in an in vitro setup that allows control of pressure and flow conditions. The optimum pulsatile volume measure is obtained by comparing parameters extracted from the photoplethysmographic signal (AC amplitude, normalized pulse volume (NPV) and adjusted pulse volume (APV)). Pulsatile volume can then provide pressure measurements using the exponential pressure-volume (P-V) relationship and validated using the gold standard catheter pressure measurement. Pressure, red (R) and infrared (IR) PPG signals were recorded continuously in two arterial models with different cross-sectional areas (Model 1 and Model 2) utilising a pulsatile pump. Flow rates were controlled by varying pumping frequencies at low and high stroke volumes. The optimum method for estimation of the pulsatile volume is through APV, which had a highly significant correlation (r (2)  =  0.99, p  <  0.001) for Model 1 and (r (2)  =  0.98, p  <  0.001) for Model 2. APV obtained a significantly better fit when compared to NPVIR (r (2)  =  0.73, z  =  25.85, p  <  0.001), NPVR (r (2)  =  0.95, z  =  12.26, p  <  0.001), IRAC (r (2)  =  0.52, z  =  28.29, p  <  0.0001) and RAC (r (2)  =  0.92, z  =  15.27, p  <  0.0001) in Model 1, and when compared to NPVIR (r (2)  =  0.92, z  =  10.23, p  <  0.0001), NPVR (r (2)  =  0.96, z  =  5.08, p  <  0.001) IRAC (r (2)  =  0.63, z  =  22.47, p  <  0.0001) and RAC (r (2)  =  0.92, z  =  17.70, p  <  0.0001) in Model 2. These preliminary findings suggest that APV could be used as a potential non-invasive continuous method of blood pressure

  8. Analysis of pulsatile blood flow in constricted bifurcated arteries with vorticity-stream function approach.

    PubMed

    Chakravarty, S; Sen, S

    2008-01-01

    This theoretical investigation deals with an analysis of pulsatile blood flow in a model bifurcated artery having a stenosis in the parent arterial lumen. The geometry of the bifurcated arterial segment with an implanted stenosis in the parent duct is given an appropriate mathematical shape with the introduction of suitable curvature at the lateral junction and the flow divider. The vascular wall deformability is duly accounted for although the development of atherosclerosis in the arteries reduces its elastic property to some extent. The streaming blood contained in the bifurcated artery is treated to be Newtonian. The flow dynamic analysis applies two-dimensional unsteady incompressible nonlinear Navier-Stokes equations rewritten in the vorticity-stream function formulation. Following a radial coordinate transformation, these equations are solved numerically by a finite difference scheme with the approximate choice of the inlet and boundary conditions in concert with the biophysical point of view. The final numerical results are highlighted at the end of the paper through the exhibition of the wall shear stress and several time-variant patterns of streamlines and vorticity contours of the flow phenomena, which are highly influenced by the severity of the stenosis and the angle of bifurcation. The applicability of the present model is thus established.

  9. Assessment of turbulence models for pulsatile flow inside a heart pump.

    PubMed

    Al-Azawy, Mohammed G; Turan, A; Revell, A

    2016-02-01

    Computational fluid dynamics (CFD) is applied to study the unsteady flow inside a pulsatile pump left ventricular assist device, in order to assess the sensitivity to a range of commonly used turbulence models. Levels of strain and wall shear stress are directly relevant to the evaluation of risk from haemolysis and thrombosis, and thus understanding the sensitivity to these turbulence models is important in the assessment of uncertainty in CFD predictions. The study focuses on a positive displacement or pulsatile pump, and the CFD model includes valves and moving pusher plate. An unstructured dynamic layering method was employed to capture this cyclic motion, and valves were simulated in their fully open position to mimic the natural scenario, with in/outflow triggered at control planes away from the valves. Six turbulence models have been used, comprising three relevant to the low Reynolds number nature of this flow and three more intended to investigate different transport effects. In the first group, we consider the shear stress transport (SST) [Formula: see text] model in both its standard and transition-sensitive forms, and the 'laminar' model in which no turbulence model is used. In the second group, we compare the one equation Spalart-Almaras model, the standard two equation [Formula: see text] and the full Reynolds stress model (RSM). Following evaluation of spatial and temporal resolution requirements, results are compared with available experimental data. The model was operated at a systolic duration of 40% of the pumping cycle and a pumping rate of 86 BPM (beats per minute). Contrary to reasonable preconception, the 'transition' model, calibrated to incorporate additional physical modelling specifically for these flow conditions, was not noticeably superior to the standard form of the model. Indeed, observations of turbulent viscosity ratio reveal that the transition model initiates a premature increase of turbulence in this flow, when compared with

  10. Ocular rigidity, ocular pulse amplitude, and pulsatile ocular blood flow: the effect of axial length.

    PubMed

    Dastiridou, Anna I; Ginis, Harilaos; Tsilimbaris, Miltiadis; Karyotakis, Nikos; Detorakis, Efstathios; Siganos, Charalambos; Cholevas, Pierros; Tsironi, Evangelia E; Pallikaris, Ioannis G

    2013-03-01

    Previous studies have shown a negative correlation between axial length (AL) and pulsatile ocular blood flow (POBF). This relation has been questioned because of the possible confounding effect of ocular volume on ocular rigidity (OR). The purpose of this study was to investigate the relation between AL, as a surrogate parameter for ocular volume, and OR, ocular pulse amplitude (OPA), and POBF. Eighty-eight cataract patients were enrolled in this study. A computer-controlled device comprising a microdosimetric pump and a pressure sensor was used intraoperatively. The system was connected to the anterior chamber and used to raise the intraocular pressure (IOP) from 15 to 40 mm Hg, by infusing the eye with a saline solution. After each infusion step, the IOP was continuously recorded for 2 seconds. Blood pressure and pulse rate were measured during the procedure. The OR coefficient was calculated from the pressure volume data. OPA and POBF were measured from pressure recordings. Median AL was 23.69 (interquartile range 3.53) mm. OR coefficient was 0.0218 (0.0053) μL(-1). A negative correlation between the OR coefficient and AL (ρ = -0.641, P < 0.001) was documented. Increasing AL was associated with decreased OPA (ρ = -0.637, P < 0.001 and ρ = -0.690, P < 0.001) and POBF (ρ = -0.207, P = 0.053 and ρ = -0.238, P = 0.028) at baseline and elevated IOP, respectively. Based on manometric data, increasing AL is associated with decreased OR, OPA, and POBF. These results suggest decreased pulsatility in high myopia and may have implications on ocular pulse studies and the pathophysiology of myopia.

  11. Deformation of a membrane in a pulsatile flow: implications in heart valve design

    NASA Astrophysics Data System (ADS)

    Hernandez, C.; Guzman, J. E. V.; Zenit, R.

    2011-11-01

    Current designs of heart valves prosthetics have serious disadvantages and health issues for patients who use them. For this reason, a new design that combines durability (mechanical valves) and biocompatibility (biological valves) has to be conceived. Natural valves have very complex geometry because their leaflets have two principal curvatures, one imposed by the holding ring and a second one imposed by the bending of the closing arrangement. The objective of this research is to study the effects of both curvatures on the performance of a leaflet. It is well known that the increase of the curvature results in a larger stiffness, which, in turn, reduces the deflection of a leaflet. We conducted a study to determine the effect of changing the curvature (in two directions) of a flexible membrane when exposed to a steady and pulsatile flows. A study of the flow field that results from this interaction is also conducted by PIV measurements. Preliminary results of the leaflet deflection for many stiffnesses, curvatures and flow conditions will be presented and discussed.

  12. Comparison of two types of neonatal extracorporeal life support systems with pulsatile and nonpulsatile flow.

    PubMed

    Haines, Nikkole; Wang, Shigang; Myers, John L; Undar, Akif

    2009-11-01

    We compared the effects of two neonatal extracorporeal life support (ECLS) systems on circuit pressures and surplus hemodynamic energy levels in a simulated ECLS model. The clinical set-up included the Jostra HL-20 heart-lung machine, either the Medtronic ECMO (0800) or the MEDOS 800LT systems with company-provided circuit components, a 10 Fr arterial cannula, and a pseudo-patient. We tested the system in nonpulsatile and pulsatile flow modes at two flow rates using a 40/60 glycerin/water blood analog, for a total of 48 trials, with n = 6 for each set-up. The pressure drops over the Medtronic ECLS were significantly higher than those over the MEDOS system regardless of the flow rate or perfusion mode (144.8 +/- 0.2 mm Hg vs. 35.7 +/- 0.2 mm Hg, respectively, at 500 mL/min in nonpulsatile mode, P < 0.001). The preoxygenator mean arterial pressures were significantly increased and the precannula hemodynamic energy values were decreased with the Medtronic ECLS circuit. These results suggest that the MEDOS ECLS circuit better transmits hemodynamic energy to the patient, keeps mean circuit pressures lower, and has lower pressure drops than the Medtronic Circuit.

  13. Mathematical Modeling of Rotary Blood Pumps in a Pulsatile In Vitro Flow Environment.

    PubMed

    Pirbodaghi, Tohid

    2017-01-18

    Nowadays, sacrificing animals to develop medical devices and receive regulatory approval has become more common, which increases ethical concerns. Although in vivo tests are necessary for development and evaluation of new devices, nonetheless, with appropriate in vitro setups and mathematical models, a part of the validation process can be performed using these models to reduce the number of sacrificed animals. The main aim of this study is to present a mathematical model simulating the hydrodynamic function of a rotary blood pump (RBP) in a pulsatile in vitro flow environment. This model relates the pressure head of the RBP to the flow rate, rotational speed, and time derivatives of flow rate and rotational speed. To identify the model parameters, an in vitro setup was constructed consisting of a piston pump, a compliance chamber, a throttle, a buffer reservoir, and the CentriMag RBP. A 40% glycerin-water mixture as a blood analog fluid and deionized water were used in the hydraulic circuit to investigate the effect of viscosity and density of the working fluid on the model parameters. First, model variables were physically measured and digitally acquired. Second, an identification algorithm based on regression analysis was used to derive the model parameters. Third, the completed model was validated with a totally different set of in vitro data. The model is usable for both mathematical simulations of the interaction between the pump and heart and indirect pressure measurement in a clinical context.

  14. Pulsatile Poiseuille flows in microfluidic channels with back-and-forth mode

    NASA Astrophysics Data System (ADS)

    Kim, Kwang Seok; Chun, Myung-Suk

    2012-06-01

    The numerical solver for the velocity field equation describing laminar pulsatile flows driven by a time-dependent pressure drop in the straight microfluidic channel of square cross-section is developed. In the computational algorithm, an orthogonal collocation on finite element scheme for spatial discretizations is combined with an adaptive Runge-Kutta method for time integration. The algorithm with the 1,521 computational nodes and the accuracy up to O(10-5) is applied to the flow in the back-and-forth standing mode with the channel hydraulic diameter ( D h ) in the range 10-500 μm and the oscillating frequency ( f) of 1 to 100 Hz. As a result, a periodic steady state is defined as the flow condition where there would be no net movement after long time elapses. Following by the retardation phenomena in a cycle, reversal of the axial velocity is observed at the channel center. Major attention is focused on the influences of the size of channel cross-section and the oscillating frequency. Increasing D h and f results in the decrease in the amplitude of mean velocity but the increase in the start-up time. Larger time delay occurs by low-frequency pulsation.

  15. Computational solution of the velocity and wall shear stress distribution inside a left carotid artery under pulsatile flow conditions

    NASA Astrophysics Data System (ADS)

    Arslan, Nurullah; Turmuş, Hakan

    2014-08-01

    Stroke is still one of the leading causes for death after heart diseases and cancer in all over the world. Strokes happen because an artery that carries blood uphill from the heart to the head is clogged. Most of the time, as with heart attacks, the problem is atherosclerosis, hardening of the arteries, calcified buildup of fatty deposits on the vessel wall. In this study, the fluid dynamic simulations were done in a left carotid bifurcation under the pulsatile flow conditions computationally. Pulsatile flow waveform is given in the paper. In vivo geometry and boundary conditions were obtained from a patient who has stenosis located at external carotid artery (ECA) and internal carotid artery (ICA) of his common carotid artery (CCA). The location of critical flow fields such as low wall shear stress (WSS), stagnation regions and separation regions were detected near the highly stenosed region and at branching region.

  16. Computational study of pulsatile blood flow in prototype vessel geometries of coronary segments

    PubMed Central

    Chaniotis, A.K.; Kaiktsis, L.; Katritsis, D.; Efstathopoulos, E.; Pantos, I.; Marmarellis, V.

    2010-01-01

    The spatial and temporal distributions of wall shear stress (WSS) in prototype vessel geometries of coronary segments are investigated via numerical simulation, and the potential association with vascular disease and specifically atherosclerosis and plaque rupture is discussed. In particular, simulation results of WSS spatio-temporal distributions are presented for pulsatile, non-Newtonian blood flow conditions for: (a) curved pipes with different curvatures, and (b) bifurcating pipes with different branching angles and flow division. The effects of non-Newtonian flow on WSS (compared to Newtonian flow) are found to be small at Reynolds numbers representative of blood flow in coronary arteries. Specific preferential sites of average low WSS (and likely atherogenesis) were found at the outer regions of the bifurcating branches just after the bifurcation, and at the outer-entry and inner-exit flow regions of the curved vessel segment. The drop in WSS was more dramatic at the bifurcating vessel sites (less than 5% of the pre-bifurcation value). These sites were also near rapid gradients of WSS changes in space and time – a fact that increases the risk of rupture of plaque likely to develop at these sites. The time variation of the WSS spatial distributions was very rapid around the start and end of the systolic phase of the cardiac cycle, when strong fluctuations of intravascular pressure were also observed. These rapid and strong changes of WSS and pressure coincide temporally with the greatest flexion and mechanical stresses induced in the vessel wall by myocardial motion (ventricular contraction). The combination of these factors may increase the risk of plaque rupture and thrombus formation at these sites. PMID:20400349

  17. Computational study of pulsatile blood flow in prototype vessel geometries of coronary segments.

    PubMed

    Chaniotis, A K; Kaiktsis, L; Katritsis, D; Efstathopoulos, E; Pantos, I; Marmarellis, V

    2010-01-01

    The spatial and temporal distributions of wall shear stress (WSS) in prototype vessel geometries of coronary segments are investigated via numerical simulation, and the potential association with vascular disease and specifically atherosclerosis and plaque rupture is discussed. In particular, simulation results of WSS spatio-temporal distributions are presented for pulsatile, non-Newtonian blood flow conditions for: (a) curved pipes with different curvatures, and (b) bifurcating pipes with different branching angles and flow division. The effects of non-Newtonian flow on WSS (compared to Newtonian flow) are found to be small at Reynolds numbers representative of blood flow in coronary arteries. Specific preferential sites of average low WSS (and likely atherogenesis) were found at the outer regions of the bifurcating branches just after the bifurcation, and at the outer-entry and inner-exit flow regions of the curved vessel segment. The drop in WSS was more dramatic at the bifurcating vessel sites (less than 5% of the pre-bifurcation value). These sites were also near rapid gradients of WSS changes in space and time - a fact that increases the risk of rupture of plaque likely to develop at these sites. The time variation of the WSS spatial distributions was very rapid around the start and end of the systolic phase of the cardiac cycle, when strong fluctuations of intravascular pressure were also observed. These rapid and strong changes of WSS and pressure coincide temporally with the greatest flexion and mechanical stresses induced in the vessel wall by myocardial motion (ventricular contraction). The combination of these factors may increase the risk of plaque rupture and thrombus formation at these sites.

  18. Pulsatile flows and wall-shear stresses in models simulating normal and stenosed aortic arches

    NASA Astrophysics Data System (ADS)

    Huang, Rong Fung; Yang, Ten-Fang; Lan, Y.-K.

    2010-03-01

    Pulsatile aqueous glycerol solution flows in the models simulating normal and stenosed human aortic arches are measured by means of particle image velocimetry. Three transparent models were used: normal, 25% stenosed, and 50% stenosed aortic arches. The Womersley parameter, Dean number, and time-averaged Reynolds number are 17.31, 725, and 1,081, respectively. The Reynolds numbers based on the peak velocities of the normal, 25% stenosed, and 50% stenosed aortic arches are 2,484, 3,456, and 3,931, respectively. The study presents the temporal/spatial evolution processes of the flow pattern, velocity distribution, and wall-shear stress during the systolic and diastolic phases. It is found that the flow pattern evolving in the central plane of normal and stenosed aortic arches exhibits (1) a separation bubble around the inner arch, (2) a recirculation vortex around the outer arch wall upstream of the junction of the brachiocephalic artery, (3) an accelerated main stream around the outer arch wall near the junctions of the left carotid and the left subclavian arteries, and (4) the vortices around the entrances of the three main branches. The study identifies and discusses the reasons for the flow physics’ contribution to the formation of these features. The oscillating wall-shear stress distributions are closely related to the featured flow structures. On the outer wall of normal and slightly stenosed aortas, large wall-shear stresses appear in the regions upstream of the junction of the brachiocephalic artery as well as the corner near the junctions of the left carotid artery and the left subclavian artery. On the inner wall, the largest wall-shear stress appears in the region where the boundary layer separates.

  19. The Relationship Between Pulsatile Flow Impingement and Intraluminal Thrombus Deposition in Abdominal Aortic Aneurysms.

    PubMed

    Lozowy, Richard J; Kuhn, David C S; Ducas, Annie A; Boyd, April J

    2017-03-01

    Direct numerical simulations were performed on four patient-specific abdominal aortic aneurysm (AAA) geometries and the resulting pulsatile blood flow dynamics were compared to aneurysm shape and correlated with intraluminal thrombus (ILT) deposition. For three of the cases, turbulent vortex structures impinged/sheared along the anterior wall and along the posterior wall a zone of recirculating blood formed. Within the impingement region the AAA wall was devoid of ILT and remote to this region there was an accumulation of ILT. The high wall shear stress (WSS) caused by the impact of vortexes is thought to prevent the attachment of ILT. WSS from impingement is comparable to peak-systolic WSS in a normal-sized aorta and therefore may not damage the wall. Expansion occurred to a greater extent in the direction of jet impingement and the wall-normal force from the continuous impact of vortexes may contribute to expansion. It was shown that the impingement region has low oscillatory shear index (OSI) and recirculation zones can have either low or high OSI. No correlation could be identified between OSI and ILT deposition since different flow dynamics can have similar OSI values.

  20. Quantitative myocardial perfusion magnetic resonance imaging: the impact of pulsatile flow on contrast agent bolus dispersion

    NASA Astrophysics Data System (ADS)

    Graafen, Dirk; Hamer, Julia; Weber, Stefan; Schreiber, Laura M.

    2011-08-01

    Myocardial blood flow (MBF) can be quantified using T1-weighted first-pass magnetic resonance imaging (MRI) in combination with a tracer-kinetic model, like MMID4. This procedure requires the knowledge of an arterial input function which is usually estimated from the left ventricle (LV). Dispersion of the contrast agent bolus may occur between the LV and the tissue of interest. The aim of this study was to investigate the dispersion under conditions of physiological pulsatile blood flow, and to simulate its effect on MBF quantification. The dispersion was simulated in coronary arteries using a computational fluid dynamics (CFD) approach. Simulations were accomplished on straight vessels with stenosis of different degrees and shapes. The results show that dispersion is more pronounced under resting conditions than during hyperemia. Stenosis leads to a reduction of dispersion. In consequence, dispersion results in a systematic MBF underestimation between -0.4% and -9.3%. The relative MBF error depends not only on the dispersion but also on the actual MBF itself. Since MBF under rest is more underestimated than under stress, myocardial perfusion reserve is overestimated between 0.1% and 4.5%. Considering other sources of errors in myocardial perfusion MRI, systematic errors of MBF by bolus dispersion are relatively small.

  1. The Effect of Arterial Curvature on Blood Flow in Arterio-Venous Fistulae: Realistic Geometries and Pulsatile Flow.

    PubMed

    Grechy, L; Iori, F; Corbett, R W; Gedroyc, W; Duncan, N; Caro, C G; Vincent, P E

    2017-07-26

    Arterio-Venous Fistulae (AVF) are regarded as the "gold standard" method of vascular access for patients with End-Stage Renal Disease (ESRD) who require haemodialysis. However, up to 60% of AVF do not mature, and hence fail, as a result of Intimal Hyperplasia (IH). Unphysiological flow and oxygen transport patterns, associated with the unnatural and often complex geometries of AVF, are believed to be implicated in the development of IH. Previous studies have investigated the effect of arterial curvature on blood flow in AVF using idealized planar AVF configurations and non-pulsatile inflow conditions. The present study takes an important step forwards by extending this work to more realistic non-planar brachiocephalic AVF configurations with pulsatile inflow conditions. Results show that forming an AVF by connecting a vein onto the outer curvature of an arterial bend does not, necessarily, suppress unsteady flow in the artery. This finding is converse to results from a previous more idealized study. However, results also show that forming an AVF by connecting a vein onto the inner curvature of an arterial bend can suppress exposure to regions of low wall shear stress and hypoxia in the artery. This finding is in agreement with results from a previous more idealized study. Finally, results show that forming an AVF by connecting a vein onto the inner curvature of an arterial bend can significantly reduce exposure to high WSS in the vein. The results are important, as they demonstrate that in realistic scenarios arterial curvature can be leveraged to reduce exposure to excessively low/high levels of WSS and regions of hypoxia in AVF. This may in turn reduce rates of IH and hence AVF failure.

  2. Laser interferometric investigations of pulsatile choroidal blood flow: review and new results on the validity of the technique

    NASA Astrophysics Data System (ADS)

    Schmetterer, Leopold F.; Wolzt, M.

    1998-07-01

    A short overview of currently available ocular blood flow techniques is given. We have recently introduced a laser interferometric technique for the measurement of ocular fundus pulsation. The eye is illuminated by a single mode laser beam which is reflected at the anterior corneal surface and the fundus. The two re-emitted waves produce interference fringes from which distance changes between cornea and retina during the cardiac cycle can be calculated. These rhythmic changes in corneo-retinal distance are caused by the arterial pulsatile inflow of blood, which increases the ocular volume. The fundus pulsation amplitude (FPA) is the maximum distance change between cornea and retina during the cardiac cycle and is taken as a relative measure of pulsatile choroidal blood flow. The high reproducibility and the high sensitivity of the method are discussed. In addition, the present article reviews comparative measurement with other techniques for the assessment of choroidal blood flow, which validates the method. Furthermore, we present new data on a comparison of color Doppler imaging in the posterior ciliary arteries and laser interferometric measurement of FPA. Applications of laser interferometric measurement of FPA to study the physiology, the pharmacology, and the pathophysiology of the choroidal circulation are reviewed. In conclusion, FPA can be taken as a relative measure of pulsatile choroidal blood flow. The technique is particularly suitable for pharmacodynamic studies.

  3. Pulsatile flow decreases gaseous micro-bubble filtering properties of oxygenators without integrated arterial filters during cardiopulmonary bypass

    PubMed Central

    Milano, Aldo D.; Dodonov, Mikhail; Onorati, Francesco; Menon, Tiziano; Gottin, Leonardo; Malerba, Giovanni; Mazzucco, Alessandro; Faggian, Giuseppe

    2013-01-01

    OBJECTIVES Cardiopulmonary bypass (CPB) has a risk of embolic injury with an important role of gaseous micro-bubbles (GMBs), coming from CPB-circuit. Pulsatile perfusion (PP) can provide specific conditions for supplementary GMB-activity with respect to non-pulsatile (NP). We aimed to test GMB-filtering properties of three modern oxygenators under pulsatile and non-pulsatile conditions. METHODS Seventy-eight patients undergoing on-pump myocardial revascularization were randomized prospectively into three equal groups according to the oxygenator model used during CPB. Terumo Capiox-FX25, Sorin Synthesis or Maquet Quadrox-i-Adult membrane oxygenators were tested. Each group was divided equally to undergo PP or NP. GMBs were counted by means of a GAMPT-BCC200 bubble-counter with two probes placed at preoxygenator and arterial post-filter positions. Results were evaluated in terms of GMB-volume, GMB-number, amount of large over-ranged GMBs, a series of filtering indices and major neurological outcomes. RESULTS PP decreased GMB-filtering properties of the tested oxygenators. Those with integrated filters (CAPIOX-FX25 and SYNTHESIS) did not show significant differences between perfusion groups, while QUADROX-i oxygenator with external arterial filter showed significantly higher GMB-volume (P < 0.001), GMB-number (P < 0.001) and amount of over-ranged bubbles (P < 0.001) detected in arterial line during PP. Despite the differences in filtering capacity of all circuits with both types of perfusion, no important differences in clinical outcomes and major neurological events were observed. CONCLUSIONS Pulsatile flow decreases gaseous micro-bubble filtering properties of oxygenators without integrated arterial filters during CPB. PP requires specially designed circuit components to avoid the risk of additional GMB delivery. PMID:23842758

  4. Pulsatile flow decreases gaseous micro-bubble filtering properties of oxygenators without integrated arterial filters during cardiopulmonary bypass.

    PubMed

    Milano, Aldo D; Dodonov, Mikhail; Onorati, Francesco; Menon, Tiziano; Gottin, Leonardo; Malerba, Giovanni; Mazzucco, Alessandro; Faggian, Giuseppe

    2013-11-01

    Cardiopulmonary bypass (CPB) has a risk of embolic injury with an important role of gaseous micro-bubbles (GMBs), coming from CPB-circuit. Pulsatile perfusion (PP) can provide specific conditions for supplementary GMB-activity with respect to non-pulsatile (NP). We aimed to test GMB-filtering properties of three modern oxygenators under pulsatile and non-pulsatile conditions. Seventy-eight patients undergoing on-pump myocardial revascularization were randomized prospectively into three equal groups according to the oxygenator model used during CPB. Terumo Capiox-FX25, Sorin Synthesis or Maquet Quadrox-i-Adult membrane oxygenators were tested. Each group was divided equally to undergo PP or NP. GMBs were counted by means of a GAMPT-BCC200 bubble-counter with two probes placed at preoxygenator and arterial post-filter positions. Results were evaluated in terms of GMB-volume, GMB-number, amount of large over-ranged GMBs, a series of filtering indices and major neurological outcomes. PP decreased GMB-filtering properties of the tested oxygenators. Those with integrated filters (CAPIOX-FX25 and SYNTHESIS) did not show significant differences between perfusion groups, while QUADROX-i oxygenator with external arterial filter showed significantly higher GMB-volume (P < 0.001), GMB-number (P < 0.001) and amount of over-ranged bubbles (P < 0.001) detected in arterial line during PP. Despite the differences in filtering capacity of all circuits with both types of perfusion, no important differences in clinical outcomes and major neurological events were observed. Pulsatile flow decreases gaseous micro-bubble filtering properties of oxygenators without integrated arterial filters during CPB. PP requires specially designed circuit components to avoid the risk of additional GMB delivery.

  5. Effects of elevated perfusion pressure and pulsatile flow on human saphenous veins isolated from diabetic and non-diabetic patients.

    PubMed

    Rosique, Marina J F; Rosique, Rodrigo G; Tirapelli, Luis F; Joviliano, Edwaldo E; Dalio, Marcelo B; Bassetto, Solange; Rodrigues, Alfredo J; Evora, Paulo R B

    2013-05-01

    This study was carried out to determine high pressure and pulsatile flow perfusion effects on human saphenous vein (HSV) segments obtained from diabetic and non-diabetic patients. The veins were perfused with oxygenated Krebs solution for 3 h, with a pulsatile flow rate of 100 mL/min and pressures of 250 × 200 or 300 × 250 mmHg. After perfusion, veins were studied by light microscopy; nitric oxide synthase (NOS) isoforms, CD34 and nitrotyrosine immunohistochemistry and tissue nitrite/nitrate (NO(x)) and malondialdehyde (MDA) quantification. Light microscopy revealed endothelial denuding areas in all HSV segments subjected to 300 × 250 mmHg perfusion pressure, but the luminal area was similar. The percentage of luminal perimeter covered by endothelium decreased as perfusion pressures increased, and significant differences were observed between groups. The endothelial nitric oxide synthase (eNOS) isoform immunostaining decreased significantly in diabetic patients' veins independent of the perfusion pressure levels. The inducible NOS (iNOS), neuronal NOS (nNOS) and nitrotyrosine immunostaining were similar. Significant CD34 differences were observed between the diabetic 300 × 250 mmHg perfusion pressure group and the non-diabetic control group. Tissue nitrite/nitrate and MDA were not different among groups. Pulsatile flow and elevated pressures for 3 h caused morphological changes and decreased the eNOS expression in the diabetic patients' veins.

  6. Chest-MRI under pulsatile flow ventilation: A new promising technique.

    PubMed

    Beigelman-Aubry, Catherine; Peguret, Nicolas; Stuber, Matthias; Delacoste, Jean; Belmondo, Bastien; Lovis, Alban; Simons, Julien; Long, Olivier; Grant, Kathleen; Berchier, Gregoire; Rohner, Chantal; Bonanno, Gabriele; Coppo, Simone; Schwitter, Juerg; Ozsahin, Mahmut; Qanadli, Salah; Meuli, Reto; Bourhis, Jean

    2017-01-01

    Magnetic resonance imaging (MRI) of the chest has long suffered from its sensitivity to respiratory and cardiac motion with an intrinsically low signal to noise ratio and a limited spatial resolution. The purpose of this study was to perform chest MRI under an adapted non invasive pulsatile flow ventilation system (high frequency percussive ventilation, HFPV®) allowing breath hold durations 10 to 15 times longer than other existing systems. One volunteer and one patient known for a thymic lesion underwent a chest MRI under ventilation percussion technique (VP-MR). Routinely used sequences were performed with and without the device during three sets of apnoea on inspiration. VP-MR was well tolerated in both cases. The mean duration of the thoracic stabilization was 10.5 min (range 8.5-12) and 5.8 min (range 5-6.2) for Volunteer 1 and Patient 1, respectively. An overall increased image quality was seen under VP-MR with a better delineation of the mediastinal lesion for Patient 1. Nodules discovered in Volunteer 1 were confirmed with low dose CT. VP-MR was feasible and increased spatial resolution of chest MRI by allowing acquisition at full inspiration during thoracic stabilization approaching prolonged apnoea. This new technique could be of benefit to numerous thoracic disorders.

  7. Ocular rigidity, ocular pulse amplitude, and pulsatile ocular blood flow: the effect of intraocular pressure.

    PubMed

    Dastiridou, Anna I; Ginis, Harilaos S; De Brouwere, Dirk; Tsilimbaris, Miltiadis K; Pallikaris, Ioannis G

    2009-12-01

    The purpose of this study was to characterize the pressure-volume relation in the living human eye, measure the ocular pulse amplitude (OPA), and calculate the corresponding pulsatile ocular blood flow (POBF) in a range of clinically relevant IOP levels. Fifty patients with cataract (50 eyes) were enrolled in the study. After cannulation of the anterior chamber, a computer-controlled device for the intraoperative measurement and control of IOP was used to artificially increase the IOP in a stepping procedure from 15 to 40 mm Hg. The IOP was continuously recorded for 2 seconds after each infusion step. The pressure-volume relation was approximated with an exponential fit, and the ocular rigidity coefficient was computed. OPA, pulse volume (PV), and POBF were measured from the continuous IOP recordings. The average rigidity coefficient was 0.0224 microL(-1) (SD 0.0049). OPA increased by 91% and PV and POBF decreased by 29% and 30%, respectively, when increasing the IOP from 15 to 40 mm Hg. The OPA is positively correlated with the coefficient of ocular rigidity (r = 0.65, P < 0.01). The present results suggest a nonlinear pressure-volume relation in the living human eye characterized by an increase in rigidity at higher IOP levels. The increased OPA and decreased pulse volume relate to the decreased POBF and the increased mechanical resistance of the ocular wall at high IOP levels.

  8. Expansion of bubbles under a pulsatile flow regime in decompressed ovine blood vessels.

    PubMed

    Arieli, Ran; Marmur, Abraham

    2016-02-01

    After decompression of ovine large blood vessels, bubbles nucleate and expand at active hydrophobic spots on their luminal aspect. These bubbles will be in the path of the blood flow within the vessel, which might replenish the supply of gas-supersaturated plasma in their vicinity and thus, in contrast with our previous estimations, enhance their growth. We used the data from our previous study on the effect of pulsatile flow in ovine blood vessels stretched on microscope slides and photographed after decompression from hyperbaric exposure. We measured the diameter of 46 bubbles in 4 samples taken from 3 blood vessels (pulmonary artery, pulmonary vein, and aorta) in which both a "multi-bubble active spot" (MBAS)--which produces several bubbles at a time, and at least one "single-bubble active spot" (SBAS)--which produces a single bubble at a time, were seen together. The linear expansion rate for diameter in SBAS ranged from 0.077 to 0.498 mm/min and in MBAS from 0.001 to 0.332 mm/min. There was a trend toward a reduced expansion rate for bubbles in MBAS compared with SBAS. The expansion rate for bubbles in an MBAS when it was surrounded by others was very low. Bubble growth is related to gas tension, and under a flow regime, bubbles expand from a diameter of 0.1 to 1mm in 2-24 min at a gas supersaturation of 620 kPa and lower. There are two phases of bubble development. The slow and disperse initiation of active spots (from nanobubbles to gas micronuclei) continues for more than 1h, whereas the fast increase in size (2-24 min) is governed by diffusion. Bubble-based decompression models should not artificially reduce diffusion constants, but rather take both phases of bubble development into consideration. Copyright © 2015 Elsevier B.V. All rights reserved.

  9. An original valveless artificial heart providing pulsatile flow tested in mock circulatory loops.

    PubMed

    Tozzi, Piergiorgio; Maertens, Audrey; Emery, Jonathan; Joseph, Samuel; Kirsch, Matthias; Avellan, François

    2017-08-11

    We present the test bench results of a valveless total artificial heart that is potentially compatible with the pediatric population. The RollingHeart is a valveless volumetric pump generating pulsatile flow. It consists of a single spherical cavity divided into 4 chambers by 2 rotating disks. The combined rotations of both disks produce changes in the volumes of the 4 cavities (suction and ejection). The blood enters/exits the spherical cavity through 4 openings that are symmetrical to the fixed rotation axis of the first disk.Mock circulatory system: The device pumps a 37% glycerin solution through 2 parallel circuits, simulating the pulmonary and systemic circulations. Flow rates are acquired with a magnetic inductive flowmeter, while pressure sensors collect pressure in the left and right outflow and inflow tracts.In vitro test protocol: The pump is run at speeds ranging from 20 to 180 ejections per minute. The waveform of the pressure generated at the inflow and outflow of the 4 chambers and the flow rate in the systemic circulation are measured. At an ejection rate of 178 min-1, the RollingHeart pumps 5.3 L/min for a systemic maximal pressure gradient of 174 mmHg and a pulmonary maximal pressure gradient of 75 mmHg. The power input was 14 W, corresponding to an efficiency of 21%. The RollingHeart represents a new approach in the domain of total artificial heart. This preliminary study endorses the feasibility of a single valveless device acting as a total artificial heart.

  10. Arterial stiffness, pressure and flow pulsatility and brain structure and function: the Age, Gene/Environment Susceptibility--Reykjavik study.

    PubMed

    Mitchell, Gary F; van Buchem, Mark A; Sigurdsson, Sigurdur; Gotal, John D; Jonsdottir, Maria K; Kjartansson, Ólafur; Garcia, Melissa; Aspelund, Thor; Harris, Tamara B; Gudnason, Vilmundur; Launer, Lenore J

    2011-11-01

    Aortic stiffness increases with age and vascular risk factor exposure and is associated with increased risk for structural and functional abnormalities in the brain. High ambient flow and low impedance are thought to sensitize the cerebral microcirculation to harmful effects of excessive pressure and flow pulsatility. However, haemodynamic mechanisms contributing to structural brain lesions and cognitive impairment in the presence of high aortic stiffness remain unclear. We hypothesized that disproportionate stiffening of the proximal aorta as compared with the carotid arteries reduces wave reflection at this important interface and thereby facilitates transmission of excessive pulsatile energy into the cerebral microcirculation, leading to microvascular damage and impaired function. To assess this hypothesis, we evaluated carotid pressure and flow, carotid-femoral pulse wave velocity, brain magnetic resonance images and cognitive scores in participants in the community-based Age, Gene/Environment Susceptibility--Reykjavik study who had no history of stroke, transient ischaemic attack or dementia (n = 668, 378 females, 69-93 years of age). Aortic characteristic impedance was assessed in a random subset (n = 422) and the reflection coefficient at the aorta-carotid interface was computed. Carotid flow pulsatility index was negatively related to the aorta-carotid reflection coefficient (R = -0.66, P<0.001). Carotid pulse pressure, pulsatility index and carotid-femoral pulse wave velocity were each associated with increased risk for silent subcortical infarcts (hazard ratios of 1.62-1.71 per standard deviation, P<0.002). Carotid-femoral pulse wave velocity was associated with higher white matter hyperintensity volume (0.108 ± 0.045 SD/SD, P = 0.018). Pulsatility index was associated with lower whole brain (-0.127 ± 0.037 SD/SD, P<0.001), grey matter (-0.079 ± 0.038 SD/SD, P = 0.038) and white matter (-0.128 ± 0.039 SD/SD, P<0.001) volumes. Carotid-femoral pulse

  11. The occurrence of the Coanda effect in pulsatile flow through static models of the human vocal folds.

    PubMed

    Erath, Byron D; Plesniak, Michael W

    2006-08-01

    Pulsatile flow through a one-sided diffuser and static divergent vocal-fold models is investigated to ascertain the relevance of viscous-driven flow asymmetries in the larynx. The models were 7.5 times real size, and the flow was scaled to match Reynolds and Strouhal numbers, as well as the translaryngeal pressure drop. The Reynolds number varied from 0-2000, for flow oscillation frequencies corresponding to 100 and 150 Hz life-size. Of particular interest was the development of glottal flow skewing by attachment to the bounding walls, or Coanda effect, in a pulsatile flow field, and its impact on speech. The vocal folds form a divergent passage during phases of the phonation cycle when viscous effects such as flow separation are important. It was found that for divergence angles of less than 20 degrees, the attachment of the flow to the vocal-fold walls occurred when the acceleration of the forcing function was zero, and the flow had reached maximum velocity. For a divergence angle of 40 degrees, the fully separated central jet never attached to the vocal-fold walls. Inferences are made regarding the impact of the Coanda effect on the sound source contribution in speech.

  12. Osteoblasts respond to pulsatile fluid flow with short-term increases in PGE(2) but no change in mineralization

    NASA Technical Reports Server (NTRS)

    Nauman, E. A.; Satcher, R. L.; Keaveny, T. M.; Halloran, B. P.; Bikle, D. D.

    2001-01-01

    Although there is no consensus as to the precise nature of the mechanostimulatory signals imparted to the bone cells during remodeling, it has been postulated that deformation-induced fluid flow plays a role in the mechanotransduction pathway. In vitro, osteoblasts respond to fluid shear stress with an increase in PGE(2) production; however, the long-term effects of fluid shear stress on cell proliferation and differentiation have not been examined. The goal of this study was to apply continuous pulsatile fluid shear stresses to osteoblasts and determine whether the initial production of PGE(2) is associated with long-term biochemical changes. The acute response of bone cells to a pulsatile fluid shear stress (0.6 +/- 0.5 Pa, 3.0 Hz) was characterized by a transient fourfold increase in PGE(2) production. After 7 days of static culture (0 dyn/cm(2)) or low (0.06 +/- 0.05 Pa, 0.3 Hz) or high (0.6 +/- 0.5 Pa, 3.0 Hz) levels of pulsatile fluid shear stress, the bone cells responded with an 83% average increase in cell number, but no statistical difference (P > 0.53) between the groups was observed. Alkaline phosphatase activity per cell decreased in the static cultures but not in the low- or high-flow groups. Mineralization was also unaffected by the different levels of applied shear stress. Our results indicate that short-term changes in PGE(2) levels caused by pulsatile fluid flow are not associated with long-term changes in proliferation or mineralization of bone cells.

  13. Smoothed particle hydrodynamics method applied to pulsatile flow inside a rigid two-dimensional model of left heart cavity.

    PubMed

    Shahriari, S; Kadem, L; Rogers, B D; Hassan, I

    2012-11-01

    This paper aims to extend the application of smoothed particle hydrodynamics (SPH), a meshfree particle method, to simulate flow inside a model of the heart's left ventricle (LV). This work is considered the first attempt to simulate flow inside a heart cavity using a meshfree particle method. Simulating this kind of flow, characterized by high pulsatility and moderate Reynolds number using SPH is challenging. As a consequence, validation of the computational code using benchmark cases is required prior to simulating the flow inside a model of the LV. In this work, this is accomplished by simulating an unsteady oscillating flow (pressure amplitude: A = 2500 N ∕ m(3) and Womersley number: W(o)  = 16) and the steady lid-driven cavity flow (Re = 3200, 5000). The results are compared against analytical solutions and reference data to assess convergence. Then, both benchmark cases are combined and a pulsatile jet in a cavity is simulated and the results are compared with the finite volume method. Here, an approach to deal with inflow and outflow boundary conditions is introduced. Finally, pulsatile inlet flow in a rigid model of the LV is simulated. The results demonstrate the ability of SPH to model complex cardiovascular flows and to track the history of fluid properties. Some interesting features of SPH are also demonstrated in this study, including the relation between particle resolution and sound speed to control compressibility effects and also order of convergence in SPH simulations, which is consistently demonstrated to be between first-order and second-order at the moderate Reynolds numbers investigated.

  14. Numerical investigation of the non-Newtonian pulsatile blood flow in a bifurcation model with a non-planar branch.

    PubMed

    Chen, Jie; Lu, Xi-Yun

    2006-01-01

    The pulsatile flow of non-Newtonian fluid in a bifurcation model with a non-planar daughter branch is investigated numerically by using the Carreau-Yasuda model to take into account the shear thinning behavior of the analog blood fluid. The objective of this study is to deal with the influence of the non-Newtonian property of fluid and of out-of-plane curvature in the non-planar daughter vessel on wall shear stress (WSS), oscillatory shear index (OSI), and flow phenomena during the pulse cycle. The non-Newtonian property in the daughter vessels induces a flattened axial velocity profile due to its shear thinning behavior. The non-planarity deflects flow from the inner wall of the vessel to the outer wall and changes the distribution of WSS along the vessel, in particular in systole phase. Downstream of the bifurcation, the velocity profiles are shifted toward the flow divider, and low WSS and high shear stress temporal oscillations characterized by OSI occur on the outer wall region of the daughter vessels close to the bifurcation. Secondary motions become stronger with the addition of the out-of-plane curvature induced by the bending of the vessel, and the secondary flow patterns swirl along the non-planar daughter vessel. A significant difference between the non-Newtonian and the Newtonian pulsatile flow is revealed during the pulse cycle; however, reasonable agreement between the non-Newtonian and the rescaled Newtonian flow is found. Calculated results for the pulsatile flow support the view that the non-planarity of blood vessels and the non-Newtonian properties of blood are an important factor in hemodynamics and may play a significant role in vascular biology and pathophysiology.

  15. Non-invasive estimation of pulsatile flow and differential pressure in an implantable rotary blood pump for heart failure patients.

    PubMed

    AlOmari, A H; Savkin, A V; Karantonis, D M; Lim, E; Lovell, N H

    2009-04-01

    We propose dynamical models for pulsatile flow and head estimation in an implantable rotary blood pump. Pulsatile flow and head data were obtained using a circulatory mock loop where fluid solutions with different values of viscosities were used as a blood analogue with varying haematocrit (HCT). Noninvasive measurements of power and pump speed were used with HCT values as inputs to the flow model while the estimated flow was used with the speed as inputs to a head estimation model. Linear regression analysis between estimated and measured flows obtained from a mock loop resulted in a highly significant correlation (R2=0.982) and a mean absolute error (e) of 0.323 L min(-1), while for head, R2=0.933 and e=7.682 mmHg were obtained. R2=0.849 and e=0.584 L min(-1) were obtained when the same model derived in the mock loop was used for flow estimation in ex vivo porcine data (N=6). Furthermore, in the steady state, the solution of the presented flow model can be described by a previously designed and verified static model. The models developed herein will play a vital role in developing a robust control system of the pump flow coping with changing physiological demands.

  16. Pulsatile flow in the aorta of the LVAD supported heart studied using particle image velocimetry

    NASA Astrophysics Data System (ADS)

    Moyedi, Zahra

    Currently many patients die because of the end-stage heart failure, mainly due to the reduced number of donor heart transplant organs. Studies show that a permanent left ventricular assist device (LVAD), a battery driven pump which is surgically implanted, increased the survival rate of patients with end-stage heart failure and improved considerably their quality of life. The inlet conduit of the LVAD is attached to the left ventricle and the outflow conduit anastomosed to the ascending aorta. The purpose of LVAD support is to help a weakened heart to pump blood to the rest of the body. However LVAD can cause some alterations of the natural blood flow. When your blood comes in contact with something that isn't a natural part of your body blood clots can occur and disrupt blood flow. Aortic valve integrity is vital for optimal support of left ventricular assist LVAD. Due to the existence of high continuous transvalvular pressure on the aortic valve, the opening frequency of the valve is reduced. To prevent the development of aortic insufficiency, aortic valve closure during LVAD implantation has been performed. However, the closed aortic valve reduces wash out of the aortic root, which causes blood stagnation and potential thrombus formation. So for this reason, there is a need to minimize the risks of occurring blood clot, by having more knowledge about the flow structure in the aorta during LVAD use. The current study focuses on measuring the flow field in the aorta of the LVAD assisted heart with two different types of aortic valve (Flat and Finned) using the SDSU cardiac simulator. The pulsatile pump that mimics the natural pulsing action of the heart also added to the system. The flow field is visualized using Particle Image Velocimetry (PIV). Furthermore, The fluid mechanics of aorta has been studied when LVAD conduit attached to two different locations (proximal and distal to the aortic valve) with pump speeds of 8,000 to 10,000 revolutions per minute (RPM

  17. Development of a microimpedance pump for pulsatile flow transport - Part : Flow characteristics of the microimpedance pump. Part 2: A systematic study of steady and pulsatile transport in microscale cavities

    NASA Astrophysics Data System (ADS)

    Rinderknecht, Derek

    Microfluidics offers an effective means to carry out a wide range of transport processes within a controlled microenvironment by drawing on the benefits imparted by increasing surface area to volume ratio at the microscale. Critical to the impact of microfluidics on integrated devices in the fields of bioengineering and biomedicine is the ability to transport fluids and biomolecules effectively particularly at the size scales involved. In this context a bio-inspired pumping mechanism, the valveless impedance pump, was explored for applications in microfluidics ranging from micro total analysis systems to microchannel cooling. Adhering to the basic principles of the impedance pump mechanism, pumps have been constructed at a variety of size scales from a few centimeters to a few hundred microns. The micro impedance pump is valveless, bidirectional, and can be constructed simply from a wide range of materials. Depending on the size of the pump flow rates range from nL/min to mL/min and pressures can be generated that exceed 20 kPa. Another benefit of the impedance pump is the pulsatile flow output which can be used in the context of microfluidic applications to enhance transport at low Reynolds numbers as well as metering in drug delivery. Pulsatile flow was therefore investigated as a method of augmenting transport in microfluidic systems. Micro PIV was used to study the affect of both steady and pulsatile flows on transport at low Reynolds number was examined in microscale rectangular cavities. Ventilation of the cavity contents was examined in terms of the residence time or average time a particle remains in the cavity region. Lagrangian coherent structures (LCS) were applied to empirical velocity fields to determine the impact of unsteadiness on time dependent boundaries to fluid transport present in the flow. Experimental results show that there are both frequencies which are beneficial and detrimental to cavity ventilation as well as certain frequencies which

  18. Nonlinear dynamics of shells conveying pulsatile flow with pulse-wave propagation. Theory and numerical results for a single harmonic pulsation

    NASA Astrophysics Data System (ADS)

    Tubaldi, Eleonora; Amabili, Marco; Païdoussis, Michael P.

