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Sample records for filters pulsatile flow

  1. 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

  2. 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.

  3. 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.

  4. 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.

  5. 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).

  6. 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.

  7. 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...

  8. 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...

  9. 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...

  10. 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...

  11. 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...

  12. 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

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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'.

  18. 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

  19. 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

  20. 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

  1. 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.

  2. 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.

  3. 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

  4. 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

  5. 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.

  6. 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

  7. 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

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. [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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Concentric Split Flow Filter

    NASA Technical Reports Server (NTRS)

    Stapleton, Thomas J. (Inventor)

    2015-01-01

    A concentric split flow filter may be configured to remove odor and/or bacteria from pumped air used to collect urine and fecal waste products. For instance, filter may be designed to effectively fill the volume that was previously considered wasted surrounding the transport tube of a waste management system. The concentric split flow filter may be configured to split the air flow, with substantially half of the air flow to be treated traveling through a first bed of filter media and substantially the other half of the air flow to be treated traveling through the second bed of filter media. This split flow design reduces the air velocity by 50%. In this way, the pressure drop of filter may be reduced by as much as a factor of 4 as compare to the conventional design.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. 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

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. 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

  15. 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.

  16. 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.

  17. 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

  18. 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.

  19. 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

  20. 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.

  1. 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

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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.

  17. High flow ceramic pot filters.

    PubMed

    van Halem, D; van der Laan, H; Soppe, A I A; Heijman, S G J

    2017-07-20

    Ceramic pot filters are considered safe, robust and appropriate technologies, but there is a general consensus that water revenues are limited due to clogging of the ceramic element. The objective of this study was to investigate the potential of high flow ceramic pot filters to produce more water without sacrificing their microbial removal efficacy. High flow pot filters, produced by increasing the rice husk content, had a higher initial flow rate (6-19 L h(-1)), but initial LRVs for E. coli of high flow filters was slightly lower than for regular ceramic pot filters. This disadvantage was, however, only temporarily as the clogging in high flow filters had a positive effect on the LRV for E. coli (from below 1 to 2-3 after clogging). Therefore, it can be carefully concluded that regular ceramic pot filters perform better initially, but after clogging, the high flow filters have a higher flow rate as well as a higher LRV for E. coli. To improve the initial performance of new high flow filters, it is recommended to further utilize residence time of the water in the receptacle, since additional E. coli inactivation was observed during overnight storage. Although a relationship was observed between flow rate and LRV of MS2 bacteriophages, both regular and high flow filters were unable to reach over 2 LRV. Copyright © 2017 Elsevier Ltd. All rights reserved.

  18. 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.

  19. 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

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. Particle flow superpositional GLMB filter

    NASA Astrophysics Data System (ADS)

    Saucan, Augustin-Alexandru; Li, Yunpeng; Coates, Mark

    2017-05-01

    In this paper we propose a Superpositional Marginalized δ-GLMB (SMδ-GLMB) filter for multi-target tracking and we provide bootstrap and particle flow particle filter implementations. Particle filter implementations of the marginalized δ-GLMB filter are computationally demanding. As a first contribution we show that for the specific case of superpositional observation models, a reduced complexity update step can be achieved by employing a superpositional change of variables. The resulting SMδ-GLMB filter can be readily implemented using the unscented Kalman filter or particle filtering methods. As a second contribution, we employ particle flow to produce a measurement-driven importance distribution that serves as a proposal in the SMδ-GLMB particle filter. In high-dimensional state systems or for highly- informative observations the generic particle filter often suffers from weight degeneracy or otherwise requires a prohibitively large number of particles. Particle flow avoids particle weight degeneracy by guiding particles to regions where the posterior is significant. Numerical simulations showcase the reduced complexity and improved performance of the bootstrap SMδ-GLMB filter with respect to the bootstrap Mδ-GLMB filter. The particle flow SMδ-GLMB filter further improves the accuracy of track estimates for highly informative measurements.

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. [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.

  18. [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.

  19. 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.

  20. 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

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. 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.

  8. 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.

  9. 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).

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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

  10. 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.