    2017-05-01

    In deformable shells conveying pulsatile flow, oscillatory pressure changes cause local movements of the fluid and deformation of the shell wall, which propagate downstream in the form of a wave. In biomechanics, it is the propagation of the pulse that determines the pressure gradient during the flow at every location of the arterial tree. In this study, a woven Dacron aortic prosthesis is modelled as an orthotropic circular cylindrical shell described by means of the Novozhilov nonlinear shell theory. Flexible boundary conditions are considered to simulate connection with the remaining tissue. Nonlinear vibrations of the shell conveying pulsatile flow and subjected to pulsatile pressure are investigated taking into account the effects of the pulse-wave propagation. For the first time in literature, coupled fluid-structure Lagrange equations of motion for a non-material volume with wave propagation in case of pulsatile flow are developed. The fluid is modeled as a Newtonian inviscid pulsatile flow and it is formulated using a hybrid model based on the linear potential flow theory and considering the unsteady viscous effects obtained from the unsteady time-averaged Navier-Stokes equations. Contributions of pressure and velocity propagation are also considered in the pressure drop along the shell and in the pulsatile frictional traction on the internal wall in the axial direction. A numerical bifurcation analysis employs a refined reduced order model to investigate the dynamic behavior of a pressurized Dacron aortic graft conveying blood flow. A pulsatile time-dependent blood flow model is considered by applying the first harmonic of the physiological waveforms of velocity and pressure during the heart beating period. Geometrically nonlinear vibration response to pulsatile flow and transmural pulsatile pressure, considering the propagation of pressure and velocity changes inside the shell, is here presented via frequency-response curves, time histories, bifurcation

  19. Estimation of ocular rigidity in glaucoma using ocular pulse amplitude and pulsatile choroidal blood flow.

    PubMed

    Wang, Jing; Freeman, Ellen E; Descovich, Denise; Harasymowycz, Paul J; Kamdeu Fansi, Alvine; Li, Gisele; Lesk, Mark R

    2013-03-07

    Theoretical models and animal studies have suggested that scleral rigidity plays an important role in the pathogenesis of glaucoma. The aim of this study was to present a noninvasive technique for estimating ocular rigidity (E) in vivo, and to compare the estimated rigidity between patients with open-angle glaucoma (OAG); ocular hypertension (OHT); suspect glaucomatous disc (GS); and normal subjects (N). We hypothesized that OHT patients would have higher rigidity. All patients underwent measurements of ocular pulse amplitude (OPA) using dynamic contour tonometry, pulsatile choroidal blood flow (ChBFP) using laser Doppler flowmetry; axial length (AL); and assessment of automated visual field mean deviation (MD). The ratio between OPA and ChBFP was calculated according to the Friedenwald's equation of ocular rigidity. The calculated ratio is denoted as (ER). The average ER values of the four diagnostic groups were compared using nonparametric tests. The relationship between ER and other ocular and systemic factors was examined using correlation and regression analysis. A total of 257 subjects were included in the study (56 N, 108 OAG, 48 GS, and 45 OHT). ER correlated negatively with AL and positively with MD, signifying that a lower rigidity was associated with a longer eye and a worse (more negative) MD. ER was also found to be highest in OHT (0.235 ± 0.16) and lowest in OAG (0.188 ± 0.14; P = 0.01). Estimated coefficient of ocular rigidity by OPA and ChBFP suggested that glaucoma patients had the lowest rigidity and OHT the highest. It supports the idea that a more compliant ocular shell may predispose the optic nerve head to intraocular pressure (IOP)-related damage.

  20. Pulsatile ocular blood flow investigation in asymmetric normal tension glaucoma and normal subjects.

    PubMed

    Fontana, L; Poinoosawmy, D; Bunce, C V; O'Brien, C; Hitchings, R A

    1998-07-01

    This study was designed to investigate pulsatile ocular blood flow (POBF) in normal tension glaucoma (NTG) patients and in normal controls. NTG patients with unilateral field loss were evaluated to compare POBF values between eyes with and without field loss. POBF measurements from more than 1500 subjects were collected during a period of 6 months from six optometric centres. Subjects with systemic vascular diseases (such as systemic hypertension and diabetes), ophthalmic diseases, a positive family history of glaucoma, and those individuals receiving treatment with systemic beta blockers were excluded on the basis of a questionnaire. For comparison, 95 NTG patients with unilateral field loss, selected from 403 consecutive patients with NTG, underwent POBF testing. For each individual age, sex, intraocular pressure, refraction, and pulse rate were entered into a database. Data from 777 subjects were included in the analysis. POBF measurements of patients and subjects were compared allowing for differences in age, sex, intraocular pressure, refraction, and pulse rate. POBF was significantly lower in eyes of NTG patients with and without field loss (p < 0.001 and p = 0.01 respectively). Eyes of NTG patients with field loss showed significantly lower POBF than the contralateral eyes with normal field (p < 0.001). POBF was significantly lower in eyes of NTG patients with and without field loss than in normal subjects, suggesting that differences in ocular blood perfusion are relevant to the development of NTG and are detectable from the early stage of the disease. Furthermore, the finding of lower POBF in NTG eyes with field loss than in the contralateral eyes with normal field suggests that haemodynamic differences between fellow eyes contribute to determine the side of onset of the disease.

  1. Impact of oxygenator selection on hemodynamic energy indicators under pulsatile and nonpulsatile flow in a neonatal extracorporeal life support model.

    PubMed

    Vasavada, Rahul; Khan, Sameer; Qiu, Feng; Kunselman, Allen; Undar, Akif

    2011-06-01

    This study compared the quality of perfusion delivered by two oxygenators--the hollow-fiber membrane Capiox Baby RX05 and silicone membrane Medtronic 0800--using hemodynamic energy indicators. The oxygenators were tested across varying flow rates and perfusion modes in a neonatal extracorporeal life support (ECLS) model. The experimental ECLS circuit included a Jostra HL-20 heart/lung machine with Jostra Roller pump, oxygenators with associated tubing and components, and a neonatal pseudo-patient. We used a 40/60 glycerin/water solution in the circuit as a blood analog. Testing occurred at flow rates of 250, 500, and 750 mL/min at 37°C under both pulsatile and nonpulsatile flow conditions. Hemodynamic data points consisted of recording 20-s intervals of data, and a total of 96 experimental repetitions were conducted. The pressure drop across the Capiox Baby RX05 oxygenator was significantly lower than the pressure drop across the Medtronic 0800 at all flow rates and perfusion modes. Furthermore, the Medtronic 0800 oxygenator showed significantly lower post-oxygenator energy equivalent pressures, total hemodynamic energy values, and surplus hemodynamic energy retention values compared to those of the Capiox Baby RX05. These results indicate the Medtronic 0800 oxygenator significantly dampens the hemodynamic energy compared to the Capiox Baby RX05. Consequently, clinical use of the Medtronic 0800 in a pulsatile ECLS setting is likely to mitigate the benefits provided by pulsatile flow. In contrast, the Capiox Baby RX05 better transmits hemodynamic energy to the patient with much lower pressure drop.

  2. New understanding of the role of cerebrospinal fluid: offsetting of arterial and brain pulsation and self-dissipation of cerebrospinal fluid pulsatile flow energy.

    PubMed

    Min, Kyung Jay; Yoon, Soo Han; Kang, Jae-Kyu

    2011-06-01

    Many theories have been postulated to date regarding the mechanisms involved in the absorption of the intracranial arterial blood flow energy in the intracranial space, but it is as yet nor clearly defined. The blood flow energy that is transmitted from the heart formulates the cerebrospinal fluid (CSF) pulsatile flow, and is known to constitute the major energy of the CSF flow, while the bulk flow carries only small energy. The intracranial space that is enclosed in a solid cranium and is an isolate system as in the Monroe-Kellie doctrine, and the authors propose to re-analyze the Monroe-Kellie doctrine concept in terms of energy transfer and dissipation of the Windkessel effect. We propose that the large blood flow energy that initiates in the heart is transferred in order of precedence to the arteries, arterioles, brain parenchyma, and finally to CSF within the cranium, in which the energy is confined and unable to be transferred, so that the final transfer of energy to the CSF pulsatile flow is self-dissipated in terms of direction and chronology in CSF pulsatile flow. In order for the CSF pulsatile flow that is transferred from arterial blood flow energy to be dissipated in the intracranial space, this cannot be explained with bulk flow energy in any perspective, since the pulsatile flow kinetic energy is greater than the bulk flow kinetic energy by at least a 100-fold. The pulsatile flow energy within the closed intracranial space cannot be transferred and is confined, as postulated by the Monroe-Kellie doctrine, and therefore the authors propound that the pulsatile flow dissipates by itself. The dissipation of the CSF pulsatile flow kinetic energy will be in all directions in a diffuse and random manner, and is offset by the CSF flow energy vector due to the CSF mixing process. Such energy dissipation will lead to maintenance of low CSF flow energy, which will result in maintaining low intracranial pressure (ICP), and sufficient brain perfusion. It is our

  3. Antegrade selective cerebral perfusion combined with deep hypothermic circulatory arrest on cerebral circulation: comparison between pulsatile and nonpulsatile blood flows.

    PubMed

    Soeda, Masao

    2007-04-01

    In aortic arch surgeries, antegrade selective cerebral perfusion (SCP) combined with deep hypothermic circulatory arrest (DHCA) has been recently widely used in institutions as one of the most reliable methods for cerebral protection. However, some studies reported a 3.7-9.3% incidence of postoperative cerebral complications. To perform antegrade SCP more safely, we sought to examine the impact of pulsatile flow perfusion during DHCA on cerebral tissue metabolism, focusing on physiological effects of pulsatile flow perfusion. Sixteen pigs were divided into 2 groups. In each group, antegrade SCP combined with DHCA was conducted. During circulatory arrest, for SCP, a pulsatile flow (group P) and a nonpulsatile flow (group N) were used. We compared results between group P and group N. Jugular venous oxygen saturation (SjO(2)) and cerebral tissue oxygen partial pressure (PtO(2)) were measured at baseline, and continuously throughout the extracorporeal circulation. Hematocrit (Ht), and concentrations of S-100 protein and CK-BB in blood and the cerebrospinal fluid (CSF) were measured at baseline (before the beginning of extracorporeal circulation), following SCP, and after rewarming. Following rewarming, each brain under perfused fixation was removed, and histopathological examinations were conducted using Kluver-Barrera and Tunnel staining methods, electron micrograph. SjO(2) was found to be within normal ranges until after SCP, but decreased with rewarming in both groups. In Group N, changes in SjO(2) were significant, with a decrease to < or =50%. In Group N, concentrations of S-100 protein and CK-BB in CSF after SCP and after rewarming were significantly higher than those in Group P. The time needed for rewarming to 36 degrees C in Group P was shorter than that in Group N. Our results suggest that the pulsatile flow circulation method shows cerebral protection effects with increasing blood flow in small cerebral tissues. In addition, it is effective for improving the

  4. Numerical Simulation of Steady and Pulsatile Flow Through Vascular Stenoses and Comparisons with Experiments Using Phase Contrast Magnetic Resonance Imaging

    NASA Astrophysics Data System (ADS)

    Behrens, Geoffrey; Agarwal, Ramesh; Moghaddam, Abbas N.; Choi, Eric T.; Amini, Amir A.

    2003-11-01

    A commercially available numerical flow solver "FLUENT" is employed in simulation of blood flow through vascular stenoses. Fluid properties are set to match those of the blood mimicking fluid used in flow phantom experiments at the Washington University School of Medicine. Computational results are compared for steady flow through axisymmetric and three-dimensional phantoms modeling mild to severe stenonses with the data collected using Phase Contrast Magnetic Resonance Imaging (PC-MRI) technique by colleagues in the CVIA laboratory at Washington University School of Medicine. Computations are also performed for pulsatile flow through vascular stenoses. Comparisons of PC-MRI and FLUENT output data show qualitative agreement in streamline patterns and good quantitative agreement for pressure drop across the stenoses.

  5. Simultaneous assessment of red blood cell aggregation and oxygen saturation under pulsatile flow using high-frequency photoacoustics.

    PubMed

    Bok, Tae-Hoon; Hysi, Eno; Kolios, Michael C

    2016-07-01

    We investigate the feasibility of photoacoustic (PA) imaging for assessing the correlation between red blood cell (RBC) aggregation and the oxygen saturation (sO2) in a simulated pulsatile blood flow system. For the 750 and 850 nm illuminations, the PA amplitude (PAA) increased and decreased as the mean blood flow velocity decreased and increased, respectively, at all beat rates (60, 120 and 180 bpm). The sO2 also cyclically varied, in phase with the PAA for all beat rates. However, the linear correlation between the sO2 and the PAA at 850 nm was stronger than that at 750 nm. These results suggest that the sO2 can be correlated with RBC aggregation induced by decreased mean shear rate in pulsatile flow, and that the correlation is dependent on the optical wavelength. The hemodynamic properties of blood flow assessed by PA imaging may be used to provide a new biomarker for simultaneous monitoring blood viscosity related to RBC aggregation, oxygen delivery related to the sO2 and their clinical correlation.

  6. Detection of total assist and sucking points based on the pulsatility of a continuous flow artificial heart: in vivo evaluation.

    PubMed

    Oshikawa, M; Araki, K; Nakamura, K; Anai, H; Onitsuka, T

    1998-01-01

    Our novel control strategy for a continuous flow artificial heart by detecting the total assist and sucking points based on pump pulsatility was evaluated in acute animal experiments using beagle dogs and our mixed flow pump. The pump was installed as a left ventricular (LV) bypass through a left thoracotomy. To change LV contractility, the left coronary arteries were occluded for 30 min, followed by a 120 min reperfusion. To change LV end diastolic pressure (LVEDP), dextran solution was rapidly infused. To estimate the pump pulsatility without any specific sensor, we calculated the index of current amplitude (ICA), which was obtained from the amplitude of the motor current waveform divided by the simultaneous mean value. To investigate the basic characteristics of the ICA, the pump speed was changed temporarily from 2,300 rpm to 5,000 rpm. In 92% of all measurements, the ICA plotted against the pump speed had a peak point (t-point) that corresponded highly with the turning point from partial to total assistance. The ICA also had a trough (s-point) that corresponded with the beginning of severe sucking in most cases. Only preload significantly influenced pump flow rate at the t-point from among preload (LVEDP), afterload (SAoP), and contractility (max LV dP/dt), by which we can simulate Starling's law of the natural heart. We concluded that a continuous flow artificial heart could be well controlled by detecting the t-point and s-point.

  7. Simultaneous assessment of red blood cell aggregation and oxygen saturation under pulsatile flow using high-frequency photoacoustics

    PubMed Central

    Bok, Tae-Hoon; Hysi, Eno; Kolios, Michael C.

    2016-01-01

    We investigate the feasibility of photoacoustic (PA) imaging for assessing the correlation between red blood cell (RBC) aggregation and the oxygen saturation (sO2) in a simulated pulsatile blood flow system. For the 750 and 850 nm illuminations, the PA amplitude (PAA) increased and decreased as the mean blood flow velocity decreased and increased, respectively, at all beat rates (60, 120 and 180 bpm). The sO2 also cyclically varied, in phase with the PAA for all beat rates. However, the linear correlation between the sO2 and the PAA at 850 nm was stronger than that at 750 nm. These results suggest that the sO2 can be correlated with RBC aggregation induced by decreased mean shear rate in pulsatile flow, and that the correlation is dependent on the optical wavelength. The hemodynamic properties of blood flow assessed by PA imaging may be used to provide a new biomarker for simultaneous monitoring blood viscosity related to RBC aggregation, oxygen delivery related to the sO2 and their clinical correlation. PMID:27446705

  8. A novel, low cost, disposable, pediatric pulsatile rotary ventricular pump for cardiac surgery that provides a physiological flow pattern.

    PubMed

    Mazur, Daniel E; Osterholzer, Kathryn R; Toomasian, John M; Merz, Scott I

    2008-01-01

    Research is underway to develop a novel, low cost, disposable pediatric pulsatile rotary ventricular pump (PRVP) for cardiac surgery that provides a physiological flow pattern. This is believed to offer reduced morbidity and risk exposure within this population. The PRVP will have a durable design suitable for use in short- to mid-length prolonged support after surgery without changing pumps. The design is based on proprietary MC3 technology which provides variable pumping volume per stroke, thereby allowing the pump to respond to hemodynamic status changes of the patient. The novel pump design also possesses safety advantages that prevent retrograde flow, and maintain safe circuit pressures upon occlusion of the inlet and outlet tubing. The design is ideal for simple, safe and natural flow support. Computational methods have been developed that predict output for pump chambers of varying geometry. A scaled chamber and pump head (diameter = 4 in) were prototyped to demonstrate target performance for pediatrics (2 L/min at 100 rpm). A novel means of creating a pulsatile flow and pressure output at constant RPM was developed and demonstrated to create significant surplus hydraulic energy (>10%) in a simplified mock patient circuit.

  9. An Ultrasound Simulation Model for the Pulsatile Blood Flow Modulated by the Motion of Stenosed Vessel Wall.

    PubMed

    Zhang, Qinghui; Zhang, Yufeng; Zhou, Yi; Zhang, Kun; Zhang, Kexin; Gao, Lian

    2016-01-01

    This paper presents an ultrasound simulation model for pulsatile blood flow, modulated by the motion of a stenosed vessel wall. It aims at generating more realistic ultrasonic signals to provide an environment for evaluating ultrasound signal processing and imaging and a framework for investigating the behaviors of blood flow field modulated by wall motion. This model takes into account fluid-structure interaction, blood pulsatility, stenosis of the vessel, and arterial wall movement caused by surrounding tissue's motion. The axial and radial velocity distributions of blood and the displacement of vessel wall are calculated by solving coupled Navier-Stokes and wall equations. With these obtained values, we made several different phantoms by treating blood and the vessel wall as a group of point scatterers. Then, ultrasound echoed signals from oscillating wall and blood in the axisymmetric stenotic-carotid arteries were computed by ultrasound simulation software, Field II. The results show better consistency with corresponding theoretical values and clinical data and reflect the influence of wall movement on the flow field. It can serve as an effective tool not only for investigating the behavior of blood flow field modulated by wall motion but also for quantitative or qualitative evaluation of new ultrasound imaging technology and estimation method of blood velocity.

  10. An Ultrasound Simulation Model for the Pulsatile Blood Flow Modulated by the Motion of Stenosed Vessel Wall

    PubMed Central

    Zhou, Yi; Zhang, Kun; Zhang, Kexin; Gao, Lian

    2016-01-01

    This paper presents an ultrasound simulation model for pulsatile blood flow, modulated by the motion of a stenosed vessel wall. It aims at generating more realistic ultrasonic signals to provide an environment for evaluating ultrasound signal processing and imaging and a framework for investigating the behaviors of blood flow field modulated by wall motion. This model takes into account fluid-structure interaction, blood pulsatility, stenosis of the vessel, and arterial wall movement caused by surrounding tissue's motion. The axial and radial velocity distributions of blood and the displacement of vessel wall are calculated by solving coupled Navier-Stokes and wall equations. With these obtained values, we made several different phantoms by treating blood and the vessel wall as a group of point scatterers. Then, ultrasound echoed signals from oscillating wall and blood in the axisymmetric stenotic-carotid arteries were computed by ultrasound simulation software, Field II. The results show better consistency with corresponding theoretical values and clinical data and reflect the influence of wall movement on the flow field. It can serve as an effective tool not only for investigating the behavior of blood flow field modulated by wall motion but also for quantitative or qualitative evaluation of new ultrasound imaging technology and estimation method of blood velocity. PMID:27478840

  11. Minimal enteral feeding, fetal blood flow pulsatility, and postnatal intestinal permeability in preterm infants with intrauterine growth retardation

    PubMed Central

    van Elburg, R M; van den Berg, A; Bunkers, C; van Lingen, R A; Smink, E; van Eyck, J; Fetter, W

    2004-01-01

    Objective: To study the effect of minimal enteral feeding (MEF) on intestinal permeability and feeding tolerance in preterm infants with intrauterine growth retardation (gestational age < 37 weeks, birth weight for gestational age p < 10). Furthermore, to determine whether fetal blood flow pulsatility or intestinal permeability predict feeding tolerance in these infants. Design: Randomised controlled trial. Methods: Within 48 hours of birth, infants were randomised to MEF or no enteral feeding (NEF) for five days in addition to parenteral feeding. Intestinal permeability was measured by the sugar absorption test before (SAT1) and after (SAT2) the study. The sugar absorption test measured the urinary lactulose/mannitol (LM) ratio after oral ingestion of a solution (375 mosm) containing mannitol and lactulose. Charts of all infants were assessed for measures of feeding tolerance. Fetal blood flow pulsatility index (U/C ratio) was measured within the seven days before birth. Results: Of the 56 infants enrolled, 42 completed the study: 20 received MEF and 22 NEF. The decrease in LM ratio (LM ratio 1 – LM ratio 2) was not significantly different between the two groups (0.25 v 0.11; p  =  0.14). Feeding tolerance, growth, and incidence of necrotising enterocolitis were not significantly different between the two groups. Neither the U/C nor the LM ratio 1 predicted feeding tolerance. Conclusions: The results suggest that MEF of preterm infants with intrauterine growth retardation has no effect on the decrease in intestinal permeability after birth. Neither fetal blood flow pulsatility nor intestinal permeability predicts feeding tolerance. PMID:15210658

  12. Acute Biventricular Interaction in Pediatric Patients Implanted with Continuous Flow and Pulsatile Flow LVAD: A Simulation Study.

    PubMed

    Di Molfetta, Arianna; Ferrari, Gianfranco; Iacobelli, Roberta; Fresiello, Libera; Pilati, Mara; Toscano, Alessandra; Filippelli, Sergio; Morelli, Stefano; Amodeo, Antonio

    2016-01-01

    Left ventricular assist devices (LVADs) are used to bridge pediatric patients till transplantation. However, the LVADs effects on right ventricular (RV) function are controversial. This work aims at studying the ventricular interdependency in the presence of continuous (c-) and pulsatile (p-) flow LVAD in pediatric patients using a lumped parameter model including the representation of the septum. Five pediatric patients' data were used to simulate patients' baseline. The effects on LV and RV functions, energetics, preloads and afterloads of different c-LVAD speeds, p-LVAD rate, p-LVAD systole duration, p-LVAD filling and ejection pressures were simulated. c-LVAD and p-LVAD unload the LV decreasing the LV external work and improving the LV ventriculo-arterial coupling and these effects are more evident increasing the c-LVAD speed and the p-LVAD rate. Continuous-LVAD and p-LVAD decrease the RV afterload, increase the RV ejection fraction and improve the RV ventriculo-arterial coupling. The changes in RV function are inversely proportional to the degree of the interventricular septum leftward shift that increased by increasing the LVAD contribution. The study of the interventricular interaction could lead to the development of a dedicated algorithm to optimize LVAD setting in pediatric population.

  13. Particle image velocimetry study of pulsatile flow in bi-leaflet mechanical heart valves with image compensation method.

    PubMed

    Shi, Yubing; Yeo, Tony Joon Hock; Zhao, Yong; Hwang, Ned H C

    2006-12-01

    Particle Image Velocimetry (PIV) is an important technique in studying blood flow in heart valves. Previous PIV studies of flow around prosthetic heart valves had different research concentrations, and thus never provided the physical flow field pictures in a complete heart cycle, which compromised their pertinence for a better understanding of the valvular mechanism. In this study, a digital PIV (DPIV) investigation was carried out with improved accuracy, to analyse the pulsatile flow field around the bi-leaflet mechanical heart valve (MHV) in a complete heart cycle. For this purpose a pulsatile flow test rig was constructed to provide the necessary in vitro test environment, and the flow field around a St. Jude size 29 bi-leaflet MHV and a similar MHV model were studied under a simulated physiological pressure waveform with flow rate of 5.2 l/min and pulse rate at 72 beats/min. A phase-locking method was applied to gate the dynamic process of valve leaflet motions. A special image-processing program was applied to eliminate optical distortion caused by the difference in refractive indexes between the blood analogue fluid and the test section. Results clearly showed that, due to the presence of the two leaflets, the valvular flow conduit was partitioned into three flow channels. In the opening process, flow in the two side channels was first to develop under the presence of the forward pressure gradient. The flow in the central channel was developed much later at about the mid-stage of the opening process. Forward flows in all three channels were observed at the late stage of the opening process. At the early closing process, a backward flow developed first in the central channel. Under the influence of the reverse pressure gradient, the flow in the central channel first appeared to be disturbed, which was then transformed into backward flow. The backward flow in the central channel was found to be the main driving factor for the leaflet rotation in the valve

  14. [Pulsatile rotary pumps with low hemolysis].

    PubMed

    Qian, K; Zeng, P; Ru, W; Yuan, H; Feng, Z; Li, L

    2001-09-01

    As is well known, a pulsatile flow is important in assisted-circulation but it is difficult to produce a pulsatile flow with rotary pump, because excessive hemolysis will be generated. The authors have found that the turbulent shear is the main factor for red cell damage and therefore the key point of pulsatile rotary pumps is to reduce the turbulence by producing a pulsatile flow. In the authors' pulsatile axial pump, the pulsatile flow is obtained by axial reciprocation of constant rotating impeller; the rotation and reciprocation of the impeller are driven separately by a DC motor and a pneumatic device. Though a physiological pulsatile flow could be achieved and turbulence would not increase remarkably because the impeller rotates constantly, a second driver except a DC motor is nevertheless necessary, thus the system will become complicated. In the authors' pulsatile radial pump, a pulsatile flow is achieved by changing the rotating speed of the impeller periodically. Turbulence is minimized by a special design of twisted vanes which enable the blood flow to change its direction rather than its dimension during periodic change of rotating speed. Hemolysis tests demonstrated that the index of hemolysis(IH) of the author's pulsatile radial pump is 0.020, with is slightly more than that of the author's nonpulsatile radial pump(IH = 0.015). Animal experiments indicated that the pulsatile radial pump can assist the circulation of calves for several months without harm to blood elements and organ functions of the recipients.

  15. Concept of left atrial pressure estimation using its pulsatile amplitude in the helical flow total artificial heart.

    PubMed

    Wu, Sheng-Yuan; Saito, Itsuro; Isoyama, Takashi; Inoue, Yusuke; Sato, Masami; Hara, Shintaro; Li, Xin-Yang; Yurimoto, Terumi; Murakami, Haruka; Kawase, Yukino; Ono, Toshiya; Abe, Yusuke

    2014-12-01

    The total artificial heart (TAH) requires physiological control to respond to the metabolic demand of the body. To date, 1/R control is a single physiological control method that can control venous pressure. To realize an implantable 1/R control system, we are developing a new pressure measuring method using absolute pressure sensor. To find a method for absolute pressure sensor, which went well without calibration, concept of left atrial pressure (LAP) estimation using its pulsatile amplitude was proposed. Its possibility was investigated with two long-term survived goats whose hearts were replaced with the helical flow TAHs. In manual control condition, there existed a positive relation between mean LAP (mLAP) and normalized pulsatile amplitude (NPA). Percent systole revealed not to affect the relationship between mLAP and NPA. Dispersion was observed between different pulse rates. As for cardiac output difference (QLD) that is the difference of flow rate between systolic and diastolic phases, similar results were obtained except in low QLDs. In the 1/R control condition, relatively high correlation between mLAP and NPA could be obtained. In estimation of mLAP using the correlating function of individual goat, fairly good correlation was obtained between measured mLAP and estimated mLAP. Despite that further studies are necessary, it was demonstrated that the concept of the LAP estimation could be possible.

  16. Determination of prestenotic flow volume using an automated method based on colour Doppler imaging for evaluating orifice area by the continuity equation: validation in a pulsatile flow model

    PubMed Central

    Dennig, K; Nesser, H; Hall, D; Haase, H; Schomig, A

    1998-01-01

    Objective—To evaluate, in a pulsatile flow model simulating flow conditions in valvar stenoses, whether accurate determination of orifice area can be achieved by the continuity equation using automated determination of flow volumes based on spatiotemporal integration of digital colour Doppler flow velocities.
Methods—A method for automated determination of flow volumes which takes into account the velocity distribution across a region of interest was examined using flow through a tube and various restrictive outlet orifices with areas ranging between 0.2 and 3.1 cm2. The sampling rectangle of the Doppler method was positioned proximal to the obstructions within the flow convergence zone for evaluating prestenotic flow volume. Stenotic jet velocities were recorded by continuous wave Doppler to obtain the integral under the velocity curve. Prestenotic flow volume was then divided by the velocity integral to calculate functional orifice area according to the continuity equation.
Results—The presence of parabolically shaped velocity profiles across the prestenotic region was demonstrated by the Doppler method. Excellent agreement was found between prestenotic flow volumes measured by the Doppler technique and actual values (r = 0.99, SEE = 1.35 ml, y = 0.99x−0.24). Use of the continuity equation led to a close correlation, with a systematic underestimation of geometric orifice sizes. Correction of Doppler data for flow contraction yielded an excellent agreement with actual orifice areas.
Conclusions—The study validated the accuracy of a Doppler method for automated determination of flow volumes for quantifying orifice area by the continuity equation. Prestenotic flow volume and functional orifice area could be evaluated reliably in the presence of non-flat velocity profiles. Thus the method contributes to the non-invasive assessment of valvar stenoses.

 Keywords: Doppler echocardiography;  automated flow volume determination;  valvar

  17. A hybrid one-dimensional/Womersley model of pulsatile blood flow in the entire coronary arterial tree.

    PubMed

    Huo, Yunlong; Kassab, Ghassan S

    2007-06-01

    Using a frequency-domain Womersley-type model, we previously simulated pulsatile blood flow throughout the coronary arterial tree. Although this model represents a good approximation for the smaller vessels, it does not take into account the nonlinear convective energy losses in larger vessels. Here, using Womersley's theory, we present a hybrid model that considers the nonlinear effects for the larger epicardial arteries while simulating the distal vessels (down to the 1st capillary segments) with the use of Womersley's Theory. The main trunk and primary branches were discretized and modeled with one-dimensional Navier-Stokes equations, while the smaller-diameter vessels were treated as Womersley-type vessels. Energy losses associated with vessel bifurcations were incorporated in the present analysis. The formulation enables prediction of impedance and pressure and pulsatile flow distribution throughout the entire coronary arterial tree down to the first capillary segments in the arrested, vasodilated state. We found that the nonlinear convective term is negligible and the loss of energy at a bifurcation is small in the larger epicardial vessels of an arrested heart. Furthermore, we found that the flow waves along the trunk or at the primary branches tend to scale (normalized with respect to their mean values) to a single curve, except for a small phase angle difference. Finally, the model predictions for the inlet pressure and flow waves are in excellent agreement with previously published experimental results. This hybrid one-dimensional/Womersley model is an efficient approach that captures the essence of the hemodynamics of a complex large-scale vascular network. The present model has numerous applications to understanding the dynamics of coronary circulation.

  18. Morphological and functional analysis of rat hepatocyte spheroids generated on poly(L-lactic acid) polymer in a pulsatile flow bioreactor.

    PubMed

    Török, Eva; Vogel, Christian; Lütgehetmann, Marc; Ma, Peter X; Dandri, Maura; Petersen, Joerg; Burda, Martin R; Siebert, Klaus; Düllmann, Jochen; Rogiers, Xavier; Pollok, Joerg-M

    2006-07-01

    Liver neo-tissue suitable for transplantation has not been established. Primary rat hepatocytes were cultured on three-dimensional biodegradable polymer matrices in a pulsatile flow bioreactor with the intention of inducing tissue formation and improving cell survival. Functional and structural analysis of the hepatocytes forming liver neo-tissue was performed. Biodegradable poly(L-lactic acid) (PLLA) polymer discs were seeded with 4 x 10(6) primary rat hepatocytes each, were exposed to a pulsatile medium flow of 24 mL/min for 1, 2, 4, or 6 days and were investigated for monoethylglycinexylidine (MEGX) formation, ammonia detoxification, Cytokeratin 18 (CK18) expression, and preserved glycogen storage. Fine structural details were obtained using scanning and transmission electron microscopy. Spheroids of viable hepatocytes were formed. MEGX-specific production was maintained and ammonia removal capacity remained high during the entire flow-culture period of 6 days. CK18 distribution was normal. Periodic-acid- Schiff reaction demonstrated homogenous glycogen storage. The hepatocytes reassembled to form intercellular junctions and bile canaliculi. Functional and morphological analysis of rat hepatocytes forming spheroids in a pulsatile flow bioreactor indicated preserved and intact hepatocyte morphology and specific function. Pulsatile flow culture on PLLA scaffolds is a promising new method of hepatic tissue engineering leading to liver neo-tissue formation.

  19. 2D Computational Fluid Dynamic Modeling of Human Ventricle System Based on Fluid-Solid Interaction and Pulsatile Flow

    PubMed Central

    Masoumi, Nafiseh; Framanzad, F.; Zamanian, Behnam; Seddighi, A.S.; Moosavi, M.H.; Najarian, S.; Bastani, Dariush

    2013-01-01

    Many diseases are related to cerebrospinal fluid (CSF) hydrodynamics. Therefore, understanding the hydrodynamics of CSF flow and intracranial pressure is helpful for obtaining deeper knowledge of pathological processes and providing better treatments. Furthermore, engineering a reliable computational method is promising approach for fabricating in vitro models which is essential for inventing generic medicines. A Fluid-Solid Interaction (FSI)model was constructed to simulate CSF flow. An important problem in modeling the CSF flow is the diastolic back flow. In this article, using both rigid and flexible conditions for ventricular system allowed us to evaluate the effect of surrounding brain tissue. Our model assumed an elastic wall for the ventricles and a pulsatile CSF input as its boundary conditions. A comparison of the results and the experimental data was done. The flexible model gave better results because it could reproduce the diastolic back flow mentioned in clinical research studies. The previous rigid models have ignored the brain parenchyma interaction with CSF and so had not reported the back flow during the diastolic time. In this computational fluid dynamic (CFD) analysis, the CSF pressure and flow velocity in different areas were concordant with the experimental data. PMID:25337330

  20. 2D Computational Fluid Dynamic Modeling of Human Ventricle System Based on Fluid-Solid Interaction and Pulsatile Flow.

    PubMed

    Masoumi, Nafiseh; Framanzad, F; Zamanian, Behnam; Seddighi, A S; Moosavi, M H; Najarian, S; Bastani, Dariush

    2013-01-01

    Many diseases are related to cerebrospinal fluid (CSF) hydrodynamics. Therefore, understanding the hydrodynamics of CSF flow and intracranial pressure is helpful for obtaining deeper knowledge of pathological processes and providing better treatments. Furthermore, engineering a reliable computational method is promising approach for fabricating in vitro models which is essential for inventing generic medicines. A Fluid-Solid Interaction (FSI)model was constructed to simulate CSF flow. An important problem in modeling the CSF flow is the diastolic back flow. In this article, using both rigid and flexible conditions for ventricular system allowed us to evaluate the effect of surrounding brain tissue. Our model assumed an elastic wall for the ventricles and a pulsatile CSF input as its boundary conditions. A comparison of the results and the experimental data was done. The flexible model gave better results because it could reproduce the diastolic back flow mentioned in clinical research studies. The previous rigid models have ignored the brain parenchyma interaction with CSF and so had not reported the back flow during the diastolic time. In this computational fluid dynamic (CFD) analysis, the CSF pressure and flow velocity in different areas were concordant with the experimental data.

  1. Application of large-eddy simulation to the study of pulsatile flow in a modeled arterial stenosis.

    PubMed

    Mittal, R; Simmons, S P; Udaykumar, H S

    2001-08-01

    The technique of large-eddy simulation (LES) has been applied to the study of pulsatile flow through a modeled arterial stenosis. A simple stenosis model has been used that consists of a one-sided 50 percent semicircular constriction in a planar channel. The inlet volume flux is varied sinusoidally in time in a manner similar to the laminar flow simulations of Tutty (1992). LES is used to compute flow at a peak Reynolds number of 2000 and a Strouhal number of 0.024. At this Reynolds number, the flow downstream of the stenosis transitions to turbulence and exhibits all the classic features of post-stenotic flow as described by Khalifa and Giddens (1981) and Lieber and Giddens (1990). These include the periodic shedding of shear layer vortices and transition to turbulence downstream of the stenosis. Computed frequency spectra indicate that the vortex shedding occurs at a distinct high frequency, and the potential implication of this for noninvasive diagnosis of arterial stenoses is discussed. A variety of statistics have been also extracted and a number of other physical features of the flow are described in order to demonstrate the usefulness of LES for the study of post-stenotic flows.

  2. Carotid flow pulsatility is higher in women with greater decrement in gait speed during multi-tasking.

    PubMed

    Gonzales, Joaquin U; James, C Roger; Yang, Hyung Suk; Jensen, Daniel; Atkins, Lee; Al-Khalil, Kareem; O'Boyle, Michael

    2017-05-01

    Central arterial hemodynamics is associated with cognitive impairment. Reductions in gait speed during walking while performing concurrent tasks known as dual-tasking (DT) or multi-tasking (MT) is thought to reflect the cognitive cost that exceeds neural capacity to share resources. We hypothesized that central vascular function would associate with decrements in gait speed during DT or MT. Gait speed was measured using a motion capture system in 56 women (30-80y) without mild-cognitive impairment. Dual-tasking was considered walking at a fast-pace while balancing a tray. Multi-tasking was the DT condition plus subtracting by serial 7's. Applanation tonometry was used for measurement of aortic stiffness and central pulse pressure. Doppler-ultrasound was used to measure blood flow velocity and β-stiffness index in the common carotid artery. The percent change in gait speed was larger for MT than DT (14.1±11.2 vs. 8.7±9.6%, p <0.01). Tertiles were formed based on the percent change in gait speed for each condition. No vascular parameters differed across tertiles for DT. In contrast, carotid flow pulsatility (1.85±0.43 vs. 1.47±0.42, p=0.02) and resistance (0.75±0.07 vs. 0.68±0.07, p=0.01) indices were higher in women with more decrement (third tertile) as compared to women with less decrement (first tertile) in gait speed during MT after adjusting for age, gait speed, and task error. Carotid pulse pressure and β-stiffness did not contribute to these tertile differences. Elevated carotid flow pulsatility and resistance are characteristics found in healthy women that show lower cognitive capacity to walk and perform multiple concurrent tasks. Copyright © 2017 Elsevier B.V. All rights reserved.

  3. An efficient approach to study the pulsatile blood flow in femoral and coronary arteries by Differential Quadrature Method

    NASA Astrophysics Data System (ADS)

    Ghasemi, Seiyed E.; Hatami, M.; Hatami, J.; Sahebi, S. A. R.; Ganji, D. D.

    2016-02-01

    In this paper, flow analysis for a non-Newtonian third grade blood in coronary and femoral arteries is simulated numerically. Blood is considered as the third grade non-Newtonian fluid under periodic body acceleration motion and pulsatile pressure gradient. Differential Quadrature Method (DQM) and Crank Nicholson Method (CNM) are used to solve the Partial Differential Equation (PDE) governing equation by which a good agreement between them was observed in the results. The influences of some physical parameters such as amplitude, lead angle and body acceleration frequency on non-dimensional velocity and profiles are considered. For instance, the results show that increasing the amplitude, Ag, and reducing the lead angle of body acceleration, ϕ, make higher velocity profiles in the center line of both arteries.

  4. Effects of frictional losses and pulsatile flow on the collapse of stenotic arteries.

    PubMed

    Downing, J M; Ku, D N

    1997-08-01

    High-grade stenosis can produce conditions in which the artery may collapse. A one-dimensional numerical model of a compliant stenosis was developed from the collapsible tube theory of Shapiro. The model extends an earlier model by including the effects of frictional losses and unsteadiness. The model was used to investigate the relative importance of several physical parameters present in the in vivo environment. The results indicated that collapse can occur within the stenosis. Frictional loss was influential in reducing the magnitude of collapse. Large separation losses could prevent collapse outright even with low downstream resistances. However, the degree of stenosis was still the primary parameter governing the onset of collapse. Pulsatile solutions demonstrated conditions that produce cyclic collapse within the stenosis. This study predicts certain physiologic conditions in which collapse of arteries may occur for high-grade stenoses.

  5. High-frequency photoacoustic imaging of erythrocyte aggregation and oxygen saturation: probing hemodynamic relations under pulsatile blood flow

    NASA Astrophysics Data System (ADS)

    Bok, Tae-Hoon; Hysi, Eno; Kolios, Michael C.

    2015-03-01

    In this paper, we investigate the feasibility of high-frequency photoacoustic (PA) imaging to study the shear rate dependent relationship between red blood cell (RBC) aggregation and oxygen saturation (SO2) in a simulated blood flow system. The PA signal amplitude increased during the formation of aggregates and cyclically varied at intervals corresponding to the beat rate (30, 60, 120, 180 and 240 bpm) for all optical wavelengths of illumination (750 and 850 nm).The SO2 also cyclically varied in phase with the PA signal amplitude for all beat rates. In addition, the mean blood flow velocity cyclically varied at the same interval of beat rate, and the shear rate (i.e. the radial gradient of flow velocity) also cyclically varied. On the other hand, the phase of the cyclic variation in the shear rate was reversed compared to that in the PA signal amplitude. This study indicates that RBC aggregation induced by periodic changes in the shear rate can be correlated with the SO2 under pulsatile blood flow. Furthermore, PA imaging of flowing blood may be capable of providing a new biomarker for the clinical application in terms of monitoring blood viscosity, oxygen delivery and their correlation.

  6. Non-Newtonian perspectives on pulsatile blood-analog flows in a 180° curved artery model

    NASA Astrophysics Data System (ADS)

    van Wyk, Stevin; Prahl Wittberg, Lisa; Bulusu, Kartik V.; Fuchs, Laszlo; Plesniak, Michael W.

    2015-07-01

    Complex, unsteady fluid flow phenomena in the arteries arise due to the pulsations of the heart that intermittently pumps the blood to the extremities of the body. The many different flow waveform variations observed throughout the arterial network are a result of this process and a function of the vessel properties. Large scale secondary flow structures are generated throughout the aortic arch and larger branches of the arteries. An experimental 180° curved artery test section with physiological inflow conditions was used to validate the computational methods implemented in this study. Good agreement of the secondary flow structures is obtained between experimental and numerical studies of a Newtonian blood-analog fluid under steady-state and pulsatile, carotid artery flow rate waveforms. Multiple vortical structures, some of opposite rotational sense to Dean vortices, similar to Lyne-type vortices, were observed to form during the systolic portion of the pulse. Computational tools were used to assess the effect of blood-analog fluid rheology (i.e., Newtonian versus non-Newtonian). It is demonstrated that non-Newtonian, blood-analog fluid rheology results in shear layer instabilities that alter the formation of vortical structures during the systolic deceleration and onwards during diastole. Additional vortices not observed in the Newtonian cases appear at the inside and outside of the bend at various times during the pulsation. The influence of blood-analog shear-thinning viscosity decreases mean pressure losses in contrast to the Newtonian blood analog fluid.

  7. Flow Visualization of Three-Dimensionality Inside the 12 cc Penn State Pulsatile Pediatric Ventricular Assist Device

    PubMed Central

    Roszelle, Breigh N.; Deutsch, Steven; Manning, Keefe B.

    2010-01-01

    In order to aid the ongoing concern of limited organ availability for pediatric heart transplants, Penn State has continued development of a pulsatile Pediatric Ventricular Assist Device (PVAD). Initial studies of the PVAD observed an increase in thrombus formation due to differences in flow field physics when compared to adult sized devices, which included a higher degree of three-dimensionality. This unique flow field brings into question the use of 2D planar particle image velocimetry (PIV) as a flow visualization technique, however the small size and high curvature of the PVAD make other tools such as stereoscopic PIV impractical. In order to test the reliability of the 2D results, we perform a pseudo-3D PIV study using planes both parallel and normal to the diaphragm employing a mock circulatory loop containing a viscoelastic fluid that mimics 40% hematocrit blood. We find that while the third component of velocity is extremely helpful to a physical understanding of the flow, particularly of the diastolic jet and the development of a desired rotational pattern, the flow data taken parallel to the diaphragm is sufficient to describe the wall shear rates, a critical aspect to the study of thrombosis and design of such pumps. PMID:19936926

  8. Pulsatile magneto-hydrodynamic blood flows through porous blood vessels using a third grade non-Newtonian fluids model.

    PubMed

    Akbarzadeh, Pooria

    2016-04-01

    In this paper, the unsteady pulsatile magneto-hydrodynamic blood flows through porous arteries concerning the influence of externally imposed periodic body acceleration and a periodic pressure gradient are numerically simulated. Blood is taken into account as the third-grade non-Newtonian fluid. Besides the numerical solution, for small Womersley parameter (such as blood flow through arterioles and capillaries), the analytical perturbation method is used to solve the nonlinear governing equations. Consequently, analytical expressions for the velocity profile, wall shear stress, and blood flow rate are obtained. Excellent agreement between the analytical and numerical predictions is evident. Also, the effects of body acceleration, magnetic field, third-grade non-Newtonian parameter, pressure gradient, and porosity on the flow behaviors are examined. Some important conclusions are that, when the Womersley parameter is low, viscous forces tend to dominate the flow, velocity profiles are parabolic in shape, and the center-line velocity oscillates in phase with the driving pressure gradient. In addition, by increasing the pressure gradient, the mean value of the velocity profile increases and the amplitude of the velocity remains constant. Also, when non-Newtonian effect increases, the amplitude of the velocity profile. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

  9. AN INNOVATIVE, SENSORLESS, PULSATILE, CONTINUOUS-FLOW TOTAL ARTIFICIAL HEART: DEVICE DESIGN AND INITIAL IN VITRO STUDY

    PubMed Central

    Fukamachi, Kiyotaka; Horvath, David J.; Massiello, Alex L.; Fumoto, Hideyuki; Horai, Tetsuya; Rao, Santosh; Golding, Leonard A. R.

    2009-01-01

    Background We are developing a very small, innovative, continuous-flow total artificial heart (CFTAH) that passively self-balances left and right pump flows and atrial pressures without sensors. This report details the CFTAH design concept and our initial in vitro data. Methods System performance of the CFTAH was evaluated using a mock circulatory loop to determine the range of systemic and pulmonary vascular resistances (SVR and PVR) over which the design goal of a maximum absolute atrial pressure difference of 10 mm Hg is achieved for a steady-state flow condition. Pump speed was then modulated at 2,600 ± 900 rpm to induce flow and arterial pressure pulsation to evaluate the effects of speed pulsations on the system performance. An automatic control mode was also evaluated. Results Using only passive self-regulation, pump flows were balanced and absolute atrial pressure differences were maintained below 10 mm Hg over a range of SVR (750-2,750 dyne·sec·cm-5) and PVR (135-600 dyne·sec·cm-5) values far exceeding normal levels. The magnitude of induced speed pulsatility affected relative left/right performance, allowing for an additional active control to improve balanced flow and pressure. The automatic control mode adjusted pump speed to achieve targeted pump flows based on sensorless calculations of SVR and CFTAH flow. Conclusions The initial in vitro testing of the CFTAH with a single, valveless, continuous-flow pump demonstrated its passive self-regulation of flows and atrial pressures and a new automatic control mode. PMID:19782599

  10. VASCULAR INFLAMMATION AND ABNORMAL AORTIC HISTOMORPHOMETRY IN PATIENTS FOLLOWING PULSATILE AND CONTINUOUS FLOW LEFT VENTRICULAR ASSIST DEVICE PLACEMENT

    PubMed Central

    Lee, Mike; Akashi, Hirokazu; Kato, Tomoko S.; Takayama, Hiroo; Wu, Christina; Xu, Katherine; Collado, Elias; Weber, Matthew P.; Kennel, Peter J.; Brunjes, Danielle L; Ji, Ruiping; Naka, Yoshifumi; George, Isaac; Mancini, Donna; Farr, Maryjane; Schulze, P. Christian

    2017-01-01

    Objective Left ventricular assist devices are increasingly used in patients with advanced heart failure as both destination therapy and bridge-to-transplantation. We aimed to analyze histomorphometric, structural and inflammatory changes following pulsatile and continuous flow left ventricular assist device placement. Method Clinical and echocardiographic data were collected from medical records. Aortic wall diameter, cellularity and inflammation were assessed by immunohistochemistry on aortic tissue collected at left ventricular assist device placement and at explantation during heart transplantation. Expression of adhesion molecules was quantified by western blot. Results Decellularization of the aortic tunica media was observed in patients receiving continuous flow support. Both device types showed an increased inflammatory response following left ventricular assist device placement with variable T cell and macrophage accumulations and increased expression of vascular E-selectin, ICAM and VCAM in the aortic wall. Conclusion Left ventricular assist device implantation is associated with distinct vascular derangements with development of vascular inflammation. These changes are pronounced in patients on continuous flow left ventricular assist and associated with aortic media decellularization. These findings help to explain the progressive aortic root dilation and vascular dysfunction in patients following continuous flow device placement. PMID:26899764

  11. Transcranial Doppler ultrasound blood flow velocity and pulsatility index as systemic indicators for Alzheimer’s disease

    PubMed Central

    Roher, Alex E.; Garami, Zsolt; Tyas, Suzanne L.; Maarouf, Chera L.; Kokjohn, Tyler A.; Belohlavek, Marek; Vedders, Linda J.; Connor, Donald; Sabbagh, Marwan N.; Beach, Thomas G.; Emmerling, Mark R.

    2010-01-01

    Background Multiple lines of evidence suggest cardiovascular co-morbidities hasten the onset of Alzheimer’s disease (AD) or accelerate its course. Methods To evaluate the utility of cerebral vascular physical function/condition parameters as potential systemic indicators of AD, we employed transcranial Doppler (TCD) ultrasound to assess cerebral blood flow and vascular resistance of the 16 arterial segments comprising the circle of Willis and its major tributaries. Results Our study revealed decreased arterial mean flow velocity (MFV) and increased pulsatility index (PI) are associated with a clinical diagnosis of presumptive AD. Cerebral blood flow impairment revealed by these parameters reflects the global hemodynamic and structural consequences of a multifaceted disease process yielding diffuse congestive microvascular pathology, increased arterial rigidity, and decreased arterial compliance combined with putative age-associated cardiovascular output declines. Conclusions TCD evaluation offers direct physical confirmation of brain perfusion impairment and may ultimately provide a convenient, noninvasive means to assess the efficacy of medical interventions on cerebral blood flow or reveal incipient AD. In the near term, TCD-based direct assessments of brain perfusion may offer the prospect of preventing or mitigating AD simply by revealing patients who would benefit from interventions to improve circulatory system function. PMID:21388892

  12. A fluid--structure interaction finite element analysis of pulsatile blood flow through a compliant stenotic artery

    NASA Technical Reports Server (NTRS)

    Bathe, M.; Kamm, R. D.

    1999-01-01

    A new model is used to analyze the fully coupled problem of pulsatile blood flow through a compliant, axisymmetric stenotic artery using the finite element method. The model uses large displacement and large strain theory for the solid, and the full Navier-Stokes equations for the fluid. The effect of increasing area reduction on fluid dynamic and structural stresses is presented. Results show that pressure drop, peak wall shear stress, and maximum principal stress in the lesion all increase dramatically as the area reduction in the stenosis is increased from 51 to 89 percent. Further reductions in stenosis cross-sectional area, however, produce relatively little additional change in these parameters due to a concomitant reduction in flow rate caused by the losses in the constriction. Inner wall hoop stretch amplitude just distal to the stenosis also increases with increasing stenosis severity, as downstream pressures are reduced to a physiological minimum. The contraction of the artery distal to the stenosis generates a significant compressive stress on the downstream shoulder of the lesion. Dynamic narrowing of the stenosis is also seen, further augmenting area constriction at times of peak flow. Pressure drop results are found to compare well to an experimentally based theoretical curve, despite the assumption of laminar flow.

  13. Fluid dynamic characterization of a polymeric heart valve prototype (Poli-Valve) tested under continuous and pulsatile flow conditions.

    PubMed

    De Gaetano, Francesco; Serrani, Marta; Bagnoli, Paola; Brubert, Jacob; Stasiak, Joanna; Moggridge, Geoff D; Costantino, Maria Laura

    2015-11-01

    Only mechanical and biological heart valve prostheses are currently commercially available. The former show longer durability but require anticoagulant therapy; the latter display better fluid dynamic behavior but do not have adequate durability. New Polymeric Heart Valves (PHVs) could potentially combine the hemodynamic properties of biological valves with the durability of mechanical valves. This work presents a hydrodynamic evaluation of 2 groups of newly developed supra-annular, trileaflet prosthetic heart valves made from styrenic block copolymers (SBC): Poli-Valves. 2 types of Poli-Valves made of SBC and differing in polystyrene fraction content were tested under continuous and pulsatile flow conditions as prescribed by ISO 5840 Standard. A pulse duplicator designed ad hoc allowed the valve prototypes to be tested at different flow rates and frequencies. Pressure and flow were recorded; pressure drops, effective orifice area (EOA), and regurgitant volume were computed to assess the behavior of the valve. Both types of Poli-Valves met the minimum requirements in terms of regurgitation and EOA as specified by the ISO 5840 Standard. Results were compared with 5 mechanical heart valves (MHVs) and 5 tissue heart valves (THVs), currently available on the market. Based on these results, PHVs based on styrenic block copolymers, as are Poli-Valves, can be considered a promising alternative for heart valve replacement in the near future.

  14. Fluid Dynamic Characterization of a Polymeric Heart Valve Prototype (Poli-Valve) tested under Continuous and Pulsatile Flow Conditions

    PubMed Central

    De Gaetano, Francesco; Serrani, Marta; Bagnoli, Paola; Brubert, Jacob; Stasiak, Joanna; Moggridge, Geoff D.; Costantino, Maria Laura

    2016-01-01

    Introduction Only mechanical and biological heart valve prostheses are currently commercially available. The former show longer durability but require anticoagulant therapy, the latter display better fluid dynamic behaviour but do not have adequate durability. New Polymeric Heart Valves (PHVs) could potentially combine the haemodynamic properties of biological valves with the durability of mechanical valves. This work presents a hydrodynamic evaluation of two groups of newly developed supra-annular tri-leaflet prosthetic heart valves made from styrenic block copolymers (SBC): Poli-Valves. Methods Two types of Poli-Valves made of SBC differing in polystyrene fraction content were tested under continuous and pulsatile flow conditions as prescribed by ISO 5840 Standard. An ad - hoc designed pulse duplicator allowed the valve prototypes to be tested at different flow rates and frequencies. Pressure and flow were recorded; pressure drops, effective orifice area (EOA), and regurgitant volume were computed to assess the valve’s behaviour. Results Both types Poli-Valves met the minimum requirements in terms of regurgitation and EOA as specified by ISO 5840 Standard. Results were compared with five mechanical heart valves (MHVs) and five tissue heart valves (THVs), currently available on the market. Conclusion Based on these results, polymeric heart valves based on styrenic block copolymers, as Poli-Valves are, can be considered as promising alternative for heart valve replacement in near future. PMID:26689146

  15. Cerebral oxygen saturation during pulsatile and non-pulsatile cardiopulmonary bypass in patients with carotid stenosis.

    PubMed

    Tovedal, T; Thelin, S; Lennmyr, F

    2016-01-01

    Pulsatile and non-pulsatile cardiopulmonary bypass (CPB) flows may have different impact on cerebral oxygen saturation in patients with restricted cerebral arterial blood supply. Twenty patients, ten diagnosed with carotid stenosis (CS, n = 10) and ten without known carotid disease (Controls, n = 10), were subjected to one period of pulsatile and one period of non-pulsatile flow (6-8 min each) during CPB at 32°C. Cerebral oxygen saturation was registered by near-infrared light spectroscopy (NIRS).The mean arterial pressure (MAP) was significantly lowered by pulsatile CPB flow. The NIRS tissue oxygenation index (TOI) tended to decrease in the CS group and increase in the Controls during pulsatile flow compared with non-pulsatile; however, the changes were not statistically significant.No significant correlations were seen between the changes in MAP and TOI across the observation periods.In conclusion, pulsatile CPB flow caused slightly decreased mean arterial pressure while the effect on cerebral oxygenation was unclear. Pulsatile flow was not found superior to non-pulsatile flow in patients with or without carotid stenosis. © The Author(s) 2015.

  16. Effect of treatment by medicine or surgery on intraocular pressure and pulsatile ocular blood flow in normal-pressure glaucoma.

    PubMed

    Poinoosawmy, D; Indar, A; Bunce, C; Garway-Heath, D F; Hitchings, R A

    2002-09-01

    To study the effect of trabeculectomy and monotherapy with topical betaxolol, brimonidine and latanoprost on intraocular pressure (IOP) and pulsatile ocular blood flow (POBF) in patients with normal-pressure glaucoma (NPG). In this retrospective study NPG patients attending the glaucoma research unit at Moorfields Eye Hospital were reviewed. Patients treated by surgery or topical medication (betaxolol, brimonidine or latanoprost) who had pre- and post-treatment IOP and POBF measurements were studied. For those patients who were having treatment to both eyes, one eye was selected at random for analysis. A total of 147 patients were reviewed. Forty-three eyes were receiving betaxolol 0.5%, 58 eyes latanoprost 0.005%, 23 eyes brimonidine 0.2% and 23 eyes had undergone trabeculectomy surgery. There were more female than male patients in all four groups, and the groups were similar with regards age. Pre-treatment IOP and POBF values were similar among the groups ( P=0.27, P=0.08 respectively). Post-treatment IOP values tended to be lower than pre-treatment values for all four groups. All groups had an increased POBF except for betaxolol, where POBF decreased. Patients treated by trabeculectomy and those receiving topical latanoprost and brimonidine had lower IOP and higher POBF following treatment. The betaxolol-treated group, despite a slight decrease in IOP, had a decreased POBF. Lowering IOP by treatment may not necessarily be associated with an increase in POBF.

  17. Pulsatile arterial wall-blood flow interaction with wall pre-stress computed using an inverse algorithm

    PubMed Central

    2015-01-01

    Background The computation of arterial wall deformation and stresses under physiologic conditions requires a coupled compliant arterial wall-blood flow interaction model. The in-vivo arterial wall motion is constrained by tethering from the surrounding tissues. This tethering, together with the average in-vivo pressure, results in wall pre-stress. For an accurate simulation of the physiologic conditions, it is important to incorporate the wall pre-stress in the computational model. The computation of wall pre-stress is complex, as the un-loaded and un-tethered arterial shape with residual stress is unknown. In this study, the arterial wall deformation and stresses in a canine femoral artery under pulsatile pressure was computed after incorporating the wall pre-stresses. A nonlinear least square optimization based inverse algorithm was developed to compute the in-vivo wall pre-stress. Methods First, the proposed inverse algorithm was used to obtain the un-loaded and un-tethered arterial geometry from the unstressed in-vivo geometry. Then, the un-loaded, and un-tethered arterial geometry was pre-stressed by applying a mean in-vivo pressure of 104.5 mmHg and an axial stretch of 48% from the un-tethered length. Finally, the physiologic pressure pulse was applied at the inlet and the outlet of the pre-stressed configuration to calculate the in-vivo deformation and stresses. The wall material properties were modeled with an incompressible, Mooney-Rivlin model derived from previously published experimental stress-strain data (Attinger et al., 1968). Results The un-loaded and un-tethered artery geometry computed by the inverse algorithm had a length, inner diameter and thickness of 35.14 mm, 3.10 mm and 0.435 mm, respectively. The pre-stressed arterial wall geometry was obtained by applying the in-vivo axial-stretch and average in-vivo pressure to the un-loaded and un-tethered geometry. The length of the pre-stressed artery, 51.99 mm, was within 0.01 mm (0.019%) of the in

  18. Pulsatile arterial wall-blood flow interaction with wall pre-stress computed using an inverse algorithm.

    PubMed

    Das, Ashish; Paul, Anup; Taylor, Michael D; Banerjee, Rupak K

    2015-01-01

    The computation of arterial wall deformation and stresses under physiologic conditions requires a coupled compliant arterial wall-blood flow interaction model. The in-vivo arterial wall motion is constrained by tethering from the surrounding tissues. This tethering, together with the average in-vivo pressure, results in wall pre-stress. For an accurate simulation of the physiologic conditions, it is important to incorporate the wall pre-stress in the computational model. The computation of wall pre-stress is complex, as the un-loaded and un-tethered arterial shape with residual stress is unknown. In this study, the arterial wall deformation and stresses in a canine femoral artery under pulsatile pressure was computed after incorporating the wall pre-stresses. A nonlinear least square optimization based inverse algorithm was developed to compute the in-vivo wall pre-stress. First, the proposed inverse algorithm was used to obtain the un-loaded and un-tethered arterial geometry from the unstressed in-vivo geometry. Then, the un-loaded, and un-tethered arterial geometry was pre-stressed by applying a mean in-vivo pressure of 104.5 mmHg and an axial stretch of 48% from the un-tethered length. Finally, the physiologic pressure pulse was applied at the inlet and the outlet of the pre-stressed configuration to calculate the in-vivo deformation and stresses. The wall material properties were modeled with an incompressible, Mooney-Rivlin model derived from previously published experimental stress-strain data (Attinger et al., 1968). The un-loaded and un-tethered artery geometry computed by the inverse algorithm had a length, inner diameter and thickness of 35.14 mm, 3.10 mm and 0.435 mm, respectively. The pre-stressed arterial wall geometry was obtained by applying the in-vivo axial-stretch and average in-vivo pressure to the un-loaded and un-tethered geometry. The length of the pre-stressed artery, 51.99 mm, was within 0.01 mm (0.019%) of the in-vivo length of 52.0 mm; the

  19. Effect of Body Acceleration on Pulsatile Flow of Micropolar Fluid through an Irregular Arterial Stenosis

    NASA Astrophysics Data System (ADS)

    Abdullah, Ilyani; Amin, Norsarahaida

    2008-01-01

    The present study deals with the effect of body acceleration together with surface irregularities on blood flow in artery. Prolonged exposure to high level unintended acceleration may cause serious health problems in the cardiovascular system. The situations like riding in vehicles, flying in airplanes and fast body movements during sport activities can lead to the impairment of certain physiological functions. A micropolar model of blood flow through an irregular arterial stenosis is considered. The governing equations involving unsteady nonlinear two-dimensional partial differential equations are solved employing finite difference scheme. Computational results on the velocity profiles and the flow characteristics are presented.

  20. Particle image velocimetry measurements of three proximal anastomosis models under a pulsatile flow condition.

    PubMed

    Chua, L P; Ji, W-F; Yu, C M; Zhou, T-M; Tan, Y S

    2008-04-01

    This study was designed to examine the effects of the anastomotic angle on the flow and haemodynamic parameter distribution patterns of the proximal anastomoses, with emphasis on identifying site-specific haemodynamic features that could reasonably be expected to trigger the initiation and further development of anastomotic intimal hyperplasia. Particle image velocimetry measurements were carried out with three simplified glass proximal models under a physiological flow condition. The results revealed that the disturbed flow and the induced shear stress patterns including low recirculation flow, stagnation point, high wall shear stress, high temporal wall shear stress gradient, low time-averaged wall shear stress (TAWSS), and high oscillating shear index (OSI) occurred around the anastomotic joints and the flow field at proximal anastomosis was strongly affected by the anastomotic angle. Among the three models investigated, the 45 degrees backward anastomosis is found to have a smaller low-recirculation-flow region along the graft inner wall, non-stationary stagnation, and separation points, a higher TAWSS and smaller high-OSI low-TAWSS and low-OSI high-TAWSS regions.

  1. Viscosity-adjusted estimation of pressure head and pump flow with quasi-pulsatile modulation of rotary blood pump for a total artificial heart.

    PubMed

    Yurimoto, Terumi; Hara, Shintaro; Isoyama, Takashi; Saito, Itsuro; Ono, Toshiya; Abe, Yusuke

    2016-09-01

    Estimation of pressure and flow has been an important subject for developing implantable artificial hearts. To realize real-time viscosity-adjusted estimation of pressure head and pump flow for a total artificial heart, we propose the table estimation method with quasi-pulsatile modulation of rotary blood pump in which systolic high flow and diastolic low flow phased are generated. The table estimation method utilizes three kinds of tables: viscosity, pressure and flow tables. Viscosity is estimated from the characteristic that differential value in motor speed between systolic and diastolic phases varies depending on viscosity. Potential of this estimation method was investigated using mock circulation system. Glycerin solution diluted with salty water was used to adjust viscosity of fluid. In verification of this method using continuous flow data, fairly good estimation could be possible when differential pulse width modulation (PWM) value of the motor between systolic and diastolic phases was high. In estimation under quasi-pulsatile condition, inertia correction was provided and fairly good estimation was possible when the differential PWM value was high, which was not different from the verification results using continuous flow data. In the experiment of real-time estimation applying moving average method to the estimated viscosity, fair estimation could be possible when the differential PWM value was high, showing that real-time viscosity-adjusted estimation of pressure head and pump flow would be possible with this novel estimation method when the differential PWM value would be set high.

  2. Hemodialysis using a valveless pulsatile blood pump.

    PubMed

    Lee, Kyungsoo; Mun, Cho Hae; Lee, Sa Ram; Min, Byoung Goo; Yoo, Kyu Jae; Park, Yong Woo; Won, Yong Soon

    2008-01-01

    Research on pulsatile blood pumps for extracorporeal life support has been widely performed because of the proven advantageous effects of blood pulsation. However, studies on the use of pulsatile blood pumps for hemodialysis are limited, although available evidence demonstrates that pulsatile blood flow has a positive influence on dialysis outcome. Therefore, the authors designed a new pulsatile pump, which is characterized by minimal-occlusion of blood-containing tubing, no requirement for valves, and no blood flow regurgitation. In-vitro hemolysis tests were conducted using fresh bovine blood, and the normalized index of hemolysis was adopted to compare blood traumas induced by the devised pulsatile pump and a conventional roller pump. In addition, experimental hemodialyses with a canine renal failure model were performed using the devised pump. Normalized index of hemolysis levels obtained was much smaller for the devised pulse pump (45 +/- 21 mg/100 L) than for the roller pump (103 +/- 10 mg/100 L), and no technical problems were encountered during dialysis sessions. Blood and dialysate flow rates were maintained at predetermined values and molecular removal was satisfactory. Postdialysis urea and creatinine reduction ratios were 61.8% +/- 10.6% and 57.4% +/- 9.0%, respectively. Pulsatile flow has usually been generated using pulsatile devices containing valves, but the valves cause concern in terms of the clinical applications of these devices. However, the described pulsatile pump does not require valves, and yet no blood flow regurgitation was observed.

  3. Multi-time-lag PIV analysis of steady and pulsatile flows in a sidewall aneurysm

    NASA Astrophysics Data System (ADS)

    Bouillot, P.; Brina, O.; Ouared, R.; Lovblad, K. O.; Pereira, V. Mendes; Farhat, M.

    2014-06-01

    The effect of inflow waveform on the hemodynamics of a real-size idealized sidewall intracranial aneurysm (IA) model was investigated using particle imaging velocimetry (PIV). For this purpose, we implemented an error analysis based on several PIV measurements with different time lags to ensure high precision of velocity fields measured in both the IA and the parent artery. The relative error measured in the main part of the circulating volume was <1 % despite the three orders of magnitude difference of parent artery and IA dome velocities. Moreover, important features involved in IA evolution were potentially emphasized from the qualitative and quantitative flow pattern comparison resulting from steady and unsteady inflows. In particular, the flow transfer in IA and the vortical structure were significantly modified when increasing the number of harmonics for a typical physiological flow, in comparison with quasi-steady conditions.

  4. On the characterization of a non-Newtonian blood analog and its response to pulsatile flow downstream of a simplified stenosis.

    PubMed

    Walker, Andrew M; Johnston, Clifton R; Rival, David E

    2014-01-01

    Particle image velocimetry (PIV) was used to investigate the influence of a non-Newtonian blood analog of aqueous xanthan gum on flow separation in laminar and transitional environments and in both steady and pulsatile flow. Initial steady pressure drop measurements in laminar and transitional flow for a Newtonian analog showed an extension of laminar behavior to Reynolds number (Re) ~ 2900 for the non-Newtonian case. On a macroscale level, this showed good agreement with porcine blood. Subsequently, PIV was used to measure flow patterns and turbulent statistics downstream of an axisymmetric stenosis in the aqueous xanthan gum solution and for a Newtonian analog at Re ~ 520 and Re ~ 1250. The recirculation length for the non-Newtonian case was reduced at Re ~ 520 resultant from increased viscosity at low shear strain rates. At Re ~ 1250, peak turbulent intensities and turbulent shear stresses were dampened by the non-Newtonian fluid in close proximity to the blockage outlet. Although the non-Newtonian case's recirculation length was increased at peak pulsatile flow, turbulent shear stress was found to be elevated for the Newtonian case downstream from the blockage, suggesting shear layer fragmentation and radial transport. Our findings conclude that the xanthan gum elastic polymer prolongs flow stabilization, which in turn emphasizes the importance of non-Newtonian blood characteristics on the resulting flow patterns in such cardiovascular environments.

  5. Numerical Simulation of Nonlinear Pulsatile Newtonian Blood Flow through a Multiple Stenosed Artery.

    PubMed

    Changdar, Satyasaran; De, Soumen

    2015-01-01

    An appropriate nonlinear blood flow model under the influence of periodic body acceleration through a multiple stenosed artery is investigated with the help of finite difference method. The arterial segment is simulated by a cylindrical tube filled with a viscous incompressible Newtonian fluid described by the Navier-Stokes equation. The nonlinear equation is solved numerically with the proper boundary conditions and pressure gradient that arise from the normal functioning of the heart. Results are discussed in comparison with the existing models.

  6. Large eddy simulation of a stenosed artery using a femoral artery pulsatile flow profile.

    PubMed

    Barber, Tracie J; Simmons, Anne

    2011-07-01

    Computational fluid dynamics simulation of stenosed arteries allows the analysis of quantities including wall shear stress, velocity, and pressure; detailed in vivo measurement is difficult yet the analysis of the fluid dynamics related to stenosis is important in understanding the likely causes and ongoing effects on the integrity of the vessel. In this study, a three-dimensional Large Eddy Simulation is conducted of a 50% occluded vessel, with a typical femoral artery profile used as the transient inlet conditions. The fluid is assumed to be homogenous, Newtonian and incompressible and the walls are assumed rigid. The stenosis is axisymmetric, however the three-dimensional study allows for a flow field that is not axisymmetric and results show significant three-dimensionality. High values of wall shear stress and oscillatory values of wall shear stress (varying in both space time) are observed. The results of the study give insight into the time-varying flow structures for a mildly stenosed artery and indicate that three-dimensional simulations may be important to gain a complete understanding of the flow field.

  7. Numerical study on the pulsatile flow characteristics of proximal anastomotic models.

    PubMed

    Chua, L P; Zhang, J-M; Yu, S C M; Ghista, D N; Tan, Y S

    2005-09-01

    Haemodynamics was widely believed to correlate with anastomosis restenosis. Utilizing the haemodynamic parameters as indicator functions, distal anastomosis was redesigned by some researchers so as to improve the long-term graft patency rate. However, there were few studies upon the proximal anastomosis. Therefore, in this study, flow characteristics and distributions of the haemodynamic parameters in proximal anastomosis under physiological flow condition have been investigated numerically for three different grafting angles: namely, 45 degrees forward facing, 45 degrees backward facing, and 90 degrees anastomotic joints. The simulation results showed a flow separation region along the graft inner wall immediately after the heel at peak flow phase and it decreased in size with the grafting angle shifting from 45 degrees forward facing to 45 degrees backward facing. At the same time, a pair of vortex was found in the cross-sectional planes of the 45 degrees backward facing and 90 degrees grafts. In addition, stagnation point was found along the graft outer wall with small shifting during the physiological cycle. High spatial and temporal wall shear stresses gradients (WSSG) were observed around the anastomotic joint. Low time-averaged wall shear stress (WSS) with elevated oscillation shear index (OSI) was found near the middle of anastomosis at the aorta wall and along the graft inner wall respectively, while high time-averaged WSS with low OSI was found at the heel, the toe, and the region downstream of the toe. These regions correlated to early lesion growth. Elevated time-averaged WSSG was found at the same region, where the elevated low-density lipoprotein (LDL) permeability was observed as reported in the literature. The existence of nearly fixed stagnating location, flow separation, vortex, high time-averaged WSS with low OSI, low time-averaged WSS with elevated OSI, and high time-averaged WSSG may lead to graft stenosis. Moreover, the simulation results

  8. PIV-validated numerical modeling of pulsatile flows in distal coronary end-to-side anastomoses.

    PubMed

    Xiong, F L; Chong, C K

    2007-01-01

    This study employed particle image velocimetry (PIV) to validate a numerical model in a complementary approach to quantify hemodynamic factors in distal coronary anastomoses and to gain more insights on their relationship with anastomotic geometry. Instantaneous flow fields and wall shear stresses (WSS) were obtained from PIV measurement in a modified life-size silastic anastomosis model adapted from a conventional geometry by incorporating a smooth graft-artery transition. The results were compared with those predicted by a concurrent numerical model. The numerical method was then used to calculate cycle-averaged WSS (WSS(cyc)) and spatial wall shear stress gradient (SWSSG), two critical hemodynamic factors in the pathogenesis of intimal thickening (IT), to compare the conventional and modified geometries. Excellent qualitative agreement and satisfactory quantitative agreement with averaged normalized error in WSS between 0.8% and 8.9% were achieved between the PIV experiment and numerical model. Compared to the conventional geometry, the modified geometry produces a more uniform WSS(cyc) distribution eliminating both high and low WSS(cyc) around the toe, critical in avoiding IT. Peak SWSSG on the artery floor of the modified model is less than one-half that in the conventional case, and high SWSSG at the toe is eliminated. The validated numerical model is useful for modeling unsteady coronary anastomotic flows and elucidating the significance of geometry regulated hemodynamics. The results suggest the clinical relevance of constructing smooth graft-artery transition in distal coronary anastomoses to improve their hemodynamic performance.

  9. Flow Features and Device-Induced Blood Trauma in CF-VADs under a pulsatile blood flow condition: A CFD Comparative Study.

    PubMed

    Chen, Zengsheng; Jena, Sofen K; Giridharan, Guruprasad A; Koenig, Steven C; Slaughter, Mark S; Griffith, Bartley P; Wu, Zhongjun J

    2017-08-31

    In this study, the flow features and device-associated blood trauma in four clinical ventricular assist devices (VADs) (two implantable axial VADs, one implantable centrifugal VAD, and one extracorporeal VAD) were computationally analyzed under clinically relevant pulsatile flow conditions. The four VADs were operated at fixed pump speed at a mean rate of 4.5 L/min. Mean pressure difference, wall shear stress (WSS), volume distribution of scalar shear stress (SSS), and shear-induced hemolysis index (HI) were derived from the flow field of each VAD and were compared. The computationally predicted mean pressure difference across the three implantable VADs was ~ 70mm Hg and the extracorporeal VAD was ~ 345 mmHg, which matched well with their reported pressure-flow curves. The axial VADs had higher mean WSS and SSS compared to the centrifugal VADs. However, the residence time of the centrifugal VADs was much longer compared to the axial VADs because of the large volume of the centrifugal VADs. The highest SSS was observed in one axial VAD and the longest exposure time was observed in one centrifugal VAD. These two VADs generated the highest HI. The shear-induced HI varied as a function of flow rate within each cardiac cycle. At fixed pump speed, the HI was greatest at low flow rate due to longer exposure time to shear stress compared to at high flow rate. Subsequently, we hypothesize that in order to reduce the risk of blood trauma during VAD support, shear stress magnitude and exposure time need to be minimized. This article is protected by copyright. All rights reserved.

  10. Mathematical Modeling of Magneto Pulsatile Blood Flow Through a Porous Medium with a Heat Source

    NASA Astrophysics Data System (ADS)

    Sharma, B. K.; Sharma, M.; Gaur, R. K.; Mishra, A.

    2015-05-01

    In the present study a mathematical model for the hydro-magnetic non-Newtonian blood flow in the non-Darcy porous medium with a heat source and Joule effect is proposed. A uniform magnetic field acts perpendicular to the porous surface. The governing non-linear partial differential equations have been solved numerically by applying the explicit finite difference Method (FDM). The effects of various parameters such as the Reynolds number, hydro-magnetic parameter, Forchheimer parameter, Darcian parameter, Prandtl number, Eckert number, heat source parameter, Schmidt number on the velocity, temperature and concentration have been examined with the help of graphs. The present study finds its applications in surgical operations, industrial material processing and various heat transfer operations.

  11. Ocular rigidity, outflow facility, ocular pulse amplitude, and pulsatile ocular blood flow in open-angle glaucoma: a manometric study.

    PubMed

    Dastiridou, Anna I; Tsironi, Evangelia E; Tsilimbaris, Miltiadis K; Ginis, Harilaos; Karyotakis, Nikos; Cholevas, Pierros; Androudi, Sofia; Pallikaris, Ioannis G

    2013-07-10

    To compare ocular rigidity (OR) and outflow facility (C) coefficients in medically treated open-angle glaucoma (OAG) patients and controls, and to investigate differences in ocular pulse amplitude (OPA) and pulsatile ocular blood flow (POBF) between the two groups. Twenty-one OAG patients and 21 controls undergoing cataract surgery were enrolled. Patients with early or moderate primary or pseudoexfoliative OAG participated in the glaucoma group. A computer-controlled system, consisting of a pressure transducer and a microstepping device was employed intraoperatively. After cannulation of the anterior chamber, IOP was increased by infusing the eye with microvolumes of saline solution. IOP was recorded after each infusion step. At an IOP of 40 mm Hg, an IOP decay curve was recorded for 4 minutes. OR coefficients, C, OPA, and POBF were estimated from IOP and volume recordings. There were no differences in age or axial length in the two groups. The OR coefficient was 0.0220 ± 0.0053 μl(-1) in the OAG and 0.0222 ± 0.0039 μl(-1) in the control group (P = 0.868). C was 0.092 ± 0.082 μL/min/mm Hg in the glaucoma group compared with 0.149 ± 0.085 μL/min/mm Hg in the control group at an IOP of 35 mm Hg (P < 0.001) and 0.178 ± 0.133 μL/min/mm Hg vs. 0.292 ± 0.166 μL/min/mm Hg, respectively, at an IOP of 25 mm Hg (P < 0.001). There were no differences in OPA or POBF between the two groups in baseline and increased levels of IOP (P > 0.05). Manometric data reveal lower C in OAG patients and increased C with increasing IOP. There were no differences in the OR coefficient, OPA, and POBF between medically treated OAG patients and controls, failing to provide evidence of altered scleral distensibility and choroidal blood flow in OAG.

  12. Design of a pulsatile flow facility to evaluate thrombogenic potential of implantable cardiac devices.

    PubMed

    Arjunon, Sivakkumar; Ardana, Pablo Hidalgo; Saikrishnan, Neelakantan; Madhani, Shalv; Foster, Brent; Glezer, Ari; Yoganathan, Ajit P

    2015-04-01

    Due to expensive nature of clinical trials, implantable cardiac devices should first be extensively characterized in vitro. Prosthetic heart valves (PHVs), an important class of these devices, have been shown to be associated with thromboembolic complications. Although various in vitro systems have been designed to quantify blood-cell damage and platelet activation caused by nonphysiological hemodynamic shear stresses in these PHVs, very few systems attempt to characterize both blood damage and fluid dynamics aspects of PHVs in the same test system. Various numerical modeling methodologies are also evolving to simulate the structural mechanics, fluid mechanics, and blood damage aspects of these devices. This article presents a completely hemocompatible small-volume test-platform that can be used for thrombogenicity studies and experimental fluid mechanics characterization. Using a programmable piston pump to drive freshly drawn human blood inside a cylindrical column, the presented system can simulate various physiological and pathophysiological conditions in testing PHVs. The system includes a modular device-mounting chamber, and in this presented case, a 23 mm St. Jude Medical (SJM) Regents® mechanical heart valve (MHV) in aortic position was used as the test device. The system was validated for its capability to quantify blood damage by measuring blood damage induced by the tester itself (using freshly drawn whole human blood). Blood damage levels were ascertained through clinically relevant assays on human blood while fluid dynamics were characterized using time-resolved particle image velocimetry (PIV) using a blood-mimicking fluid. Blood damage induced by the tester itself, assessed through Thrombin-anti-Thrombin (TAT), Prothrombin factor 1.2 (PF1.2), and hemolysis (Drabkins assay), was within clinically accepted levels. The hydrodynamic performance of the tester showed consistent, repeatable physiological pressure and flow conditions. In addition, the

  13. Finite Element Simulation of Two-Dimensional Pulsatile Blood Flow Through a Stenosed Artery in the Presence of External Magnetic Field

    NASA Astrophysics Data System (ADS)

    Alimohamadi, Haleh; Imani, Mohsen

    2014-07-01

    This paper introduces the impact of external magnetic field on blood flow patterns in a stenosis artery. Considering the fatty deposited lump, arterial walls as porous media, and pulsatile inflow base on human-heart-beating rate closes our model to the actual stenosis blood artery. In this study, by solving transient fluid dynamic equations in coupled porous and free media, the velocity, temperature, and shear stress distribution along the lump are investigated. The results show that applying 105 magnetic field intensity (MnF) creates two vortexes on the lumps' edges and 15X (16.6X) higher shear stress (temperature) in the stenosis region.

  14. A refractive index-matched facility for fluid-structure interaction studies of pulsatile and oscillating flow in elastic vessels of adjustable compliance

    NASA Astrophysics Data System (ADS)

    Burgmann, S.; Große, S.; Schröder, W.; Roggenkamp, J.; Jansen, S.; Gräf, F.; Büsen, M.

    2009-10-01

    The flow field in the respiratory and vascular system is known to be influenced by the flexibility of the walls. However, up to now, most of the experimental biofluidic investigations have been performed in rigid models due to the complexity and necessity of optical access. In this paper, a facility and measurement techniques for studying oscillating and pulsatile flow in elastic vessels will be described. The investigated vessel models have been adapted such that fluid-mechanical and structure-mechanical characteristics represent realistic blood flows in medium blood vessels. That is, characteristic parameters, i.e., the Reynolds and Womersley number, as well as mechanical properties of the flexible wall, i.e., the Young’s modulus and the material compliance, have been chosen to reasonably represent realistic flow conditions. First, a method to manufacture elastic models, which mimic the structure-mechanical properties of vascular vessels is described. The models possess a tunable compliance and are made of transparent polydimethylsiloxane. Second, the experimental setup of the flow facility will be elucidated. The flow facility allows to mimic pulsatile flow at physiologically relevant Reynolds and Womersley numbers. The precise form of the flow cycle can individually be controlled. Water/glycerine is used as flow medium for refractive index matching particle image velocimetry (PIV) measurements. The PIV recordings not only allow to assess the mean cross-sectional flow field but also further enable to simultaneously detect the movement of the flexible wall. Additionally, the local wall-shear stress can be obtained from the single-pixel line resolved near-wall flow field. To confirm the flow conditions of the oscillatory laminar flow inside the flow facility and to evaluate the ability to assess the flow field, measurements in a straight, uniform diameter, rigid Plexiglas pipe under identical conditions to those of the oscillating flow in the flexible vessel

  15. Time-resolved OCT-μPIV: a new microscopic PIV technique for noninvasive depth-resolved pulsatile flow profile acquisition

    NASA Astrophysics Data System (ADS)

    Chen, Chia-Yuan; Menon, Prahlad G.; Kowalski, William; Pekkan, Kerem

    2013-01-01

    In vivo acquisition of endothelial wall shear stress requires instantaneous depth-resolved whole-field pulsatile flow profile measurements in microcirculation. High-accuracy, quantitative and non- invasive velocimetry techniques are essential for emerging real-time mechano-genomic investigations. To address these research needs, a novel biological flow quantification technique, OCT-μPIV, was developed utilizing high-speed optical coherence tomography (OCT) integrated with microscopic Particle Image Velocimetry (μPIV). This technique offers the unique advantage of simultaneously acquiring blood flow profiles and vessel anatomy along arbitrarily oriented sagittal planes. The process is instantaneous and enables real-time 3D flow reconstruction without the need for computationally intensive image processing compared to state-of-the-art velocimetry techniques. To evaluate the line-scanning direction and speed, four sets of parametric synthetic OCT-μPIV data were generated using an in-house code. Based on this investigation, an in vitro experiment was designed at the fastest scan speed while preserving the region of interest providing the depth-resolved velocity profiles spanning across the width of a micro-fabricated channel. High-agreement with the analytical flow profiles was achieved for different flow rates and seed particle types and sizes. Finally, by employing blood cells as non-invasive seeding particles, in vivo embryonic vascular velocity profiles in multiple vessels were measured in the early chick embryo. The pulsatile flow frequency and peak velocity measurements were also acquired with OCT-μPIV, which agreed well with previous reported values. These results demonstrate the potential utility of this technique to conduct practical microfluidic and non-invasive in vivo studies for embryonic blood flows.

  16. Time-resolved OCT-μPIV: a new microscopic PIV technique for noninvasive depth-resolved pulsatile flow profile acquisition

    NASA Astrophysics Data System (ADS)

    Chen, Chia-Yuan; Menon, Prahlad G.; Kowalski, William; Pekkan, Kerem

    2012-12-01

    In vivo acquisition of endothelial wall shear stress requires instantaneous depth-resolved whole-field pulsatile flow profile measurements in microcirculation. High-accuracy, quantitative and non- invasive velocimetry techniques are essential for emerging real-time mechano-genomic investigations. To address these research needs, a novel biological flow quantification technique, OCT-μPIV, was developed utilizing high-speed optical coherence tomography (OCT) integrated with microscopic Particle Image Velocimetry (μPIV). This technique offers the unique advantage of simultaneously acquiring blood flow profiles and vessel anatomy along arbitrarily oriented sagittal planes. The process is instantaneous and enables real-time 3D flow reconstruction without the need for computationally intensive image processing compared to state-of-the-art velocimetry techniques. To evaluate the line-scanning direction and speed, four sets of parametric synthetic OCT-μPIV data were generated using an in-house code. Based on this investigation, an in vitro experiment was designed at the fastest scan speed while preserving the region of interest providing the depth-resolved velocity profiles spanning across the width of a micro-fabricated channel. High-agreement with the analytical flow profiles was achieved for different flow rates and seed particle types and sizes. Finally, by employing blood cells as non-invasive seeding particles, in vivo embryonic vascular velocity profiles in multiple vessels were measured in the early chick embryo. The pulsatile flow frequency and peak velocity measurements were also acquired with OCT-μPIV, which agreed well with previous reported values. These results demonstrate the potential utility of this technique to conduct practical microfluidic and non-invasive in vivo studies for embryonic blood flows.

  17. SU-D-18C-04: The Feasibility of Quantifying MRI Contrast Agent in Pulsatile Flowing Blood Using DCE-MRI

    SciTech Connect

    N, Gwilliam M; J, Collins D; O, Leach M; R, Orton M

    2014-06-01

    Purpose: To assess the feasibility of accurately quantifying the concentration of MRI contrast agent (CA) in pulsatile flowing blood by measuring its T{sub 1}, as is common for the purposes of obtaining a patientspecific arterial input function (AIF). Dynamic contrast enhanced (DCE) - MRI and pharmacokinetic (PK) modelling is widely used to produce measures of vascular function but accurate measurement of the AIF undermines their accuracy. A proposed solution is to measure the T{sub 1} of blood in a large vessel using the Fram double flip angle method during the passage of a bolus of CA. This work expands on previous work by assessing pulsatile flow and the changes in T{sub 1} seen with a CA bolus. Methods: A phantom was developed which used a physiological pump to pass fluid of a known T{sub 1} (812ms) through the centre of a head coil of a clinical 1.5T MRI scanner. Measurements were made using high temporal resolution sequences suitable for DCE-MRI and were used to validate a virtual phantom that simulated the expected errors due to pulsatile flow and bolus of CA concentration changes typically found in patients. Results: : Measured and virtual results showed similar trends, although there were differences that may be attributed to the virtual phantom not accurately simulating the spin history of the fluid before entering the imaging volume. The relationship between T{sub 1} measurement and flow speed was non-linear. T{sub 1} measurement is compromised by new spins flowing into the imaging volume, not being subject to enough excitations to have reached steady-state. The virtual phantom demonstrated a range of recorded T{sub 1} for various simulated T{sub 1} / flow rates. Conclusion: T{sub 1} measurement of flowing blood using standard DCE-MRI sequences is very challenging. Measurement error is non-linear with relation to instantaneous flow speed. Optimising sequence parameters and lowering baseline T{sub 1} of blood should be considered.

  18. Effects of Pulsatile Versus Nonpulsatile Flow on Cerebral Hemodynamics During Pediatric Cardiopulmonary Bypass With Deep Hypothermic Circulatory Arrest

    DTIC Science & Technology

    2007-11-02

    after cardiac surgery . This study is designed to determine the effects of pulsatile versus nonpulsatile perfusion on regional and global cerebral blood...A. Anesthesia / Surgery Animals were premedicated with intramuscular ketamine hydrochloride (20 mg/kg), acepromazine maleate (1 mg/kg), and...DEEP HYPOTHERMIC CIRCULATORY ARREST A. Ündar1,2,3, W. K. Vaughn4, and J. H. Calhoon5 1Congenital Heart Surgery Service, Texas Children’s Hospital

  19. Experimental investigation of the flow field past a bileaflet mechanical heart valve in pulsatile flow within an anatomical aorta model

    NASA Astrophysics Data System (ADS)

    Brown, Laura; Tavoularis, Stavros

    2011-11-01

    A bileaflet mechanical heart valve (BMHV) has been mounted at the inlet of an anatomical model of the human aorta, and placed within a mock circulation loop that simulates physiological flow conditions. The working fluid matches the refractive index of silicone, from which the aorta model and other parts of the test section are made, and the viscosity of blood. Flow characteristics past the BMHV are measured using stereoscopic and planar particle image velocimetry and laser Doppler velocimetry. In contrast to previous experiments, in which heart valves have been tested in simplified aortic geometries, this arrangement permits the study of the dependence of flow past the valve upon recirculation in the sinuses of Valsalva, the flow rate through the coronary arteries, and the aorta curvature. The effect of valve orientation will also be investigated with the objective to determine a hemodynamically optimal configuration with potential benefits to implantation procedures. The measured viscous shear stress distribution will be analyzed towards predicting the initiation of thrombosis in patients and identifying regions of stagnation, which could facilitate thrombus attachment.

  20. The pulsatile motion of a semi-infinite bubble in a channel: flow fields, and transport of an inactive surface-associated contaminant

    NASA Astrophysics Data System (ADS)

    Zimmer, Maximillian E.; Williams, Harvey A. R.; Gaver, Donald P.

    2005-08-01

    We investigate a theoretical model of the pulsatile motion of a contaminant-doped semi-infinite bubble in a rectangular channel. We examine the fluid mechanical behaviour of the pulsatile bubble, and its influence on the transport of a surface-inactive contaminant (termed surfinactant). This investigation is used to develop a preliminary understanding of surfactant responses during unsteady pulmonary airway reopening. Reopening is modelled as the pulsatile motion of a semi-infinite gas bubble in a horizontal channel of width 2a filled with a Newtonian liquid of viscosity mu and constant surface tension gamma. A modified Langmuir sorption model is assumed, which allows for the creation and respreading of a surface multilayer. The bubble is forced via a time-dependent volume flux Q(t) with mean and oscillatory components (Q_{M} and Q_{omega }, respectively) at frequency omega . The flow behaviour is governed by the dimensionless parameters: Ca_{M} {=} mu Q_{M}/(2agamma ), a steady-state capillary number, which represents the ratio of viscous to surface tension forces; Ca_{Omega } {=} mu Q_{omega }/(2agamma ), an oscillatory forcing magnitude; Omega {=} omega mu a/gamma , a dimensionless frequency that represents the ratio of viscous relaxation to oscillatory-forcing timescales; and A {=} 2Ca_{Omega }/Omega , a dimensionless oscillation amplitude. Our simulations indicate that contaminant deposition and retention in the bubble cap region occurs at moderate frequencies if retrograde bubble motion develops during the oscillation cycle. However, if oscillations are too rapid the ensuing large forward tip velocities cause a net loss of contaminant from the bubble tip. Determination of an optimal oscillation range may be important in reducing ventilator-induced lung injury associated with infant and adult respiratory distress syndromes by increasing surfactant transport to regions of collapsed airways.

  1. Central Pulsatile Pressure and Flow Relationship in the Time and Frequency Domain to Characterise Hydraulic Input to the Brain and Cerebral Vascular Impedance.

    PubMed

    Kim, Mi Ok; O'Rourke, Michael F; Adji, Audrey; Avolio, Alberto P

    2016-01-01

    In the time domain, pulsatile flow and pressure can be characterised as the ratio of the late systolic boost of flow or pressure to the pulse amplitude so as to estimate the hydraulic input to the brain. While vascular impedance has been widely used to represent the load presented to the heart by the systemic circulation, it has not been applied to the cerebral circulation.We set out to study the relationship between the pressure and the flow augmentation index (AIx) in the time domain and to determine cerebral vascular impedance using aortic blood pressure and cerebral blood flow waveforms in the frequency domain. Twenty-four young subjects (aged 21-39 years) were recruited; aortic pressure was derived using SphygmoCor from radial pressure. Flow waveforms were recorded from the middle cerebral artery. In three subjects, we performed the Valsalva manoeuvre to investigate their response to physiological intervention. There was a linear relationship between flow and pressure AIx, and cerebral impedance values were similar to those estimated for low resistance vascular beds. Substantial change in pressure and flow wave contour was observed during the Valsalva manoeuvre; however, the relationship in both the time and the frequency domains were unchanged. This confirms that aortic pressure and cerebral flow waveform can be used to study cerebral impedance.

  2. Mechanical buckling of artery under pulsatile pressure.

    PubMed

    Liu, Qin; Han, Hai-Chao

    2012-04-30

    Tortuosity that often occurs in carotid and other arteries has been shown to be associated with high blood pressure, atherosclerosis, and other diseases. However the mechanisms of tortuosity development are not clear. Our previous studies have suggested that arteries buckling could be a possible mechanism for the initiation of tortuous shape but artery buckling under pulsatile flow condition has not been fully studied. The objectives of this study were to determine the artery critical buckling pressure under pulsatile pressure both experimentally and theoretically, and to elucidate the relationship of critical pressures under pulsatile flow, steady flow, and static pressure. We first tested the buckling pressures of porcine carotid arteries under these loading conditions, and then proposed a nonlinear elastic artery model to examine the buckling pressures under pulsatile pressure conditions. Experimental results showed that under pulsatile pressure arteries buckled when the peak pressures were approximately equal to the critical buckling pressures under static pressure. This was also confirmed by model simulations at low pulse frequencies. Our results provide an effective tool to predict artery buckling pressure under pulsatile pressure.

  3. Mechanical Buckling of Artery under Pulsatile Pressure

    PubMed Central

    Liu, Qin; Han, Hai-Chao

    2012-01-01

    Tortuosity that often occurs in carotid and other arteries has been shown to be associated with high blood pressure, atherosclerosis, and other diseases. However the mechanisms of tortuosity development are not clear. Our previous studies have suggested that arteries buckling could be a possible mechanism for the initiation of tortuous shape but artery buckling under pulsatile flow condition has not been fully studied. The objectives of this study were to determine the artery critical buckling pressure under pulsatile pressure both experimentally and theoretically, and to elucidate the relationship of critical pressures under pulsatile flow, steady flow, and static pressure. We first tested the buckling pressures of porcine carotid arteries under these loading conditions, and then proposed a nonlinear elastic artery model to examine the buckling pressures under pulsatile pressure conditions. Experimental results showed that under pulsatile pressure arteries buckled when the peak pressures were approximately equal to the critical buckling pressures under static pressure. This was also confirmed by model simulations at low pulse frequencies. Our results provide an effective tool to predict artery buckling pressure under pulsatile pressure. PMID:22356844

  4. Basic study of intrinsic elastography: Relationship between tissue stiffness and propagation velocity of deformation induced by pulsatile flow

    NASA Astrophysics Data System (ADS)

    Nagaoka, Ryo; Iwasaki, Ryosuke; Arakawa, Mototaka; Kobayashi, Kazuto; Yoshizawa, Shin; Umemura, Shin-ichiro; Saijo, Yoshifumi

    2015-07-01

    We proposed an estimation method for a tissue stiffness from deformations induced by arterial pulsation, and named this proposed method intrinsic elastography (IE). In IE, assuming that the velocity of the deformation propagation in tissues is closely related to the stiffness, the propagation velocity (PV) was estimated by spatial compound ultrasound imaging with a high temporal resolution of 1 ms. However, the relationship between tissue stiffness and PV has not been revealed yet. In this study, the PV of the deformation induced by the pulsatile pump was measured by IE in three different poly(vinyl alcohol) (PVA) phantoms of different stiffnesses. The measured PV was compared with the shear wave velocity (SWV) measured by shear wave imaging (SWI). The measured PV has trends similar to the measured SWV. These results obtained by IE in a healthy male show the possibility that the mechanical properties of living tissues could be evaluated by IE.

  5. In vitro measurements of velocity and wall shear stress in a novel sequential anastomotic graft design model under pulsatile flow conditions.

    PubMed

    Kabinejadian, Foad; Ghista, Dhanjoo N; Su, Boyang; Nezhadian, Mercedeh Kaabi; Chua, Leok Poh; Yeo, Joon Hock; Leo, Hwa Liang

    2014-10-01

    This study documents the superior hemodynamics of a novel coupled sequential anastomoses (SQA) graft design in comparison with the routine conventional end-to-side (ETS) anastomoses in coronary artery bypass grafts (CABG). The flow fields inside three polydimethylsiloxane (PDMS) models of coronary artery bypass grafts, including the coupled SQA graft design, a conventional ETS anastomosis, and a parallel side-to-side (STS) anastomosis, are investigated under pulsatile flow conditions using particle image velocimetry (PIV). The velocity field and distributions of wall shear stress (WSS) in the models are studied and compared with each other. The measurement results and WSS distributions, computed from the near wall velocity gradients reveal that the novel coupled SQA design provides: (i) a uniform and smooth flow at its ETS anastomosis, without any stagnation point on the artery bed and vortex formation in the heel region of the ETS anastomosis within the coronary artery; (ii) more favorable WSS distribution; and (iii) a spare route for the blood flow to the coronary artery, to avoid re-operation in case of re-stenosis in either of the anastomoses. This in vitro investigation complements the previous computational studies of blood flow in this coupled SQA design, and is another necessary step taken toward the clinical application of this novel design. At this point and prior to the clinical adoption of this novel design, in vivo animal trials are warranted, in order to investigate the biological effects and overall performance of this anastomotic configuration in vivo.

  6. In vivo two-photon excited fluorescence microscopy reveals cardiac- and respiration-dependent pulsatile blood flow in cortical blood vessels in mice.

    PubMed

    Santisakultarm, Thom P; Cornelius, Nathan R; Nishimura, Nozomi; Schafer, Andrew I; Silver, Richard T; Doerschuk, Peter C; Olbricht, William L; Schaffer, Chris B

    2012-04-01

    Subtle alterations in cerebral blood flow can impact the health and function of brain cells and are linked to cognitive decline and dementia. To understand hemodynamics in the three-dimensional vascular network of the cerebral cortex, we applied two-photon excited fluorescence microscopy to measure the motion of red blood cells (RBCs) in individual microvessels throughout the vascular hierarchy in anesthetized mice. To resolve heartbeat- and respiration-dependent flow dynamics, we simultaneously recorded the electrocardiogram and respiratory waveform. We found that centerline RBC speed decreased with decreasing vessel diameter in arterioles, slowed further through the capillary bed, and then increased with increasing vessel diameter in venules. RBC flow was pulsatile in nearly all cortical vessels, including capillaries and venules. Heartbeat-induced speed modulation decreased through the vascular network, while the delay between heartbeat and the time of maximum speed increased. Capillary tube hematocrit was 0.21 and did not vary with centerline RBC speed or topological position. Spatial RBC flow profiles in surface vessels were blunted compared with a parabola and could be measured at vascular junctions. Finally, we observed a transient decrease in RBC speed in surface vessels before inspiration. In conclusion, we developed an approach to study detailed characteristics of RBC flow in the three-dimensional cortical vasculature, including quantification of fluctuations in centerline RBC speed due to cardiac and respiratory rhythms and flow profile measurements. These methods and the quantitative data on basal cerebral hemodynamics open the door to studies of the normal and diseased-state cerebral microcirculation.