  11. 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).

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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.

  17. 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

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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

  4. DEMONSTRATION BULLETIN: COLLOID POLISHING FILTER METHOD - FILTER FLOW TECHNOLOGY, INC.

    EPA Science Inventory

    The Filter Flow Technology, Inc. (FFT) Colloid Polishing Filter Method (CPFM) was tested as a transportable, trailer mounted, system that uses sorption and chemical complexing phenomena to remove heavy metals and nontritium radionuclides from water. Contaminated waters can be pro...

  5. DEMONSTRATION BULLETIN: COLLOID POLISHING FILTER METHOD - FILTER FLOW TECHNOLOGY, INC.

    EPA Science Inventory

    The Filter Flow Technology, Inc. (FFT) Colloid Polishing Filter Method (CPFM) was tested as a transportable, trailer mounted, system that uses sorption and chemical complexing phenomena to remove heavy metals and nontritium radionuclides from water. Contaminated waters can be pro...

  6. 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.

  7. 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

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. 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.

  13. 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.

  14. 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

  15. 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.

  16. 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

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. Gaussian particle flow implementation of PHD filter

    NASA Astrophysics Data System (ADS)

    Zhao, Lingling; Wang, Junjie; Li, Yunpeng; Coates, Mark J.

    2016-05-01

    Particle filter and Gaussian mixture implementations of random finite set filters have been proposed to tackle the issue of jointly estimating the number of targets and their states. The Gaussian mixture PHD (GM-PHD) filter has a closed-form expression for the PHD for linear and Gaussian target models, and extensions using the extended Kalman filter or unscented Kalman Filter have been developed to allow the GM-PHD filter to accommodate mildly nonlinear dynamics. Errors resulting from linearization or model mismatch are unavoidable. A particle filter implementation of the PHD filter (PF-PHD) is more suitable for nonlinear and non-Gaussian target models. The particle filter implementations are much more computationally expensive and performance can suffer when the proposal distribution is not a good match to the posterior. In this paper, we propose a novel implementation of the PHD filter named the Gaussian particle flow PHD filter (GPF-PHD). It employs a bank of particle flow filters to approximate the PHD; these play the same role as the Gaussian components in the GM-PHD filter but are better suited to non-linear dynamics and measurement equations. Using the particle flow filter allows the GPF-PHD filter to migrate particles to the dense regions of the posterior, which leads to higher efficiency than the PF-PHD. We explore the performance of the new algorithm through numerical simulations.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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

  3. 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

  4. 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

  5. Angle only tracking with particle flow filters

    NASA Astrophysics Data System (ADS)

    Daum, Fred; Huang, Jim

    2011-09-01

    We show the results of numerical experiments for tracking ballistic missiles using only angle measurements. We compare the performance of an extended Kalman filter with a new nonlinear filter using particle flow to compute Bayes' rule. For certain difficult geometries, the particle flow filter is an order of magnitude more accurate than the EKF. Angle only tracking is of interest in several different sensors; for example, passive optics and radars in which range and Doppler data are spoiled by jamming.

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. 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

  15. 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.

  16. 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.

  17. 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

  18. 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

  19. 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.

  20. 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

  1. [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.

  2. 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.

  3. Mechanical analysis of a cross flow filter

    SciTech Connect

    Alvin, M.A.; Lippert, T.E.; Attaar, M.H.; McNerney, K.R.