  7. In vivo two-photon excited fluorescence microscopy reveals cardiac- and respiration-dependent pulsatile blood flow in cortical blood vessels in mice

    PubMed Central

    Santisakultarm, Thom P.; Cornelius, Nathan R.; Nishimura, Nozomi; Schafer, Andrew I.; Silver, Richard T.; Doerschuk, Peter C.; Olbricht, William L.

    2012-01-01

    Subtle alterations in cerebral blood flow can impact the health and function of brain cells and are linked to cognitive decline and dementia. To understand hemodynamics in the three-dimensional vascular network of the cerebral cortex, we applied two-photon excited fluorescence microscopy to measure the motion of red blood cells (RBCs) in individual microvessels throughout the vascular hierarchy in anesthetized mice. To resolve heartbeat- and respiration-dependent flow dynamics, we simultaneously recorded the electrocardiogram and respiratory waveform. We found that centerline RBC speed decreased with decreasing vessel diameter in arterioles, slowed further through the capillary bed, and then increased with increasing vessel diameter in venules. RBC flow was pulsatile in nearly all cortical vessels, including capillaries and venules. Heartbeat-induced speed modulation decreased through the vascular network, while the delay between heartbeat and the time of maximum speed increased. Capillary tube hematocrit was 0.21 and did not vary with centerline RBC speed or topological position. Spatial RBC flow profiles in surface vessels were blunted compared with a parabola and could be measured at vascular junctions. Finally, we observed a transient decrease in RBC speed in surface vessels before inspiration. In conclusion, we developed an approach to study detailed characteristics of RBC flow in the three-dimensional cortical vasculature, including quantification of fluctuations in centerline RBC speed due to cardiac and respiratory rhythms and flow profile measurements. These methods and the quantitative data on basal cerebral hemodynamics open the door to studies of the normal and diseased-state cerebral microcirculation. PMID:22268102

  8. Ultrasound imaging velocimetry with interleaved images for improved pulsatile arterial flow measurements: a new correction method, experimental and in vivo validation.

    PubMed

    Fraser, Katharine H; Poelma, Christian; Zhou, Bin; Bazigou, Eleni; Tang, Meng-Xing; Weinberg, Peter D

    2017-02-01

    Blood velocity measurements are important in physiological science and clinical diagnosis. Doppler ultrasound is the most commonly used method but can only measure one velocity component. Ultrasound imaging velocimetry (UIV) is a promising technique capable of measuring two velocity components; however, there is a limit on the maximum velocity that can be measured with conventional hardware which results from the way images are acquired by sweeping the ultrasound beam across the field of view. Interleaved UIV is an extension of UIV in which two image frames are acquired concurrently, allowing the effective interframe separation time to be reduced and therefore increasing the maximum velocity that can be measured. The sweeping of the ultrasound beam across the image results in a systematic error which must be corrected: in this work, we derived and implemented a new velocity correction method which accounts for acceleration of the scatterers. We then, for the first time, assessed the performance of interleaved UIV for measuring pulsatile arterial velocities by measuring flows in phantoms and in vivo and comparing the results with spectral Doppler ultrasound and transit-time flow probe data. The velocity and flow rate in the phantom agreed within 5-10% of peak velocity, and 2-9% of peak flow, respectively, and in vivo the velocity difference was 9% of peak velocity. The maximum velocity measured was 1.8 m s(-1), the highest velocity reported with UIV. This will allow flows in diseased arteries to be investigated and so has the potential to increase diagnostic accuracy and enable new vascular research. © 2017 The Author(s).

  9. Spatial-temporal three-dimensional ultrasound plane-by-plane active cavitation mapping for high-intensity focused ultrasound in free field and pulsatile flow.

    PubMed

    Ding, Ting; Hu, Hong; Bai, Chen; Guo, Shifang; Yang, Miao; Wang, Supin; Wan, Mingxi

    2016-07-01

    Cavitation plays important roles in almost all high-intensity focused ultrasound (HIFU) applications. However, current two-dimensional (2D) cavitation mapping could only provide cavitation activity in one plane. This study proposed a three-dimensional (3D) ultrasound plane-by-plane active cavitation mapping (3D-UPACM) for HIFU in free field and pulsatile flow. The acquisition of channel-domain raw radio-frequency (RF) data in 3D space was performed by sequential plane-by-plane 2D ultrafast active cavitation mapping. Between two adjacent unit locations, there was a waiting time to make cavitation nuclei distribution of the liquid back to the original state. The 3D cavitation map equivalent to the one detected at one time and over the entire volume could be reconstructed by Marching Cube algorithm. Minimum variance (MV) adaptive beamforming was combined with coherence factor (CF) weighting (MVCF) or compressive sensing (CS) method (MVCS) to process the raw RF data for improved beamforming or more rapid data processing. The feasibility of 3D-UPACM was demonstrated in tap-water and a phantom vessel with pulsatile flow. The time interval between temporal evolutions of cavitation bubble cloud could be several microseconds. MVCF beamformer had a signal-to-noise ratio (SNR) at 14.17dB higher, lateral and axial resolution at 2.88times and 1.88times, respectively, which were compared with those of B-mode active cavitation mapping. MVCS beamformer had only 14.94% time penalty of that of MVCF beamformer. This 3D-UPACM technique employs the linear array of a current ultrasound diagnosis system rather than a 2D array transducer to decrease the cost of the instrument. Moreover, although the application is limited by the requirement for a gassy fluid medium or a constant supply of new cavitation nuclei that allows replenishment of nuclei between HIFU exposures, this technique may exhibit a useful tool in 3D cavitation mapping for HIFU with high speed, precision and resolution

  10. Fabrication of novel high surface area mushroom gilled fibers and their effects on human adipose derived stem cells under pulsatile fluid flow for tissue engineering applications.

    PubMed

    Tuin, Stephen A; Pourdeyhimi, Behnam; Loboa, Elizabeth G

    2016-05-01

    The fabrication and characterization of novel high surface area hollow gilled fiber tissue engineering scaffolds via industrially relevant, scalable, repeatable, high speed, and economical nonwoven carding technology is described. Scaffolds were validated as tissue engineering scaffolds using human adipose derived stem cells (hASC) exposed to pulsatile fluid flow (PFF). The effects of fiber morphology on the proliferation and viability of hASC, as well as effects of varied magnitudes of shear stress applied via PFF on the expression of the early osteogenic gene marker runt related transcription factor 2 (RUNX2) were evaluated. Gilled fiber scaffolds led to a significant increase in proliferation of hASC after seven days in static culture, and exhibited fewer dead cells compared to pure PLA round fiber controls. Further, hASC-seeded scaffolds exposed to 3 and 6dyn/cm(2) resulted in significantly increased mRNA expression of RUNX2 after one hour of PFF in the absence of soluble osteogenic induction factors. This is the first study to describe a method for the fabrication of high surface area gilled fibers and scaffolds. The scalable manufacturing process and potential fabrication across multiple nonwoven and woven platforms makes them promising candidates for a variety of applications that require high surface area fibrous materials. We report here for the first time the successful fabrication of novel high surface area gilled fiber scaffolds for tissue engineering applications. Gilled fibers led to a significant increase in proliferation of human adipose derived stem cells after one week in culture, and a greater number of viable cells compared to round fiber controls. Further, in the absence of osteogenic induction factors, gilled fibers led to significantly increased mRNA expression of an early marker for osteogenesis after exposure to pulsatile fluid flow. This is the first study to describe gilled fiber fabrication and their potential for tissue engineering

  11. Nonlinear model on pulsatile flow of blood through a porous bifurcated arterial stenosis in the presence of magnetic field and periodic body acceleration.

    PubMed

    Ponalagusamy, R; Priyadharshini, S

    2017-04-01

    Background and Objective: The motivation of cardiovascular modeling is to understand the haemodynamic and mechanical factors in the diagnosis and treatment of cardiovascular diseases. Several investigations have been carried out by many authors to understand the flow properties of blood in modelling blood flows in the circulatory system. In the present article, the pulsatile flow of Herschel-Bulkley fluid through a bifurcated arterial stenosis in a porous medium with magnetic field and periodic body acceleration has been investigated in view of understanding the role of rheological behaviour of blood, stenotic height, bifurcation angle, magnetic field and porosity of wall in the initiation and proliferation of cardiovascular diseases. The governing equations involving shear stress are solved numerically using finite difference schemes and the shear stress values in parent and daughter arteries are obtained using MATLAB software. The constitutive equation of Herschel-Bulkley fluid is highly nonlinear and using the equation, velocity distribution has been obtained. From the obtained velocity distribution, the numerical solutions of wall shear stress and flow resistance are found. The plug core radius is, for the first time, computed for various stenotic heights and it is found that the magnetic field and porosity increase the plug core radius. The wall shear stress and flow resistance increase as stenotic height, yield stress, power law index, consistency and Hartmann number increase and decrease with increase in Darcy number and half of the bifurcation angle. It is significant to note that when the value of yield stress is increased from 0.1 to 0.2, the plug core radius is increased by 7.3%. In the presence of yield stress in blood, the applied magnetic field causes 33.87% increase in the plug core radius. The mathematical model clearly shows that the increase in wall shear stress affects the aggregation of human platelets and rearranging the alignment of

  12. Nonlinear Flow Rate Response to Pumping Frequency and Reduced Hemolysis in the Drastically Under-Occluded Pulsatile Roller Pump.

    PubMed

    Yap, Choon Hwai; Lai, Chang Quan; Loh, Ivan Guang Hui; Ong, Thaddaeus Zhongren

    2017-02-01

    Roller pumps are widely used in many medical procedures including cardiopulmonary bypass, left/right ventricular assist, and hemodialysis. However, to date, the problem of the roller pumping mechanism causing significant hemolysis remains unresolved. It has been shown that with under-occlusion of the roller pump, hemolysis can be reduced, but significant reduction of the mean flow rate also takes place due to backflow through the under-occlusion. We performed an investigation of the flow dynamics of an under-occluded roller pump which featured significantly higher amount of under-occlusion than previously investigated. Our results showed that the mean flow rate produced by the pump has a strong, nonlinear dependence on pumping frequency. Mean flow rate generally increases with the pumping frequency and the degree of maximum occlusion except at certain frequencies where sharp reductions were observed. These frequencies coincide with the fundamental frequency of the system and its harmonics, bearing resemblance to the impedance pump, suggesting that the drastically under-occluded roller pump is a unique device that employs the pumping mechanisms of both roller pumping and impedance pumping. At the appropriate frequencies, this under-occluded roller pump could sustain sufficiently high flow rates for clinical uses. Blood damage potential of the under-occluded roller pump was compared to a fully occluded roller pump via the assay of free-plasma hemoglobin, and it was found that the under-occlusion reduced hemolysis by about half for any given flow rate. The drastically under-occluded roller pumping reported in this study, therefore, has the potential of being translated into an improved clinical blood pump.

  13. Chaotic and mode-locked interactions between flow-induced collapsible-tube oscillation and pulsatile upstream forcing

    NASA Astrophysics Data System (ADS)

    Bertram, C. D.; She, Jianwei

    2000-02-01

    Interactions were examined between the otherwise periodic self-excited oscillation of a pneumatically compressed flexible tube conveying an aqueous flow, and pulsations induced by connecting the output of a hydraulically controlled piston pump executing sinusoidal piston displacements in parallel with the steady flow-driving head. Depending on pump amplitude and frequency, the oscillatory interaction consisted of either resonance, periodic entrainment or aperiodicity. Despite limitations imposed by intrinsic turbulent noise, aperiodic interactions were shown to exhibit characteristics of a low-dimensional chaotic attractor.

  14. Wall Shear Stress in Aorta with Coarctation and Post-Stenotic Dilatation - Scale Resolved Simulation of Pulsatile Blood Flow

    NASA Astrophysics Data System (ADS)

    Gardhagen, Roland; Karlsson, Matts

    2012-11-01

    Large eddy simulations of pulsating blood flow in an idealized model of a human aorta with a coarctation and a post-stenotic dilatation were conducted before and after treatment of the stenosis using Ansys Fluent. The aim was to study wall shear stress (WSS), which influences the function of endothelial cells, and turbulence, which may play a role in thrombus formation. Phase average values of WSS before the treatment revealed high shear in the stenosis at peak systole, as expected, but also at the end of the dilatation. In the dilatation backflow causes a negative peak. Diastolic WSS is characterized by low amplitude oscillations, which promotes atherogenesis. Also noticeable is the asymmetric pattern between the inner and outer sides of the vessel caused by the arch upstream of the stenosis. Thus, large spatial, temporal, and probably asymmetric WSS gradients in the already diseased region suggest increased risk for further endothelial dysfunction. This reflects a complex, partly turbulent, flow pattern that may disturb the blood flow in the abdominal aorta. After treatment of the stenosis, but not the dilatation, fluctuations of velocity and WSS were still found, thus harmful flow conditions still exist.

  15. Pulsatile flow in an end-to-side vascular graft model: comparison of computations with experimental data.

    PubMed

    Lei, M; Giddens, D P; Jones, S A; Loth, F; Bassiouny, H

    2001-02-01

    Various hemodynamic factors have been implicated in vascular graft intimal hyperplasia, the major mechanism contributing to chronic failure of small-diameter grafts. However, a thorough knowledge of the graft flow field is needed in order to determine the role of hemodynamics and how these factors affect the underlying biological processes. Computational fluid dynamics offers much more versatility and resolution than in vitro or in vivo methods, yet computations must be validated by careful comparison with experimental data. Whereas numerous numerical and in vitro simulations of arterial geometries have been reported, direct point-by-point comparisons of the two techniques are rare in the literature. We have conducted finite element computational analyses for a model of an end-to-side vascular graft and compared the results with experimental data obtained using laser-Doppler velocimetry. Agreement for velocity profiles is found to be good, with some clear differences near the recirculation zones during the deceleration and reverse-flow segments of the flow waveform. Wall shear stresses are determined from velocity gradients, whether by computational or experimental methods, and hence the agreement for this quantity, while still good, is less consistent than for velocity itself from the wall shear stress numerical results, we computed four variables that have been cited in the development of intiimal hyperplasia-the time-averaged wall shear stress, an oscillating shear index, and spatial and temporal wall shear stress gradients in order to illustrate the versatility of numerical methods. We conclude that the computational approach is a valid alternative to the experimental approach for quantitative hemodynamic studies. Where differences in velocity were found by the two methods, it was generally attributed to the inability of the numerical method to model the fluid dynamics when flow conditions are destabilizing. Differences in wall shear, in the absence of

  16. The influence of out-of-plane geometry on pulsatile flow within a distal end-to-side anastomosis.

    PubMed

    Papaharilaou, Y; Doorly, D J; Sherwin, S J

    2002-09-01

    We present an experimental and computational investigation of time-varying flow in an idealized fully occluded 45 degrees distal end-to-side anastomosis. Two geometric configurations are assessed, one where the centerlines of host and bypass vessels lie within a plane, and one where the bypass vessel is deformed out of the plane of symmetry, respectively, termed planar and non-planar. Flow experiments were conducted by magnetic resonance imaging in rigid wall models and computations were performed using a high order spectral/hp algorithm. Results indicate a significant change in the spatial distribution of wall shear stress and a reduction of the time-averaged peak wall shear stress magnitude by 10% in the non-planar model as compared to the planar configuration. In the planar geometry the stagnation point follows a straight-line path along the host artery bed with a path length of 0.8 diameters. By contrast in the non-planar case the stagnation point oscillates about a center that is located off the symmetry plane intersection with the host artery bed wall, and follows a parabolic path with a 0.7 diameter longitudinal and 0.5 diameter transverse excursion. A definition of the oscillatory shear index (OSI) is introduced that varies between 0 and 0.5 and that accounts for a continuous range of wall shear stress vector angles. In both models, regions of elevated oscillatory shear were spatially associated with regions of separated or oscillating stagnation point flow. The mean oscillatory shear magnitude (considering sites where OSI>0.1) in the non-planar geometry was reduced by 22% as compared to the planar configuration. These changes in the dynamic behavior of the stagnation point and the oscillatory shear distribution introduced by out-of-plane graft curvature may influence the localization of vessel wall sites exposed to physiologically unfavorable flow conditions.

  17. Assessment of subgrid-scale models with a large-eddy simulation-dedicated experimental database: The pulsatile impinging jet in turbulent cross-flow

    NASA Astrophysics Data System (ADS)

    Baya Toda, Hubert; Cabrit, Olivier; Truffin, Karine; Bruneaux, Gilles; Nicoud, Franck

    2014-07-01

    Large-Eddy Simulation (LES) in complex geometries and industrial applications like piston engines, gas turbines, or aircraft engines requires the use of advanced subgrid-scale (SGS) models able to take into account the main flow features and the turbulence anisotropy. Keeping this goal in mind, this paper reports a LES-dedicated experiment of a pulsatile hot-jet impinging a flat-plate in the presence of a cold turbulent cross-flow. Unlike commonly used academic test cases, this configuration involves different flow features encountered in complex configurations: shear/rotating regions, stagnation point, wall-turbulence, and the propagation of a vortex ring along the wall. This experiment was also designed with the aim to use quantitative and nonintrusive optical diagnostics such as Particle Image Velocimetry, and to easily perform a LES involving a relatively simple geometry and well-controlled boundary conditions. Hence, two eddy-viscosity-based SGS models are investigated: the dynamic Smagorinsky model [M. Germano, U. Piomelli, P. Moin, and W. Cabot, "A dynamic subgrid-scale eddy viscosity model," Phys. Fluids A 3(7), 1760-1765 (1991)] and the σ-model [F. Nicoud, H. B. Toda, O. Cabrit, S. Bose, and J. Lee, "Using singular values to build a subgrid-scale model for large eddy simulations," Phys. Fluids 23(8), 085106 (2011)]. Both models give similar results during the first phase of the experiment. However, it was found that the dynamic Smagorinsky model could not accurately predict the vortex-ring propagation, while the σ-model provides a better agreement with the experimental measurements. Setting aside the implementation of the dynamic procedure (implemented here in its simplest form, i.e., without averaging over homogeneous directions and with clipping of negative values to ensure numerical stability), it is suggested that the mitigated predictions of the dynamic Smagorinsky model are due to the dynamic constant, which strongly depends on the mesh resolution

  18. Calculation of arterial wall temperature in atherosclerotic arteries: effect of pulsatile flow, arterial geometry, and plaque structure

    PubMed Central

    Ley, Obdulia; Kim, Taehong

    2007-01-01

    Background This paper presents calculations of the temperature distribution in an atherosclerotic plaque experiencing an inflammatory process; it analyzes the presence of hot spots in the plaque region and their relationship to blood flow, arterial geometry, and inflammatory cell distribution. Determination of the plaque temperature has become an important topic because plaques showing a temperature inhomogeneity have a higher likelihood of rupture. As a result, monitoring plaque temperature and knowing the factors affecting it can help in the prevention of sudden rupture. Methods The transient temperature profile in inflamed atherosclerotic plaques is calculated by solving an energy equation and the Navier-Stokes equations in 2D idealized arterial models of a bending artery and an arterial bifurcation. For obtaining the numerical solution, the commercial package COMSOL 3.2 was used. The calculations correspond to a parametric study where arterial type and size, as well as plaque geometry and composition, are varied. These calculations are used to analyze the contribution of different factors affecting arterial wall temperature measurements. The main factors considered are the metabolic heat production of inflammatory cells, atherosclerotic plaque length lp, inflammatory cell layer length lmp, and inflammatory cell layer thickness dmp. Results The calculations indicate that the best location to perform the temperature measurement is at the back region of the plaque (0.5 ≤ l/lp ≤ 0.7). The location of the maximum temperature, or hot spot, at the plaque surface can move during the cardiac cycle depending on the arterial geometry and is a direct result of the blood flow pattern. For the bending artery, the hot spot moves 0.6 millimeters along the longitudinal direction; for the arterial bifurcation, the hot spot is concentrated at a single location due to the flow recirculation observed at both ends of the plaque. Focusing on the thermal history of different

  19. The impact of pump settings on the quality of pulsatility.

    PubMed

    Rider, Alan R; Ressler, Noel M; Karkhanis, Tushar R; Kunselman, Allen R; Wang, Shigang; Undar, Akif

    2009-01-01

    The study objective was to evaluate the Jostra HL-20 roller pump under different baseflow and pump head settings with quantified energy values from pressure and flow waveforms, in a simulated pediatric bypass circuit. Pump flow rate was set at 800 mL/min for both pulsatile and nonpulsatile perfusion modes and the mean arterial pressure (MAP) of the pseudopatient was maintained at 40 mm Hg for each experiment. Pulsatile baseflow settings and pump head start points varied with each experiment. Pressure and flow waveforms were recorded at preoxygenator, precannula, and postcannula sites under each pump setting. A total of 91 experiments were performed (n=7, nonpulsatile; n=84, pulsatile). Increasing baseflow caused decreases in the mean circuit pressure and surplus hemodynamic energy (SHE) levels for all pump head start times. When increasing pump head start time within each baseflow, values for MAP and SHE increased significantly. Regardless of baseflow or pump head start time, values for mean circuit pressure and SHE were lower for nonpulsatile flow than for pulsatile flow. Total hemodynamic energy values were also significantly higher under pulsatile perfusion and increased pump start times while decreasing with increased baseflows in the circuit. This study concludes that decreased baseflows with increased pump head settings on the Jostra HL-20 roller pump could significantly increase quality of generated pulsatile energy. Further research is necessary to evaluate these various pump settings under microembolic loads and with different circuit components.

  20. Pulsatile-flow mechanical circulatory support (MCS) as a bridge to transplantation or recovery. Single-centre experience with the POLCAS system in 2014.

    PubMed

    Kuśmierczyk, Mariusz; Kuć, Mateusz; Szymański, Jarosław; Juraszek, Andrzej; Kołsut, Piotr; Kuśmierski, Krzysztof; Zieliński, Tomasz; Sobieszczańska-Małek, Małgorzata; Sitkowska-Rysiak, Ewa

    2015-09-01

    Mechanical circulatory support (MCS) is a recognised method of treatment for patients with end-stage chronic or acute heart failure. The POLCAS pulsatile-flow system has been used in our institution for 15 years. Currently, it is being widely replaced by continuous-flow mechanical circulatory support equipment of the second and third generations (HeartMateII, HeartWare). The MCS presented in this study is associated with a significant risk of complications and its use is increasingly considered controversial. The aim of the study was an evaluation of the results of treatment utilising the POLCAS MCS system at our institution in 2014. The POLCAS system was implanted in 12 patients aged 16-63 years (42 ± 17 years) during a period of 12 months (from January to December, 2014). Full-blown cardiogenic shock was observed in all patients before MCS implantation. Four of the analysed patients (33%) required prior circulatory support with other devices: IABP (n = 2) or ECMO (n = 2). Episodes of cardiac arrest were reported in three patients; three other patients experienced serious arrhythmias, which accelerated the decision to implant MCS. The presented data was retrospectively obtained from the CliniNET system of the Institute of Cardiology. OpenOffice Calc spreadsheet was used for data analysis. Average MCS time was 41 days ± 25 (from 15 to 91 days). Survival until transplantation or explantation was 91.67%. The most frequent complications following the therapy were: cardiac tamponade or bleeding requiring an intervention - 25% (n = 3), renal failure requiring dialysis - 25% (n = 3), ischaemic stroke associated with the MCS - 16.6% (n = 2), bacteraemia - 16.6% (n = 2), and wound infection - 8% (n = 1). No malfunctions of the MCS system were reported. Early survival in patients who completed the MCS therapy, defined as discharge, amounted to 63.6% (n = 7). The POLCAS heart assist system is an effective method of treatment as a bridge to transplantation or recovery in

  1. A computer controlled pulsatile pump: preliminary study.

    PubMed

    Zwarts, M S; Topaz, S R; Jones, D N; Kolff, W J

    1996-12-01

    A Stepper Motor Driven Reciprocating Pump (SDRP) can replace roller pumps and rotary pumps for cardio pulmonary bypass, hemodialysis and regional perfusion. The blood pumping ventricles are basically the same as ventricles used for air driven artificial hearts and ventricular assist devices. The electric stepper motor uses a flexible linkage belt to produce a reciprocating movement, which pushes a hard sphere into the diaphragm of the blood ventricles. The SDRP generates pulsatile flow and has a small priming volume. The preset power level of the motor driver limits the maximum potential outflow pressure, so the driver acts as a safety device. A double pump can be made by connecting two fluid pumping chambers to opposing sides of the motor base. Each pump generates pulsatile flow. Pressure and flow studies with water were undertaken. Preliminary blood studies showed low hemolysis, even when circulating a small amount of blood up to 16 hours.

  2. Tissue vibration pulsatility for arterial bleeding detection using Doppler ultrasound.

    PubMed

    Xie, Zhiyong; Kim, Eung-Hun; Kim, Yongmin

    2009-01-01

    Trauma is the number one cause of death among Americans between 1 and 44 years old, and exsanguination due to internal bleeding resulting from arterial injuries is a major factor in trauma deaths. We have evaluated the feasibility of using tissue vibration pulsatility in arterial bleeding detection. Eight femoral arteries from four juvenile pigs were punctured transcutaneously with a 6 or 9-French catheter. Also, 11 silicone vessels wrapped with turkey breast were placed in a pulsatile flow phantom and penetrated with an 18-gauge needle. The tissue vibration pulsatility was derived as a ratio of the maximum spectral energy from 200 to 2500 Hz of tissue vibration in systole over a baseline value in diastole. Then, the tissue vibration pulsatility index (TVPI) was defined as the maximum tissue vibration pulsatility value for each experimental condition. Both in vitro and in vivo results showed that the TVPI from injured vessels is significantly higher (p<0.005) than that of intact vessels. In addition, we constructed the 2D map of tissue vibration pulsatility during in vitro studies and found that it could be used for spatial localization of the puncture site. Our preliminary results indicate that the tissue vibration pulsatility may be useful for detecting arterial bleeding and localizing the bleeding site.

  3. Characteristics of pulsatile blood flow through the curved bileaflet mechanical heart valve installed in two different types of blood vessels: velocity and pressure of blood flow.

    PubMed

    Bang, Jin Seok; Yoo, Song Min; Kim, Chang Nyung

    2006-01-01

    The aim of this study was to investigate the flow fields of blood flowing through the curved bileaflet mechanical heart valve. A numerical analysis was carried out with the fluid-structure interaction between the blood flow and the motion of leaflets in two different types of blood vessels (type A, with sinus blood vessel, and type B, without sinus blood vessel). When the leaflet was fully opened, a fluttering phenomenon was detected in association with the blood flow, and recirculation flows were observed in the sinus region of the blood vessel for type A. During the closing phase, regurgitation was formed between the ring and the edge of the each leaflet for both types. When the leaflet came into contact with the valve ring at the end of the closing phase, rebound of the leaflet occurred. In consideration of the entire domain, the pressure drop occurs mainly in the valve region. The present results showed tendencies similar to those obtained by previous experiments for blood flow and contribute to the development of the curved bileaflet mechanical heart valve prostheses.

  4. Application of a Lumped Parameter Model to Study the Feasibility of Simultaneous Implantation of a Continuous Flow Ventricular Assist Device (VAD) and a Pulsatile Flow VAD in BIVAD Patients.

    PubMed

    Di Molfetta, Arianna; Ferrari, Gianfranco; Iacobelli, Roberta; Filippelli, Sergio; Fresiello, Libera; Guccione, Paolo; Toscano, Alessandra; Amodeo, Antonio

    2017-03-01

    The aim of this work is to develop and test a lumped parameter model of the cardiovascular system to simulate the simultaneous use of pulsatile (P) and continuous flow (C) ventricular assist devices (VADs) on the same patient. Echocardiographic and hemodynamic data of five pediatric patients undergoing VAD implantation were retrospectively collected and used to simulate the patients' baseline condition with the numerical model. Once the baseline hemodynamic was reproduced for each patient, the following assistance modalities were simulated: (a) CVAD assisting the right ventricle and PVAD assisting the left ventricle (RCF + LPF), (b) CVAD assisting the left ventricle and PVAD assisting the right ventricle (LCF + RPF). The numerical model can well reproduce patients' baseline. The cardiac output increases in both assisted configurations (RCF + LPF: +17%, LCF + RPF: +21%, P = ns), left (right) ventricular volumes decrease more evidently in the configuration LCF + RPF (RCF + LPF), left (right) atrial pressure decreases in the LCF + RPF (RCF + LPF) modality. The pulmonary arterial pressure slightly decreases in the configuration LCF + RPF and it increases with RCF + LPF. Left and right ventricular external work increases in both configurations probably because of the total cardiac output increment. However, left and right artero-ventricular coupling improves especially in the LCF + RPF (-36% for the left ventricle and -21% for the right ventricle, P = ns). The pulsatility index decreases by 8.5% in the configuration LCF + RPF and increases by 6.4% with RCF + LPF (P = 0.0001). A numerical model could be useful to tailor on patients the choice of the VAD that could be implanted to improve the hemodynamic benefits. Moreover, a model could permit to simulate extreme physiological conditions and innovative configurations, as the implantation of both CVAD and PVAD on the same patient. © 2017 International Center

  5. Human endothelial cell responses to cardiovascular inspired pulsatile shear stress

    NASA Astrophysics Data System (ADS)

    Watson, Matthew; Baugh, Lauren; Black, Lauren, III; Kemmerling, Erica

    2016-11-01

    It is well established that hemodynamic shear stress regulates blood vessel structure and the development of vascular pathology. This process can be studied via in vitro models of endothelial cell responses to pulsatile shear stress. In this study, a macro-scale cone and plate viscometer was designed to mimic various shear stress waveforms found in the body and apply these stresses to human endothelial cells. The device was actuated by a PID-controlled DC gear-motor. Cells were exposed to 24 hours of pulsatile shear and then imaged and stained to track their morphology and secretions. These measurements were compared with control groups of cells exposed to constant shear and no shear. The results showed that flow pulsatility influenced levels of secreted proteins such as VE-cadherin and neuroregulin IHC. Cell morphology was also influenced by flow pulsatility; in general cells exposed to pulsatile shear stress developed a higher aspect ratio than cells exposed to no flow but a lower aspect ratio than cells exposed to steady flow.

  6. Measuring blood oxygenation of pulsatile arteries using photoacoustic microscopy

    NASA Astrophysics Data System (ADS)

    Li, Qian; Yu, Tianhao; Li, Lin; Chai, Xinyu; Zhou, Chuanqing

    2016-10-01

    Heart pumps blood through the blood vessels to provide body with oxygen and nutrients. As the result, the blood flow, volume and oxygenation in arteries has a pulsatile nature. Measuring these pulsatile parameters enables more precise monitoring of oxygen metabolic rate and is thus valuable for researches and clinical applications. Photoacoustic microscopy (PAM) is a proven label-free method for in vivo measuring blood oxygenation at single blood vessel level. However, studies using PAM to observe the pulsatile nature of blood oxygenation in arteries were not reported. In this paper, we use optical-resolution PAM (OR-PAM) technology to study the blood oxygenation dynamics of pulsatile arteries. First, the ability of our OR-PAM system to accurately reflect the change of optical absorption in imaged objects is demonstrated in a phantom study. Then the system is used to image exposed cortical blood vessels of cat. The pulsatile nature of blood volume and oxygenation in arteries is clearly reflected in photoacoustic (PA) signals, whereas it's not observable in veins. By using a multi-wavelength laser, the dynamics of the blood oxygenation of pulsatile arteries in cardiac cycles can be measured, based on the spectroscopic method.

  7. Analysis of Computational Fluid Dynamics and Particle Image Velocimetry Models of Distal-End Side-to-Side and End-to-Side Anastomoses for Coronary Artery Bypass Grafting in a Pulsatile Flow.

    PubMed

    Shintani, Yoshiko; Iino, Kenji; Yamamoto, Yoshitaka; Kato, Hiroki; Takemura, Hirofumi; Kiwata, Takahiro

    2017-08-19

    Intimal hyperplasia (IH) is a major cause of graft failure. Hemodynamic factors such as stagnation and disturbed blood flow are involved in IH formation. The aim of this study is to perform a comparative analysis of distal-end side-to-side (deSTS) and end-to-side (ETS) anastomoses using computational fluid dynamics (CFD) after validating the results via particle image velocimetry (PIV).Methods and Results:We investigated the characteristics of our target flow fields using CFD under steady and pulsatile flows. CFD via PIV under steady flow in a 10-times-actual-size model was validated. The CFD analysis revealed a recirculation zone in the heel region in the deSTS and ETS anastomoses and at the distal end of the graft, and just distal to the toe of the host artery in the deSTS anastomoses. The recirculation zone sizes changed with the phase shift. We found regions of low wall shear stress and high oscillating shear index in the same areas. The PIV and CFD results were similar. It was demonstrated that the hemodynamic characteristics of CFD and PIV is the difference between the deSTS and ETS anastomoses; that is, the deSTS flow peripheral to the distal end of the graft, at the distal end and just distal to the toe of the host artery is involved in the IH formation.

  8. Initial European clinical experience with pulsatile extracorporeal membrane oxygenation.

    PubMed

    Agati, Salvatore; Mignosa, Carmelo; Ciccarello, Giuseppe; Salvo, Dario; Undar, Akif

    2006-04-01

    Extracorporeal membrane oxygenation (ECMO) for post-cardiotomy heart failure in neonates and infants still carries high mortality and morbidity rates. In this study we present the first European clinical experience with the Medos DeltaStream DP1, a new pulsatile flow pump, in neonates and infants. The DP1 is an extracorporeal rotary blood pump. The pump features a diagonal flow impeller, and can be used for both continuous and pulsatile output. Special characteristics include its small priming volume of approximately 30 ml and a high pumping capacity. A temperature sensor and speed sensors are integrated into the pump. The pump has a delivery rate of up to 8 liters/min and a speed range of 100 to 10,000 rpm. Two patients being assisted with the pulsatile pump system were successfully weaned after 36 and 53 hours, respectively. Based on our limited experience with 2 patients, we believe that pulsatile DP1 device is a reasonable alternative to current conventional non-pulsatile systems.

  9. Pulsatile extracorporeal circulation during on-pump cardiac surgery enhances aortic wall shear stress.

    PubMed

    Assmann, Alexander; Benim, Ali Cemal; Gül, Fethi; Lux, Philipp; Akhyari, Payam; Boeken, Udo; Joos, Franz; Feindt, Peter; Lichtenberg, Artur

    2012-01-03

    Controversy on superiority of pulsatile versus non-pulsatile extracorporeal circulation in cardiac surgery still continues. Stroke as one of the major adverse events during cardiopulmonary bypass is, in the majority of cases, caused by mobilization of aortic arteriosclerotic plaques that is inducible by pathologically elevated wall shear stress values. The present study employs computational fluid dynamics to evaluate the aortic blood flow and wall shear stress profiles under the influence of antegrade or retrograde perfusion with pulsatile versus non-pulsatile extracorporeal circulation. While, compared to physiological flow, a non-pulsatile perfusion resulted in generally decreased blood velocities and only moderately increased shear forces (48 Pa versus 20 Pa antegradely and 127 Pa versus 30 Pa retrogradely), a pulsatile perfusion extensively enhanced the occurrence of turbulences, maximum blood flow speed and maximum wall shear stress (1020 Pa versus 20 Pa antegradely and 1178 Pa versus 30 Pa retrogradely). Under these circumstances arteriosclerotic embolism has to be considered. Further simulations and experimental work are necessary to elucidate the impact of our findings on the scientific discourse of pulsatile versus non-pulsatile extracorporeal circulation. Copyright © 2011 Elsevier Ltd. All rights reserved.

  10. New investigations of a pulsatile impeller blood pump.

    PubMed

    Qian, K X

    1990-01-01

    For circulatory assist devices and total artificial heart systems, impeller blood pumps with small total volumes would be fully implantable. One of the main obstacles, however, is generation of a pulsatile flow. The simplest way to overcome this problem is by changing the pump's revolutions per minute (rpm) periodically, but this often results in severe hemolysis. After theoretic analysis, two in vitro models of impeller blood pumps have been devised, producing pulsatile flow with constant rpm. In the first model, the impeller oscillates in an axial direction during constant rotation. The pump is driven by a DC motor (rotating) and a pneumatic device (oscillating). The form of the pulsatile pressure wave depends upon duration and amplitude of the oscillation. With 40% systolic duration and a 50 mm axial amplitude, a 70 mmHg pressure amplitude (170/100) is achieved with a semiphysiologic shape at a flow of 12 L/min. The second model produces a pulsatile flow by differing the gaps between impeller and cap on the inlet pipe. Both the cap and impeller have cone-shaped heads, and impeller oscillations of 1.5-2 mm, for example, results in a pressure pulse of 40 mmHg (150-110) at 7 L/min flow. Results of theoretic analyses have shown that both models create less turbulence in the impeller, with a consequent reduction in blood cell damage as compared to pumps with changing rpms.

  11. Functional tissue pulsatility imaging of the brain during visual stimulation.

    PubMed

    Kucewicz, John C; Dunmire, Barbrina; Leotta, Daniel F; Panagiotides, Heracles; Paun, Marla; Beach, Kirk W

    2007-05-01

    Functional tissue pulsatility imaging is a new ultrasonic technique being developed to map brain function by measuring changes in tissue pulsatility as a result of changes in blood flow with neuronal activation. The technique is based in principle on plethysmography, an older, nonultrasound technology for measuring expansion of a whole limb or body part as a result of perfusion. Perfused tissue expands by a fraction of a percent early in each cardiac cycle when arterial inflow exceeds venous outflow, and it relaxes later in the cardiac cycle when venous drainage dominates. Tissue pulsatility imaging (TPI) uses tissue Doppler signal processing methods to measure this pulsatile "plethysmographic" signal from hundreds or thousands of sample volumes in an ultrasound image plane. A feasibility study was conducted to determine if TPI could be used to detect regional brain activation during a visual contrast-reversing checkerboard block paradigm study. During a study, ultrasound data were collected transcranially from the occipital lobe as a subject viewed alternating blocks of a reversing checkerboard (stimulus condition) and a static, gray screen (control condition). Multivariate analysis of variance was used to identify sample volumes with significantly different pulsatility waveforms during the control and stimulus blocks. In 7 of 14 studies, consistent regions of activation were detected from tissue around the major vessels perfusing the visual cortex.

  12. Functional Tissue Pulsatility Imaging of the Brain during Visual Stimulation

    PubMed Central

    Kucewicz, John C.; Dunmire, Barbrina; Leotta, Daniel F.; Panagiotides, Heracles; Paun, Marla; Beach, Kirk W.

    2007-01-01

    Functional tissue pulsatility imaging (fTPI) is a new ultrasonic technique being developed to map brain function by measuring changes in tissue pulsatility due to changes in blood flow with neuronal activation. The technique is based in principle on plethysmography, an older, non-ultrasound technology for measuring expansion of a whole limb or body part due to perfusion. Perfused tissue expands by a fraction of a percent early in each cardiac cycle when arterial inflow exceeds venous outflow and relaxes later in the cardiac cycle when venous drainage dominates. Tissue pulsatility imaging (TPI) uses tissue Doppler signal processing methods to measure this pulsatile “plethysmographic” signal from hundreds or thousands of sample volumes in an ultrasound image plane. A feasibility study was conducted to determine if TPI could be used to detect regional brain activation during a visual contrast-reversing checkerboard block paradigm study. During a study, ultrasound data were collected transcranially from the occipital lobe as a subject viewed alternating blocks of a reversing checkerboard (stimulus condition) and a static, gray screen (control condition). Multivariate Analysis of Variance (MANOVA) was used to identify sample volumes with significantly different pulsatility waveforms during the control and stimulus blocks. In 7 out 14 studies, consistent regions of activation were detected from tissue around the major vessels perfusing the visual cortex. PMID:17346872

  13. Pulsatility of Parafoveal Capillary Leukocytes

    PubMed Central

    Martin, Joy A.; Roorda, Austin

    2009-01-01

    The use of adaptive optics (AO) in a confocal scanning laser ophthalmoscope (AOSLO) allows for long-term imaging of parafoveal capillary leukocyte movement and measurement of leukocyte velocity without contrast dyes. We applied the AOSLO to investigate the possible role of the cardiac cycle on capillary leukocyte velocity by directly measuring capillary leukocyte pulsatility. The parafoveal regions of 8 eight normal healthy subjects with clear ocular media were imaged with an AOSLO. All subjects were dilated and cyclopleged. The AOSLO field of view was either 1.4 × 1.5 degrees or 2.35 × 2.5 degrees, the imaging wavelength was 532 nm and the frame rate was 30 fps. A photoplethysmograph was used to record the subject’s pulse synchronously with each AOSLO video. Parafoveal capillary leukocyte velocities and pulsatility were determined for two or three capillaries per subject. Leukocyte velocity and pulsatility were determined for all eight subjects. The mean parafoveal capillary leukocyte velocity for all subjects was Vmean = 1.30 mm/sec (SD = +/− 0.40 mm/sec). There was a statistically significant difference between leukocyte velocities, Vmax and Vmin, over the pulse cycle for each subject (p<0.05). The mean pulsatility was Pmean= 0.45 (+/− 0.09). Parafoveal capillary leukocyte pulsatility can be directly and non-invasively measured without the use of contrast dyes using an AOSLO. A substantial amount of the variation found in leukocyte velocity is due to the pulsatility that is induced by the cardiac cycle. By controlling for the variation in leukocyte velocity caused by the cardiac cycle, we can better detect other changes in retinal leukocyte velocity induced by disease or pharmaceutical agents. PMID:18708051

  14. Computational fluid dynamics characterization of pulsatile flow in central and Sano shunts connected to the pulmonary arteries: importance of graft angulation on shear stress-induced, platelet-mediated thrombosis.

    PubMed

    Ascuitto, Robert; Ross-Ascuitto, Nancy; Guillot, Martin; Celestin, Carey

    2017-09-01

    Central (aorta) and Sano (right ventricle)-to-pulmonary artery (PA) shunts, palliative operations for infants with complex heart defects, can develop life-threatening thrombosis. We employed computational fluid dynamics (CFD) to study pulsatile flow in these shunts, with the goal to identify haemodynamic characteristics conducive to thrombus formation. CFD, using the finite volume method with cardiac catheterization data, and computer simulations, based on angiography, were employed to determine flow-velocity field, wall shear stress (WSS) profile and oscillatory shear index (OSI). At prominent angulation, in central shunts (4 and 3.5 mm), WSS reached 245 and 123 (Pascal-Pa), peak systole and 137 and 46 Pa, end diastole; and, in Sano shunts (5 and 6 mm), WSS attained 203 and 133 Pa, peak systole and 1.6 and 1.5 Pa, end diastole. Counter-rotating flow vortices augmented WSS. These high WSSs can promote platelet aggregation, leading to thrombus formation. The OSIs averaged 0.39, indicative of multidirectional shearing forces. Shunt burden was assessed by averaging WSS, over its luminal area and the cardiac cycle. For the central shunts, these WSSs were 73.0 and 67.2 Pa; whereas, for the Sano shunts, 34.9 and 19.6 Pa. For modified Blalock-Taussig shunts (4 and 3.5 mm), the averaged WSSs were significantly lower at 26.0 and 27.5 Pa, respectively. CFD modelling is an important tool to determine blood flow behaviour in shunts. Graft angulation presents a risk for shear stress-induced, platelet- mediated thrombosis, which is more likely to occur in elongated central than in Sano shunts.

  15. Index of consciousness and bispectral index values are interchangeable during normotension and hypotension but not during non pulsatile flow state during cardiac surgical procedures: a prospective study.

    PubMed

    Chakravarthy, Murali; Holla, Srinivasa; Jawali, Vivek

    2010-04-01

    analysis of value during cardiopulmonary bypass suggested non interchangeability (bias 3.87, precision 3.05, r value 0.3 and P value = 0.0067. The bispectral index and index of consciousness values may be interchangeable. The interchangeability is better appreciated during normotension and hypotension but not during non pulsatile state of cardiopulmonary bypass.

  16. Better and faster velocity pulsatility assessment in cerebral white matter perforating arteries with 7T quantitative flow MRI through improved slice profile, acquisition scheme, and postprocessing.

    PubMed

    Geurts, Lennart; Biessels, Geert Jan; Luijten, Peter; Zwanenburg, Jaco

    2017-07-11

    A previously published cardiac-gated 2D Qflow protocol at 7 T in cerebral perforating arteries was optimized to reduce velocity underestimation and improve temporal resolution. First, the signal-to-noise ratio (SNR) gain of the velocity measurement (SNRv ) was tested for two signal averages versus one. Second, the decrease in velocity underestimation with a tilted optimized nonsaturating excitation (TONE) pulse was tested. Third, the decrease in pulsatility index (PI) underestimation through improved temporal resolution was tested. Test-retest agreement was measured for the resulting acquisition in older volunteers (mean age 63 years), and the results were compared with the other volunteers (mean age 26 years). Using two signal averages increased SNRv by only 12% (P = 0.04), probably due to motion of the subvoxel-size arteries. The TONE decreased velocity underestimation, thereby increasing the mean velocity from 0.52 to 0.67 cm/s (P < 0.001). The PI increased substantially with increasing temporal resolution. The test-retest agreement showed good coefficients of repeatability of 0.18 cm/s for velocity and 0.14 for PI. The measured velocity was lower in the older group: 0.42 versus 0.51 cm/s (P = 0.05). The optimized sequence yields better velocity and PI estimates in small vessels, has twice as good test-retest agreement, and has a suitable scan time for use in patients. Magn Reson Med, 2017. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance

  17. Pulsatile fluidic pump demonstration and predictive model application

    SciTech Connect

    Morgan, J.G.; Holland, W.D.

    1986-04-01

    Pulsatile fluidic pumps were developed as a remotely controlled method of transferring or mixing feed solutions. A test in the Integrated Equipment Test facility demonstrated the performance of a critically safe geometry pump suitable for use in a 0.1-ton/d heavy metal (HM) fuel reprocessing plant. A predictive model was developed to calculate output flows under a wide range of external system conditions. Predictive and experimental flow rates are compared for both submerged and unsubmerged fluidic pump cases.

  18. The quantification of hemodynamic parameters downstream of a Gianturco Zenith stent wire using newtonian and non-newtonian analog fluids in a pulsatile flow environment.

    PubMed

    Walker, Andrew M; Johnston, Clifton R; Rival, David E

    2012-11-01

    Although deployed in the vasculature to expand vessel diameter and improve blood flow, protruding stent struts can create complex flow environments associated with flow separation and oscillating shear gradients. Given the association between magnitude and direction of wall shear stress (WSS) and endothelial phenotype expression, accurate representation of stent-induced flow patterns is critical if we are to predict sites susceptible to intimal hyperplasia. Despite the number of stents approved for clinical use, quantification on the alteration of hemodynamic flow parameters associated with the Gianturco Z-stent is limited in the literature. In using experimental and computational models to quantify strut-induced flow, the majority of past work has assumed blood or representative analogs to behave as Newtonian fluids. However, recent studies have challenged the validity of this assumption. We present here the experimental quantification of flow through a Gianturco Z-stent wire in representative Newtonian and non-Newtonian blood analog environments using particle image velocimetry (PIV). Fluid analogs were circulated through a closed flow loop at physiologically appropriate flow rates whereupon PIV snapshots were acquired downstream of the wire housed in an acrylic tube with a diameter characteristic of the carotid artery. Hemodynamic parameters including WSS, oscillatory shear index (OSI), and Reynolds shear stresses (RSS) were measured. Our findings show that the introduction of the stent wire altered downstream hemodynamic parameters through a reduction in WSS and increases in OSI and RSS from nonstented flow. The Newtonian analog solution of glycerol and water underestimated WSS while increasing the spatial coverage of flow reversal and oscillatory shear compared to a non-Newtonian fluid of glycerol, water, and xanthan gum. Peak RSS were increased with the Newtonian fluid, although peak values were similar upon a doubling of flow rate. The introduction of the

  19. Testing neonate-infant membrane oxygenators with the University of Texas neonatal pulsatile cardiopulmonary bypass system in vitro.

    PubMed

    Undar, A; Holland, M C; Howelton, R V; Benson, C K; Ybarra, J R; Miller, O L; Rossbach, M M; Runge, T M; Johnson, S B; Sako, E Y; Calhoon, J H

    1998-09-01

    Neurologic complications are already well documented after cardiopulmonary bypass (CPB) procedures in neonates and infants. Physiologic pulsatile flow CPB systems may be the alternative to the currently used steady-flow CPB circuits. In addition to the pulsatile pump, a membrane oxygenator should be chosen carefully, because only a few membrane oxygenators are suitable for physiologic pulsatile flow. We have tested four different types of neonate-infant membrane oxygenators for physiologic pulsatility with The University of Texas neonate-infant pulsatile CPB system in vitro. Evaluation criteria were based on mean ejection time, extracorporeal circuit (ECC) pressure, and upstroke of dp/dt. The results suggested that the Capiox 308 hollow-fibre membrane oxygenator produced the best physiologic pulsatile waveform according to the ejection time, ECC pressure, and the upstroke of dp/dt. The Minimax Plus and Masterflo Infant hollow-fibre membrane oxygenators also produced adequate pulsatile flow. Only the Variable Prime Cobe Membrane Lung (VPCML) Plus flat-sheet membrane oxygenator failed to reach the criteria for physiologic pulsatility. Depending on the oxygenator used, the lowest priming volume of the infant CPB circuit was 415 ml and the highest 520 ml.

  20. Optimal Branching Asymmetry of Hydrodynamic Pulsatile Trees

    NASA Astrophysics Data System (ADS)

    Florens, Magali; Sapoval, Bernard; Filoche, Marcel

    2011-04-01

    Most of the studies on optimal transport are done for steady state regime conditions. Yet, there exists numerous examples in living systems where supply tree networks have to deliver products in a limited time due to the pulsatile character of the flow, as it is the case for mammalian respiration. We report here that introducing a systematic branching asymmetry allows the tree to reduce the average delivery time of the products. It simultaneously increases its robustness against the inevitable variability of sizes related to morphogenesis. We then apply this approach to the human tracheobronchial tree. We show that in this case all extremities are supplied with fresh air, provided that the asymmetry is smaller than a critical threshold which happens to match the asymmetry measured in the human lung. This could indicate that the structure is tuned at the maximum asymmetry level that allows the lung to feed all terminal units with fresh air.

  1. Reduced Pulsatility Induces Periarteritis in Kidney: Role of the Local Renin-Angiotensin System

    PubMed Central

    Ootaki, Chiyo; Yamashita, Michifumi; Ootaki, Yoshio; Kamohara, Keiji; Weber, Stephan; Klatte, Ryan S.; Smith, William A.; Massiello, Alex L.; Emancipator, Steven N.; Golding, Leonard A.R.; Fukamachi, Kiyotaka

    2008-01-01

    Background The need for pulsatility in the circulation during long-term mechanical support has been a subject of debate. We compared histological changes in calf renal arteries subjected to various degrees of pulsatile circulation in vivo. We addressed the hypothesis that the local reninangiotensin system (RAS) may be implicated in these histological changes. Methods and Results Sixteen calves were implanted with devices giving differing degrees of pulsatile circulation: six had a continuous flow left ventricular assist device (LVAD); six had a continuous flow right ventricular assist device (RVAD); and four had a pulsatile total artificial heart (TAH). Six other calves were histological and immunohistochemical controls. In the LVAD group, the pulsatility index was significantly lower (0.28 ± 0.07 LVAD vs 0.56 ± 0.08 RVAD, vs 0.53 ± 0.10 TAH; p < 0.01), and we observed severe periarteritis in all cases in the LVAD group. The number of angiotensin II type 1 receptor (AT1R)-positive cells and angiotensin converting enzyme (ACE)-positive cells in periarterial areas was significantly higher in the LVAD group (AT1R: 350 ± 139 LVAD vs 8 ± 6 RVAD, vs 3 ± 2 TAH, vs 3 ± 2 in control; p < 0.001 and ACE: 325 ± 59 LVAD vs 6 ± 4 RVAD, vs 6 ± 5 TAH, vs 3 ± 1 control; p < 0.001). Conclusions The reduced pulsatility produced by a continuous flow LVAD implantation induced severe periarteritis in the kidney. The local RAS was upregulated in the inflammatory cells only in the continuous flow LVAD group. ULTAMINI-ABSTRACT We compared histological changes in calf renal arteries subjected to various degrees of pulsatile circulation; continuous flow left ventricular assist device (LVAD), continuous flow right ventricular assist device, pulsatile total artificial heart and control. We observed severe periarteritis, and upregulation of local renin angiotensin system only in the LVAD group. The necessity of maintaining pulsatility in the systemic circulation during long

  2. Electrocardiogram-synchronized rotational speed change mode in rotary pumps could improve pulsatility.

    PubMed

    Ando, Masahiko; Nishimura, Takashi; Takewa, Yoshiaki; Yamazaki, Kenji; Kyo, Shunei; Ono, Minoru; Tsukiya, Tomonori; Mizuno, Toshihide; Taenaka, Yoshiyuki; Tatsumi, Eisuke

    2011-10-01

    Continuous-flow left ventricular assist devices (LVADs) have greatly improved the prognosis of patients with end-stage heart failure, even if continuous flow is different from physiological flow in that it has less pulsatility. A novel pump controller of continuous-flow LVADs has been developed, which can change its rotational speed (RS) in synchronization with the native cardiac cycle, and we speculated that pulsatile mode, which increases RS just in the systolic phase, can create more pulsatility than the current system with constant RS does. The purpose of the present study is to evaluate the effect of this pulsatile mode of continuous-flow LVADs on pulsatility in in vivo settings. Experiments were performed on eight adult goats (61.7 ± 7.5 kg). A centrifugal pump, EVAHEART (Sun Medical Technology Research Corporation, Nagano, Japan), was installed by the apex drainage and the descending aortic perfusion. A pacing lead for the detection of ventricular electrocardiogram was sutured on the anterior wall of the right ventricle. In the present study, we compared pulse pressure or other parameters in the following three conditions, including Circuit-Clamp (i.e., no pump support), Continuous mode (constant RS), and Pulsatile mode (increase RS in systole). Assist rate was calculated by dividing pump flow (PF) by the sum of PF and ascending aortic flow (AoF). In continuous and pulsatile modes, these assist rates were adjusted around 80-90%. The following three parameters were used to evaluate pulsatility, including pulse pressure, dp/dt of aortic pressure (AoP), and energy equivalent pulse pressure (EEP = (∫PF*AoP dt)/(∫PF dt), mm Hg). The percent difference between EEP and mean AoP is used as an indicator of pulsatility, and normally it is around 10% of mean AoP in physiological pulse. Both pulse pressure and mean dp/dt max were decreased in continuous mode compared with clamp condition, while those were regained by pulsatile mode nearly to clamp condition (pulse

  3. Comparison of pumps and oxygenators with pulsatile and nonpulsatile modes in an infant cardiopulmonary bypass model.

    PubMed

    Haines, Nikkole M; Wang, Shigang; Kunselman, Allen; Myers, John L; Undar, Akif

    2009-11-01

    As the evidence mounts in favor of pulsatile perfusion during CPB, it is necessary to investigate the effect of circuit components on the quality of pulsatility delivered throughout the circuit. We compared two bloodpumps, the Jostra HL-20 heart-lung machine and the MEDOS DELTASTREAM DP1 Bloodpump, and two oxygenators, the Capiox Baby RX05 and the MEDOS HILITE 800LT, in terms of mean arterial pressure, energy equivalent pressure, surplus hemodynamic energy, total hemodynamic energy, and pressure drop over the oxygenators using a blood analog. The pumps and oxygenators were combined in unique circuits and tested in nonpulsatile and pulsatile modes, at two flow rates (500 and 800 mL/min), and three rotational speed differentials when using the MEDOS DELTASTREAM DP1 Bloodpump for 144 trials in total. The Jostra Roller pump produced some pulsatility in nonpulsatile mode and better pulsatility in pulsatile mode than the MEDOS DP1 Bloodpump at a rotational speed differential of 2500 rpm, but not at 3500 or 4500 rpm. The MEDOS DP1 Bloodpump produced almost no pulsatility in nonpulsatile mode. Pressure drops over the Capiox Baby RX05 were markedly higher, at 92.5 +/- 0.4 mm Hg with the MEDOS DP1 Bloodpump at 800 mL/min and 4500 rpm in pulsatile mode, than those of the MEDOS HILITE 800LT oxygenator, which was 67.0 +/- 0.1 mm Hg at the same settings. These results suggest that careful selection of each circuit component, based on the individual clinical case and component specifics, are necessary to achieve the best quality of pulsatility.

  4. Pulsatile operation of the BiVACOR TAH - Motor design, control and hemodynamics.

    PubMed

    Kleinheyer, Matthias; Timms, Daniel L; Greatrex, Nicholas A; Masuzawa, Toru; Frazier, O Howard; Cohn, William E

    2014-01-01

    Although there is limited consensus about the strict requirement to deliver pulsatile perfusion to the human circulatory system, speed modulation of rotary blood pumps is an approach that may capture the benefits of both positive displacement and continuous flow blood pumps. In the current stage of development of the BiVACOR Total Artificial Heart emphasis is placed on providing pulsatile outflow from the pump. Multiple pulsatile speed profiles have been applied in preliminary in-vivo operation in order to assess the capability of the TAH to recreate a physiologic pulse. This paper provides an overview about recent research towards pulsatile BiVACOR operation with special emphasis on motor and control requirements and developments.

  5. Pulsatility Produced by the Hemodialysis Roller Pump as Measured by Doppler Ultrasound.

    PubMed

    Fulker, David; Keshavarzi, Gholamreza; Simmons, Anne; Pugh, Debbie; Barber, Tracie

    2015-11-01

    Microbubbles have previously been detected in the hemodialysis extracorporeal circuit and can enter the blood vessel leading to potential complications. A potential source of these microbubbles is highly pulsatile flow resulting in cavitation. This study quantified the pulsatility produced by the roller pump throughout the extracorporeal circuit. A Sonosite S-series ultrasound probe (FUJIFILM Sonosite Inc., Tokyo, Japan) was used on a single patient during normal hemodialysis treatment. The Doppler waveform showed highly pulsatile flow throughout the circuit with the greatest pulse occurring after the pump itself. The velocity pulse after the pump ranged from 57.6 ± 1.74 cm/s to -72 ± 4.13 cm/s. Flow reversal occurred when contact between the forward roller and tubing ended. The amplitude of the pulse was reduced from 129.6 cm/s to 16.25 cm/s and 6.87 cm/s following the dialyzer and venous air trap. This resulted in almost nonpulsatile, continuous flow returning to the patient through the venous needle. These results indicate that the roller pump may be a source of microbubble formation from cavitation due to the highly pulsatile blood flow. The venous air trap was identified as the most effective mechanism in reducing the pulsatility. The inclusion of multiple rollers is also recommended to offer an effective solution in dampening the pulse produced by the pump.

  6. A simple physiologic pulsatile perfusion system for the study of intact vascular tissue.

    PubMed

    Conklin, B S; Surowiec, S M; Lin, P H; Chen, C

    2000-07-01

    Perfusion vascular culture models may provide a useful link between cell culture models and animal culture models by allowing a high level of control over important parameters while maintaining physiologic structure. The purpose of this study was to develop and test a new vascular culture system for pulsatile perfusion culture of intact vascular tissue. The system generates a pulsatile component of flow by means of a cam-driven syringe and a peristaltic pump and compliance chamber. Cams were designed, constructed and tested to simulate canine femoral and common carotid artery flows. The mean pressure was adjusted between 60 and 200 mmHg without significantly affecting flow rate, flow waveform, or the pressure waveform. Porcine common carotid artery segments were cultured in this pulsatile perfusion system. The viability of vascular segments was tested after various culture times with a functional assay that demonstrated both smooth muscle cell and endothelial cell response to vasomotor challenge.

  7. Tissue pulsatility imaging of cerebral vasoreactivity during hyperventilation.

    PubMed

    Kucewicz, John C; Dunmire, Barbrina; Giardino, Nicholas D; Leotta, Daniel F; Paun, Marla; Dager, Stephen R; Beach, Kirk W

    2008-08-01

    Tissue pulsatility imaging (TPI) is an ultrasonic technique that is being developed at the University of Washington to measure tissue displacement or strain as a result of blood flow over the cardiac and respiratory cycles. This technique is based in principle on plethysmography, an older nonultrasound technology for measuring expansion of a whole limb or body part due to perfusion. TPI adapts tissue Doppler signal processing methods to measure the "plethysmographic" signal from hundreds or thousands of sample volumes in an ultrasound image plane. This paper presents a feasibility study to determine if TPI can be used to assess cerebral vasoreactivity. Ultrasound data were collected transcranially through the temporal acoustic window from four subjects before, during and after voluntary hyperventilation. In each subject, decreases in tissue pulsatility during hyperventilation were observed that were statistically correlated with the subject's end-tidal CO2 measurements. (

  8. Comparison of the effects of bimatoprost and timolol on intraocular pressure and pulsatile ocular blood flow in patients with primary open-angle glaucoma: A prospective, open-label, randomized, two-arm, parallel-group study

    PubMed Central

    Vetrugno, Michele; Cardascia, Nicola; Cantatore, Francesco; Sborgia, Carlo

    2004-01-01

    Abstract Background: The current objective of antiglaucomatous therapy is to reduce intraocular pressure (IOP), and thus to preserve visual function. Many ophthalmologists believe this objective is best achieved by methods that improve ocular blood flow to the optic nerve head. Beta-blockers are effective ocular hypotensive agents, but they can reduce choroidal blood flow. Bimatoprost, a new prostamide analogue, has been shown to have a better IOP-lowering effect compared with the nonselective beta-adrenergic receptor blocker timolol maleate, but little is known about its effects on the vascular bed of the eye. Objective: The aim of this study was to compare the effects of bimatoprost and timolol on IOP and choroidal blood flow (as measured using pulsatile ocular blood flow [pOBF]) in patients with primary open-angle glaucoma (POAG). Methods: This prospective, open-label, randomized, 2-arm, parallel-group study was conducted at the Glaucoma Research Centre, Department of Ophthalmology, University Hospital of Bari, Bari, Italy. Patients with POAG having well-controlled IOP (<16 mm Hg) on monotherapy with timolol 0.5% ophthalmic solution (2 drops per affected eye BID) for ≥12 months but with a progressive decrease in pOBF during the same time period were randomly allocated to 1 of 2 treatment groups. One group continued monotherapy with timolol, 2 drops per affected eye BID. The other group was switched (without washout) to bimatoprost 0.3% ophthalmic solution (2 drops per affected eye QD [9 pm]). Treatment was given for 180 days. IOP and pOBF were assessed at the diagnostic visit (pre-timolol), baseline (day 0), and treatment days 15, 30, 60, 90, and 180. Primary adverse effects (AEs) (ie, conjunctival hyperemia, conjunctival papillae, stinging, burning, foreign body sensation, and pigmentation of periorbital skin) were monitored throughout the study. Results: Thirty-eight patients were enrolled (22 men, 16 women; mean [SD] age, 51.7 [4.8] years; 19 patients per

  9. Comparison of the effects of bimatoprost and timolol on intraocular pressure and pulsatile ocular blood flow in patients with primary open-angle glaucoma: A prospective, open-label, randomized, two-arm, parallel-group study.

    PubMed

    Vetrugno, Michele; Cardascia, Nicola; Cantatore, Francesco; Sborgia, Carlo

    2004-11-01

    Abstract. The current objective of antiglaucomatous therapy is to reduce intraocular pressure (IOP), and thus to preserve visual function. Many ophthalmologists believe this objective is best achieved by methods that improve ocular blood flow to the optic nerve head. Beta-blockers are effective ocular hypotensive agents, but they can reduce choroidal blood flow. Bimatoprost, a new prostamide analogue, has been shown to have a better IOP-lowering effect compared with the nonselective beta-adrenergic receptor blocker timolol maleate, but little is known about its effects on the vascular bed of the eye. The aim of this study was to compare the effects of bimatoprost and timolol on IOP and choroidal blood flow (as measured using pulsatile ocular blood flow [pOBF]) in patients with primary open-angle glaucoma (POAG). This prospective, open-label, randomized, 2-arm, parallel-group study was conducted at the Glaucoma Research Centre, Department of Ophthalmology, University Hospital of Bari, Bari, Italy. Patients with POAG having well-controlled IOP (<16 mm Hg) on monotherapy with timolol 0.5% ophthalmic solution (2 drops per affected eye BID) for ≥12 months but with a progressive decrease in pOBF during the same time period were randomly allocated to 1 of 2 treatment groups. One group continued monotherapy with timolol, 2 drops per affected eye BID. The other group was switched (without washout) to bimatoprost 0.3% ophthalmic solution (2 drops per affected eye QD [9 pm]). Treatment was given for 180 days. IOP and pOBF were assessed at the diagnostic visit (pre-timolol), baseline (day 0), and treatment days 15, 30, 60, 90, and 180. Primary adverse effects (AEs) (ie, conjunctival hyperemia, conjunctival papillae, stinging, burning, foreign body sensation, and pigmentation of periorbital skin) were monitored throughout the study. Thirty-eight patients were enrolled (22 men, 16 women; mean [SD] age, 51.7 [4.8] years; 19 patients per treatment group; 38 eligible eyes). At

  10. Changing pulsatility by delaying the rotational speed phasing of a rotary left ventricular assist device.

    PubMed

    Date, Kazuma; Nishimura, Takashi; Arakawa, Mamoru; Takewa, Yoshiaki; Kishimoto, Satoru; Umeki, Akihide; Ando, Masahiko; Mizuno, Toshihide; Tsukiya, Tomonori; Ono, Minoru; Tatsumi, Eisuke

    2017-03-01

    Continuous-flow left ventricular assist devices (LVADs) have improved the prognosis of end-stage heart failure. However, continuous-flow LVADs diminish pulsatility, which possibly result in bleeding, aortic insufficiency, and other adverse effects. We previously developed a novel control system for a continuous-flow LVAD (EVAHEART(®); Sun Medical), and demonstrated that we could create sufficient pulsatility by increasing its rotational speed (RS) in the systolic phase (Pulsatile Mode) in the normal heart model. Here, we aimed to evaluate differences between systolic assist with advanced and delayed loads by shifting the timing of increased RS. We implanted EVAHEART in six goats (55.3 ± 4.3 kg) with normal hearts. We reduced their heart rates to <60 bpm using propranolol and controlled the heart rates at 80 and 120 bpm using ventricular pacing. We shifted the timing of increasing RS from -60 to +60 ms in the systolic phase. We found significant increases in all the following parameters when assessments of delayed timing (+60 ms) were compared with assessments of advanced timing (-60 ms): pulse pressure, mean dP/dt max of aortic pressure, and energy-equivalent pulse pressure. During continuous-flow LVAD support, pulsatility can be controlled using a rotary pump. In particular, pulsatility can be shifted by delaying increased RS.

  11. A Pulsatile Cardiovascular Computer Model for Teaching Heart-Blood Vessel Interaction.

    ERIC Educational Resources Information Center

    Campbell, Kenneth; And Others

    1982-01-01

    Describes a model which gives realistic predictions of pulsatile pressure, flow, and volume events in the cardiovascular system. Includes computer oriented laboratory exercises for veterinary and graduate students; equations of the dynamic and algebraic models; and a flow chart for the cardiovascular teaching program. (JN)

  12. The pulsating brain: A review of experimental and clinical studies of intracranial pulsatility

    PubMed Central

    2011-01-01

    The maintenance of adequate blood flow to the brain is critical for normal brain function; cerebral blood flow, its regulation and the effect of alteration in this flow with disease have been studied extensively and are very well understood. This flow is not steady, however; the systolic increase in blood pressure over the cardiac cycle causes regular variations in blood flow into and throughout the brain that are synchronous with the heart beat. Because the brain is contained within the fixed skull, these pulsations in flow and pressure are in turn transferred into brain tissue and all of the fluids contained therein including cerebrospinal fluid. While intracranial pulsatility has not been a primary focus of the clinical community, considerable data have accrued over the last sixty years and new applications are emerging to this day. Investigators have found it a useful marker in certain diseases, particularly in hydrocephalus and traumatic brain injury where large changes in intracranial pressure and in the biomechanical properties of the brain can lead to significant changes in pressure and flow pulsatility. In this work, we review the history of intracranial pulsatility beginning with its discovery and early characterization, consider the specific technologies such as transcranial Doppler and phase contrast MRI used to assess various aspects of brain pulsations, and examine the experimental and clinical studies which have used pulsatility to better understand brain function in health and with disease. PMID:21349153

  13. Novel ECG-Synchronized Pulsatile ECLS System With Various Heart Rates and Cardiac Arrhythmias: An In Vitro Study.

    PubMed

    Wang, Shigang; Spencer, Shannon B; Kunselman, Allen R; Ündar, Akif

    2017-01-01

    The objective of this study is to evaluate electrocardiography (ECG)-synchronized pulsatile flow under varying heart rates and different atrial and ventricular arrhythmias in a simulated extracorporeal life support (ECLS) system. The ECLS circuit consisted of an i-cor diagonal pump and console, an iLA membrane ventilator, and an 18 Fr arterial cannula. The circuit was primed with lactated Ringer's solution and packed red blood cells (hematocrit 35%). An ECG simulator was used to trigger pulsatile flow and to generate selected cardiac rhythms. All trials were conducted at a flow rate of 2.5 L/min at room temperature for normal sinus rhythm at 45-180 bpm under non-pulsatile and pulsatile modes. Various atrial and ventricular arrhythmias were also tested. Real-time pressure and flow data were recorded using a custom-based data acquisition system. The energy equivalent pressure (EEP) generated by pulsatile flow was always higher than the mean pressure. No surplus hemodynamic energy (SHE) was recorded under non-pulsatile mode. Under pulsatile mode, SHE levels increased with increasing heart rates (45-120 bpm). SHE levels under a 1:2 assist ratio were higher than the 1:1 and 1:3 assist ratios with a heart rate of 180 bpm. A similar trend was recorded for total hemodynamic energy levels. There was no statistical difference between the two perfusion modes with regards to pressure drops across the ECLS circuit. The main resistance and energy loss came from the arterial cannula. The i-cor console successfully tracked electrocardiographic signals of 12 atrial and ventricular arrhythmias. Our results demonstrated that the i-cor pulsatile ECLS system can be synchronized with a normal heart rate or with various atrial/ventricular arrhythmias. Further in vivo studies are warranted to confirm our findings.

  14. Does Flexible Arterial Tubing Retain More Hemodynamic Energy During Pediatric Pulsatile Extracorporeal Life Support?

    PubMed

    Wang, Shigang; Kunselman, Allen R; Ündar, Akif

    2017-01-01

    The objective of this study was to evaluate the hemodynamic performance and energy transmission of flexible arterial tubing as the arterial line in a simulated pediatric pulsatile extracorporeal life support (ECLS) system. The ECLS circuit consisted of a Medos Deltastream DP3 diagonal pump head, Medos Hilite 2400 LT oxygenator, Biomedicus arterial/venous cannula (10 Fr/14 Fr), 3 feet of polyvinyl chloride (PVC) arterial tubing or latex rubber arterial tubing, primed with lactated Ringer's solution and packed red blood cells (hematocrit 40%). Trials were conducted at flow rates of 300 to 1200 mL/min (300 mL/min increments) under nonpulsatile and pulsatile modes at 36°C using either PVC arterial tubing (PVC group) or latex rubber tubing (Latex group). Real-time pressure and flow data were recorded using a custom-based data acquisition system. Mean pressures and energy equivalent pressures (EEP) were the same under nonpulsatile mode between the two groups. Under pulsatile mode, EEPs were significantly great than mean pressure, especially in the Latex group (P < 0.05). There was no difference between the two groups with regards to pressure drops across ECLS circuit, but pulsatile flow created more pressure drops than nonpulsatile flow (P < 0.05). Surplus hemodynamic energy (SHE) levels were always higher in the Latex group than in the PVC group at all sites. Although total hemodynamic energy (THE) losses were higher under pulsatile mode compared to nonpulsatile mode, more THE was delivered to the pseudopatient, particularly in the Latex group (P < 0.05). The results showed that the flexible arterial tubing retained more hemodynamic energy passing through it under pulsatile mode while mean pressures and pressure drops across the ECLS circuit were similar between PVC and latex rubber arterial tubing. Further studies are warranted to verify our findings.

  15. Placental pulsatility index: a new, more sensitive parameter for predicting adverse outcome in pregnancies suspected of fetal growth restriction.

    PubMed

    Gudmundsson, Saemundur; Flo, Kari; Ghosh, Gisela; Wilsgaard, Tom; Acharya, Ganesh

    2017-02-01

    The pulsatility indices of the umbilical and uterine arteries are used as the surrogate measures of utero-placental perfusion. Combining the two might simplify the evaluation of total placental vascular impedance, possibly improve prediction of adverse outcomes, and help identify pregnancies with suspected fetal growth restriction that need more intense surveillance. Umbilical and uterine blood flow velocities were recorded using pulsed-wave Doppler in a longitudinal study of 53 low-risk pregnancies (248 observations) during 20-40 weeks of gestation. Pulsatility indices was calculated for each of these vessels. A new placental pulsatility index was constructed as: (umbilical artery pulsatility index + mean of the left and right uterine artery pulsatility indices)/2, and mean +2 SD defined as abnormal. Gestational age-specific reference percentiles were calculated for the second half of pregnancy and related to values obtained from 340 pregnancies with suspected intra-uterine growth restriction to test its ability to predict adverse pregnancy outcome. The placental pulsatility index was closely associated with gestational age and decreased with advancing gestation in normal pregnancy. The placental pulsatility index had a higher sensitivity and comparable specificity in predicting adverse outcome in pregnancies suspected of intra-uterine fetal growth restriction when compared with conventional umbilical and uterine artery pulsatility indices. The new placental pulsatility index, reflecting placental vascular impedance on both the fetal and maternal side of placenta, improves prediction of adverse outcome in pregnancies suspected of intra-uterine fetal growth restriction. © 2017 Nordic Federation of Societies of Obstetrics and Gynecology.

  16. Arachnoid Cyst in the Middle Cranial Fossa Presenting with Pulsatile Exophthalmos: Case Report and Literature Review

    PubMed Central

    SAITO, Atsushi; KON, Hiroyuki; HARYU, Shinya; MINO, Masaki; SASAKI, Tatsuya; NISHIJIMA, Michiharu

    2014-01-01

    A 20-year-old woman suffered gradual progression of right pulsatile exophthalmos and slight headache. Computed tomography (CT) demonstrated outward and downward displacement of the right globe and an arachnoid cyst in the right middle cranial fossa associated with thinned and anterior protrusion of a bony orbit. Microscopic cystocisternotomy was performed and the cerebrospinal fluid (CSF) inside of the cyst communicated into the carotid cistern and cistern in the posterior cranial fossa. Pulsatile exophthalmos improved immediately after surgery. Arachnoid cyst in the middle cranial fossa presenting with exophthalmos is rare. Microscopic cystocisternotomy might successfully improve CSF flow and relieve exophthalmos. PMID:24305013

  17. Shear Stress, Energy Losses, and Costs: A Resolved Dilemma of Pulsatile Cardiac Assist Devices

    PubMed Central

    Liu, Jia; Dai, Gang; Carbognani, Daniel; Yang, Daya; Wu, Guifu; Wang, Qinmei; Chachques, Juan Carlos

    2014-01-01

    Cardiac assist devices (CAD) cause endothelial dysfunction with considerable morbidity. Employment of pulsatile CAD remains controversial due to inadequate perfusion curves and costs. Alternatively, we are proposing a new concept of pulsatile CAD based on a fundamental revision of the entire circulatory system in correspondence with the physiopathology and law of physics. It concerns a double lumen disposable tube device that could be adapted to conventional cardiopulmonary bypass (CPB) and/or CAD, for inducing a homogenous, downstream pulsatile perfusion mode with lower energy losses. In this study, the device's prototypes were tested in a simulated conventional pediatric CPB circuit for energy losses and as a left ventricular assist device (LVAD) in ischemic piglets model for endothelial shear stress (ESS) evaluations. In conclusion and according to the study results the pulsatile tube was successfully capable of transforming a conventional CPB and/or CAD steady flow into a pulsatile perfusion mode, with nearly physiologic pulse pressure and lower energy losses. This represents a cost-effective promising method with low mortality and morbidity, especially in fragile cardiac patients. PMID:24511541

  18. Nutrient Sensing Overrides Somatostatin and Growth Hormone-Releasing Hormone to Control Pulsatile Growth Hormone Release.

    PubMed

    Steyn, F J

    2015-07-01

    Pharmacological studies reveal that interactions between hypothalamic inhibitory somatostatin and stimulatory growth hormone-releasing hormone (GHRH) govern pulsatile GH release. However, in vivo analysis of somatostatin and GHRH release into the pituitary portal vasculature and peripheral GH output demonstrates that the withdrawal of somatostatin or the appearance of GHRH into pituitary portal blood does not reliably dictate GH release. Consequently, additional intermediates acting at the level of the hypothalamus and within the anterior pituitary gland are likely to contribute to the release of GH, entraining GH secretory patterns to meet physiological demand. The identification and validation of the actions of such intermediates is particularly important, given that the pattern of GH release defines several of the physiological actions of GH. This review highlights the actions of neuropeptide Y in regulating GH release. It is acknowledged that pulsatile GH release may not occur selectively in response to hypothalamic control of pituitary function. As such, interactions between somatotroph networks, the median eminence and pituitary microvasculature and blood flow, and the emerging role of tanycytes and pericytes as critical regulators of pulsatility are considered. It is argued that collective interactions between the hypothalamus, the median eminence and pituitary vasculature, and structural components within the pituitary gland dictate somatotroph function and thereby pulsatile GH release. These interactions may override hypothalamic somatostatin and GHRH-mediated GH release, and modify pulsatile GH release relative to the peripheral glucose supply, and thereby physiological demand.

  19. Oral pulsatile delivery: rationale and chronopharmaceutical formulations.

    PubMed

    Maroni, Alessandra; Zema, Lucia; Del Curto, Maria Dorly; Loreti, Giulia; Gazzaniga, Andrea

    2010-10-15

    Oral pulsatile/delayed delivery systems are designed to elicit programmable lag phases preceding a prompt and quantitative, repeated or prolonged release of drugs. Accordingly, they draw increasing interest because of the inherent suitability for accomplishing chronotherapeutic goals, which have recently been highlighted in connection with a number of widespread chronic diseases with typical night or early-morning recurrence of symptoms (e.g. bronchial asthma, cardiovascular disease, rheumatoid arthritis, early-morning awakening). In addition, time-based colonic release can be attained when pulsatile delivery systems are properly adapted to overcome unpredictable gastric emptying and provide delay phases that would approximately match the small intestinal transit time. Oral pulsatile delivery is pursued by means of a variety of release platforms, namely reservoir, capsular and osmotic devices. The aim of the present review is to outline the rationale and main formulation strategies behind delayed-release dosage forms intended for the pharmacological treatment of chronopathologies.

  20. A new imaging technique on strength and phase of pulsatile tissue-motion in brightness-mode ultrasonogram

    NASA Astrophysics Data System (ADS)

    Fukuzawa, Masayuki; Yamada, Masayoshi; Nakamori, Nobuyuki; Kitsunezuka, Yoshiki

    2007-03-01

    A new imaging technique has been developed for observing both strength and phase of pulsatile tissue-motion in a movie of brightness-mode ultrasonogram. The pulsatile tissue-motion is determined by evaluating the heartbeat-frequency component in Fourier transform of a series of pixel value as a function of time at each pixel in a movie of ultrasonogram (640x480pixels/frame, 8bit/pixel, 33ms/frame) taken by a conventional ultrasonograph apparatus (ATL HDI5000). In order to visualize both the strength and the phase of the pulsatile tissue-motion, we propose a pulsatile-phase image that is obtained by superimposition of color gradation proportional to the motion phase on the original ultrasonogram only at which the motion strength exceeds a proper threshold. The pulsatile-phase image obtained from a cranial ultrasonogram of normal neonate clearly reveals that the motion region gives good agreement with the anatomical shape and position of the middle cerebral artery and the corpus callosum. The motion phase is fluctuated with the shape of arteries revealing local obstruction of blood flow. The pulsatile-phase images in the neonates with asphyxia at birth reveal decreases of the motion region and increases of the phase fluctuation due to the weakness and local disturbance of blood flow, which is useful for pediatric diagnosis.

  1. Feasibility of Pump Speed Modulation for Restoring Vascular Pulsatility with Rotary Blood Pumps.

    PubMed

    Ising, Mickey S; Sobieski, Michael A; Slaughter, Mark S; Koenig, Steven C; Giridharan, Guruprasad A

    2015-01-01

    Continuous flow (CF) left ventricular assist devices (LVAD) diminish vascular pressure pulsatility, which may be associated with clinically reported adverse events including gastrointestinal bleeding, aortic valve insufficiency, and hemorrhagic stroke. Three candidate CF LVAD pump speed modulation algorithms designed to augment aortic pulsatility were evaluated in mock flow loop and ischemic heart failure (IHF) bovine models by quantifying hemodynamic performance as a function of mean pump speed, modulation amplitude, and timing. Asynchronous and synchronous copulsation (high revolutions per minute [RPM] during systole, low RPM during diastole) and counterpulsation (low RPM during systole, high RPM during diastole) algorithms were tested for defined modulation amplitudes (±300, ±500, ±800, and ±1,100 RPM) and frequencies (18.75, 37.5, and 60 cycles/minute) at low (2,900 RPM) and high (3,200 RPM) mean LVAD speeds. In the mock flow loop model, asynchronous, synchronous copulsation, and synchronous counterpulsation algorithms each increased pulse pressure (ΔP = 931%, 210%, and 98% and reduced left ventricular external work (LVEW = 20%, 22%, 16%). Similar improvements in vascular pulsatility (1,142%) and LVEW (40%) were observed in the IHF bovine model. Asynchronous modulation produces the largest vascular pulsatility with the advantage of not requiring sensor(s) for timing pump speed modulation, facilitating potential clinical implementation.

  2. Design and hydrodynamic evaluation of a novel pulsatile bioreactor for biologically active heart valves.

    PubMed

    Hildebrand, Daniel K; Wu, Zhongjun J; Mayer, John E; Sacks, Michael S

    2004-08-01

    Biologically active heart valves (tissue engineered and recellularized tissue-derived heart valves) have the potential to offer enhanced function when compared to current replacement value therapies since they can possibly remodel, and grow to meet the needs of the patient, and not require chronic medication. However, this technology is still in its infancy and many fundamental questions remain as to how these valves will function in vivo. It has been shown that exposing biologically active tissue constructs to pulsatile pressures and flows during in vitro culture produces enhanced extracellular matrix protein expression and cellularity, although the ideal hydrodynamic conditioning regime is as yet unknown. Moreover, in vitro organ-level studies of living heart valves aimed at studying the remodeling processes require environments that can accurately reproduce in vivo hemodynamics under sterile conditions. To this end, we have developed a system to study the effects of subjecting biologically active heart valves to highly controlled pulsatile pressure and flow waveforms under sterile conditions. The device fits inside a standard incubator and utilizes a computer-controlled closed loop feedback system to provide a high degree of control. The mean pressure, mean flow rate, driving frequency, and shape of the pulsatile pressure waveform can be changed automatically in order to simulate both physiologic and nonphysiologic hemodynamic conditions. Extensive testing and evaluation demonstrated the device's ability to subject a biologically active heart valve to highly controlled pulsatile waveforms that can be modulated during the course of sterile incubation.

  3. Algorithm for evaluation of pulsatile tinnitus.

    PubMed

    Mattox, Douglas E; Hudgins, Patricia

    2008-04-01

    Pulsatile tinnitus requires a careful physical examination and evaluation with selected imaging techniques to identify the origin of the symptoms. To evaluate the incidence of identifiable anomalies in patients with pulsatile tinnitus. This was a retrospective chart review undertaken in a tertiary care center. Patients seen in the outpatient otolaryngology clinic with the chief complaint of pulsatile tinnitus were evaluated by physical examination and imaging including CT angiography. The outcome measure was the incidence of identifiable abnormalities on imaging studies. Fifty-four patients were seen between January 2002 and June 2007 with the chief complaint of constant pulsatile tinnitus, excluding those with chemodectomas. On the basis of physical examination and imaging, 14 were considered arterial, 23 venous, and 15 were indeterminate in origin. Among patients with venous tinnitus, sigmoid sinus diverticulum was the most common finding. Among patients with arterial tinnitus, carotid atherosclerotic disease was the most common. One patient had erosion of the cochlea by the carotid artery. Non-vascular entities identified include superior semicircular canal dehiscence and benign intracranial hypertension.

  4. Impact of Distinct Oxygenators on Pulsatile Energy Indicators in an Adult Cardiopulmonary Bypass Model.

    PubMed

    Griep, Lonneke M; van Barneveld, Laurentius J M; Simons, Antoine P; Boer, Christa; Weerwind, Patrick W

    2017-02-01

    The quantification of pulse energy during cardiopulmonary bypass (CPB) post-oxygenator is required prior to the evaluation of the possible beneficial effects of pulsatile flow on patient outcome. We therefore, evaluated the impact of three distinctive oxygenators on the energy indicators energy equivalent pressure (EEP) and surplus hemodynamic energy (SHE) in an adult CPB model under both pulsatile and laminar flow conditions. The pre- and post-oxygenator pressure and flow were measured at room temperature using a 40% glycerin-water mixture at flow rates of 1, 2, 3, 4, 5, and 6 L/min. The pulse settings at frequencies of 40, 50, 60, 70, and 80 beats per minute were according to the internal algorithm of the Sorin CP5 centrifugal pump. The EEP is equal to the mean pressure, hence no SHE is present under laminar flow conditions. The Quadrox-i Adult oxygenator was associated with the highest preservation of pulsatile energy irrespective of flow rates. The low pressure drop-high compliant Quadrox-i Adult oxygenator shows the best SHE performance at flow rates of 5 and 6 L/min, while the intermediate pressure drop-low compliant Fusion oxygenator and the high pressure drop-low compliant Inspire 8F oxygenator behave optimally at flow rates of 5 L/min and up to 4 L/min, respectively. In conclusion, our findings contributed to studies focusing on SHE values post-oxygenator as well as post-cannula in clinical practice. In addition, our findings may give guidance to the clinical perfusionist for oxygenator selection prior to pulsatile CPB based on the calculated flow rate for the individual patient. © 2017 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.

  5. A meta-analysis of pulmonary function with pulsatile perfusion in cardiac surgery.

    PubMed

    Lim, Choon-Hak; Nam, Myung-Ji; Lee, Ji-Sung; Kim, Hyun-Jung; Kim, Ji-Yeon; Shin, Hye-Won; Lee, Hye-Won; Sun, Kyung

    2015-02-01

    The aim of this study was to determine whether pulsatile or nonpulsatile perfusion had a greater effect on pulmonary dysfunction in randomized controlled trials. MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials were used to identify available articles published before April 13, 2013. A meta-analysis was conducted on the effects of pulsatile perfusion on postoperative pulmonary function, intubation time, and the lengths of intensive care unit (ICU) and hospital stays. Eight studies involving 474 patients who received pulsatile perfusion and 496 patients who received nonpulsatile perfusion during cardiopulmonary bypass (CPB) were considered in the meta-analysis. Patients receiving pulsatile perfusion had a significantly greater PaO2 /FiO2 ratio 24 h and 48 h post-operation (P < 0.00001, both) and significantly lower chest radiograph scores at 24 h and 48 h post-operation (P < 0.00001 and P = 0.001, respectively) compared with patients receiving nonpulsatile perfusion. The incidence of noninvasive ventilation for acute respiratory insufficiency was significantly lower (P < 0.00001), and intubation time and ICU and hospital stays were shorter (P = 0.004, P < 0.00001, and P < 0.00001, respectively) in patients receiving pulsatile perfusion during CPB compared with patients receiving nonpulsatile perfusion. In conclusion, our meta-analysis suggests that the use of pulsatile flow during CPB results in better postoperative pulmonary function and shorter ICU and hospital stays. Copyright © 2014 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.

  6. [A review of drive system for pulsatile blood pump].

    PubMed

    Han, Yuan-jie; Yang, Ming

    2009-01-01

    Many varieties of pulsatile blood pumps exist in the fields of artificial hearts and ventricular assist devices. Effective sorts can be achieved with the differences in power source and transmission mechanism. Horizontal comparison across different pulsatile blood pumps, together with evolution of similar species is studied to find the commonness and evolution laws for pulsatile blood pumps. After a review of typical pulsatile blood pumps from the angle of power source and transmission mechanism, much analysis is focus on a pulsatile drive structure with flexible electro-hydraulic transmission, and importance of hydraulic transmission to improve the implantation property of pulsatile blood pumps is discussed. Finally new application of electro-hydraulic pulsatile blood pumps in the future, such as the application in Direct Mechanical Ventricular Assistant Device (DMVAD) is given.

  7. Pulsatile diastolic increase and systolic decrease in arterial blood pressure: their mechanism of production and physiological role.

    PubMed

    Mandoki, Juan José; Casa-Tirao, Beatriz; Molina-Guarneros, Juan Arcadio; Jiménez-Orozco, Fausto Alejandro; García-Mondragón, María Juana; Maldonado-Espinoza, Amelia

    2013-08-01

    The diastolic pulsatile increase in arterial blood pressure is shown to occur earlier in the aorta than in other arteries. It is thus not a reflection of the systolic pressure wave, as has been generally assumed, but an independent pressure wave produced by the sequential contraction of the arterial tree. Conversely, a systolic pulsatile decrease in the rate of blood pressure rise is also produced by an active relaxation of the arterial tree. Simultaneously with the pulsatile changes in arterial blood pressure, there are corresponding changes in arterial blood flow. All these cyclic changes are reflex responses to decreasing diastolic and increasing systolic baroreceptor firing rates, respectively. The two reflexes contribute, together with the known compliance of the large arteries and the great arteriolar blood flow resistance, to the steadiness of capillary blood flow throughout the systolic and the much longer-lasting diastolic phases of the cardiac cycle. Copyright © 2013 Elsevier Ltd. All rights reserved.

  8. Precise quantification of pulsatility is a necessity for direct comparisons of six different pediatric heart-lung machines in a neonatal CPB model.

    PubMed

    Undar, Akif; Eichstaedt, Harald C; Masai, Takafumi; Bigley, Joyce E; Kunselman, Allen R

    2005-01-01

    Generation of pulsatile flow depends on an energy gradient. Surplus hemodynamic energy (SHE) is the extra hemodynamic energy generated by a pulsatile device when the adequate pulsatility is achieved. The objective of this study was to precisely quantify and compare pressure-flow waveforms in terms of surplus hemodynamic energy levels of six different pediatric heart-lung machines in a neonatal piglet model during cardiopulmonary bypass (CPB) procedures with deep hypothermic circulatory arrest (DHCA). Thirty-nine piglets (average weight, 3 kg) were subjected to CPB with a hydraulically driven physiologic pulsatile pump (PPP; n=7), Jostra-HL 20 pulsatile roller pump (Jostra-PR; n=6), Stockert Sill pulsatile roller pump (SIII-PR; n=6), Stockert Sill mast-mounted pulsatile roller pump with a miniature roller head (Mast-PR; n=7), Stockert Sill mast-mounted nonpulsatile roller pump (Mast-NP; n=7), or Stockert CAPS nonpulsatile roller pump (CAPS-NP, n=7). Once CPB was begun, each animal underwent 20 minutes of hypothermia, 60 minutes of DHCA, 10 minutes of cold reperfusion, and 40 minutes of rewarming. The pump flow rate was maintained at 150 ml x kg(-1) x min(-1) and the mean arterial pressure (MAP) at 45 mm Hg. In the pulsatile experiments, the pump rate was kept at 150 bpm and the stroke volume at 1 ml/kg. The SHE (ergs/cm3) = 1,332 ([(integral fpdt) / (integral fdt)] - MAP) was calculated at each experimental stage. During normothermic CPB (15 minutes on pump), the physiologic pulsatile pump generated the highest surplus hemodynamic energy (8563 +/- 1918 ergs/cm3, p < 0.001) compared with all other pumps. The Jostra HL-20 and Stockert Sill pulsatile roller pumps also produced adequate surplus hemodynamic energy. Nonpulsatile roller pumps and the Stockert Sill mast-mounted pulsatile roller pump did not generate any extra hemodynamic energy. During hypothermic CPB and after DHCA and rewarming, the results were extremely similar to those seen during normothermic CPB. The

  9. Non-dimensional physics of pulsatile cardiovascular networks and energy efficiency.

    PubMed

    Yigit, Berk; Pekkan, Kerem

    2016-01-01

    In Nature, there exist a variety of cardiovascular circulation networks in which the energetic ventricular load has both steady and pulsatile components. Steady load is related to the mean cardiac output (CO) and the haemodynamic resistance of the peripheral vascular system. On the other hand, the pulsatile load is determined by the simultaneous pressure and flow waveforms at the ventricular outlet, which in turn are governed through arterial wave dynamics (transmission) and pulse decay characteristics (windkessel effect). Both the steady and pulsatile contributions of the haemodynamic power load are critical for characterizing/comparing disease states and for predicting the performance of cardiovascular devices. However, haemodynamic performance parameters vary significantly from subject to subject because of body size, heart rate and subject-specific CO. Therefore, a 'normalized' energy dissipation index, as a function of the 'non-dimensional' physical parameters that govern the circulation networks, is needed for comparative/integrative biological studies and clinical decision-making. In this paper, a complete network-independent non-dimensional formulation that incorporates pulsatile flow regimes is developed. Mechanical design variables of cardiovascular flow systems are identified and the Buckingham Pi theorem is formally applied to obtain the corresponding non-dimensional scaling parameter sets. Two scaling approaches are considered to address both the lumped parameter networks and the distributed circulation components. The validity of these non-dimensional number sets is tested extensively through the existing empirical allometric scaling laws of circulation systems. Additional validation studies are performed using a parametric numerical arterial model that represents the transmission and windkessel characteristics, which are adjusted to represent different body sizes and non-dimensional haemodynamic states. Simulations demonstrate that the proposed non

  10. The type of aortic cannula and membrane oxygenator affect the pulsatile waveform morphology produced by a neonate-infant cardiopulmonary bypass system in vivo.

    PubMed

    Undar, A; Lodge, A J; Daggett, C W; Runge, T M; Ungerleider, R M; Calhoon, J H

    1998-08-01

    Although the debate still continues over the effectiveness of pulsatile versus nonpulsatile perfusion, it has been clearly proven that there are several significant physiological benefits of pulsatile perfusion during cardiopulmonary bypass (CPB) compared to nonpulsatile perfusion. However, the components of the extracorporeal circuit have not been fully investigated regarding the quality of the pulsatility. In addition, most of these results have been gathered from adult patients, not from neonates and infants. We have designed and tested a neonate-infant pulsatile CPB system using 2 different types of 10 Fr aortic cannulas and membrane oxygenators in 3 kg piglets to evaluate the effects of these components on the pulsatile waveform produced by the system. In terms of the methods, Group 1 (Capiox 308 hollow-fiber membrane oxygenator and DLP aortic cannula with a very short 10 Fr tip [n = 2]) was subjected to a 2 h period of normothermic pulsatile CPB with a pump flow rate of 150 ml/kg/min. Data were obtained at 5, 30, 60, 90, and 120 min of CPB. In Group 2 (Capiox 308 hollow-fiber membrane oxygenator and Elecath aortic cannula with a very long 10 Fr tip [n = 7]) and Group 3 (cobe VPCML Plus flat sheet membrane oxygenator and DLP aortic cannula with a very short 10 Fr tip [n = 7]), the subjects' nasopharyngeal temperatures were reduced to 18 degrees C followed by 1 h of deep hypothermic circulatory arrest (DHCA) and then 40 min rewarming. Data were obtained during normothermic CPB in the pre- and post-DHCA periods. The criteria of pulsatility evaluations were based upon pulse pressure (between 30 and 40 mm Hg), aortic dp/dt (greater than 1000 mm Hg/s), and ejection time (less than 250 ms). The results showed that Group 1 produced flow which was significantly more pulsatile than that of the other 2 groups. Although the same oxygenator was used for Group 2, the quality of the pulsatile flow decreased when using a different aortic cannula. Group 3 did not meet any of

  11. Pulsatile Lipid Vesicles under Osmotic Stress

    NASA Astrophysics Data System (ADS)

    Chabanon, Morgan; Ho, James C. S.; Liedberg, Bo; Parikh, Atul N.; Rangamani, Padmini

    2017-04-01

    The response of lipid bilayers to osmotic stress is an important part of cellular function. Previously, in [Oglecka et al. 2014], we reported that cell-sized giant unilamellar vesicles (GUVs) exposed to hypotonic media, respond to the osmotic assault by undergoing a cyclical sequence of swelling and bursting events, coupled to the membrane's compositional degrees of freedom. Here, we seek to deepen our quantitative understanding of the essential pulsatile behavior of GUVs under hypotonic conditions, by advancing a comprehensive theoretical model for vesicle dynamics. The model quantitatively captures our experimentally measured swell-burst parameters for single-component GUVs, and reveals that thermal fluctuations enable rate dependent pore nucleation, driving the dynamics of the swell-burst cycles. We further identify new scaling relationships between the pulsatile dynamics and GUV properties. Our findings provide a fundamental framework that has the potential to guide future investigations on the non-equilibrium dynamics of vesicles under osmotic stress.

  12. Strategies for temporary mechanical support: contemporary experience with pulsatile and non-pulsatile support systems.

    PubMed

    Moazami, Nader; Moon, Marc R; Pasque, Michael K; Lawton, Jennifer S; Bailey, Marci S; Damiano, Ralph J

    2005-01-01

    Despite advances in mechanical circulatory support, cardiogenic shock continues to have a high mortality. We reviewed our experience with pulsatile versus non-pulsatile temporary mechanical support at our institution to determine optimal strategy for survival. From January 2001 to December 2003, mechanical support for cardiogenic shock was instituted in 38 patients. Non-pulsatile devices (NP group) were used in 22 patients and pulsatile devices (P group) in 16 patients. Indications for the NP group were post-cardiotomy shock (PCS) in 17, myocardial infarction in 2, and isolated post-cardiotomy right ventricular failure in 3 patients. In the P group, 9 had the device placed for PCS, 3 for viral myocarditis, 1 after myocardial infarction, and 3 for right ventricular (RV) failure. Overall, bleeding, limb ischemia, and multi-system organ failure were higher in NP group with 5 weaned and 3 surviving to discharge (14%). In the P group, survivors included 7 weaned and 3 transplanted patients (63%). With the exception of isolated RV failure, we obtained a dismal survival result with ECMO/centrifugal circuits for treatment of cardiogenic shock. For refractory pump failure, improved survival was achieved by using intermediate-term pulsatile devices with early transition to a chronic device and/or heart transplantation.

  13. Evolution of vortical structures in a curved artery model with non-Newtonian blood-analog fluid under pulsatile inflow conditions

    NASA Astrophysics Data System (ADS)

    Najjari, Mohammad Reza; Plesniak, Michael W.