    1992-12-01

    Material properties have also been generated at the Argonne National Laboratories which detail the fracture toughness, Weibull modulus, and critical flaw size for a specifically fabricated lot of P-100A alumina/mullite cross flow filters.(Singh, 1990) The critical flaw size within the P-100A matrix was estimated to be {approximately}500 {mu},m which includes both large interconnected pores, as well as potentially debonded areas along the mid-rib or gas channel seams. Critical flaws are generally considered as potential failure initiation sites within the ceramic matrix. In addition maximum filter element stress levels induced by the process system have been estimated at ANL through the use of finite element computer analyses. These efforts project that the highest stresses result within the flange region of the cross flow filter. As a result of these projections, efforts at Coors Ceramics were directed to improving the overall strength of the alumina/mullite material which is used for cross flow filter fabrication. The results of the efforts at Coors Ceramics provide a significant improvement in the hot strength of the P-100A alumina/mullite filter matrix. Westinghouse assessed the existing nondestructive evaluation (NDE) techniques in terms of identifying methods for detecting critical flaws within the cross flow filter body. To date viable, cost effective methods for detecting critical flaws within the P-100A alumina/mullite matrix, or along the mid-rib bonds or gas channel seams in the full-scale, porous ceramic cross flow filter element are not readily available. As an alternate approach, Westinghouse focused its attention on developing NDE techniques as inspection methods for evaluating the extent of bonding along the mid-rib bonds and gas channel seams which results during the various fabrication stages of the cross flow filter element.

  4. Mechanical analysis of a cross flow filter

    SciTech Connect

    Alvin, M.A.; Lippert, T.E.; Attaar, M.H.; McNerney, K.R.

    1992-01-01

    Material properties have also been generated at the Argonne National Laboratories which detail the fracture toughness, Weibull modulus, and critical flaw size for a specifically fabricated lot of P-100A alumina/mullite cross flow filters.(Singh, 1990) The critical flaw size within the P-100A matrix was estimated to be [approximately]500 [mu],m which includes both large interconnected pores, as well as potentially debonded areas along the mid-rib or gas channel seams. Critical flaws are generally considered as potential failure initiation sites within the ceramic matrix. In addition maximum filter element stress levels induced by the process system have been estimated at ANL through the use of finite element computer analyses. These efforts project that the highest stresses result within the flange region of the cross flow filter. As a result of these projections, efforts at Coors Ceramics were directed to improving the overall strength of the alumina/mullite material which is used for cross flow filter fabrication. The results of the efforts at Coors Ceramics provide a significant improvement in the hot strength of the P-100A alumina/mullite filter matrix. Westinghouse assessed the existing nondestructive evaluation (NDE) techniques in terms of identifying methods for detecting critical flaws within the cross flow filter body. To date viable, cost effective methods for detecting critical flaws within the P-100A alumina/mullite matrix, or along the mid-rib bonds or gas channel seams in the full-scale, porous ceramic cross flow filter element are not readily available. As an alternate approach, Westinghouse focused its attention on developing NDE techniques as inspection methods for evaluating the extent of bonding along the mid-rib bonds and gas channel seams which results during the various fabrication stages of the cross flow filter element.

  5. 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

  6. Velocity filtering applied to optical flow calculations

    NASA Technical Reports Server (NTRS)

    Barniv, Yair

    1990-01-01

    Optical flow is a method by which a stream of two-dimensional images obtained from a forward-looking passive sensor is used to map the three-dimensional volume in front of a moving vehicle. Passive ranging via optical flow is applied here to the helicopter obstacle-avoidance problem. Velocity filtering is used as a field-based method to determine range to all pixels in the initial image. The theoretical understanding and performance analysis of velocity filtering as applied to optical flow is expanded and experimental results are presented.

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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

  18. 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.

  19. 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

  20. 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

  1. 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

  2. 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.

  3. 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.

  4. 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

  5. A Filtering Method For Gravitationally Stratified Flows

    SciTech Connect

    Gatti-Bono, Caroline; Colella, Phillip

    2005-04-25

    Gravity waves arise in gravitationally stratified compressible flows at low Mach and Froude numbers. These waves can have a negligible influence on the overall dynamics of the fluid but, for numerical methods where the acoustic waves are treated implicitly, they impose a significant restriction on the time step. A way to alleviate this restriction is to filter out the modes corresponding to the fastest gravity waves so that a larger time step can be used. This paper presents a filtering strategy of the fully compressible equations based on normal mode analysis that is used throughout the simulation to compute the fast dynamics and that is able to damp only fast gravity modes.

  6. 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.

  7. Spin selective filtering of polariton condensate flow

    SciTech Connect

    Gao, T.; Antón, C.; Martín, M. D.; Liew, T. C. H.; Hatzopoulos, Z.; Viña, L.; Eldridge, P. S.; Savvidis, P. G.