    2016-06-01

    Steady flow and physiological pulsatile flow in a rigid 180° curved tube are investigated using particle image velocimetry. A non-Newtonian blood-analog fluid is used, and in-plane primary and secondary velocity fields are measured. A vortex detection scheme ( d 2-method) is applied to distinguish vortical structures. In the pulsatile flow case, four different vortex types are observed in secondary flow: deformed-Dean, Dean, Wall and Lyne vortices. Investigation of secondary flow in multiple cross sections suggests the existence of vortex tubes. These structures split and merge over time during the deceleration phase and in space as flow progresses along the 180° curved tube. The primary velocity data for steady flow conditions reveal additional vortices rotating in a direction opposite to Dean vortices—similar to structures observed in pulsatile flow—if the Dean number is sufficiently high.

  14. A hemodynamic evaluation of the Levitronix Pedivas centrifugal pump and Jostra Hl-20 roller pump under pulsatile and nonpulsatile perfusion in an infant CPB model.

    PubMed

    Ressler, Noel; Rider, Alan R; Kunselman, Allen R; Richardson, J Scott; Dasse, Kurt A; Wang, Shigang; Undar, Akif

    2009-01-01

    The hemodynamic comparison of the Jostra HL-20 and the Levitronix PediVAS blood pumps is the focus this study, where pressure-flow waveforms and hemodynamic energy values are analyzed in the confines of a pediatric cardiopulmonary bypass circuit.The pseudo pediatric patient was perfused with flow rates between 500 and 900 ml/min (100 ml/min increments) under pulsatile and nonpulsatile mode. The Levitronix continuous flow pump utilized a customized controller to engage in pulsatile perfusion with equivalent pulse settings to the Jostra HL-20 roller pump. Hemodynamic measurements and waveforms were recorded at the precannula location, while the mean arterial pressure was maintained at 40 mm Hg for each test. Glycerin water was used as the blood analog circuit perfusate. At each flow rate 24 trials were conducted yielding a total of 120 experiments (n=60 pulsatile and n=60 nonpulsatile).Under nonpulsatile perfusion the Jostra roller pump produced small values for surplus hemodynamic energy (SHE) due to its inherent pulsatility, while the Levitronix produced values of essentially zero for SHE. When switching to pulsatile perfusion, the SHE levels for both the Jostra and Levitronix pump made considerable increases. In comparing the two pumps under pulsatile perfusion, the Levitronix PediVAS produced significantly more surplus and total hemodynamic energy than did the Jostra roller pump each pump flow rate.The study suggests that the Levitronix PediVAS centrifugal pump has the capability of achieving quality pulsatile waveforms and delivering more SHE to the pseudo patient than the Jostra HL-20 roller pump. Further studies are warranted to investigate the Levitronix under bovine blood studies and with various pulsatile settings.

  15. Hemodynamic controller for left ventricular assist device based on pulsatility ratio.

    PubMed

    Choi, Seongjin; Boston, J Robert; Antaki, James F

    2007-02-01

    Hemodynamic control of left ventricular assist devices (LVADs) is generally a complicated problem due to diverse operating environments and the variability of the patients: both the changes in the circulatory and metabolic parameters as well as disturbances that require adjustment to the operating point. This challenge is especially acute with control of turbodynamic blood pumps. This article presents a pulsatility ratio controller for LVAD that provides a proper perfusion according to the physiological demands of the patient, while avoiding adverse conditions. It utilizes the pulsatility ratio of the flow through the pump and pressure difference across the pump as a control index and adjusts the pump speed according to the reference pulsatility ratio under the different operating conditions. The simulation studies were performed to evaluate the controller in consideration of the sensitivity to afterload and preload, influence of the contractility, and effect of suction sensitivity. The controller successfully adjusts the pump speed according to the reference pulsatility ratio, and supports the natural heart under diverse pump operating conditions. The resulting safe pump operations demonstrate the solid performance of the controller in terms of sensitivity to afterload and preload, influence of the contractility, and effect of suction sensitivity.

  16. Flap raising on pulsatile perfused cadaveric tissue: a novel method for surgical teaching and exercise.

    PubMed

    Wolff, Klaus-Dietrich; Fichter, Andreas; Braun, Christian; Bauer, Florian; Humbs, Martin

    2014-10-01

    Exercising flap raising procedures on cadavers is considered a prerequisite to prepare for clinical practise. To improve teaching and create conditions as realistic as possible, a perfusion device was developed providing pulsatile flow through the vessels of different donor sites. A plastic bag filled with red stained tab water was placed into a pump, which was driven by an electric motor. The bag was set under rhythmic compression with variable frequency and pressure. The pedicles of the radial forearm, anterolateral thigh, rectus abdominis, fibular and iliac crest flap were cannulated at the origin from their source arteries. Flap raising was performed under pulsatile perfusion in 15 fresh bodies and subsequently in 6 Thiel-embalmed cadavers during a flap raising course. We regularly observed staining of the skin and skin bleeding in fresh bodies and less reliable in embalmed cadavers. All flap pedicles showed pulsatile movements, and the radial pulse became palpable. Most perforators of the anterolateral thigh and osteocutaneous fibular flap could be identified by their pulse. Bleeding from bony tissue and venous return was seldom observed. We conclude that pulsatile perfusion of cadaveric tissue creates more realistic conditions for flap raising and improves teaching for beginners and advanced surgeons.

  17. Development and validation of a computational fluid dynamics methodology for simulation of pulsatile left ventricular assist devices.

    PubMed

    Medvitz, Richard B; Kreider, James W; Manning, Keefe B; Fontaine, Arnold A; Deutsch, Steven; Paterson, Eric G

    2007-01-01

    An unsteady computational fluid dynamic methodology was developed so that design analyses could be undertaken for devices such as the 50cc Penn State positive-displacement left ventricular assist device (LVAD). The piston motion observed in vitro was modeled, yielding the physiologic flow waveform observed during pulsatile experiments. Valve closure was modeled numerically by locally increasing fluid viscosity during the closed phase. Computational geometry contained Bjork-Shiley Monostrut mechanical heart valves in mitral and aortic positions. Cases for computational analysis included LVAD operation under steady-flow and pulsatile-flow conditions. Computations were validated by comparing simulation results with previously obtained in vitro particle image velocimetry (PIV) measurements. The steady portion of the analysis studied effects of mitral valve orientation, comparing the computational results with in vitro data obtained from mock circulatory loop experiments. The velocity field showed good qualitative agreement with the in vitro PIV data. The pulsatile flow simulations modeled the unsteady flow phenomena associated with a positive-displacement LVAD operating through several beat cycles. Flow velocity gradients allowed computation of the scalar wall strain rate, an important factor for determining hemodynamics of the device. Velocity magnitude contours compared well with PIV data throughout the cycle. Computational wall shear rates over the pulsatile cycle were found to be in the same range as wall shear rates observed in vitro.

  18. Experimental Fluid Mechanics of Pulsatile Artificial Blood Pumps

    NASA Astrophysics Data System (ADS)

    Deutsch, Steven; Tarbell, John M.; Manning, Keefe B.; Rosenberg, Gerson; Fontaine, Arnold A.

    2006-01-01

    The fluid mechanics of artificial blood pumps has been studied since the early 1970s in an attempt to understand and mitigate hemolysis and thrombus formation by the device. Pulsatile pumps are characterized by inlet jets that set up a rotational "washing" pattern during filling. Strong regurgitant jets through the closed artificial heart valves have Reynolds stresses on the order of 10,000 dynes/cm2 and are the most likely cause of red blood cell damage and platelet activation. Although the flow in the pump chamber appears benign, low wall shear stresses throughout the pump cycle can lead to thrombus formation at the wall of the smaller pumps (10 50 cc). The local fluid mechanics is critical. There is a need to rapidly measure or calculate the wall shear stress throughout the device so that the results may be easily incorporated into the design process.

  19. Brain Tissue Pulsatility is Increased in Midlife Depression: a Comparative Study Using Ultrasound Tissue Pulsatility Imaging.

    PubMed

    Desmidt, Thomas; Brizard, Bruno; Dujardin, Paul-Armand; Ternifi, Redouane; Réméniéras, Jean-Pierre; Patat, Frédéric; Andersson, Frédéric; Cottier, Jean-Philippe; Vierron, Emilie; Gissot, Valérie; Kim, Kang; Aizenstein, Howard; El-Hage, Wissam; Camus, Vincent

    2017-06-06

    Cerebrovascular disease (CVD) is consistently associated with late-life depression but poorly documented in midlife depression. It can be hypothesized that the relatively low sensitivity of conventional neuroimaging techniques does not allow the detection of subtle CVD in midlife depression. We used tissue pulsatility imaging (TPI), a novel ultrasound (US) neuroimaging technique that has demonstrated good sensitivity to detect changes in the pulsatility of small brain volumes, to identify early and subtle changes in brain vascular function in midlife depression. We compared the maximum and mean brain tissue pulsatility (MaxBTP and MeanBTP), as identified by TPI, between three groups of middle-aged females matched for age: patients with depression (n=25), patients with remitted depression (n=24) and community controls (n=25). MRI arterial spin labeling, white matter hyperintensities (WMHs) and transcranial doppler (TCD) were used as control conventional markers for CVD. We found no difference in the MRI and TCD measures among the three groups. In contrast, depressive patients showed an increased BTP related to the mean global brain pulsatility (MeanBTP) and no change related to large vessels (MaxBTP) in comparison with the remitted and control groups. US neuroimaging is a highly accurate method to detect brain pulsatility changes related to cerebrovascular functioning, and TPI identified an increased BTP in midlife depressed patients, suggesting early and subtle vascular impairments in this population at risk for CVD such as stroke or WMHs. Because high pulsatility could represent prodromal cerebrovascular changes that damage the brain over time, this paper provides a potential target for blocking the progression of CVD.Neuropsychopharmacology advance online publication, 26 July 2017; doi:10.1038/npp.2017.113.

  20. Power consumption of rotary blood pumps: pulsatile versus constant-speed mode.

    PubMed

    Pirbodaghi, Tohid; Cotter, Chris; Bourque, Kevin

    2014-12-01

    We investigated the power consumption of a HeartMate III rotary blood pump based on in vitro experiments performed in a cardiovascular simulator. To create artificial-pulse mode, we modulated the pump speed by decreasing the mean speed by 2000 rpm for 200 ms and then increasing speed by 4000 rpm (mean speeds plus 2000 rpm) for another 200 ms, creating a square waveform shape. The HeartMate III was connected to a cardiovascular simulator consisting of a hydraulic pump system to simulate left ventricle pumping action, arterial and venous compliance chambers, and an adjustable valve for peripheral resistance to facilitate the desired aortic pressure. The simulator operated based on Suga's elastance model to mimic the Starling response of the heart, thereby reproducing physiological blood flow and pressure conditions. We measured the instantaneous total electrical current and voltage of the pump to evaluate its power consumption. The aim was to answer these fundamental questions: (i) How does pump speed modulation affect pump power consumption? (ii) How does the power consumption vary in relation to external pulsatile flow? The results indicate that speed modulation and external pulsatile flow both moderately increase the power consumption. Increasing the pump speed reduces the impact of external pulsatile flow.

  1. Numerical simulation of global hydro-dynamics in a pulsatile bioreactor for cardiovascular tissue engineering.

    PubMed

    Shi, Yubing

    2008-01-01

    Previous numerical simulations of the hydro-dynamic response in the various bioreactor designs were mostly concentrated on the local flow field analysis using computational fluid dynamics, which cannot provide the global hydro-dynamics information to assist the bioreactor design. In this research, a mathematical model is developed to simulate the global hydro-dynamic changes in a pulsatile bioreactor design by considering the flow resistance, the elasticity of the vessel and the inertial effect of the media fluid in different parts of the system. The developed model is used to study the system dynamic response in a typical pulsatile bioreactor design for the culturing of cardiovascular tissues. Simulation results reveal the detailed pressure and flow-rate changes in the different positions of the bioreactor, which are very useful for the evaluation of hydro-dynamic performance in the bioreactor designed. Typical pressure and flow-rate changes simulated agree well with the published experimental data, thus validates the mathematical model developed. The proposed mathematical model can be used for design optimization of other pulsatile bioreactors that work under different experimental conditions and have different system configurations.

  2. Pulsatile ECMO in neonates and infants: first European clinical experience with a new device.

    PubMed

    Agati, Salvatore; Mignosa, Carmelo; Ciccarello, Giuseppe; Dario, Salvo; Undar, Akif

    2005-01-01

    This study presents the first European clinical experience with the Medos DeltaStream DP1, a new pulsatile flow pump, in neonates and infants. Between January 2002 and December 2004, 420 patients at our institution underwent congenital heart surgery on cardiopulmonary bypass. During this period, 10 patients required extracorporeal membrane oxygenation (ECMO) support for acute postcardiotomy heart failure. Seven patients (median age 7 days, range 1-70 days), were supported by a nonpulsatile Biomedicus centrifugal pump, whereas three patients (aged 1 month, 1 year, and 12 years) were supported by a pulsatile Medos DP1. The DP1 is an extracorporeal rotary blood pump. The pump features a diagonal-flow impeller, and can be used for both continuous and pulsatile output. Special characteristics include a small priming volume of approximately 30 ml and a high pumping capacity. A temperature sensor and speed sensors are integrated in the pump. The pump has a delivery rate of up to 8 l/min and a speed range of 100-10,000 rpm. Overall mortality was 40% (4 of 10 patients), and all four deaths were in the nonpulsatile Biomedicus group. In the nonpulsatile group, the median support duration was 95 hours with a range of 48-140 hours. Two patients assisted with the pulsatile pump system were successfully weaned after 36 and 53 hours, respectively; the 12-year-old patient was successfully transplanted on the eighth postimplant day and discharged from the hospital on the 32nd posttransplant day. Although this preliminary experience doesn't allow for statistical analysis, clinically it was possible to observe a better performance in pulsatile flow recipients with faster lactate recovery, reduced need for inotropic support, reduced assistance duration in bridge-to-recovery settings, and smoother intensive care management. ECMO for postcardiotomy heart failure in neonates and infants still carries high mortality and morbidity rates. Pulsatile flow with the Medos DeltaStream DP1 pump

  3. White matter hyperintensities in migraine: Clinical significance and central pulsatile hemodynamic correlates.

    PubMed

    Cheng, Chun-Yu; Cheng, Hao-Min; Chen, Shih-Pin; Chung, Chih-Ping; Lin, Yung-Yang; Hu, Han-Hwa; Chen, Chen-Huan; Wang, Shuu-Jiun

    2017-01-01

    Background The role of central pulsatile hemodynamics in the pathogenesis of white matter hyperintensities in migraine patients has not been clarified. Methods Sixty patients with migraine (20-50 years old; women, 68%) without overt vascular risk factors and 30 demographically-matched healthy controls were recruited prospectively. Cerebral white matter hyperintensities volume was determined by T1-weighted magnetic resonance imaging with CUBE-fluid-attenuated-inversion-recovery sequences. Central systolic blood pressure, carotid-femoral pulse wave velocity, and carotid augmentation index were measured by applanation tonometry. Carotid pulsatility index was derived from Doppler ultrasound carotid artery flow analysis. Results Compared to the controls, the migraine patients had higher white matter hyperintensities frequency (odds ratio, 2.75; p = 0.04) and greater mean white matter hyperintensities volume (0.174 vs. 0.049, cm(3), p = 0.04). Multivariable regression analysis showed that white matter hyperintensities volume in migraine patients was positively associated with central systolic blood pressure ( p = 0.04) and carotid-femoral pulse wave velocity ( p < 0.001), but negatively associated with carotid pulsatility index ( p = 0.04) after controlling for potential confounding factors. The interaction effects observed indicated that the influence of carotid-femoral pulse wave velocity ( p = 0.004) and central systolic blood pressure ( p = 0.03) on white matter hyperintensities formation was greater for the lower-carotid pulsatility index subgroup of migraine patients. White matter hyperintensities volume in migraine patients increased with decreasing carotid pulsatility index and with increasing central systolic blood pressure or carotid-femoral pulse wave velocity. Conclusions White matter hyperintensities are more common in patients with migraine than in healthy controls. Increased aortic stiffness or central systolic blood pressure in

  4. Pulsatile cerebrospinal fluid dynamics in the human brain.

    PubMed

    Linninger, Andreas A; Tsakiris, Cristian; Zhu, David C; Xenos, Michalis; Roycewicz, Peter; Danziger, Zachary; Penn, Richard

    2005-04-01

    Disturbances of the cerebrospinal fluid (CSF) flow in the brain can lead to hydrocephalus, a condition affecting thousands of people annually in the US. Considerable controversy exists about fluid and pressure dynamics, and about how the brain responds to changes in flow patterns and compression in hydrocephalus. This paper presents a new model based on the first principles of fluid mechanics. This model of fluid-structure interactions predicts flows and pressures throughout the brain's ventricular pathways consistent with both animal intracranial pressure (ICP) measurements and human CINE phase-contrast magnetic resonance imaging data. The computations provide approximations of the tissue deformations of the brain parenchyma. The model also quantifies the pulsatile CSF motion including flow reversal in the aqueduct as well as the changes in ICPs due to brain tissue compression. It does not require the existence of large transmural pressure differences as the force for ventricular expansion. Finally, the new model gives an explanation of communicating hydrocephalus and the phenomenon of asymmetric hydrocephalus.

  5. Physiologic benefits of pulsatile perfusion during mechanical circulatory support for the treatment of acute and chronic heart failure in adults.

    PubMed

    Guan, Yulong; Karkhanis, Tushar; Wang, Shigang; Rider, Alan; Koenig, Steven C; Slaughter, Mark S; El Banayosy, Aly; Undar, Akif

    2010-07-01

    A growing population experiencing heart failure (100,000 patients/year), combined with a shortage of donor organs (less than 2200 hearts/year), has led to increased and expanded use of mechanical circulatory support (MCS) devices. MCS devices have successfully improved clinical outcomes, which are comparable with heart transplantation and result in better 1-year survival than optimal medical management therapies. The quality of perfusion provided during MCS therapy may play an important role in patient outcomes. Despite demonstrated physiologic benefits of pulsatile perfusion, continued use or development of pulsatile MCS devices has been widely abandoned in favor of continuous flow pumps owing to the large size and adverse risks events in the former class, which pose issues of thrombogenic surfaces, percutaneous lead infection, and durability. Next-generation MCS device development should ideally implement designs that offer the benefits of rotary pump technology while providing the physiologic benefits of pulsatile end-organ perfusion.

  6. Pulsatile Varicose Veins Secondary to Severe Tricuspid Regurgitation: Report of a Case Successfully Managed by Endovenous Laser Treatment.

    PubMed

    Chihara, Shingo; Sawada, Kentaro; Tomoeda, Hiroshi; Aoyagi, Shigeaki

    2017-02-01

    We report a case of pulsatile varicose veins successfully managed by endovenous laser treatment (EVLT) of the great saphenous vein (GSV). A 77-year-old woman taking an anticoagulant was transferred to our hospital for pulsatile varicose veins complicated with repeated venous bleeding from an ulcer of her left lower leg. Doppler echocardiography showed severe tricuspid regurgitation, and duplex ultrasonography revealed an arterial-like pulsating flow in the saphenofemoral junction and along the GSV, but an arteriovenous fistula, obstruction of the deep veins, and the distal incompetent perforators were not detected. Because of a significant bleeding risk due to elevated venous pressure and anticoagulant therapy, EVLT was performed for the GSV, which resulted in the complete occlusion of the GSV and healing of the ulcer. EVLT presents a safe and useful therapeutic technique for pulsatile varicose veins in the limbs. Copyright © 2016 Elsevier Inc. All rights reserved.

  7. Pulsatile Versus Oscillatory Shear Stress Regulates NADPH Oxidase Subunit Expression

    PubMed Central

    Hwang, Juliana; Ing, Michael H.; Salazar, Adler; Lassègue, Bernard; Griendling, Kathy; Navab, Mohamad; Sevanian, Alex; Hsiai, Tzung K.

    2015-01-01

    Shear stress regulates endothelial nitric oxide and superoxide (O2−·) production, implicating the role of NADPH oxidase activity. It is unknown whether shear stress regulates the sources of reactive species production, consequent low-density lipoprotein (LDL) modification, and initiation of inflammatory events. Bovine aortic endothelial cells (BAECs) in the presence of 50 μg/mL of native LDL were exposed to (1) pulsatile flow with a mean shear stress (τave) of 25 dyne/cm2 and (2) oscillating flow at τave of 0. After 4 hours, aliquots of culture medium were collected for high-performance liquid chromatography analyses of electronegative LDL species, described as LDL− and LDL2−. In response to oscillatory shear stress, gp91phox mRNA expression was upregulated by 2.9±0.3-fold, and its homologue, Nox4, by 3.9±0.9-fold (P<0.05, n=4), with a corresponding increase in O2−· production rate. The proportion of LDL− and LDL2− relative to static conditions increased by 67±17% and 30±7%, respectively, with the concomitant upregulation of monocyte chemoattractant protein-1 expression and increase in monocyte/BAEC binding (P<0.05, n=5). In contrast, pulsatile flow downregulated both gp91phox and Nox4 mRNA expression (by 1.8±0.2-fold and 3.0±0.12-fold, respectively), with an accompanying reduction in O2−· production, reduction in the extent of LDL modification (51±12% for LDL− and 30±7% for LDL2−), and monocyte/BAEC binding. The flow-dependent LDL oxidation is determined in part by the NADPH oxidase activity. The formation of modified LDL via O2−· production may also affect the regulation of monocyte chemoattractant protein-1 expression and monocyte/BAEC binding. PMID:14593003

  8. Compound Doppler ultrasound signal simulation for pulsatile carotid arteries with a stenosis.

    PubMed

    Gao, Lian; Zhang, Yufeng; Zhou, Yi; Hu, Xiao; Deng, Li; Zhang, Kexin; Cai, Guanghui; Zhang, Junhua

    2016-08-12

    The simulated Doppler blood flow signals are widely used to assess the performance of the clutter filters for removing wall components while reserving low-velocity signals scattered from physiological blood flow approaching the inner vessel-wall injured by a stenosed lesion. By simultaneously taking into account the natural attributes of the Doppler equipment, blood flow as well as vessel wall of pulsatile carotid arteries with a stenosis, a computer simulation method is presented to produce the compound Doppler ultrasound blood flow signals. The in-phase and quadrature (I/Q) axial as well as radial blood flow signals are simulated by superposing a series of cosine functions regulated by the spectrograms estimated from the axial and radial velocity profiles firstly obtained through the solution of the incompressible Navier-Stokes equations, respectively. Meanwhile, the I/Q Doppler signals echoed from pulsatile near (anterior) and far (posterior) walls are reproduced based on their radial movements during a cardiac cycle. Ultimately, those confirmed quadrature signals are summed to generate the compound Doppler signals including the contribution from both blood flow and stenosed vessel-wall. The compound Doppler ultrasound signals echoed from both axial and radial blood flows as well as vessel walls with obstruction grades of 0% (normal arteries), 10% and 25% are simulated respectively. The real signals from the left carotid artery with an approximately 10% stenosis degree are also collected for further assessing the believability of simulated versions. The simulated and clinical tests demonstrate that the proposed computer simulation method can produce compound Doppler signals with confirmed qualitative and quantitative characteristics resembled with the clinical versions, which could be used as an theoretical data source for evaluating the performance of the signal separation between pulsatile blood flows and vessel walls with mild stenosed-lesions.

  9. Pulsatile reperfusion after cardiac arrest improves neurologic outcome.

    PubMed Central

    Anstadt, M P; Stonnington, M J; Tedder, M; Crain, B J; Brothers, M F; Hilleren, D J; Rahija, R J; Menius, J A; Lowe, J E

    1991-01-01

    Cardiopulmonary bypass (CPB) using nonpulsatile flow (NPF) is advocated for refractory cardiac arrest. This study examined cerebral outcome after resuscitation with pulsatile flow (PF) versus NPF. Dogs arrested for 12.5 minute were reperfused with NPF (n = 11) using roller pump CPB or PF (n = 11) using mechanical biventricular cardiac massage. Pump flows were similar between groups; however early arterial pressures were greater during PF versus NPF, *p less than 0.05. Circulatory support was weaned at 60 minutes' reperfusion. Neurologic recovery of survivors (n = 16) was significantly better after PF versus NPF, *p = 0.01. The presence of brain lesions on magnetic resonance images did not significantly differ between groups at 7 days. Brain then were removed and regions examined for ischemic changes. Loss of CA1 pyramidal neurons was more severe after NPF versus PF, +p = 0.009. Ischemic changes were more frequent after NPF in the caudate nucleus (+p = 0.009) and watershed regions of the cerebral cortex (+p = 0.062), compared with PF. These results demonstrate that PF improves cerebral resuscitation when treating cardiac arrest with mechanical circulatory support (* = MANOVA with repeated measures, + = categorical data analysis. Images Fig. 5. Fig. 7. PMID:1953100

  10. Detection and measurement of retinal blood vessel pulsatile motion

    NASA Astrophysics Data System (ADS)

    Xiao, Di; Frost, Shaun; Vignarajan, Janardhan; An, Dong; Tay-Kearney, Mei-Ling; Kanagasingam, Yogi

    2016-03-01

    Retinal photography is a non-invasive and well-accepted clinical diagnosis of ocular diseases. Qualitative and quantitative assessment of retinal images is crucial in ocular diseases related clinical application. Pulsatile properties caused by cardiac rhythm, such as spontaneous venous pulsation (SVP) and pulsatile motion of small arterioles, can be visualized by dynamic retinal imaging techniques and provide clinical significance. In this paper, we aim at vessel pulsatile motion detection and measurement. We proposed a novel approach for pulsatile motion measurement of retinal blood vessels by applying retinal image registration, blood vessel detection and blood vessel motion detection and measurement on infrared retinal image sequences. The performance of the proposed methods was evaluated on 8 image sequences with 240 images. A preliminary result has demonstrated the good performance of the method for blood vessel pulsatile motion observation and measurement.

  11. Pulsatile Dynamics in the Yeast Proteome

    PubMed Central

    Dalal, Chiraj K.; Cai, Long; Lin, Yihan; Rahbar, Kasra; Elowitz, Michael B.

    2014-01-01

    The activation of transcription factors in response to environmental conditions is fundamental to cellular regulation. Recent work has revealed that some transcription factors are activated in stochastic pulses of nuclear localization, rather than at a constant level, even in a constant environment. In such cases, signals control the mean activity of the transcription factor by modulating the frequency, duration, or amplitude of these pulses. Although specific pulsatile transcription factors have been identified in diverse cell types, it has remained unclear how prevalent pulsing is within the cell, how variable pulsing behaviors are between genes, and whether pulsing is specific to transcriptional regulators or employed more broadly. To address these issues, we performed a proteome-wide movie-based screen to systematically identify localization-based pulsing behaviors in Saccharomyces cerevisiae. The screen examined all genes in a previously developed fluorescent protein fusion library of 4159 strains in multiple media conditions. This approach revealed stochastic pulsing in 10 proteins, all transcription factors. In each case, pulse dynamics were heterogeneous and unsynchronized among cells in clonal populations. Pulsing is the only dynamic localization behavior we observed, and it tends to occur in pairs of paralagous and redundant proteins. Taken together, these results suggest that pulsatile dynamics play a pervasive role in yeast and may be similarly prevalent in other eukaryotic species. PMID:25220054

  12. Atraumatic Pulsatile Leukocyte Circulation for Long-Term In Vitro Dynamic Culture and Adhesion Assays.

    PubMed

    Mazza, Giulia; Stoiber, Martin; Pfeiffer, Dagmar; Schima, Heinrich

    2015-11-01

    Low flow rate pumping of cell suspensions finds current applications in bioreactors for short-term dynamic cell culture and adhesion assays. The aim of this study was to develop an atraumatic pump and hemodynamically adapted test circuit to allow operating periods of at least several hours. A computer-controlled mini-pump (MP) was constructed based on non-occlusive local compression of an elastic tube with commercial bi-leaflet valves directing the pulsatile flow into a compliant circuit. Cell damage and activation in the system were tested with whole blood in comparison with a set with a conventional peristaltic pump (PP). Activation of circulating THP-1 monocytes was tested by measuring the expression of CD54 (ICAM-1). Additionally, monocyte-endothelial interactions were monitored using a parallel-plate flow chamber with an artificial stenosis. The system required a priming volume of only 20 mL, delivering a peak pulsatile flow of up to 35 mL/min. After 8 h, blood hemolysis was significantly lower for MP with 11 ± 3 mg/dL compared with PP with 100 ± 16 mg/dL. CD142 (tissue factor) expression on blood monocytes was 50% lower for MP. With MP, THP-1 cells could be pumped for extended periods (17 h), with no enhanced expression of CD54 permitting the long-term co-culture of THP-1 with endothelial cells and the analysis of flow pattern effects on cell adhesion. A low-damage assay setup was developed, which allows the pulsatile flow of THP-1 cells and investigation of their interaction with other cells or surfaces for extended periods of time.

  13. Numerical washout study of a pulsatile total artificial heart.

    PubMed

    Sonntag, Simon J; Kaufmann, Tim A S; Büsen, Martin R; Laumen, Marco; Gräf, Felix; Linde, Torsten; Steinseifer, Ulrich

    2014-03-01

    For blood pumps with long term indication, blood stagnation can result in excessive thromboembolic risks for patients. This study numerically investigates the washout performance of the left pump chamber of a pulsatile total artificial heart (TAH) as well as the sensitivity of the rotational orientation of the inlet bileaflet mechanical heart valve (MHV) on blood stagnation. To quantitatively evaluate the washout efficiency, a fluid-structure interaction (FSI) simulation of the artificial heart pumping process was combined with a blood washout model. Four geometries with different orientations (0°, 45°, 90° and 135°) of the inlet valve were compared with respect to washout performance. The calculated flow field showed a high level of agreement with particle image velocimetry (PIV) measurements. Almost complete washout was achievable after three ejection phases. Remains of old blood in relation to the chamber volume was below 0.6% for all configurations and were mainly detected opposite to the inlet and outlet port at the square edge where the membrane and the pump chamber are connected. Only a small variation in the washout efficiency and the general flow field was observed. An orientation of 0° showed minor advantages with respect to blood stagnation and recirculation. Bileaflet MHVs were demonstrated to be only slightly sensitive to rotation regarding the washout performance of the TAH. The proposed numerical washout model proved to be an adequate tool to quantitatively compare different configurations and designs of the artificial organ regarding the potential for blood stagnation where experimental measurements are limited.

  14. Mechano-active tissue engineering of vascular smooth muscle using pulsatile perfusion bioreactors and elastic PLCL scaffolds.

    PubMed

    Jeong, Sung In; Kwon, Jae Hyun; Lim, Jin Ik; Cho, Seung-Woo; Jung, Youngmee; Sung, Won Jun; Kim, Soo Hyun; Kim, Young Ha; Lee, Young Moo; Kim, Byung-Soo; Choi, Cha Yong; Kim, Soo-Ja

    2005-04-01

    Blood vessels are subjected in vivo to mechanical forces in a form of radial distention, encompassing cyclic mechanical strain due to the pulsatile nature of blood flow. Vascular smooth muscle (VSM) tissues engineered in vitro with a conventional tissue engineering technique may not be functional, because vascular smooth muscle cells (VSMCs) cultured in vitro typically revert from a contractile phenotype to a synthetic phenotype. In this study, we hypothesized that pulsatile strain and shear stress stimulate VSM tissue development and induce VSMCs to retain the differentiated phenotype in VSM engineering in vitro. To test the hypothesis, rabbit aortic smooth muscle cells (SMCs) were seeded onto rubber-like elastic, three-dimensional PLCL [poly(lactide-co-caprolactone), 50:50] scaffolds and subjected to pulsatile strain and shear stress by culturing them in pulsatile perfusion bioreactors for up to 8 weeks. As control experiments, VSMCs were cultured on PLCL scaffolds statically. The pulsatile strain and shear stress enhanced the VSMCs proliferation and collagen production. In addition, a significant cell alignment in a direction radial to the distending direction was observed in VSM tissues exposed to radial distention, which is similar to that of native VSM tissues in vivo, whereas VSMs in VSM tissues engineered in the static condition randomly aligned. Importantly, the expression of SM alpha-actin, a differentiated phenotype of SMCs, was upregulated by 2.5-fold in VSM tissues engineered under the mechano-active condition, compared to VSM tissues engineered in the static condition. This study demonstrates that tissue engineering of VSM tissues in vitro by using pulsatile perfusion bioreactors and elastic PLCL scaffolds leads to the enhancement of tissue development and the retention of differentiated cell phenotype.

  15. Non-dimensional physics of pulsatile cardiovascular networks and energy efficiency

    PubMed Central

    2016-01-01

    In Nature, there exist a variety of cardiovascular circulation networks in which the energetic ventricular load has both steady and pulsatile components. Steady load is related to the mean cardiac output (CO) and the haemodynamic resistance of the peripheral vascular system. On the other hand, the pulsatile load is determined by the simultaneous pressure and flow waveforms at the ventricular outlet, which in turn are governed through arterial wave dynamics (transmission) and pulse decay characteristics (windkessel effect). Both the steady and pulsatile contributions of the haemodynamic power load are critical for characterizing/comparing disease states and for predicting the performance of cardiovascular devices. However, haemodynamic performance parameters vary significantly from subject to subject because of body size, heart rate and subject-specific CO. Therefore, a ‘normalized’ energy dissipation index, as a function of the ‘non-dimensional’ physical parameters that govern the circulation networks, is needed for comparative/integrative biological studies and clinical decision-making. In this paper, a complete network-independent non-dimensional formulation that incorporates pulsatile flow regimes is developed. Mechanical design variables of cardiovascular flow systems are identified and the Buckingham Pi theorem is formally applied to obtain the corresponding non-dimensional scaling parameter sets. Two scaling approaches are considered to address both the lumped parameter networks and the distributed circulation components. The validity of these non-dimensional number sets is tested extensively through the existing empirical allometric scaling laws of circulation systems. Additional validation studies are performed using a parametric numerical arterial model that represents the transmission and windkessel characteristics, which are adjusted to represent different body sizes and non-dimensional haemodynamic states. Simulations demonstrate that the

  16. Embolization: critical thrombus height, shear rates, and pulsatility. Patency of blood vessels.

    PubMed

    Basmadjian, D

    1989-11-01

    The present article builds on elementary fluid dynamics and previous analyses by the author to delineate approximate boundaries of mural thrombus height Hp, maximum shear rate gamma Max, and flow pulsatility beyond which thrombi are subject to either very high or very low probabilities of embolization. A thrombus height of approximately 0.1 mm emerges as a critical dividing line: Below it, the maximum embolizing shear stress tau s is independent of thrombus height and varies only linearly with shear rate. Above it, tau s quickly approaches a strong quadratic dependence on both thrombus height and shear rate: tau s approximately (Hp gamma)2, significantly increasing the likelihood of an embolizing event. By contrast, convective-diffusive removal of blood components during the initial stages of thrombus formation varies only weakly with gamma 1/3 in all but the smallest vessels. These maximum embolizing stresses are due principally to fluid drag. Acceleration (pulsatile) forces only begin to make their presence felt at gamma less than 500 s-1 and reach parity with fluid drag at gamma approximately 10 s-1, i.e., at a level where the presence of pulsatility is questionable. The results are used to provide maps of domains with high and low probabilities of an embolytic event and of vessel patency. The maps reveal that relatively modest changes in shear rate and/or vessel lumen can cause shifts from high to low likelihood of vessel patency, opening up possible ways of controlling blockage by manipulation of these variables.

  17. Numerical investigation of three patterns of motion in an electromagnetic pulsatile VAD.

    PubMed

    Shahraki, Zahra Hashemi; Oscuii, Hanieh Niroomand

    2014-01-01

    Hemolysis and thrombus formation which are critical concerns in designing a long-term implantable ventricular assist device (VAD) have impeded the widespread use of VADs. In this study, thus, the three-dimensional fluid domain of blood flow in a small bichamber positive displacement VAD (25 ml) with a magnetically levitated moving pusher plate was simulated by the means of a finite element package called ADINA. To optimize the function of the pump for minimizing shear stress induced blood damage, three different driver patterns (linear, sinusoidal, and Guyton's pulse) were investigated. The first pattern produced a constant flow, whereas the two others created pulsatile flows. The flow pattern and the distribution of shear stress of each pattern were observed for comparison. It was revealed that the three types of motions may induce less than 0.06% red blood cell damage. Moreover, in comparison to the other patterns not only did the sinusoidal motion of the pusher plate cause less risk of hemolysis, but in comparison to the linear pattern, it produced a pulsatile flow which reduced the stagnation areas in chambers, lowering the probability of thrombosis. In addition, this motion eliminates the probability of cavitations as compared with the Guyton's pulse pattern.

  18. Effect of the Pulsatile Extracorporeal Membrane Oxygenation on Hemodynamic Energy and Systemic Microcirculation in a Piglet Model of Acute Cardiac Failure.

    PubMed

    Itoh, Hideshi; Ichiba, Shingo; Ujike, Yoshihito; Douguchi, Takuma; Obata, Hideaki; Inamori, Syuji; Iwasaki, Tatsuo; Kasahara, Shingo; Sano, Shunji; Ündar, Akif

    2016-01-01

    The objective of this study was to compare the effects of pulsatile and nonpulsatile extracorporeal membrane oxygenation (ECMO) on hemodynamic energy and systemic microcirculation in an acute cardiac failure model in piglets. Fourteen piglets with a mean body weight of 6.08 ± 0.86 kg were divided into pulsatile (N = 7) and nonpulsatile (N = 7) ECMO groups. The experimental ECMO circuit consisted of a centrifugal pump, a membrane oxygenator, and a pneumatic pulsatile flow generator system developed in-house. Nonpulsatile ECMO was initiated at a flow rate of 140 mL/kg/min for the first 30 min with normal heart beating, with rectal temperature maintained at 36°C. Ventricular fibrillation was then induced with a 3.5-V alternating current to generate a cardiac dysfunction model. Using this model, we collected the data on pulsatile and nonpulsatile groups. The piglets were weaned off ECMO at the end of the experiment (180 min after ECMO was initiated). The animals did not receive blood transfusions, inotropic drugs, or vasoactive drugs. Blood samples were collected to measure hemoglobin, methemoglobin, blood gases, electrolytes, and lactic acid levels. Hemodynamic energy was calculated using the Shepard's energy equivalent pressure. Near-infrared spectroscopy was used to monitor brain and kidney perfusion. The pulsatile ECMO group had a higher atrial pressure (systolic and mean), and significantly higher regional saturation at the brain level, than the nonpulsatile group (for both, P < 0.05). Additionally, the pulsatile ECMO group had higher methemoglobin levels within the normal range than the nonpulsatile group. Our study demonstrated that pulsatile ECMO produces significantly higher hemodynamic energy and improves systemic microcirculation, compared with nonpulsatile ECMO in acute cardiac failure.

  19. Cora valveless pulsatile rotary pump: new design and control.

    PubMed

    Monties, J R; Trinkl, J; Mesana, T; Havlik, P J; Demunck, J L

    1996-01-01

    For decades, research for developing a totally implantable artificial ventricle has been carried on. For 4 to 5 years, two devices have been investigated clinically. For many years, we have studied a rotary (but not centrifugal) pump that furnishes pulsatile flow without a valve and does not need external venting or a compliance chamber. It is a hypocycloidal pump based on the principle of the Maillard-Wankel rotary compressor. Currently made of titanium, it is activated by an electrical brushless direct-current motor. The motor-pump unit is totally sealed and implantable, without noise or vibration. This pump was implanted as a left ventricular assist device in calves. The midterm experiments showed good hemodynamic function. The hemolysis was low, but serious problems were encountered: blood components collecting on the gear mechanism inside the rotor jammed the pump. We therefore redesigned the pump to seal the gear mechanism. We used a double system to seal the open end of the rotor cavity with components polished to superfine optical quality. In addition, we developed a control system based on the study of the predicted shape of the motor current. The new design is now underway. We hope to start chronic experiments again in a few months. If the problem of sealing the bearing could be solved, the Cora ventricle could be used as permanent totally implantable left ventricular assist device.

  20. Optimum Heart Rate to Minimize Pulsatile External Cardiac Power

    NASA Astrophysics Data System (ADS)

    Pahlevan, Niema; Gharib, Morteza

    2011-11-01

    The workload on the left ventricle is composed of steady and pulsatile components. Clinical investigations have confirmed that an abnormal pulsatile load plays an important role in the pathogenesis of left ventricular hypertrophy (LVH) and progression of LVH to congestive heart failure (CHF). The pulsatile load is the result of the complex dynamics of wave propagation and reflection in the compliant arterial vasculature. We hypothesize that aortic waves can be optimized to reduce the left ventricular (LV) pulsatile load. We used an in-vitro experimental approach to investigate our hypothesis. A unique hydraulic model was used for in-vitro experiments. This model has physical and dynamical properties similar to the heart-aorta system. Different compliant models of the artificial aorta were used to test the hypothesis under various aortic rigidities. Our results indicate that: i) there is an optimum heart rate that minimizes LV pulsatile power (this is in agreement with our previous computational study); ii) introducing an extra reflection site at the specific location along the aorta creates constructive wave conditions that reduce the LV pulsatile power.

  1. Development of a new disposable pulsatile pump for cardiopulmonary bypass: computational fluid-dynamic design and in vitro tests.

    PubMed

    Fiore, Gianfranco B; Redaelli, Alberto; Guadagni, Gualtiero; Inzoli, Fabio; Fumero, Roberto

    2002-01-01

    A newly conceived blood pump for pulsatile cardiopulmonary bypass (CPB) is presented. The new device's main design features (fully disposable pumping head with ring shaped valves) were intended to overcome the factors that today limit the use of pulsatile blood pumps, i.e., the complexity and costs of devices. The pump was designed and analyzed by means of three-dimensional computational models, including solid computer assisted design of the pumping head and computational fluid-dynamic (CFD) analyses of the fluid domain and of its interaction with deformable components. A prototype of the device, integrated with the venous reservoir, was built to perform hydraulic in vitro tests with aims of both validating CFD results and verifying the new device's pumping behavior. Functional evaluation of the pump was carried out by using the device in a model circuit made with standard CPB components plus a mock hydraulic bench representing an adult patient's systemic circulation. A roller pump used in pulsatile mode (RP-PM) was used for comparison. At a 5 L/min flow rate, the pulsatile hydraulic power () delivered to the patient was approximately 15 mW for the RP-PM. The new pump proved to be able to deliver up to 40 mW, thus providing a more physiological condition, closer to the delivered by the natural heart (90-140 mW).

  2. The complex distribution of arterial system mechanical properties, pulsatile hemodynamics, and vascular stresses emerges from three simple adaptive rules.

    PubMed

    Nguyen, Phuc H; Coquis-Knezek, Sarah F; Mohiuddin, Mohammad W; Tuzun, Egemen; Quick, Christopher M

    2015-03-01

    Arterial mechanical properties, pulsatile hemodynamic variables, and mechanical vascular stresses vary significantly throughout the systemic arterial system. Although the fundamental principles governing pulsatile hemodynamics in elastic arteries are widely accepted, a set of rules governing stress-induced adaptation of mechanical properties can only be indirectly inferred from experimental studies. Previously reported mathematical models have assumed mechanical properties adapt to achieve an assumed target stress "set point." Simultaneous prediction of the mechanical properties, hemodynamics, and stresses, however, requires that equilibrium stresses are not assumed a priori. Therefore, the purpose of this work was to use a "balance point" approach to identify the simplest set of universal adaptation rules that simultaneously predict observed mechanical properties, hemodynamics, and stresses throughout the human systemic arterial system. First, we employed a classical systemic arterial system model with 121 arterial segments and removed all parameter values except vessel lengths and peripheral resistances. We then assumed vessel radii increase with endothelial shear stress, wall thicknesses increase with circumferential wall stress, and material stiffnesses decrease with circumferential wall stress. Parameters characterizing adaptive responses were assumed to be identical in all arterial segments. Iteratively predicting local mechanical properties, hemodynamics, and stresses reproduced five trends observed when traversing away from the aortic root towards the periphery: decrease in lumen radii, wall thicknesses, and pulsatile flows and increase in wall stiffnesses and pulsatile pressures. The extraordinary complexity of the systemic arterial system can thus arise from independent adaptation of vessels to local stresses characterized by three simple adaptive rules.

  3. Assessment of pulsatile wall shear stress in compliant arteries: numerical model, validation and experimental data.

    PubMed

    Salvucci, Fernando P; Perazzo, Carlos A; Barra, Juan G; Armentano, Ricardo L

    2009-01-01

    There is evidence that wall shear stress (WSS) is associated with vascular disease. In particular, it is widely accepted that vascular segments with low or oscillatory values of WSS are more probable to develop vascular disease. It is then necessary to establish a realistic model of the blood flow in blood vessels in order to determine precisely WSS. We proposed a numerical 1D model which takes into account the pulsatile nature of blood flow, the elasticity of the vessel, and its geometry. The model allows the calculation of shear stress. It was validated for stationary situations. Then, we computed the time-dependent WSS distribution from experimental data in the sheep thoracic aorta. Results showed that mean WSS calculated through steady flow and rigid walls models is overestimated. Peak WSS values for pulsatile flow must be considered since they resulted to be at least one order higher than mean values. Oscillations in shear stress in a period showed to be approximately of 40%. These findings show that the proposed model is suitable for estimating time-dependent WSS distributions, and confirm the need of using this kind of model when trying to evaluate realistic WSS in blood vessels.

  4. Effect of echo artifacts on characterization of pulsatile tissues in neonatal cranial ultrasonic movies

    NASA Astrophysics Data System (ADS)

    Fukuzawa, Masayuki; Takahashi, Kazuki; Tabata, Yuki; Kitsunezuka, Yoshiki

    2016-04-01

    Effect of echo artifacts on characterization of pulsatile tissues has been examined in neonatal cranial ultrasonic movies by characterizing pulsatile intensities with different regions of interest (ROIs). The pulsatile tissue, which is a key point in pediatric diagnosis of brain tissue, was detected from a heartbeat-frequency component in Fourier transform of a time-variation of 64 samples of echo intensity at each pixel in a movie fragment. The averages of pulsatile intensity and power were evaluated in two ROIs: common fan-shape and individual cranial-shape. The area of pulsatile region was also evaluated as the number of pixels where the pulsatile intensity exceeds a proper threshold. The extracranial pulsatile region was found mainly in the sections where mirror image was dominant echo artifact. There was significant difference of pulsatile area between two ROIs especially in the specific sections where mirror image was included, suggesting the suitability of cranial-shape ROI for statistical study on pulsatile tissues in brain. The normalized average of pulsatile power in the cranial-shape ROI exhibited most similar tendency to the normalized pulsatile area which was treated as a conventional measure in spite of its requirement of thresholding. It suggests the potential of pulsatile power as an alternative measure for pulsatile area in further statistical study of pulsatile tissues because it was neither affected by echo artifacts nor threshold.

  5. Measurement of pulsatile haemodynamic forces in a model of a bifurcated stent graft for abdominal aortic aneurysm repair.

    PubMed

    Zhou, S N; How, T V; Black, R A; Vallabhaneni, S R; McWilliams, R; Brennan, J A

    2008-05-01

    The longitudinal haemodynamic force (LF) acting on a bifurcated stent graft for abdominal aortic aneurysm repair has been estimated previously using a simple one-dimensional analytical model based on the momentum equation which assumes steady flow of an inviscid fluid. Using an instrumented stent-graft model an experimental technique was developed to measure the LF under pulsatile flow conditions. The physical stent-graft model, with main trunk diameter of 30mm and limb diameters of 12 mm, was fabricated from aluminium. Strain gauges were bonded on to the main trunk to determine the longitudinal strain which is related to the LF. After calibration, the model was placed in a pulsatile flow system with 40 per cent aqueous glycerol solution as the circulating fluid. The LF was determined using a Wheatstone bridge signal-conditioning circuit. The signals were averaged over 590 cardiac cycles and saved to a personal computer for subsequent processing. The LF was strongly dependent on the pressure but less so on the flowrate. The measured forces were higher than those predicted by the simplified mathematical model by about 6-18 per cent during the cardiac cycle. The excess measured forces are due to the viscous drag and the effect of pulsatile flow. The peak measured LF in this model of 30 mm diameter may exceed the fixation force of some current clinical endovascular stent grafts.

  6. Pulsatile atheroprone shear stress affects the expression of transient receptor potential channels in human endothelial cells.

    PubMed

    Thilo, Florian; Vorderwülbecke, Bernd J; Marki, Alex; Krueger, Katharina; Liu, Ying; Baumunk, Daniel; Zakrzewicz, Andreas; Tepel, Martin

    2012-06-01

    The goal of the study was to assess whether pulsatile atheroprone shear stress modulates the expression of transient receptor potential (TRP) channels, TRPC3, TRPC6, TRPM7, and TRPV1 mRNA, in human umbilical vascular endothelial cells. Exposure of cultured vascular endothelial cells to defined shear stress, producing a constant laminar flow (generating a shear stress of 6 dyne/cm(2)), laminar pulsatile atheroprotective flow (with a mean shear stress of 20 dyne/cm(2)), or laminar atheroprone bidirectional flow (with a mean shear stress of 0 dyne/cm(2)) differentially induced TRPC6 and TRPV1 mRNA as measured by quantitative real-time RT-PCR and normalized to GAPDH expression. Thereby, TRPC6 and TRPV1 mRNA expressions were significantly increased after 24 hours of exposure to an atheroprone flow profile compared with an atheroprotective flow profile. Furthermore, the expression of transcription factors GATA1 and GATA4 was significantly correlated with the expression of TRPC6 mRNA. In contrast, after 24 hours of constant laminar flow, the expression of TRPC6 and TRPV1 mRNA was unchanged, whereas the expression of TRPC3 and TRPM7 was significantly higher in endothelial cells exposed to shear stress in comparison with endothelial cells grown under static conditions. There was a significant association between the expression of TRPC6 and tumor necrosis factor-α mRNA in human vascular tissue. No-flow and atheroprone flow conditions are equally characterized by an increase in the expression of tumor necrosis factor-α; however, inflammation-associated endothelial cell reactions may be further aggravated at atheroprone flow conditions by the increase of TRPV1 and TRPC6, as observed in our study.