    2015-07-06

    Spin-selective spatial filtering of propagating polariton condensates, using a controllable spin-dependent gating barrier, in a one-dimensional semiconductor microcavity ridge waveguide is reported. A nonresonant laser beam provides the source of propagating polaritons, while a second circularly polarized weak beam imprints a spin dependent potential barrier, which gates the polariton flow and generates polariton spin currents. A complete spin-based control over the blocked and transmitted polaritons is obtained by varying the gate polarization.

  8. 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.

  9. 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

  10. 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

  11. Effects of filter housing and ductwork configuration on air flow uniformity inside air cleaning filter housings

    SciTech Connect

    Paul, J.D.

    1992-12-31

    Each new HEPA filter installation presents a different physical configuration based on the system requirements the available space and designer preference. Each different configuration can result in variations of air flow uniformity inside the filter housing across the filter banks. This paper will present the results of air flow uniformity testing for six different filter housing/ductwork configurations and discuss if any of the variations in air flow uniformity is attributable to the difference in the physical arrangements for the six cases.

  12. Effects of filter housing and ductwork configuration on air flow uniformity inside air cleaning filter housings

    SciTech Connect

    Paul, J.D.

    1992-01-01

    Each new HEPA filter installation presents a different physical configuration based on the system requirements the available space and designer preference. Each different configuration can result in variations of air flow uniformity inside the filter housing across the filter banks. This paper will present the results of air flow uniformity testing for six different filter housing/ductwork configurations and discuss if any of the variations in air flow uniformity is attributable to the difference in the physical arrangements for the six cases.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. Clutter filter design for ultrasound color flow imaging.

    PubMed

    Bjaerum, Steinar; Torp, Hans; Kristoffersen, Kjell

    2002-02-01

    For ultrasound color flow images with high quality, it is important to suppress the clutter signals originating from stationary and slowly moving tissue sufficiently. Without sufficient clutter rejection, low velocity blood flow cannot be measured, and estimates of higher velocities will have a large bias. The small number of samples available (8 to 16) makes clutter filtering in color flow imaging a challenging problem. In this paper, we review and analyze three classes of filters: finite impulse response (FIR), infinite impulse response (IIR), and regression filters. The quality of the filters was assessed based on the frequency response, as well as on the bias and variance of a mean blood velocity estimator using an autocorrelation technique. For FIR filters, the frequency response was improved by allowing a non-linear phase response. By estimating the mean blood flow velocity from two vectors filtered in the forward and backward direction, respectively, the standard deviation was significantly lower with a minimum phase filter than with a linear phase filter. For IIR filters applied to short signals, the transient part of the output signal is important. We analyzed zero, step, and projection initialization, and found that projection initialization gave the best filters. For regression filters, polynomial basis functions provide effective clutter suppression. The best filters from each of the three classes gave comparable bias and variance of the mean blood velocity estimates. However, polynomial regression filters and projection-initialized IIR filters had a slightly better frequency response than could be obtained with FIR filters.

  20. 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.

  1. 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.

  2. 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

  3. Computationally efficient angles-only tracking with particle flow filters

    NASA Astrophysics Data System (ADS)

    Costa, Russell; Wettergren, Thomas A.

    2015-05-01

    Particle filters represent the current state of the art in nonlinear, non-Gaussian filtering. They are easy to implement and have been applied in numerous domains. That being said, particle filters can be impractical for problems with state dimensions greater than four, if some other problem specific efficiencies can't be identified. This "curse of dimensionality" makes particle filters a computationally burdensome approach, and the associated re-sampling makes parallel processing difficult. In the past several years an alternative to particle filters dubbed particle flows has emerged as a (potentially) much more efficient method to solving non-linear, non-Gaussian problems. Particle flow filtering (unlike particle filtering) is a deterministic approach, however, its implementation entails solving an under-determined system of partial differential equations which has infinitely many potential solutions. In this work we apply the filters to angles-only target motion analysis problems in order to quantify the (if any) computational gains over standard particle filtering approaches. In particular we focus on the simplest form of particle flow filter, known as the exact particle flow filter. This form assumes a Gaussian prior and likelihood function of the unknown target states and is then linearized as is standard practice for extended Kalman filters. We implement both particle filters and particle flows and perform numerous numerical experiments for comparison.