  7. In vivo assessment of a new method of pulsatile perfusion based on a centrifugal pump.

    PubMed

    Herreros, Jesús; Ubilla, Matías; Berjano, Enrique J; Vila-Nuñez, Juan E; Páramo, José A; Sola, Josu; Mercé, Salvador

    2010-02-01

    The aim of this study was to assess platelet dysfunction and damage to organs after extracorporeal circulation using a pump based on a new method that adds a pulsatile flow to the continuous flow provided by a centrifugal pump. The continuous component of the total flow (2-3 L/min) is created by a Bio-Pump centrifugal pump, while the pulsatile component is created by the pulsating of an inner membrane pneumatically controlled by an intra-aortic counterpulsation balloon console (systolic volume of 37.5 mL in an asynchronous way with a frequency of 60 bpm). Six pigs were subjected to a partial cardiopulmonary bypass lasting 180 min and were sacrificed 60 min after extracorporeal circulation was suspended. The hematological study included the measurement of hematocrit, hemoglobin, leukocytes, and platelet function. The new pump did not significantly alter either platelet count or platelet function. In contrast, hematocrit and hemoglobin were significantly reduced during extracorporeal circulation (approximately 5% P = 0.011, and 2 g/dL P = 0.01, respectively). The leukocyte count during extracorporeal circulation showed a tendency to decrease, but this was not significant. In general, the short-term use of the new pump (4 h) did not cause any serious morphological damage to the heart, lung, kidney, or liver. The results suggest that the hemodynamic performance of the new pump is similar to a conventional centrifugal pump and could therefore be appropriate for use in extracorporeal circulation.

  8. Analysis of high gradient magnetic field effects on distribution of nanoparticles injected into pulsatile blood stream

    NASA Astrophysics Data System (ADS)

    Reza Habibi, Mohammad; Ghassemi, Majid; Hossien Hamedi, Mohammad

    2012-04-01

    Magnetic nanoparticles are widely used in a wide range of applications including data storage materials, pharmaceutical industries as magnetic separation tools, anti-cancer drug carriers and micro valve applications. The purpose of the current study is to investigate the effect of a non-uniform magnetic field on bio-fluid (blood) with magnetic nanoparticles. The effect of particles as well as mass fraction on flow field and volume concentration is investigated. The governing non-linear differential equations, concentration and Navier-stokes are coupled with the magnetic field. To solve these equations, a finite volume based code is developed and utilized. A real pulsatile velocity is utilized as inlet boundary condition. This velocity is extracted from an actual experimental data. Three percent nanoparticles volume concentration, as drug carrier, is steadily injected in an unsteady, pulsatile and non-Newtonian flow. A power law model is considered for the blood viscosity. The results show that during the systole section of the heartbeat when the blood velocity increases, the magnetic nanoparticles near the magnetic source are washed away. This is due to the sudden increase of the hydrodynamic force, which overcomes the magnetic force. The probability of vein blockage increases when the blood velocity reduces during the diastole time. As nanoparticles velocity injection decreases (longer injection time) the wall shear stress (especially near the injection area) decreases and the retention time of the magnetic nanoparticles in the blood flow increases.

  9. A Bayesian approach to modeling associations between pulsatile hormones

    PubMed Central

    Johnson, Timothy D.; Brown, Morton B.

    2010-01-01

    Many hormones are secreted in pulses. The pulsatile relationship between hormones regulates many biological processes. To understand endocrine system regulation, time series of hormone concentrations are collected. The goal is to characterize pulsatile patterns and associations between hormones. Currently each hormone on each subject is fitted univariately. This leads to estimates of the number of pulses and estimates of the amount of hormone secreted; however, when the signal-to-noise ratio is small, pulse detection and parameter estimation remains difficult with existing approaches. In this paper, we present a bivariate deconvolution model of pulsatile hormone data focusing on incorporating pulsatile associations. Through simulation, we exhibit that using the underlying pulsatile association between two hormones improves the estimation of the number of pulses and the other parameters defining each hormone. We develop the one-to-one, driver-response case and show how birth-death MCMC can be used for estimation. We exhibit these features through a simulation study and on the relationship between luteinizing and follicle stimulating hormones. PMID:18759850

  10. Pulsatile insulin secretion, impaired glucose tolerance and type 2 diabetes

    PubMed Central

    Satin, Leslie S.; Butler, Peter C.; Ha, Joon; Sherman, Arthur S.

    2015-01-01

    Type 2 diabetes (T2DM) results when increases in beta cell function and/or mass cannot compensate for rising insulin resistance. Numerous studies have documented the longitudinal changes in metabolism that occur during the development of glucose intolerance and lead to T2DM. However, the role of changes in insulin secretion, both amount and temporal pattern has been understudied. Most of the insulin secreted from pancreatic beta cells of the pancreas is released in a pulsatile pattern, which is disrupted in T2DM. Here we review the evidence that changes in beta cell pulsatility occur during the progression from glucose intolerance to T2DM in humans, and contribute significantly to the etiology of the disease. We review the evidence that insulin pulsatility improves the efficacy of secreted insulin on its targets, particularly hepatic glucose production, but also examine evidence that pulsatility alters or is altered by changes in peripheral glucose uptake. Finally, we summarize our current understanding of the biophysical mechanisms responsible for oscillatory insulin secretion. Understanding how insulin pulsatility contributes to normal glucose homeostasis and is altered in metabolic disease states may help improve the treatment of T2DM. PMID:25637831

  11. Stabilizing control for a pulsatile cardiovascular mathematical model.

    PubMed

    de los Reyes, Aurelio A; Jung, Eunok; Kappel, Franz

    2014-06-01

    In this paper, we develop a pulsatile model for the cardiovascular system which describes the reaction of this system to a submaximal constant workload imposed on a person at a bicycle ergometer test after a period of rest. Furthermore, the model should allow to use measurements for the pulsatile pressure in fingertips which provide information on the diastolic and the systolic pressure for parameter estimation. Based on the assumption that the baroreceptor loop is the essential control loop in this case, we design a stabilizing feedback control for the pulsatile model which is obtained by solving a linear-quadratic regulator problem for the linearization of a non-pulsatile counterpart of the pulsatile model. We also investigate the behavior of the model with respect to changes in the weight of the term in the cost functional for the linear-quadratic regulator problem which penalizes the deviation of the momentary pressure in the aorta from the pressure at the stationary situation which should be obtained.

  12. Nonlinear analysis and prediction of pulsatile hormone secretion

    NASA Astrophysics Data System (ADS)

    Prank, Klaus; Kloppstech, Mirko; Nowlan, Steven J.; Harms, Heio M.; Brabant, Georg; Hesch, Rolf-Dieter; Sejnowski, Terrence J.

    1996-06-01

    Pulsatile hormone secretion is observed in almost every hormonal system. The frequency of episodic hormone release ranges from approximately 10 to 100 pulses in 24 hours. This temporal mode of secretion is an important feature of intercellular information transfer in addition to a dose-response dependent regulation. It has been demonstrated in a number of experiments that changes in the temporal pattern of pulsatile hormone secretion specifically regulate cellular and organ function and structure. Recent evidence links osteoporosis, a disease characterized by loss of bone mass and structure, to changes in the dynamics of pulsatile parathyroid hormone (PTH) secretion. In our study we applied nonlinear and linear time series prediction to characterize the secretory dynamics of PTH in both healthy human subjects and patients with osteoporosis. Osteoporotic patients appear to lack periods of high predictability found in normal humans. In contrast to patients with osteoporosis patients with hyperparathyroidism, a condition which despite sometimes reduced bone mass has a preserved bone architecture, show periods of high predictability of PTH secretion. Using stochastic surrogate data sets which match certain statistical properties of the original time series significant nonlinear determinism could be found for the PTH time series of a group of healthy subjects. Using classical nonlinear analytical techniques we could demonstrate that the irregular pattern of pulsatile PTH secretion in healthy men exhibits characteristics of deterministic chaos. Pulsatile secretion of PTH in healthy subjects seems to be a first example of nonlinear determinism in an apparently irregular hormonal rhythm in human physiology.

  13. Infection after implantation of pulsatile mechanical circulatory support devices.

    PubMed

    Holman, William L; Kirklin, James K; Naftel, David C; Kormos, Robert L; Desvign-Nickens, Patricia; Camacho, Margarita T; Ascheim, Deborah D

    2010-06-01

    INTERMACS is a registry of mechanical circulatory support devices sponsored by the National Institutes of Health. This analysis uses INTERMACS data to define the time course, incidence, and outcome of infection adverse events focusing on the first 3 months after implant. Patients entered into INTERMACS from June 23, 2006, to September 30, 2008, were analyzed. Preimplant data (demographics, hemodynamics, and laboratory values), infection adverse events, and other outcomes were recorded. Infection adverse events were analyzed to compare infection rates in subgroups of patients and define risk factors for death. The analysis was confined to pulsatile mechanical circulatory support devices. A total of 593 patients from 88 institutions were entered. Infection was a relatively common event within the first 3 months of implant and was significantly (P = .005) more common in patients with biventricular assist devices than in patients with left ventricular assist devices, although the prevalence of infection equalized in months 4 to 12. Infection had a significant adverse effect on survival. Independent risk factors for death included support with a biventricular assist device, older age, severity of patient illness implantation of the device (INTERMACS level 1), and higher blood urea nitrogen. Infection remains a relatively frequent adverse event and is associated with decreased survival. Interventions to prevent infection that focus on the preoperative and immediate postoperative periods are the ones most likely to achieve success by diminishing the incidence of infection during the initial 3 months after implantation. Rotary (continuous-flow) pumps are expected to have lower infection rates, but this remains to be seen. Published by Mosby, Inc.

  14. Pulsatile enophthalmos, severe esotropia, kinked optic nerve and visual loss in neurofibromatosis type-1

    PubMed Central

    Sachdeva, Virender; Haque, Nazmul; Pathengay, Avinash; Kekunnaya, Ramesh

    2015-01-01

    Neurofibromatosis Type I if associated with aplasia of greater wing of sphenoid may be associated with a pulsatile exophthalmos. However, very rarely it may be associated with a pulsatile enophthalmos. This clinical image describes a rare presentation with pulsatile enophthalmos, esotropia and kinking of the optic nerve due to neurofibomatosis type I. PMID:26903735

  15. Pulsatile support using a rotary left ventricular assist device with an electrocardiography-synchronized rotational speed control mode for tracking heart rate variability.

    PubMed

    Arakawa, Mamoru; Nishimura, Takashi; Takewa, Yoshiaki; Umeki, Akihide; Ando, Masahiko; Kishimoto, Yuichiro; Kishimoto, Satoru; Fujii, Yutaka; Date, Kazuma; Kyo, Shunei; Adachi, Hideo; Tatsumi, Eisuke

    2016-06-01

    We previously developed a novel control system for a continuous-flow left ventricular assist device (LVAD), the EVAHEART, and demonstrated that sufficient pulsatility can be created by increasing its rotational speed in the systolic phase (pulsatile mode) in a normal heart animal model. In the present study, we assessed this system in its reliability and ability to follow heart rate variability. We implanted an EVAHEART via left thoracotomy into five goats for the Study for Fixed Heart Rate with ventricular pacing at 80, 100, 120 and 140 beats/min and six goats for the Study for native heart rhythm. We tested three modes: the circuit clamp, the continuous mode and the pulsatile mode. In the pulsatile mode, rotational speed was increased during the initial 35 % of the RR interval by automatic control based on the electrocardiogram. Pulsatility was evaluated by pulse pressure and dP/dt max of aortic pressure. As a result, comparing the pulsatile mode with the continuous mode, the pulse pressure was 28.5 ± 5.7 vs. 20.3 ± 7.9 mmHg, mean dP/dt max was 775.0 ± 230.5 vs 442.4 ± 184.7 mmHg/s at 80 bpm in the study for fixed heart rate, respectively (P < 0.05). The system successfully determined the heart rate to be 94.6 % in native heart rhythm. Furthermore, pulse pressure was 41.5 ± 7.9 vs. 27.8 ± 5.6 mmHg, mean dP/dt max was 716.2 ± 133.9 vs 405.2 ± 86.0 mmHg/s, respectively (P < 0.01). In conclusion, our newly developed the pulsatile mode for continuous-flow LVADs reliably provided physiological pulsatility with following heart rate variability.

  16. Spatial probabilistic pulsatility model for enhancing photoplethysmographic imaging systems

    NASA Astrophysics Data System (ADS)

    Amelard, Robert; Clausi, David A.; Wong, Alexander

    2016-11-01

    Photoplethysmographic imaging (PPGI) is a widefield noncontact biophotonic technology able to remotely monitor cardiovascular function over anatomical areas. Although spatial context can provide insight into physiologically relevant sampling locations, existing PPGI systems rely on coarse spatial averaging with no anatomical priors for assessing arterial pulsatility. Here, we developed a continuous probabilistic pulsatility model for importance-weighted blood pulse waveform extraction. Using a data-driven approach, the model was constructed using a 23 participant sample with a large demographic variability (11/12 female/male, age 11 to 60 years, BMI 16.4 to 35.1 kg·m-2). Using time-synchronized ground-truth blood pulse waveforms, spatial correlation priors were computed and projected into a coaligned importance-weighted Cartesian space. A modified Parzen-Rosenblatt kernel density estimation method was used to compute the continuous resolution-agnostic probabilistic pulsatility model. The model identified locations that consistently exhibited pulsatility across the sample. Blood pulse waveform signals extracted with the model exhibited significantly stronger temporal correlation (W=35,p<0.01) and spectral SNR (W=31,p<0.01) compared to uniform spatial averaging. Heart rate estimation was in strong agreement with true heart rate [r2=0.9619, error (μ,σ)=(0.52,1.69) bpm].

  17. Shifting the pulsatility by increasing the change in rotational speed for a rotary LVAD using a native heart load control system.

    PubMed

    Date, Kazuma; Nishimura, Takashi; Takewa, Yoshiaki; Kishimoto, Satoru; Arakawa, Mamoru; Umeki, Akihide; Ando, Masahiko; Mizuno, Toshihide; Tsukiya, Tomonori; Ono, Minoru; Tatsumi, Eisuke

    2016-12-01

    We have previously developed a native heart load control system for a continuous-flow left ventricular assist device (LVAD) ((EVAHEART(®); Sun Medical) and demonstrated that the rotational speed (RS) in synchronization with the cardiac cycle can alter pulsatility and left ventricular (LV) load under general anesthesia. In this study, we assessed the effects of different levels of increase in RS on pulsatility and LV load in the chronic awake phase. We implanted the EVAHEART via left thoracotomy in 7 normal goats (59.3 ± 4.6 kg). Two weeks after implantation, we examined the effects of co-pulse mode (increased RS in the systolic phase) and counter-pulse mode (increased RS in the diastolic phase), as well as shifting the change in RS from 250 to 500 rpm, and 750 rpm in both modes on pulsatility and LV load. Pulsatility was assessed using pulse pressure and mean dP/dt max of aortic pressure. LV load was assessed using stroke work and left ventricle end-diastolic volume determined from LV pressure-volume loops. In the co-pulse mode, pulsatility values increased as the change in RS increased. By contrast, in the counter-pulse mode, these values decreased as the change in RS increased. LV load increased significantly in the co-pulse mode compared with the counter-pulse mode, but there were no significant differences among the three levels of RS increase in either mode. Increasing RS to varying degrees with our newly developed system could contribute to pulsatility. However, it appeared to have little effect on LV load in normal hearts.

  18. Nonlinear analysis and prediction of pulsatile hormone secretion

    SciTech Connect

    Prank, K. |; Kloppstech, M.; Nowlan, S.J.; Harms, H.M.; Brabant, G.; Hesch, R.; Sejnowski, T.J.

    1996-06-01

    Pulsatile hormone secretion is observed in almost every hormonal system. The frequency of episodic hormone release ranges from approximately 10 to 100 pulses in 24 hours. This temporal mode of secretion is an important feature of intercellular information transfer in addition to a dose-response dependent regulation. It has been demonstrated in a number of experiments that changes in the temporal pattern of pulsatile hormone secretion specifically regulate cellular and organ function and structure. Recent evidence links osteoporosis, a disease characterized by loss of bone mass and structure, to changes in the dynamics of pulsatile parathyroid hormone (PTH) secretion. In our study we applied nonlinear and linear time series prediction to characterize the secretory dynamics of PTH in both healthy human subjects and patients with osteoporosis. Osteoporotic patients appear to lack periods of high predictability found in normal humans. In contrast to patients with osteoporosis patients with hyperparathyroidism, a condition which despite sometimes reduced bone mass has a preserved bone architecture, show periods of high predictability of PTH secretion. Using stochastic surrogate data sets which match certain statistical properties of the original time series significant nonlinear determinism could be found for the PTH time series of a group of healthy subjects. Using classical nonlinear analytical techniques we could demonstrate that the irregular pattern of pulsatile PTH secretion in healthy men exhibits characteristics of deterministic chaos. Pulsatile secretion of PTH in healthy subjects seems to be a first example of nonlinear determinism in an apparently irregular hormonal rhythm in human physiology. {copyright} {ital 1996 American Institute of Physics.}

  19. Bedside assistance in freehand ultrasonic diagnosis by real-time visual feedback of 3D scatter diagram of pulsatile tissue-motion

    NASA Astrophysics Data System (ADS)

    Fukuzawa, M.; Kawata, K.; Nakamori, N.; Kitsunezuka, Y.

    2011-03-01

    By real-time visual feedback of 3D scatter diagram of pulsatile tissue-motion, freehand ultrasonic diagnosis of neonatal ischemic diseases has been assisted at the bedside. The 2D ultrasonic movie was taken with a conventional ultrasonic apparatus (ATL HDI5000) and ultrasonic probes of 5-7 MHz with the compact tilt-sensor to measure the probe orientation. The real-time 3D visualization was realized by developing an extended version of the PC-based visualization system. The software was originally developed on the DirectX platform and optimized with the streaming SIMD extensions. The 3D scatter diagram of the latest pulsatile tissues has been continuously generated and visualized as projection image with the ultrasonic movie in the current section more than 15 fps. It revealed the 3D structure of pulsatile tissues such as middle and posterior cerebral arteries, Willis ring and cerebellar arteries, in which pediatricians have great interests in the blood flow because asphyxiated and/or low-birth-weight neonates have a high risk of ischemic diseases such as hypoxic-ischemic encephalopathy and periventricular leukomalacia. Since the pulsatile tissue-motion is due to local blood flow, it can be concluded that the system developed in this work is very useful to assist freehand ultrasonic diagnosis of ischemic diseases in the neonatal cranium.

  20. EXTRACORPOREAL MEMBRANE OXYGENATION vs. COUNTERPULSATILE, PULSATILE, AND CONTINUOUS LEFT VENTRICULAR UNLOADING FOR PEDIATRIC MECHANICAL CIRCULATORY SUPPORT

    PubMed Central

    Bartoli, Carlo R.; Koenig, Steven C.; Ionan, Constantine; Gillars, Kevin J.; Mitchell, Mike E.; Austin, Erle H.; Gray, Laman A.; Pantalos, George M.

    2014-01-01

    OBJECTIVE Despite progress with adult ventricular assist devices (VADs), limited options exist to support pediatric patients with life-threatening heart disease. Extracorporeal membrane oxygenation (ECMO) remains the clinical standard. To characterize (patho)physiologic responses to different modes of mechanical unloading of the failing pediatric heart, ECMO was compared to either intraaortic balloon pump (IABP), pulsatile-flow (PF)VAD, or continuous-flow (CF)VAD support in a pediatric heart failure model. DESIGN Experimental. SETTING Large animal laboratory operating room. SUBJECTS Yorkshire piglets (n=47, 11.7±2.6 kg). INTERVENTIONS In piglets with coronary ligation-induced cardiac dysfunction, mechanical circulatory support devices were implanted and studied during maximum support. MEASUREMENTS and MAIN RESULTS Left ventricular, right ventricular, coronary, carotid, systemic arterial, and pulmonary arterial hemodynamics were measured with pressure and flow transducers. Myocardial oxygen consumption and total-body oxygen consumption (VO2) were calculated from arterial, venous, and coronary sinus blood sampling. Blood flow was measured in 17 organs with microspheres. Paired student t-tests compared baseline and heart failure conditions. One-way repeated-measures ANOVA compared heart failure, device support mode(s), and ECMO. Statistically significant (p<0.05) findings included: 1) improved left ventricular blood supply/demand ratio during PFVAD, CFVAD, and ECMO but not IABP support, 2) improved global myocardial blood supply/demand ratio during PFVAD, and CFVAD but not IABP or ECMO support, and 3) diminished pulsatility during ECMO and CFVAD but not IABP and PFVAD support. A profile of systems-based responses was established for each type of support. CONCLUSIONS Each type of pediatric VAD provided hemodynamic support by unloading the heart with a different mechanism that created a unique profile of physiological changes. These data contribute novel, clinically

  1. Laboratory Evaluation of Hemolysis and Systemic Inflammatory Response in Neonatal Nonpulsatile and Pulsatile Extracorporeal Life Support Systems.

    PubMed

    Wang, Shigang; Krawiec, Conrad; Patel, Sunil; Kunselman, Allen R; Song, Jianxun; Lei, Fengyang; Baer, Larry D; Ündar, Akif

    2015-09-01

    The objective of this study was to compare the systemic inflammatory response and hemolytic characteristics of a conventional roller pump (HL20-NP) and an alternative diagonal pump with nonpulsatile (DP3-NP) and pulsatile mode (DP3-P) in simulated neonatal extracorporeal life support (ECLS) systems. The experimental neonatal ECLS circuits consist of a conventional Jostra HL20 roller pump or an alternative Medos DP3 diagonal pump, and Medos Hilite 800 LT hollow-fiber oxygenator with diffusion membrane. Eighteen sterile circuits were primed with freshly donated whole blood and divided into three groups: conventional HL20 with nonpulsatile flow (HL20-NP), DP3 with nonpulsatile flow (DP3-NP), and DP3 with pulsatile flow (DP3-P). All trials were conducted for durations of 12 h at a flow rate of 500 mL/min at 36°C. Simultaneous blood flow and pressure waveforms were recorded. Blood samples were collected to measure plasma-free hemoglobin (PFH), human tumor necrosis factor-alpha, interleukin-6 (IL-6), and IL-8, in addition to the routine blood gas, lactate dehydrogenase, and lactic acid levels. HL20-NP group had the highest PFH levels (mean ± standard error of the mean) after a 12-h ECLS run, but the difference among groups did not reach statistical significance (HL20-NP group: 907.6 ± 253.1 mg/L, DP3-NP group: 343.7 ± 163.2 mg/L, and DP3-P group: 407.6 ± 156.6 mg/L, P = 0.06). Although there were similar trends but no statistical differences for the levels of proinflammatory cytokines among the three groups, the HL20-NP group had much greater levels than the other groups (P > 0.05). Pulsatile flow generated higher total hemodynamic energy and surplus hemodynamic energy levels at pre-oxygenator and pre-clamp sites (P < 0.01). Our study demonstrated that the alternative diagonal pump ECLS circuits appeared to have less systemic inflammatory response and hemolysis compared with the conventional roller pump ECLS circuit in simulated

  2. Optimization of the circuit configuration of a pulsatile ECLs: an in vivo experimental study.

    PubMed

    Lim, Choon Hak; Son, Ho Sung; Lee, Jung Joo; Fang, Yong Hu; Moon, Ki Chul; Ahn, Chi Bum; Kim, Kyung Hyun; Lee, Hye Won; Sun, Kyung

    2005-01-01

    An extracorporeal life support system (ECLS) with a conventional membrane oxygenator requires a driving force for the blood to pass through hollow fiber membranes. We hypothesized that if a gravity-flow hollow fiber membrane oxygenator is installed in the circuit, the twin blood sacs of a pulsatile ECLS (the Twin-Pulse Life Support, T-PLS) can be placed downstream of the membrane oxygenator. This would increase pump output by doubling pulse rate at a given pumpsetting rate while maintaining effective pulsatility. The purpose of this study was to determine the optimal circuit configuration for T-PLS with respect to energy and pump output. Animals were randomly assigned to 2 groups in a total cardiopulmonary bypass model. In the serial group, a conventional membrane oxygenator was located between the twin blood sacs of the T-PLS. In the parallel group, the twin blood sacs were placed downstream of the gravity-flow membrane oxygenator. Energy equivalent pressure (EEP), surplus hemodynamic energy (SHE) and pump output were collected at the different pump-setting rates of 30, 40, and 50 beats per minute (BPM). At a given pump-setting rate the pulse rate doubled in the parallel group. Percent changes of mean arterial pressure to EEP were 13.0 +/- 1.7, 12.0 +/- 1.9, and 7.6 +/- 0.9% in the parallel group, while 22.5 +/- 2.4, 23.2 +/- 1.9, and 21.8 +/- 1.4 in the serial group at 30, 40, and 50 BPM of pump-setting rates. SHE at each pump setting rate was 20,131 +/- 1408, 21,739 +/- 2470, and 15,048 +/- 2108 erg/ cm3 in the parallel group, while 33,968 +/- 3001, 38,232 +/- 3281, 37,964 +/- 2693 erg/cm3 in the serial group. Pump output was higher in the parallel circuit at 40, and 50 BPM pump-setting rates (3.1 +/- 0.2, 3.7 +/- 0.2 L/min vs. 2.2 +/- 0.1 and 2.5 +/- 0.1 L/min, respectively, p =0.01). Either parallel or serial circuit configuration of T-PLS generates effective pulsatility. As for the pump out, the parallel circuit configuration provides higher flow than the

  3. Chronic pulsatile shear stress alters insulin-like growth factor-I (IGF-I) binding protein release in vitro.

    PubMed

    Elhadj, Selim; Akers, R Michael; Forsten-Williams, Kimberly

    2003-02-01

    Insulin-like growth factor-I (IGF-I) is a potent smooth muscle cell mitogen indicated to have a role in vascular disease. IGF-I stimulates proliferation via receptor activation but its activity is mediated by IGF binding proteins (IGFBPs). Since hemodynamics have been linked to vascular proliferative disorders, we studied how pulsatile low (5 +/- 2 dynes/cm2) and high (23 +/- 8 dynes/cm2) shear stresses impacted IGFBP metabolism in bovine aortic endothelial cells using the Cellmax capillary system. We modeled the pulsatile flow in our system using the Womersley model for flow inside a rigid tube and harmonic analysis revealed that the flow was sinusoidal with a frequency of approximately 0.3 Hz for both shear stress treatments. Laminar flow was confirmed and the phase lag between the pressure and the flow found to be insignificant. Thus, our study provides a necessary characterization of this in vitro system as well as an investigation into how shear impacts the IGF axis. We found a significant difference in IGFBP distribution between treatments and, given that IGFBPs regulate IGF-I activity and that IGF-I-independent activities have been suggested for IGFBP-3, suggest that shear stress may indirectly regulate IGF-I activity, and, by extension, the effect of IGF-I on vascular pathologies.

  4. Recent advances in pulsatile oral drug delivery systems.

    PubMed

    Politis, Stavros N; Rekkas, Dimitrios M

    2013-08-01

    It is well established that several diseases exhibit circadian behavior, following the relevant rhythm of the physiological functions of the human body. Their study falls in the fields of chronobiology and chronotherapeutics, the latter being essentially the effort of timely matching the treatment with the disease expression, in order to maximize the therapeutic benefits and minimize side effects. Pulsatile drug delivery is one of the pillars of chronopharmaceutics, achieved through dosage form design that allows programmable release of active pharmaceutical ingredients (APIs) to follow the disease's time profile. Its major characteristic is the presence of lag phases, followed by drug release in a variety of rates, immediate, repeated or controlled. The scope of this review is to summarize the recent literature on pulsatile oral drug delivery systems and provide an overview of the ready to use solutions and early stage technologies, focusing on the awarded and pending patents in this technical field during the last few years.

  5. Pulsatility Index as a Diagnostic Parameter of Reciprocating Wall Shear Stress Parameters in Physiological Pulsating Waveforms.

    PubMed

    Avrahami, Idit; Kersh, Dikla; Liberzon, Alexander

    2016-01-01

    Arterial wall shear stress (WSS) parameters are widely used for prediction of the initiation and development of atherosclerosis and arterial pathologies. Traditional clinical evaluation of arterial condition relies on correlations of WSS parameters with average flow rate (Q) and heart rate (HR) measurements. We show that for pulsating flow waveforms in a straight tube with flow reversals that lead to significant reciprocating WSS, the measurements of HR and Q are not sufficient for prediction of WSS parameters. Therefore, we suggest adding a third quantity-known as the pulsatility index (PI)-which is defined as the peak-to-peak flow rate amplitude normalized by Q. We examine several pulsating flow waveforms with and without flow reversals using a simulation of a Womersley model in a straight rigid tube and validate the simulations through experimental study using particle image velocimetry (PIV). The results indicate that clinically relevant WSS parameters such as the percentage of negative WSS (P[%]), oscillating shear index (OSI) and the ratio of minimum to maximum shear stress rates (min/max), are better predicted when the PI is used in conjunction with HR and Q. Therefore, we propose to use PI as an additional and essential diagnostic quantity for improved predictability of the reciprocating WSS.

  6. Pulsatility Index as a Diagnostic Parameter of Reciprocating Wall Shear Stress Parameters in Physiological Pulsating Waveforms

    PubMed Central

    Avrahami, Idit; Kersh, Dikla

    2016-01-01

    Arterial wall shear stress (WSS) parameters are widely used for prediction of the initiation and development of atherosclerosis and arterial pathologies. Traditional clinical evaluation of arterial condition relies on correlations of WSS parameters with average flow rate (Q) and heart rate (HR) measurements. We show that for pulsating flow waveforms in a straight tube with flow reversals that lead to significant reciprocating WSS, the measurements of HR and Q are not sufficient for prediction of WSS parameters. Therefore, we suggest adding a third quantity—known as the pulsatility index (PI)—which is defined as the peak-to-peak flow rate amplitude normalized by Q. We examine several pulsating flow waveforms with and without flow reversals using a simulation of a Womersley model in a straight rigid tube and validate the simulations through experimental study using particle image velocimetry (PIV). The results indicate that clinically relevant WSS parameters such as the percentage of negative WSS (P[%]), oscillating shear index (OSI) and the ratio of minimum to maximum shear stress rates (min/max), are better predicted when the PI is used in conjunction with HR and Q. Therefore, we propose to use PI as an additional and essential diagnostic quantity for improved predictability of the reciprocating WSS. PMID:27893801

  7. Comparison of a tubular pulsatile pump and a volumetric pump for continuous venovenous renal replacement therapy in a pediatric animal model.

    PubMed

    Ruperez, Marta; López-Herce, Jesús; Sánchez, César; García, Cristina; García, Elena; Del Francisco, Cañizo Juan

    2005-01-01

    We compare the efficacy of a tubular pulsatile pump and a conventional volumetric pump (IVAC 571), connected to a neonatal hemofiltration circuit with an FH22 filter, for continuous renal replacement therapy in 54 Maryland pigs weighing 8-16 kg. Three different flow rates (30 ml/min in 12 cases, 15 ml/min in 22 cases, and 5 ml/min in 20 cases) were used over a 2-hour period. Hemofiltration and hemodiafiltration were performed, and measurements of ultrafiltrate flow, circuit pressures, heart rate, blood pressure, temperature, urea, creatinine, total proteins, Na, K, Cl, hematocrit, and hemolysis parameters (aspartate transaminase, lactic dehydrogenase, haptoglobin, indirect bilirubin, free hemoglobin) were made. There were no differences in ultrafiltrate flow between the two pumps. Ultrafiltrate volume was significantly higher with higher flows (p < 0.01). The technique was well tolerated by all pigs. When each blood flow was analyzed separately, cross-filter pressure drop was significantly higher in the volumetric pump than in the tubular pulsatile pump (p < 0.05). No significant differences in heart rate, blood pressure, or analytical determinations were seen between the two pumps. We conclude that pulsatile and volumetric pumps can be uses as an alternative to roller pumps for continuous venovenous renal replacement therapy in neonates and infants.

  8. Pulsatile compression of the rostral ventrolateral medulla in hypertension.

    PubMed

    Morimoto, S; Sasaki, S; Miki, S; Kawa, T; Itoh, H; Nakata, T; Takeda, K; Nakagawa, M; Naruse, S; Maeda, T

    1997-01-01

    The rostral ventrolateral medulla (RVLM) has been known to be a major regulating center of sympathetic and cardiovascular activities. An association between essential hypertension and neurovascular compression of the RVLM has been reported in clinical observations, including magnetic resonance imaging (MRI) studies. To reconfirm this relationship, we performed MRI using a high-resolution 512 x 512 matrix in patients with essential and secondary hypertension and in normotensive subjects. The duration of hypertension and the degree of organ damage by hypertension were not significantly different between the two hypertension groups. Neurovascular compression of the RVLM was observed in 74% of the essential hypertension group, and the incidence of compression was significantly higher than in the secondary hypertension group (11%) or in the normotensive group (13%) (P < .01). These results from the clinical studies suggest that neurovascular compression of the RVLM is, at least in part, causally related to essential hypertension. Although blood pressure elevation by pulsatile compression of the RVLM in an experimental baboon model has already been reported, its underlying mechanism is not well known. Accordingly, we performed experiments to investigate whether pulsatile compression of the RVLM would increase arterial pressure and to elucidate the mechanism of the pressor response in rats. Sympathetic nerve activity, arterial pressure, heart rate, and plasma levels of epinephrine and norepinephrine were increased by pulsatile compression of the RVLM. The pressor response was abolished by intravenous treatment with hexamethonium or RVLM injection of kainic acid. In summary, the results from the MRI studies suggest that neurovascular compression of the RVLM is, at least in part, causally related to essential hypertension. This was supported by the results from experimental studies using rats indicating that pulsatile compression of the RVLM increases arterial pressure by

  9. Orbital reconstruction for pulsatile exophthalmos secondary to sphenoid wing dysplasia.

    PubMed

    Dale, Elizabeth L; Strait, Timothy A; Sargent, Larry A

    2014-01-01

    Sphenoid wing dysplasia or absence of the greater sphenoid wing is a rare condition that is considered pathopneumonic for neurofibromatosis type 1 (NF1). It occurs in 4% to 11% of NF1 patients, and its precise cause is unclear. Some cases appear to be congenital, while others have demonstrated it to be a progressive degeneration of the orbital wall. In about half of cases, associated adjacent neurofibromas are described. Consistently, however, the clinical sequelae is herniation of the temporal lobe into the orbit, causing progressive proptosis and pulsatile exophthalmos. Reconstruction of the orbit has traditionally been with bone grafts, but due to problems with bone resorption and recurrence, titanium plates in conjunction with bone grafts have been reported. We present a case of a 6-year-old male patient who was first diagnosed with NF1 and associated absence of the greater sphenoid wing at the age of 2. Four years later, he was referred for reconstruction after the development of pulsatile exophthalmos. Surgical management included dissection of the dura of the temporal lobe off of the periorbita and skull base reconstruction with a combination of radial-shaped titanium mesh and split calvarial bone grafts. Postoperatively, there was near immediate resolution of the pulsatile exophthalmos, and follow-up at 1 year showed no recurrence.

  10. A multiple disk centrifugal pump as a blood flow device.

    PubMed

    Miller, G E; Etter, B D; Dorsi, J M

    1990-02-01

    A multiple disk, shear force, valveless centrifugal pump was studied to determine its suitability as a blood flow device. A pulsatile version of the Tesla viscous flow turbine was designed by modifying the original steady flow pump concept to produce physiological pressures and flows with the aid of controlling circuitry. Pressures and flows from this pump were compared to a Harvard Apparatus pulsatile piston pump. Both pumps were connected to an artificial circulatory system. Frequency and systolic duration were varied over a range of physiological conditions for both pumps. The results indicated that the Tesla pump, operating in a pulsatile mode, is capable of producing physiologic pressures and flows similar to the Harvard pump and other pulsatile blood pumps.

  11. Computation of residence time in the simulation of pulsatile ventricular assist devices

    NASA Astrophysics Data System (ADS)

    Long, C. C.; Esmaily-Moghadam, M.; Marsden, A. L.; Bazilevs, Y.

    2014-10-01

    A continuum-based model of particle residence time for moving-domain fluid mechanics and fluid-structure interaction (FSI) computations is proposed, analyzed, and applied to the simulation of an adult pulsatile ventricular assist device (PVAD). Residence time is a quantity of clinical interest for blood pumps because it correlates with thrombotic risk. The proposed technique may be easily implemented in any flow or FSI solver. In the context of PVADs the results of the model may be used to assess how efficiently the pump moves the blood through its interior. Three scalar measures of particle residence time are also proposed. These scalar quantities may be used in the PVAD design with the goal of reducing thrombotic risk.

  12. Arterial pulsatility as an index of cerebral microangiopathy in diabetes type 2.

    PubMed

    Agha, M S; Alboudi, A

    2014-01-09

    Transcranial doppler is an inexpensive, non-invasive investigation. This study assessed its validity in determining cerebral small vessel disease in patients with type 2 diabetes mellitus. Flow velocity and pulsatility index were measured in the middle cerebral, basilar and intracranial internal carotid arteries of a sample of 141 diabetic patients with no other risk factors, and 132 age- and sex-matched healthy controls. The patients were divided into 2 groups: 73 with complicated and 68 with uncomplicated diabetes. There was a statistically significant difference between the complicated diabetes and control groups for the 3 arteries and most indices. The differences between the uncomplicated diabetes patients and the controls were also statistically significant but less strongly. Transcranial doppler may be useful in early diagnosis of cerebral small vessel disease in patients with type 2 diabetes mellitus.

  13. The effects of the pulsatile period on the size of recirculation bubble in the vicinity of stent struts

    NASA Astrophysics Data System (ADS)

    Jiang, B.; Thondapu, V.; Barlis, P.; Poon, E. K. W.; Ooi, A. S. H.

    2017-04-01

    Incomplete stent apposition (ISA) is sometimes found in stent deployment at complex lesions, and it is considered to be one of the causes of post-stenting complications, such as late stent thrombosis and restenosis. The presence of ISA leads to large recirculation bubbles behind the stent struts, which can reduce shear stress at the arterial wall that retards neointimal formation process and thus lead to complications. Computational fluid dynamics (CFD) simulations are performed on simplified two-dimensional axisymmetric arterial models with stents struts of square and circular cross-sectional shapes at a malapposition distance of 120 μm from the arterial wall. To investigate the effects of pulsatile flow period on the dynamics of the recirculation bubbles, high fidelity simulations are carried out with pulsatile flows of period 0.4 s and 0.8 s. Under the condition of the same flow rate, both square and circular strut cases show that shorter period provides greater flow deceleration, leading to the formation of a larger recirculation bubble. With the same thickness, circular strut has a significant improvement over the square strut in terms of the size of the recirculation bubble, and therefore less likely to lead to complications.

  14. Pulsatile electrical impedance response from cerebrally dead adult patients is not a reliable tool for detecting cerebral perfusion changes.

    PubMed

    Basano, L; Ottonello, P; Nobili, F; Vitali, P; Pallavicini, F B; Ricca, B; Prastaro, T; Robert, A; Rodriguez, G

    2001-05-01

    The original objective of this work was to verify the possibility of using electrical pulsatile cerebral impedance measurements as a diagnostic aid for assessing the brain-death condition in adults; a subordinate target was to validate a simple method for detecting perfusional changes in the brain. To this end, impedance signals were recorded, for a comparative study, from both live subjects and brain-dead patients, using a simple four-electrode arrangement. Rather unexpectedly, pulsatile transcephalic impedance waveforms exhibiting a temporal dependance similar to those of live subjects were detected in artificially ventilated, cerebrally dead, adult subjects; distributions of the time delays between impedance peaks and ECG peaks were also recorded for the two groups (dead and live subjects). These data provided no evidence, at the 1% significance level, against the hypothesis that the two sample groups are drawn from identical populations. The detection of impedance variations from brain-dead patients can be explained by the residual persistence of blood flow through the scalp, by mechanical variations synchronous with the heart beat and by the presence of the oscillating flow and the systolic spikes that precede the final blood flow arrest. The fact that impedance variations can be traced back to a multiplicity of causes, unrelated to the normal unidirectional flow, renders the transcephalic impedance method inappropriate for detecting cerebral perfusion changes in adults. This conclusion is also strengthened by some theoretical results recently derived from a multilayer model of the head.

  15. In vitro performance testing of a pediatric oxygenator with an integrated pulsatile pump.

    PubMed

    Borchardt, Ralf; Schlanstein, Peter; Mager, Ilona; Arens, Jutta; Schmitz-Rode, Thomas; Steinseifer, Ulrich

    2012-01-01

    For different lung and heart diseases (e.g., acute respiratory distress syndrome, congenital heart failure, and cardiomyopathy) extracorporeal membrane oxygenation is a well-established therapy, particularly in the field of neonatal and pediatric medicine. To reduce the priming volume of the extracorporeal circuit, different components can be combined. In this study, an oval-shaped oxygenator (called ExMeTrA) with integrated pulsatile pump was tested in vitro using porcine blood. A feasibility study regarding the performance of collapsing and expanding silicone tubes within an oxygenator fiber bundle as a pulsatile pump was previously completed with successful results. The findings of this study improve upon the previous feasibility results, particularly in terms of gas exchange and filling volume. Five modules were manufactured in sizes of 20 ± 2.2 ml (priming volume) with fiber surface areas of 0.24 ± 0.027 m(2) and an analytically calculated volume pumping capacity of 692 ± 75 ml/min. The modules were made of polymethylpentene fibers with dense outer layer to permit long-term applications. The gas exchange rates at a gas/blood flow ratio of 2:1 were between 64 and 72.7 ml(O)(2)/l(blood) and between 62.5 and 81.5 ml/l(blood), depending on the blood flow. The individual module's pumping capacity ranged from 200-500 ml/min thus providing room for further improvements. In order to enhance the pumping capacity while maintaining sufficient gas exchange rates future optimization, adjustments will be made to the inlet and outlet geometries.

  16. Pulsatile Fluid Shear in Bone Remodeling

    NASA Technical Reports Server (NTRS)

    Frangos, John A.

    1997-01-01

    The objective of this investigation was to elucidate the sensitivity to transients in fluid shear stress in bone remodeling. Bone remodeling is clearly a function of the local mechanical environment which includes interstitial fluid flow. Traditionally, load-induced remodeling has been associated with low frequency (1-2 Hz) signals attributed to normal locomotion. McLeod and Rubin, however, demonstrated in vivo remodeling events associated with high frequency (15-30 Hz) loading. Likewise, other in vivo studies demonstrated that slowly applied strains did not trigger remodeling events. We therefore hypothesized that the mechanosensitive pathways which control bone maintenance and remodeling are differentially sensitive to varying rates of applied fluid shear stress.

  17. Polynomial analysis of placental flow patterns in growth-retarded fetuses.

    PubMed

    Hütter, W; Grab, D; Sterzik, K; Terinde, R; Wolf, A

    1993-01-01

    Correct interpretation of conspicuous blood flow velocity waveforms cannot rely solely on the evaluation of uteroplacental vascular Doppler flow patterns by means of angle-independent indices such as the resistance or pulsatility index. In addition to the degree of pulsatility, the waveform shape between the systolic and diastolic peak values is of considerable consequence. A subdivision of the total flow waveform into orthogonal polynomial components allows both pulsatility evaluation and notching to be registered, providing a higher sensitivity in identification of pathological vascular resistance. Accurate recording and assessment of the flow waveform is therefore an important qualitative criterion for the classification of Doppler flow patterns in pregnancies with reduced uteroplacental perfusion.

  18. An optimization formulation for characterization of pulsatile cortisol secretion.

    PubMed

    Faghih, Rose T; Dahleh, Munther A; Brown, Emery N

    2015-01-01

    Cortisol is released to relay information to cells to regulate metabolism and reaction to stress and inflammation. In particular, cortisol is released in the form of pulsatile signals. This low-energy method of signaling seems to be more efficient than continuous signaling. We hypothesize that there is a controller in the anterior pituitary that leads to pulsatile release of cortisol, and propose a mathematical formulation for such controller, which leads to impulse control as opposed to continuous control. We postulate that this controller is minimizing the number of secretory events that result in cortisol secretion, which is a way of minimizing the energy required for cortisol secretion; this controller maintains the blood cortisol levels within a specific circadian range while complying with the first order dynamics underlying cortisol secretion. We use an ℓ0-norm cost function for this controller, and solve a reweighed ℓ1-norm minimization algorithm for obtaining the solution to this optimization problem. We use four examples to illustrate the performance of this approach: (i) a toy problem that achieves impulse control, (ii) two examples that achieve physiologically plausible pulsatile cortisol release, (iii) an example where the number of pulses is not within the physiologically plausible range for healthy subjects while the cortisol levels are within the desired range. This novel approach results in impulse control where the impulses and the obtained blood cortisol levels have a circadian rhythm and an ultradian rhythm that are in agreement with the known physiology of cortisol secretion. The proposed formulation is a first step in developing intermittent controllers for curing cortisol deficiency. This type of bio-inspired pulse controllers can be employed for designing non-continuous controllers in brain-machine interface design for neuroscience applications.

  19. Aqueous Angiography in Living Nonhuman Primates Shows Segmental, Pulsatile, and Dynamic Angiographic Aqueous Humor Outflow.

    PubMed

    Huang, Alex S; Li, Meng; Yang, Diya; Wang, Huaizhou; Wang, Ningli; Weinreb, Robert N

    2017-06-01

    To evaluate the feasibility of safely performing aqueous angiography in intact eyes of living nonhuman primates (NHPs) for evaluating aqueous humor outflow and segmental patterns. Cross-sectional, observational study. Six nonhuman primates. Aqueous angiography was performed in 6 nonhuman primates. After anesthesia, an anterior chamber (AC) maintainer was placed through a temporal 1-mm side-port wound. Indocyanine green (ICG; 0.4%) or 2.5% fluorescein was introduced (individually or in sequence) into the eye with a gravity-driven constant-pressure system. Aqueous angiography images were obtained with a Spectralis HRA+OCT (Heidelberg Engineering GmbH, Heidelberg, Germany) suspended over the NHP eye using a custom-designed surgical boom arm. Concurrent anterior segment optical coherence tomography (OCT) was performed on distally angiographically positive and negative regions. Angiographic patterns described by location, time-course, choice of tracer, and anterior-segment OCT. Aqueous angiography in the living NHP eye demonstrated mostly stable angiographic patterns. With multimodal imaging, angiographically positive signal co-localized with episcleral veins as identified by infrared imaging and intrascleral lumens, as demonstrated by anterior segment OCT. Sequential aqueous angiography in individual eyes with ICG followed by fluorescein showed similar angiographic patterns. A pulsatile nature of aqueous angiographic outflow was sometimes observed. Aqueous angiographic patterns could also dynamically change. In some instances, positive angiographic flow suddenly arose in regions previously without an angiographic signal. Alternatively, an angiographic signal could suddenly disappear from regions in which an angiographic signal was initially documented. Aqueous angiography in living NHPs demonstrated segmental and pulsatile patterns with a newly described ability to dynamically shift. These characteristics further the understanding of live aqueous humor outflow biology

  20. A hemodynamic evaluation of the Medos Deltastream DP1 rotary pump and Jostra HL-20 roller pump under pulsatile and nonpulsatile perfusion in an infant cardiopulmonary bypass model--a pilot study.

    PubMed

    Rider, Alan R; Griffith, Kimberly; Ressler, Noel; Kunselman, Allen R; Wang, Shigang; Undar, Akif

    2008-01-01

    This study aims to compare the Jostra HL-20 roller pump to the Medos DeltaStream DP1 rotary pump in terms of pressure and flow waveforms, as well as calculated energies based on pressure/flow relationships, in a simulated pediatric cardiopulmonary perfusion system. The flow rate was set at 1,000 ml/min for each pump, under both pulsatile and nonpulsatile perfusion modes. Mean arterial pressure (MAP) was maintained at 40 mm Hg. Pressure and flow measurements and waveforms were recorded at precannula site in the bypass circuit. Blood analog test fluid was used to simulate blood properties. A total of 24 experiments were performed (n = 12 nonpulsatile and n = 12 pulsatile). A significant increase in surplus hemodynamic energy (SHE) was observed in both pumps under pulsatile perfusion. In contrast, nonpulsatile perfusion generated very little SHE in the Jostra roller pump, whereas no SHE was generated in the Medos rotary pump. However, under pulsatile perfusion, the Medos rotary pump generated more than twice the amount of SHE or "extra" energy than the Jostra roller pump. The total hemodynamic energy was also significantly higher in the Medos rotary pump than the Jostra roller pump, under pulsatile perfusion. This pilot study suggests that the Medos DeltaStream DP1 rotary pump may produce greater hemodynamic energy levels and higher quality physiologic pressure/flow waveforms than the Jostra roller pump. Further investigation of the Medos DeltaStream DP1 rotary pump is necessary to evaluate hemodynamic energy generation under various pump settings, in contrast to different flow rates.

  1. [Total cardiopulmonary bypass in rabbits. Techniques and the effect of pulsatile perfusion pressure on hemodynamic parameters].

    PubMed

    Chevalier-Cholat, A M; Friggi, A; Torresani, J

    1975-11-01

    Fifty-two total cardiopulmonary bypasses (CA) have been performed in rabbits in order to obtain a stable preparation. The present paper deals with techniques and haemodynamic results. 1. Two kinds of priming solution have been used. Best results were obtained by using Ringer-lactate-gelatin (65 ml) and T.H.A.M. (5 ml). 2. Pulsatile arterial perfusion was performed either at uniform frequency (series A:10 experiments) or in accordance with the arterial mechanical resonance frequency of each animal (series B: experiments). The later setting resulted in better levels of maximal arterial pressure throughout the experiments (p less than 0,001). 3. The perfusion pressure flows (integrated at minute intervals), and total peripheral resistances, were studied on two groups of 4 animals each, A' and B' forming a part of A and B respectively. The flows were higher in B' after 5 min of CA (p less than 0,001), and after 40 min of CA (p less than 0,025); the flow increased during the experiment in group A' but remained in a steady state in group B'. The differences in total peripheral resistances were not statistically significant after 5 min of CA, but were smaller in A' after 40 min of CA (p less than or equal to 0,025); the difference in the variation of total peripheral resistances was statistically significant (p less than 0,025).

  2. A new pulsatile volumetric device with biomorphic valves for the in vitro study of the cardiovascular system.

    PubMed

    Lanzarone, Ettore; Vismara, Riccardo; Fiore, Gianfranco B

    2009-12-01

    A pulsatile mock loop system was designed and tested. This prototype represents a versatile, adjustable, and controllable experimental apparatus for in vitro studies of devices meant to interface with the human circulatory system. The pumping system consisted of a ventricular chamber featuring two biomorphic silicone valves as the inlet and outlet valves. The chamber volume is forced by a piston pump moved by a computer-controlled, low-inertia motor. Fluid dynamic tests with the device were performed to simulate physiological conditions in terms of cardiac output (mean flow of 5 and 6 L/min, with beat rates from 60 to 80 bpm), of rheological properties of the processed fluid, and of systemic circulation impedance. The pulsating actuator performed a good replication of the physiological ventricular behavior and was able to guarantee easy control of the waveform parameters. Experimental pressure and flow tracings reliably simulated the physiological profiles, and no hemolytic subatmospheric pressures were revealed. The performance of the prototype valves was also studied in terms of dynamic and static backflow, effective orifice area, and pressure loss, resulting in their applicability for this device. Mechanical reliability was also tested over 8 h. The device proved to be a reliable lab apparatus for in vitro tests; the pumping system also represents a first step toward a possible future application of pulsating perfusion in the clinic arena, such as in short-term cardiac assist and pulsatile cardiopulmonary bypass.

  3. Central aortic pressure and pulsatility index in acute ischemic stroke.

    PubMed

    Kim, Jeong Yeon; Bushnell, Cheryl D; Park, Joong Hyun; Han, Seung Min; Im, Jin Hee; Han, Sang Won; Baik, Jong Sam; Park, Jae Hyeon

    2015-01-01

    We investigated the relationship between transcranial Doppler (TCD) pulsatility index (PI) and central aortic pressure by measurement of the aortic augmentation index (AIx). We enrolled 148 consecutive patients with a diagnosis of acute ischemic stroke. Patients were eligible for the study if they experienced their first ischemic stroke within the preceding 7 days and were 45 years of age or older. At Day 7 (±2) after stroke onset, TCD studies were performed and AIx was measured by applanation tonometry on the same days. The mean age was 66.3 (47-90) years and 37.8% were women. The mean middle cerebral artery (MCA) PI was significantly related with age (r =.361), hypertension (r = .184), peripheral systolic blood pressure (SBP; r = .211), peripheral pulse pressure (PP; r = .396), aortic SBP (r = .184), aortic DBP (r = -.181), and aortic PP (r = .371). The basilar artery (BA) PI was significantly related with age (r = .311), peripheral DBP (r = -.267), peripheral PP (r = .358), aortic DBP (r = -.266), and aortic PP (r = .347). TCD PI was significantly related with central aortic pressure, especially PP. The PI in the MCA and BA is closely associated with the pulsatile component of BP in the systemic circulation. Copyright © 2014 by the American Society of Neuroimaging.

  4. Prediction and control of neural responses to pulsatile electrical stimulation

    NASA Astrophysics Data System (ADS)

    Campbell, Luke J.; Sly, David James; O'Leary, Stephen John

    2012-04-01

    This paper aims to predict and control the probability of firing of a neuron in response to pulsatile electrical stimulation of the type delivered by neural prostheses such as the cochlear implant, bionic eye or in deep brain stimulation. Using the cochlear implant as a model, we developed an efficient computational model that predicts the responses of auditory nerve fibers to electrical stimulation and evaluated the model's accuracy by comparing the model output with pooled responses from a group of guinea pig auditory nerve fibers. It was found that the model accurately predicted the changes in neural firing probability over time to constant and variable amplitude electrical pulse trains, including speech-derived signals, delivered at rates up to 889 pulses s-1. A simplified version of the model that did not incorporate adaptation was used to adaptively predict, within its limitations, the pulsatile electrical stimulus required to cause a desired response from neurons up to 250 pulses s-1. Future stimulation strategies for cochlear implants and other neural prostheses may be enhanced using similar models that account for the way that neural responses are altered by previous stimulation.

  5. Prediction and control of neural responses to pulsatile electrical stimulation.

    PubMed

    Campbell, Luke J; Sly, David James; O'Leary, Stephen John

    2012-04-01

    This paper aims to predict and control the probability of firing of a neuron in response to pulsatile electrical stimulation of the type delivered by neural prostheses such as the cochlear implant, bionic eye or in deep brain stimulation. Using the cochlear implant as a model, we developed an efficient computational model that predicts the responses of auditory nerve fibers to electrical stimulation and evaluated the model's accuracy by comparing the model output with pooled responses from a group of guinea pig auditory nerve fibers. It was found that the model accurately predicted the changes in neural firing probability over time to constant and variable amplitude electrical pulse trains, including speech-derived signals, delivered at rates up to 889 pulses s(-1). A simplified version of the model that did not incorporate adaptation was used to adaptively predict, within its limitations, the pulsatile electrical stimulus required to cause a desired response from neurons up to 250 pulses s(-1). Future stimulation strategies for cochlear implants and other neural prostheses may be enhanced using similar models that account for the way that neural responses are altered by previous stimulation.

  6. Biomathematical Modeling of Pulsatile Hormone Secretion: A Historical Perspective

    PubMed Central

    Evans, William S.; Farhy, Leon S.; Johnson, Michael L.

    2009-01-01

    Shortly after the recognition of the profound physiological significance of the pulsatile nature of hormone secretion, computer-based modeling techniques were introduced for the identification and characterization of such pulses. Whereas these earlier approaches defined perturbations in hormone concentration-time series, deconvolution procedures were subsequently employed to separate such pulses into their secretion event and clearance components. Stochastic differential equation modeling was also used to define basal and pulsatile hormone secretion. To assess the regulation of individual components within a hormone network, a method that quantitated approximate entropy within hormone concentration-times series was described. To define relationships within coupled hormone systems, methods including cross-correlation and cross-approximate entropy were utilized. To address some of the inherent limitations of these methods, modeling techniques with which to appraise the strength of feedback signaling between and among hormone-secreting components of a network have been developed. Techniques such as dynamic modeling have been utilized to reconstruct dose–response interactions between hormones within coupled systems. A logical extension of these advances will require the development of mathematical methods with which to approximate endocrine networks exhibiting multiple feedback interactions and subsequently reconstruct their parameters based on experimental data for the purpose of testing regulatory hypotheses and estimating alterations in hormone release control mechanisms. PMID:19216934

  7. Pulsatile Release of Parathyroid Hormone from an Implantable Delivery System

    PubMed Central

    Liu, Xiaohua; Pettway, Glenda J.; McCauley, Laurie K.; Ma, Peter X.

    2007-01-01

    Intermittent (pulsatile) administration of parathyroid hormone (PTH) is known to improve bone micro-architecture, mineral density and strength. Therefore, daily injection of PTH has been clinically used for the treatment of osteoporosis. However, this regimen of administration is not convenient and is not a favorable choice of patients. In this study, an implantable delivery system has been developed to achieve pulsatile release of PTH. A well-defined cylindrical device was first fabricated with a biodegradable polymer, poly(lactic acid) (PLLA), using a reverse solid free form fabrication technique. Three-component polyanhydrides composed of sebacic acid, 1,3-bis(p-carboxyphenoxy) propane and poly(ethylene glycol) were synthesized and used as isolation layers. The polyanhydride isolation layers and PTH-loaded alginate layers were then stacked alternately within the delivery device. The gap between the stacked PTH-releasing core and the device frame was filled with PLLA to seal. Multi-pulse PTH release was achieved using the implantable device. The lag time between two adjacent pulses were modulated by the composition and the film thickness of the polyanhydride. The released PTH was demonstrated to be biologically active using an in vitro assay. Timed sequential release of multiple drugs has also been demonstrated. The implantable device holds promise for both systemic and local therapies. PMID:17576005

  8. Pulsatile ventricular assist device with pericardial inner lining.

    PubMed

    Leirner, A A; Hayashida, S A; Maizato, M J; Silva M de-L; Cestari, I A; Affeld, K

    2001-11-01

    Preserved pericardium in contact with blood is not thrombogenic, therefore avoiding the use of anticoagulants, and has excellent mechanical properties. Our objective is to take advantage of these characteristics and build a pulsatile ventricular assist device (VAD) with pericardium used as the inner lining of the blood chamber. A mold is used for the tanning of the pericardium, rendering it with an exact shape. A flexible polymeric structure is designed to serve as a base for the pericardium, guiding it and limiting its rate of strain. It consists of two halves, which when outfitted with the interior pericardium lining and connected to each other, form the blood chamber. This assembly is housed in rigid polyvinyl chloride (PVC) shells making up the air chamber for the pneumatic activation. Valves are likewise made of pericardium. Sealing of the chambers was tested statically up to 300 mm Hg with no air or fluid leakage. The device was tested for 60 continuous days in a mock loop, demonstrating hydrodynamic performance adequate for ventricular assist. Micrographs (confocal laser and scanning electron microscopy) were obtained of several pericardium areas, especially on the flexing regions that are a transition between the wet and dry regions. No sign of damage to the pericardium was observed either with the naked eye or at the microscopic level. From the hydraulic performance and materials viewpoints, a completely pericardium-lined pulsatile VAD displaying a polymeric structure that avoids unpredictable bending and limits strain is feasible. The results warrant further studies regarding biocompatibility and strength advantages.

  9. Pulsatile uptake of CO in the human lung

    PubMed Central

    Menkes, Harold A.; Sera, Kazuaki; Rogers, Robert M.; Hyde, Richard W.; Forster, Robert E.; DuBois, Arthur B.

    1970-01-01

    The instantaneous uptake of CO in the lungs was measured with a water-filled body plethysmograph in normal man. First, control measurements of plethysmograph pressure were made while the subject held his breath for 7 sec after breathing gas mixtures prepared to bring his alveolar PO2 and PCO2 close to mixed venous levels. Then, CO uptake measurements were made while he held his breath after inhaling the same gas mixtures with added CO (2.0%). The change in lung volume on CO minus the change in lung volume during the control measurement was a measure of the CO uptake in the lungs. Cardiopneumatic changes in lung gas volume were subtracted electrically. All of five subjects showed pulsatile CO uptake. The mean CO uptake was 103 ml/min. A peak uptake of 2.0 (range 1.6-2.3) times the mean uptake occurred 0.3-0.4 sec after the R wave of the EKG and a minimum uptake of 0.4 (range 0.2-0.5) times the mean uptake occurred during the tenth of a second before the R wave of the EKG. These results suggest that pulmonary capillary blood volume is pulsatile during the cardiac cycle. PMID:5411784

  10. Phantom-based ground-truth generation for cerebral vessel segmentation and pulsatile deformation analysis

    NASA Astrophysics Data System (ADS)

    Schetelig, Daniel; Säring, Dennis; Illies, Till; Sedlacik, Jan; Kording, Fabian; Werner, René

    2016-03-01

    Hemodynamic and mechanical factors of the vascular system are assumed to play a major role in understanding, e.g., initiation, growth and rupture of cerebral aneurysms. Among those factors, cardiac cycle-related pulsatile motion and deformation of cerebral vessels currently attract much interest. However, imaging of those effects requires high spatial and temporal resolution and remains challenging { and similarly does the analysis of the acquired images: Flow velocity changes and contrast media inflow cause vessel intensity variations in related temporally resolved computed tomography and magnetic resonance angiography data over the cardiac cycle and impede application of intensity threshold-based segmentation and subsequent motion analysis. In this work, a flow phantom for generation of ground-truth images for evaluation of appropriate segmentation and motion analysis algorithms is developed. The acquired ground-truth data is used to illustrate the interplay between intensity fluctuations and (erroneous) motion quantification by standard threshold-based segmentation, and an adaptive threshold-based segmentation approach is proposed that alleviates respective issues. The results of the phantom study are further demonstrated to be transferable to patient data.

  11. Development of the Marseilles pulsatile rotary blood pump for permanent implantable left ventricular assistance.

    PubMed

    Montiès, J R; Havlik, P; Mesana, T; Trinkl, J; Tourres, J L; Demunck, J L

    1994-07-01

    We have developed a low-speed, double-lobed hypocycloidal pump that furnishes a pulsatile flow without valves. The pump is coupled to a specially designed electric motor. The motor/pump unit is totally implantable and has been extensively tested in vitro and in vivo in animals. Because this pump is volumetric, it is necessary to control speed precisely to avoid overpumping. Our control system, which is based on analysis of the motor current wave form, can detect and prevent negative pressures before they occur. The physical properties and hemocompatibility of several construction materials have been studied to determine their suitability for clinical use. These materials include a graphite substrate, titanium nitrate surface coating, boric carbon, and amorphous diamond. The pumps currently being tested are made of titanium, but clinical versions will be made of composite materials selected from this preliminary study. In vivo testing of this pump confirmed its good hemodynamic performance, low hemolysis rate, and biocompatibility (i.e., low heat, noise, and vibration levels). Animal experiments were terminated after 15 days because of mechanical failure related to the accumulation of blood components on moving parts. A new pump in which the mechanism is completely sealed from the blood flow has been designed and will soon be tested. If this sealed design is effective, the pump should be ready for use as a permanent implantable ventricular assistance device.

  12. A comparison of methods for analyzing time series of pulsatile hormone data

    PubMed Central

    Carlson, N. E.; Horton, K. W.; Grunwald, G. K.

    2015-01-01

    Many endocrine systems are regulated by pulsatile hormones – hormones that are secreted intermittently in boluses rather than continuously over time. To study pulsatile secretion, blood is drawn every few minutes for an extended period. The result is a time series of hormone concentrations for each individual. The goal is to estimate pulsatile hormone secretion features such as frequency, location, duration, and amount of pulsatile and non-pulsatile secretion and compare these features between groups. Various statistical approaches to analyzing these data have been proposed, but validation has generally focused on one hormone. Thus, we lack a broad understanding of each method’s performance. By using simulated data with features seen in reproductive and stress hormones, we investigated the performance of three recently developed statistical approaches for analyzing pulsatile hormone data and compared them to a frequently used deconvolution approach. We found that methods incorporating a changing baseline modeled both constant and changing baseline shapes well; however, the added model flexibility resulted in a slight increase in bias in other model parameters. When pulses were well defined and baseline constant, Bayesian approaches performed similar to the existing deconvolution method. The increase in computation time of Bayesian approaches offered improved estimation and more accurate quantification of estimation variation in situations where pulse locations were not clearly identifiable. Within the class of deconvolution models for fitting pulsatile hormone data, the Bayesian approach with a changing baseline offered adequate results over the widest range of data. PMID:23787487

  13. Evidence of bidirectional flow in the sciatic vasa nervorum.

    PubMed

    Olver, Dylan T; Lacefield, James C; Shoemaker, Kevin J

    2014-07-01

    The purpose of this study was to determine whether bidirectional flow exists in the sciatic vasa nervorum. Images obtained using high-frequency color Doppler ultrasound in duplex imaging mode (Vevo 2100) were studied retroactively. In Fig. 1 (left panel; rat 1), the color Doppler signal and flow-velocity waveforms are indicative of pulsatile flow traveling towards (B) and away (C) from the probe. In the right panel (Fig. 1; rat 2), there appears to be three distinct vessels, reflective of non-pulsatile negative flow (D), and pulsatile positive (E) and negative (F) flows. These data confirm the presence of bidirectional arterial flow in the sciatic vasa nervorum. Investigating bidirectional flow in the intact whole nerve may be helpful in elucidating novel features of nerve blood flow control in healthy and diseased states.

  14. Motivations and Methods for Analyzing Pulsatile Hormone Secretion

    PubMed Central

    Veldhuis, Johannes D.; Keenan, Daniel M.; Pincus, Steven M.

    2008-01-01

    Endocrine glands communicate with remote target cells via a mixture of continuous and intermittent signal exchange. Continuous signaling allows slowly varying control, whereas intermittency permits large rapid adjustments. The control systems that mediate such homeostatic corrections operate in a species-, gender-, age-, and context-selective fashion. Significant progress has been made in understanding mechanisms of adaptive interglandular signaling in vivo. Principal goals are to understand the physiological origins, significance, and mechanisms of pulsatile hormone secretion. Key analytical issues are: 1) to quantify the number, size, shape, and uniformity of pulses, nonpulsatile (basal) secretion, and elimination kinetics; 2) to evaluate regulation of the axis as a whole; and 3) to reconstruct dose-response interactions without disrupting hormone connections. This review will focus on the motivations driving and the methodologies used for such analyses. PMID:18940916

  15. Measurement of pulsatile motion with millisecond resolution by MRI.

    PubMed

    Souchon, Rémi; Gennisson, Jean-Luc; Tanter, Mickael; Salomir, Rares; Chapelon, Jean-Yves; Rouvière, Olivier

    2012-06-01

    We investigated a technique based on phase-contrast cine MRI combined with deconvolution of the phase shift waveforms to measure rapidly varying pulsatile motion waveforms. The technique does not require steady-state displacement during motion encoding. Simulations and experiments were performed in porcine liver samples in view of a specific application, namely the observation of transient displacements induced by acoustic radiation force. Simulations illustrate the advantages and shortcomings of the methods. For experimental validation, the waveforms were acquired with an ultrafast ultrasound scanner (Supersonic Imagine Aixplorer), and the rates of decay of the waveforms (relaxation time) were compared. With bipolar motion-encoding gradient of 8.4 ms, the method was able to measure displacement waveforms with a temporal resolution of 1 ms over a time course of 40 ms. Reasonable agreement was found between the rate of decay of the waveforms measured in ultrasound (2.8 ms) and in MRI (2.7-3.3 ms).

  16. Multistable Jittering in Oscillators with Pulsatile Delayed Feedback

    NASA Astrophysics Data System (ADS)

    Klinshov, Vladimir; Lücken, Leonhard; Shchapin, Dmitry; Nekorkin, Vladimir; Yanchuk, Serhiy

    2015-05-01

    Oscillatory systems with time-delayed pulsatile feedback appear in various applied and theoretical research areas, and received a growing interest in recent years. For such systems, we report a remarkable scenario of destabilization of a periodic regular spiking regime. At the bifurcation point numerous regimes with nonequal interspike intervals emerge. We show that the number of the emerging, so-called "jittering" regimes grows exponentially with the delay value. Although this appears as highly degenerate from a dynamical systems viewpoint, the "multijitter" bifurcation occurs robustly in a large class of systems. We observe it not only in a paradigmatic phase-reduced model, but also in a simulated Hodgkin-Huxley neuron model and in an experiment with an electronic circuit.

  17. Electrically actuatable smart nanoporous membrane for pulsatile drug release.

    PubMed

    Jeon, Gumhye; Yang, Seung Yun; Byun, Jinseok; Kim, Jin Kon

    2011-03-09

    We report on the fabrication of electrically responsive nanoporous membrane based on polypyrrole doped with dodecylbenzenesulfonate anion (PPy/DBS) that was electropolymerized on the upper part of anodized aluminum oxide membrane. The membrane has regular pore size and very high pore density. Utilizing a large volume change of PPy/DBS depending on electrochemical state, the pore size was acutated electrically. The actuation of the pores was experimentally confirmed by in situ atomic force microscopy and in situ flux measurement. We also demonstrated successfully pulsatile (or on-demand) drug release by using fluorescently labeled protein as a model drug. Because of a fast switching time (less than 10 s) and high flux of the drugs, this membrane could be used for emergency therapy of angina pectoris and migraine, which requires acute and on-demand drug delivery, and hormone-related disease and metabolic syndrome.

  18. Mock circulation loop to investigate hemolysis in a pulsatile total artificial heart.

    PubMed

    Gräf, Felix; Finocchiaro, Thomas; Laumen, Marco; Mager, Ilona; Steinseifer, Ulrich

    2015-05-01

    Hemocompatibility of blood pumps is a crucial parameter that has to be ensured prior to in vivo testing. In contrast to rotary blood pumps, a standard for testing a pulsatile total artificial heart (TAH) has not yet been established. Therefore, a new mock circulation loop was designed to investigate hemolysis in the left ventricle of the ReinHeart TAH. Its main features are a high hemocompatibility, physiological conditions, a low priming volume, and the conduction of blood through a closed tubing system. The mock circulation loop consists of a noninvasive pressure chamber, an aortic compliance chamber, and an atrium directly connected to the ventricle. As a control pump, the clinically approved Medos-HIA ventricular assist device (VAD) was used. The pumps were operated at 120 beats per minute with an aortic pressure of 120 to 80 mm Hg and a mean atrial pressure of 10 mm Hg, generating an output flow of about 5 L/min. Heparinized porcine blood was used. A series of six identical tests were performed. A test method was established that is comparable to ASTM F 1841, which is standard practice for the assessment of hemolysis in continuous-flow blood pumps. The average normalized index of hemolysis (NIH) values of the VAD and the ReinHeart TAH were 0.018 g/100 L and 0.03 g/100 L, respectively. The standard deviation of the NIH was 0.0033 for the VAD and 0.0034 for the TAH. Furthermore, a single test with a BPX-80 Bio-Pump was performed to verify that the hemolysis induced by the mock circulation loop was negligible. The performed tests showed a good reproducibility and statistical significance. The mock circulation loop and test protocol developed in this study are valid methods to investigate the hemolysis induced by a pulsatile blood pump. Copyright © 2015 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.

  19. Hippocampal Fast Glutamatergic Transmission Is Transiently Regulated by Corticosterone Pulsatility

    PubMed Central

    Smeets, Johanna A. S.; Kerkhofs, Amber; Mikasova, Lenka; Karst, Henk; Groc, Laurent; Joëls, Marian

    2016-01-01

    In recent years it has become clear that corticosteroid hormones (such as corticosterone) are released in ultradian pulses as a natural consequence of pituitary-adrenal interactions. All organs, including the brain, are thus exposed to pulsatile changes in corticosteroid hormone level, important to ensure full genomic responsiveness to stress-induced surges. However, corticosterone also changes neuronal excitability through rapid non-genomic pathways, particularly in the hippocampus. Potentially, background excitability of hippocampal neurons could thus be changed by pulsatile exposure to corticosteroids. It is currently unknown, though, how neuronal activity alters during a sequence of corticosterone pulses. To test this, hippocampal cells were exposed in vitro to four consecutive corticosterone pulses with a 60 min inter-pulse interval. During the pulses we examined four features of hippocampal signal transfer by the main excitatory transmitter glutamate—i.e., postsynaptic responses to spontaneous release of presynaptic vesicles, postsynaptic GluA2-AMPA receptor dynamics, basal (evoked) field responses, and synaptic plasticity, using a set of high resolution imaging and electrophysiological approaches. We show that the first pulse of corticosterone causes a transient increase in miniature EPSC frequency, AMPA receptor trafficking and synaptic plasticity, while basal evoked field responses are unaffected. This pattern is not maintained during subsequent applications: responses become more variable, attenuate or even reverse over time, albeit with different kinetics for the various experimental endpoints. This may indicate that the beneficial effect of ultradian pulses on transcriptional regulation in the hippocampus is not consistently accompanied by short-term perturbations in background excitability. In general, this could be interpreted as a means to keep hippocampal neurons responsive to incoming signals related to environmental challenges. PMID:26741493

  20. Experience With a Long-term Pulsatile Ventricular Assist Device as a Bridge to Heart Transplant in Adults.

    PubMed

    Gómez Bueno, Manuel; Segovia Cubero, Javier; Serrano Fiz, Santiago; Ugarte Basterrechea, Juan; Hernández Pérez, Francisco José; Goirigolzarri Artaza, Josebe; Castedo Mejuto, Evaristo; Burgos Lázaro, Raúl; García Montero, Carlos; Moñivas Palomero, Vanessa; Mingo Santos, Susana; González Román, Ana Isabel; Álvarez Avelló, José Manuel; Vidal Fernández, Mercedes; Forteza Gil, Alberto; Alonso-Pulpón, Luis

    2017-09-01

    Most long-term ventricular assist devices (VADs) that are currently implanted are intracorporeal continuous-flow devices. Their main limitations include their high cost and inability to provide biventricular support. The aim of this study was to describe the results of using paracorporeal pulsatile-flow VADs as a bridge to transplant (BTT) in adult patients. Retrospective analysis of the characteristics, complications, and outcomes of a single-center case series of consecutive patients treated with the EXCOR VAD as BTT between 2009 and 2015. During the study period, 25 VADs were implanted, 6 of them biventricular. Ventricular assist devices were indicated directly as a BTT in 12 patients and as a bridge to decision in 13 due to the presence of potentially reversible contraindications or chance of heart function recovery. Twenty patients (80%) were successfully bridged to heart transplant after a median of 112 days (range, 8-239). The main complications included infectious (52% of patients), neurological events (32%, half of them fatal), bleeding (28%), and VAD malfunction requiring component replacement (28%). Eighty percent of patients with the EXCOR VAD as BTT achieved the goal after an average of almost 4 months of support. The most frequent complications were infectious, and the most severe were neurological. In our enivonment, the use of these pulsatile-flow VAD as BTT is a feasible strategy that obtains similar outcomes to those of intracorporeal continuous-flow devices. Copyright © 2016 Sociedad Española de Cardiología. Published by Elsevier España, S.L.U. All rights reserved.

  1. Gas exchange efficiency of an oxygenator with integrated pulsatile displacement blood pump for neonatal patients.

    PubMed

    Schlanstein, Peter C; Borchardt, Ralf; Mager, Ilona; Schmitz-Rode, Thomas; Steinseifer, Ulrich; Arens, Jutta

    2014-01-01

    Oxygenators have been used in neonatal extracorporeal membrane oxygenation (ECMO) since the 1970s. The need to develop a more effective oxygenator for this patient cohort exists due to their size and blood volume limitations. This study sought to validate the next design iteration of a novel oxygenator for neonatal ECMO with an integrated pulsatile displacement pump, thereby superseding an additional blood pump. Pulsating blood flow within the oxygenator is generated by synchronized active air flow expansion and contraction of integrated silicone pump tubes and hose pinching valves located at the oxygenator inlet and outlet. The current redesign improved upon previous prototypes by optimizing silicone pump tube distribution within the oxygenator fiber bundle; introduction of an oval shaped inner fiber bundle core, and housing; and a higher fiber packing density, all of which in combination reduced the priming volume by about 50% (50 to 27 mL and 41 to 20 mL, respectively). Gas exchange efficiency was tested for two new oxygenators manufactured with different fiber materials: one with coating and one with smaller pore size, both capable of long-term use (OXYPLUS® and CELGARD®). Results demonstrated that the oxygen transfer for both oxygenators was 5.3-24.7 mlO2/min for blood flow ranges of 100-500 mlblood/min. Carbon dioxide transfer for both oxygenators was 3.7-26.3 mlCO2/min for the same blood flow range. These preliminary results validated the oxygenator redesign by demonstrating an increase in packing density and thus in gas transfer, an increase in pumping capacity and a reduction in priming volume.

  2. The pulsatility volume index: an indicator of cerebrovascular compliance based on fast magnetic resonance imaging of cardiac and respiratory pulsatility.

    PubMed

    Bianciardi, Marta; Toschi, Nicola; Polimeni, Jonathan R; Evans, Karleyton C; Bhat, Himanshu; Keil, Boris; Rosen, Bruce R; Boas, David A; Wald, Lawrence L

    2016-05-13

    The influence of cardiac activity on the viscoelastic properties of intracranial tissue is one of the mechanisms through which brain-heart interactions take place, and is implicated in cerebrovascular disease. Cerebrovascular disease risk is not fully explained by current risk factors, including arterial compliance. Cerebrovascular compliance is currently estimated indirectly through Doppler sonography and magnetic resonance imaging (MRI) measures of blood velocity changes. In order to meet the need for novel cerebrovascular disease risk factors, we aimed to design and validate an MRI indicator of cerebrovascular compliance based on direct endogenous measures of blood volume changes. We implemented a fast non-gated two-dimensional MRI pulse sequence based on echo-planar imaging (EPI) with ultra-short repetition time (approx. 30-50 ms), which stepped through slices every approximately 20 s. We constrained the solution of the Bloch equations for spins moving faster than a critical speed to produce an endogenous contrast primarily dependent on spin volume changes, and an approximately sixfold signal gain compared with Ernst angle acquisitions achieved by the use of a 90° flip angle. Using cardiac and respiratory peaks detected on physiological recordings, average cardiac and respiratory MRI pulse waveforms in several brain compartments were obtained at 7 Tesla, and used to derive a compliance indicator, the pulsatility volume index (pVI). The pVI, evaluated in larger cerebral arteries, displayed significant variation within and across vessels. Multi-echo EPI showed the presence of significant pulsatility effects in both S0 and [Formula: see text] signals, compatible with blood volume changes. Lastly, the pVI dynamically varied during breath-holding compared with normal breathing, as expected for a compliance indicator. In summary, we characterized and performed an initial validation of a novel MRI indicator of cerebrovascular compliance, which might prove useful

  3. The pulsatility volume index: an indicator of cerebrovascular compliance based on fast magnetic resonance imaging of cardiac and respiratory pulsatility

    PubMed Central

    Toschi, Nicola; Polimeni, Jonathan R.; Evans, Karleyton C.; Bhat, Himanshu; Keil, Boris; Rosen, Bruce R.; Boas, David A.; Wald, Lawrence L.

    2016-01-01

    The influence of cardiac activity on the viscoelastic properties of intracranial tissue is one of the mechanisms through which brain–heart interactions take place, and is implicated in cerebrovascular disease. Cerebrovascular disease risk is not fully explained by current risk factors, including arterial compliance. Cerebrovascular compliance is currently estimated indirectly through Doppler sonography and magnetic resonance imaging (MRI) measures of blood velocity changes. In order to meet the need for novel cerebrovascular disease risk factors, we aimed to design and validate an MRI indicator of cerebrovascular compliance based on direct endogenous measures of blood volume changes. We implemented a fast non-gated two-dimensional MRI pulse sequence based on echo-planar imaging (EPI) with ultra-short repetition time (approx. 30–50 ms), which stepped through slices every approximately 20 s. We constrained the solution of the Bloch equations for spins moving faster than a critical speed to produce an endogenous contrast primarily dependent on spin volume changes, and an approximately sixfold signal gain compared with Ernst angle acquisitions achieved by the use of a 90° flip angle. Using cardiac and respiratory peaks detected on physiological recordings, average cardiac and respiratory MRI pulse waveforms in several brain compartments were obtained at 7 Tesla, and used to derive a compliance indicator, the pulsatility volume index (pVI). The pVI, evaluated in larger cerebral arteries, displayed significant variation within and across vessels. Multi-echo EPI showed the presence of significant pulsatility effects in both S0 and signals, compatible with blood volume changes. Lastly, the pVI dynamically varied during breath-holding compared with normal breathing, as expected for a compliance indicator. In summary, we characterized and performed an initial validation of a novel MRI indicator of cerebrovascular compliance, which might prove useful to investigate

  4. Sigmoid sinus cortical plate dehiscence induces pulsatile tinnitus through amplifying sigmoid sinus venous sound.

    PubMed

    Tian, Shan; Wang, Lizhen; Yang, Jiemeng; Mao, Rui; Liu, Zhaohui; Fan, Yubo

    2017-02-08

    Sigmoid sinus cortical plate dehiscence (SSCPD) is common in pulsatile tinnitus (PT) patients, and is treated through SSCPD resurfacing surgery in clinic, but the bio-mechanism is not clear as so far. This study aimed to clarify the bio-mechanism of PT sensation induced by SSCPD, and quantify the relationship of cortical plate (CP) thickness and PT sensation intensity. It was hypothesized that SSCPD would induce PT through significantly amplifying sigmoid sinus (SS) venous sound in this study. Finite element (FE) analysis based on radiology data of typical patient was used to verify this hypothesis, and was validated with clinical reports. In cases with different CP thickness, FE simulations of SS venous sound generation and propagation procedure were performed, involving SS venous flow field, vibration response of tissue overlying dehiscence area (including SS vessel wall and CP) and sound propagation in temporal bone air cells. It was shown in results that SS venous sound at tympanic membrane was 56.9dB in SSCPD case and -45.2dB in intact CP case, and was inaudible in all thin CP cases. It was concluded that SSCPD would directly induce PT through significantly amplifying SS venous sound, and thin CP would not be the only pathophysiology of PT. This conclusion would provide a theoretical basis for the design of SSCPD resurfacing surgery for PT patients with SSCPD or thin CP. Copyright © 2017 Elsevier Ltd. All rights reserved.

  5. Dynamic time warping and machine learning for signal quality assessment of pulsatile signals.

    PubMed

    Li, Q; Clifford, G D

    2012-09-01

    In this work, we describe a beat-by-beat method for assessing the clinical utility of pulsatile waveforms, primarily recorded from cardiovascular blood volume or pressure changes, concentrating on the photoplethysmogram (PPG). Physiological blood flow is nonstationary, with pulses changing in height, width and morphology due to changes in heart rate, cardiac output, sensor type and hardware or software pre-processing requirements. Moreover, considerable inter-individual and sensor-location variability exists. Simple template matching methods are therefore inappropriate, and a patient-specific adaptive initialization is therefore required. We introduce dynamic time warping to stretch each beat to match a running template and combine it with several other features related to signal quality, including correlation and the percentage of the beat that appeared to be clipped. The features were then presented to a multi-layer perceptron neural network to learn the relationships between the parameters in the presence of good- and bad-quality pulses. An expert-labeled database of 1055 segments of PPG, each 6 s long, recorded from 104 separate critical care admissions during both normal and verified arrhythmic events, was used to train and test our algorithms. An accuracy of 97.5% on the training set and 95.2% on test set was found. The algorithm could be deployed as a stand-alone signal quality assessment algorithm for vetting the clinical utility of PPG traces or any similar quasi-periodic signal.

  6. Shape optimization of pulsatile ventricular assist devices using FSI to minimize thrombotic risk

    NASA Astrophysics Data System (ADS)

    Long, C. C.; Marsden, A. L.; Bazilevs, Y.

    2014-10-01

    In this paper we perform shape optimization of a pediatric pulsatile ventricular assist device (PVAD). The device simulation is carried out using fluid-structure interaction (FSI) modeling techniques within a computational framework that combines FEM for fluid mechanics and isogeometric analysis for structural mechanics modeling. The PVAD FSI simulations are performed under realistic conditions (i.e., flow speeds, pressure levels, boundary conditions, etc.), and account for the interaction of air, blood, and a thin structural membrane separating the two fluid subdomains. The shape optimization study is designed to reduce thrombotic risk, a major clinical problem in PVADs. Thrombotic risk is quantified in terms of particle residence time in the device blood chamber. Methods to compute particle residence time in the context of moving spatial domains are presented in a companion paper published in the same issue (Comput Mech, doi: 10.1007/s00466-013-0931-y, 2013). The surrogate management framework, a derivative-free pattern search optimization method that relies on surrogates for increased efficiency, is employed in this work. For the optimization study shown here, particle residence time is used to define a suitable cost or objective function, while four adjustable design optimization parameters are used to define the device geometry. The FSI-based optimization framework is implemented in a parallel computing environment, and deployed with minimal user intervention. Using five SEARCH/ POLL steps the optimization scheme identifies a PVAD design with significantly better throughput efficiency than the original device.

  7. Programmed Speed Reduction Enables Aortic Valve Opening and Increased Pulsatility in the LVAD-Assisted Heart.

    PubMed

    Tolpen, Sam; Janmaat, Jochem; Reider, Claudine; Kallel, Faouzi; Farrar, David; May-Newman, Karen

    2015-01-01

    Aortic valve opening (AVO) during left ventricular assist device (LVAD) support aids in preventing valve fusion, incompetence, and thrombosis. The programmed low speed algorithm (PLSA) allows AVO intermittently by reducing continuous motor speed during a dwell time. AVO and hemodynamics in the LVAD-assisted heart were measured using a HeartMate II (Thoratec Corporation, Pleasanton, CA) LVAD with a PLSA controller in a mock circulatory loop. Left ventricle and aortic pressures, LVAD, and total aortic flow were measured during pre-LVAD, non-PLSA and PLSA combinations of cardiac function, and LVAD speed. The low cardiac setting corresponded to a pre-LVAD cardiac output of 2.8 L/min, stroke volume of 40 ml, and ejection fraction of 22%; the medium setting produced values of 3.5 L/min, 50 ml, and 28%, respectively. Results show that the PLSA controller set at 10 krpm, dropping to 7 krpm for dwell time of 6 s, adequately produced AVO for all tested cardiac functions with only minimal changes in cardiac output. However, AVO frequency was independent of opening area and systolic duration, which both decreased with increasing LVAD support. Furthermore, aortic pulsatility index quadrupled in the aortic root and doubled in the distal aorta during PLSA conditions, providing evidence that AVO and blood mixing are enabled by PLSA control at the appropriate speed.

  8. Physiological control of a rotary blood pump with selectable therapeutic options: control of pulsatility gradient.

    PubMed

    Arndt, Andreas; Nüsser, Peter; Graichen, Kurt; Müller, Johannes; Lampe, Bernhard

    2008-10-01

    A control strategy for rotary blood pumps meeting different user-selectable control objectives is proposed: maximum support with the highest feasible flow rate versus medium support with maximum ventricular washout and controlled opening of the aortic valve (AoV). A pulsatility index (PI) is calculated from the pressure difference, which is deduced from the axial thrust measured by the magnetic bearing of the pump. The gradient of PI with respect to pump speed (GPI) is estimated via online system identification. The outer loop of a cascaded controller regulates GPI to a reference value satisfying the selected control objective. The inner loop controls the PI to a reference value set by the outer loop. Adverse pumping states such as suction and regurgitation can be detected on the basis of the GPI estimates and corrected by the controller. A lumped-parameter computer model of the assisted circulation was used to simulate variations of ventricular contractility, pulmonary venous pressure, and aortic pressure. The performance of the outer control loop was demonstrated by transitions between the two control modes. Fast reaction of the inner loop was tested by stepwise reduction of venous return. For maximum support, a low PI was maintained without inducing ventricular collapse. For maximum washout, the pump worked at a high PI in the transition region between the opening and the permanently closed AoV. The cascaded control of GPI and PI is able to meet different control objectives and is worth testing in vitro and in vivo.

  9. Pulsatile Portal Vein Insulin Delivery Enhances Hepatic Insulin Action and Signaling

    PubMed Central

    Matveyenko, Aleksey V.; Liuwantara, David; Gurlo, Tatyana; Kirakossian, David; Dalla Man, Chiara; Cobelli, Claudio; White, Morris F.; Copps, Kyle D.; Volpi, Elena; Fujita, Satoshi; Butler, Peter C.

    2012-01-01

    Insulin is secreted as discrete insulin secretory bursts at ∼5-min intervals into the hepatic portal vein, these pulses being attenuated early in the development of type 1 and type 2 diabetes mellitus (T2DM). Intraportal insulin infusions (pulsatile, constant, or reproducing that in T2DM) indicated that the pattern of pulsatile insulin secretion delivered via the portal vein is important for hepatic insulin action and, therefore, presumably for hepatic insulin signaling. To test this, we examined hepatic insulin signaling in rat livers exposed to the same three patterns of portal vein insulin delivery by use of sequential liver biopsies in anesthetized rats. Intraportal delivery of insulin in a constant versus pulsatile pattern led to delayed and impaired activation of hepatic insulin receptor substrate (IRS)-1 and IRS-2 signaling, impaired activation of downstream insulin signaling effector molecules AKT and Foxo1, and decreased expression of glucokinase (Gck). We further established that hepatic Gck expression is decreased in the HIP rat model of T2DM, a defect that correlated with a progressive defect of pulsatile insulin secretion. We conclude that the physiological pulsatile pattern of insulin delivery is important in hepatic insulin signaling and glycemic control. Hepatic insulin resistance in diabetes is likely in part due to impaired pulsatile insulin secretion. PMID:22688333

  10. Pulsatile urea excretion in the gulf toadfish: mechanisms and controls.

    PubMed

    Wood, Chris M; McDonald, M Danielle; Sundin, Lena; Laurent, Pierre; Walsh, Patrick J

    2003-12-01

    Opsanus beta expresses a full complement of ornithine-urea cycle (OUC) enzymes and is facultatively ureotelic, reducing ammonia-N excretion and maintaining urea-N excretion under conditions of crowding/confinement. The switch to ureotelism is keyed by a modest rise in cortisol associated with a substantial increase in cytosolic glutamine synthetase for trapping of ammonia-N and an upregulation of the capacity of the mitochondrial OUC to use glutamine-N. The entire day's urea-N production is excreted in 1 or 2 short-lasting pulses, which occur exclusively through the gills. The pulse event is not triggered by an internal urea-N threshold, is not due to pulsatile urea-N production, but reflects pulsatile activation of a specific branchial excretion mechanism that rapidly clears urea-N from the body fluids. A bidirectional facilitated diffusion transporter, with pharmacological similarity to the UT-A type transporters of the mammalian kidney, is activated in the gills, associated with an increased trafficking of dense-cored vesicles in the pavement cells. An 1814 kB cDNA ('tUT') coding for a 475-amino acid protein with approximately 62% homology to mammalian UT-A's has been cloned and facilitates phloretin-sensitive urea transport when expressed in Xenopus oocytes. tUT occurs only in gill tissue, but tUT mRNA levels do not change over the pulse cycle, suggesting that tUT regulation occurs at a level beyond mRNA. Circulating cortisol levels consistently decline prior to a pulse event and rise thereafter. When cortisol is experimentally clamped at high levels, natural pulse events are suppressed in size but not in frequency, an effect mediated through glucocorticoid receptors. The cortisol decline appears to be permissive, rather than the actual trigger of the pulse event. Fluctuations in circulating AVT levels do not correlate with pulses; and injections of AVT (at supraphysiological levels) elicit only minute urea-N pulses. However, circulating 5-hydroxytryptamine (5

  11. Flow Field Characterization Inside an Arteriovenous Graft-to-Vein Anastomosis Under Pulsatile Flow Conditions

    DTIC Science & Technology

    2007-11-02

    to understand the affect of hemodialysis on intimal hyperplasia formation and graft failure. REFERENCES [1] N. Arslan, "Experimental...Hyperplasia", Chapter 2 of Vascular Access for Hemodialysis - II, W.L. Gore & Associates, Inc., and Precept Press, Inc., (B.G. Sommer and M.L. Henry, Eds

  12. Experiments On Flow In A Coronary Artery

    NASA Technical Reports Server (NTRS)

    Back, Lloyd H.; Kwack, Eug-Yon; Liem, Timothy K.; Crawford, Donald W.

    1993-01-01

    Report describes experiments on simulated flow of blood in atherosclerotic human coronary artery. Experiments performed on polyurethane cast made from S-shaped coronary artery of cadaver. Sucrose solution with viscosity of blood pumped through cast at physiologically realistic rates, and flow made pulsatile by mechanism alternately compressing and releasing elastic tube just upstream of cast.

  13. Experiments On Flow In A Coronary Artery

    NASA Technical Reports Server (NTRS)

    Back, Lloyd H.; Kwack, Eug-Yon; Liem, Timothy K.; Crawford, Donald W.

    1993-01-01

    Report describes experiments on simulated flow of blood in atherosclerotic human coronary artery. Experiments performed on polyurethane cast made from S-shaped coronary artery of cadaver. Sucrose solution with viscosity of blood pumped through cast at physiologically realistic rates, and flow made pulsatile by mechanism alternately compressing and releasing elastic tube just upstream of cast.

  14. Pulsatile blood pump with a linear drive actuator.

    PubMed

    Fukunaga, Kazuyoshi; Homma, Akihiko; Funakubo, Akio; Tatsumi, Eisuke; Taenaka, Yoshiyuki; Kitamura, Soichiro; Fukui, Yasuhiro

    2007-01-01

    The main purpose of this study was to develop an implantable direct-electromagnetic left ventricular assist system driven by a linear actuator (linear LVAS). The linear LVAS is a pulsatile pump with a pusher plate that is driven directly by a linear oscillatory actuator (LOA) without any movement converters. This prototype pump unit with a LOA was 100 mm in diameter, 50 mm in thickness, and weighed 740 g. The full-fill/full-eject driving method was applied to the control algorithm. In addition, a mechanism to detect and release sucking was realized to overcome this problem that accompanies the active-filling type of VAS. The performance of the linear LVAS was evaluated in a long-term animal experiment using a goat (56 kg). The goat survived for 42 days. The reason why we terminated this experiment was that thrombus was found in the pump. There was no frictional debris found around the LOA. The linear LVAS did not exhibit electrical or mechanical problems during the first animal experiment.

  15. Prevalence of Pulsatile Tinnitus Among Patients With Migraine.

    PubMed

    Weinreich, Heather M; Carey, John P

    2016-03-01

    To examine the prevalence of pulsatile tinnitus (PT) among patients with a diagnosis of migraine and to determine if treatment of migraine improves symptoms. Single-institution retrospective patient review. Academic tertiary referral center. Billing data capturing ICD-9 codes 346.xx and 388.3x was used to identify patients with history of migraine and tinnitus. Patients were excluded if the symptom of PT could be attributed to an alternate diagnosis. Data were extracted from the patients' electronic medical records. Therapeutic patients were prescribed a strict migraine diet with or without migraine medication. Subjective improvement in tinnitus as documented in electronic medical records. One thousand two hundred four patients were identified with an ICD-9 code for migraine and of those patients, 12% (n = 145) had an ICD-9 code for tinnitus. After ruling out alternative causes, the prevalence of PT among all patients with migraine was 1.9%. Of migrainers with PT who underwent migraine treatment, 11 out of 16 reported resolution or improvement of their PT. PT can be observed in the context of migraine. Migraine treatment with avoidance of dietary triggers with or without medication can possibly lead to resolution of PT.

  16. Post-stenotic plug-like jet with a vortex ring demonstrated by 4D flow MRI.

    PubMed

    Kim, Guk Bae; Ha, Hojin; Kweon, Jihoon; Lee, Sang Joon; Kim, Young-Hak; Yang, Dong Hyun; Kim, Namkug

    2016-05-01

    To investigate the details of the flow structure of a plug-like jet that had a vortex ring in pulsatile stenotic phantoms using 4D flow MRI. Pulsatile Newtonian flows in two stenotic phantoms with 50% and 75% reductions in area were scanned by 4D flow MRI. Blood analog working fluid was circulated via the stenotic phantom using a pulsatile pump at a constant pulsating frequency of 1Hz. The velocity and vorticity fields of the plug-like jet with a vortex ring were quantitatively analyzed in the spatial and temporal domains. Pulsatile stenotic flow showed a plug-like jet at the specific stenotic degree of 50% in our pulsatile waveform design. This plug-like jet was found at the decelerating period in the post-stenotic region of 26.4mm (1.2 D). It revealed a vortex ring structure with vorticity strength in the range of ±100s(-1). We observed a plug-like jet with a vortex ring in pulsatile stenotic flow by in vitro visualization using 4D flow MRI. In this plug-like jet, the local fastest flow region occurred at the post-systole phase in the post-stenotic region, which was distinguishable from a typical stenotic jet flow at systole phase. Copyright © 2015 Elsevier Inc. All rights reserved.

  17. Effects of pulsatile perfusion during cardiopulmonary bypass on biochemical markers and kidney function in patients undergoing cardiac surgeries.

    PubMed

    Mohammadzadeh, Alireza; Jafari, Naser; Hasanpour, Mohammad; Sahandifar, Soheil; Ghafari, Masoud; Alaei, Vahed

    2013-01-01

    For several years there is no conclusive guideline on the effectiveness of pulsatile or non-pulsatile perfusion during cardiopulmonary bypass (CPB) in patients undergoing cardiac surgeries. In this study, we evaluated the effect of pulsatile versus continuous perfusion on the myocardial release of the cardiac biochemical markers including, creatine phosphokinase (CPK), cardiac creatine kinase (CK-MB), and lactate dehydrogenase (LDH), and also kidney function tests including: blood urea nitrogen test (BUN) and creatinine test (Cr) in patients that underwent both pulsatile and non-pulsatile methods before and after heart surgeries. A total of 80 patients were enrolled in this study, 40 patients in each pulsatile and non-pulsatile group. Venous blood samples were drown from each patient in two groups before operation and after operation at, 24, 48, and 72 h and analyzed separately for CPK, its cardiac isoenzyme (CK-MB), LDH, BUN and Cr. There were no significant differences between the two groups with regard to preoperative parameters such as sex, age, and body surface area. Our study shows that the effect of pulsatile perfusion on cardiac and kidney function is better than the non-