  4. 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.

  5. Implementation and performance of FPGA-accelerated particle flow filter

    NASA Astrophysics Data System (ADS)

    Charalampidis, Dimitrios; Jilkov, Vesselin P.; Wu, Jiande

    2015-09-01

    The particle flow filters, proposed by Daum & Hwang, provide a powerful means for density-based nonlinear filtering but their computation is intense and may be prohibitive for real-time applications. This paper proposes a design for superfast implementation of the exact particle flow filter using a field-programmable gate array (FPGA) as a parallel environment to speedup computation. Simulation results from a nonlinear filtering example are presented to demonstrate that using FPGA can dramatically accelerate particle flow filters through parallelization at the expense of a tolerable loss in accuracy as compared to nonparallel implementation.

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. Hot gas cross flow filtering module

    DOEpatents

    Lippert, Thomas E.; Ciliberti, David F.

    1988-01-01

    A filter module for use in filtering particulates from a high temperature gas has a central gas duct and at least one horizontally extending support mount affixed to the duct. The support mount supports a filter element thereon and has a chamber therein, which communicates with an inner space of the duct through an opening in the wall of the duct, and which communicates with the clean gas face of the filter element. The filter element is secured to the support mount over an opening in the top wall of the support mount, with releasable securement provided to enable replacement of the filter element when desired. Ceramic springs may be used in connection with the filter module either to secure a filter element to a support mount or to prevent delamination of the filter element during blowback.

  11. 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.

  12. Method and apparatus for measuring flow velocity using matched filters

    DOEpatents

    Raptis, Apostolos C.

    1983-01-01

    An apparatus and method for measuring the flow velocities of individual phase flow components of a multiphase flow utilizes matched filters. Signals arising from flow noise disturbance are extracted from the flow, at upstream and downstream locations. The signals are processed through pairs of matched filters which are matched to the flow disturbance frequency characteristics of the phase flow component to be measured. The processed signals are then cross-correlated to determine the transit delay time of the phase flow component between sensing positions.

  13. Method and apparatus for measuring flow velocity using matched filters

    DOEpatents

    Raptis, A.C.

    1983-09-06

    An apparatus and method for measuring the flow velocities of individual phase flow components of a multiphase flow utilizes matched filters. Signals arising from flow noise disturbance are extracted from the flow, at upstream and downstream locations. The signals are processed through pairs of matched filters which are matched to the flow disturbance frequency characteristics of the phase flow component to be measured. The processed signals are then cross-correlated to determine the transit delay time of the phase flow component between sensing positions. 8 figs.

  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. Modeling Flow Past a Tilted Vena Cava Filter

    SciTech Connect

    Singer, M A; Wang, S L

    2009-06-29

    Inferior vena cava filters are medical devices used to prevent pulmonary embolism (PE) from deep vein thrombosis. In particular, retrievable filters are well-suited for patients who are unresponsive to anticoagulation therapy and whose risk of PE decreased with time. The goal of this work is to use computational fluid dynamics to evaluate the flow past an unoccluded and partially occluded Celect inferior vena cava filter. In particular, the hemodynamic response to thrombus volume and filter tilt is examined, and the results are compared with flow conditions that are known to be thrombogenic. A computer model of the filter inside a model vena cava is constructed using high resolution digital photographs and methods of computer aided design. The models are parameterized using the Overture software framework, and a collection of overlapping grids is constructed to discretize the flow domain. The incompressible Navier-Stokes equations are solved, and the characteristics of the flow (i.e., velocity contours and wall shear stresses) are computed. The volume of stagnant and recirculating flow increases with thrombus volume. In addition, as the filter increases tilt, the cava wall adjacent to the tilted filter is subjected to low velocity flow that gives rise to regions of low wall shear stress. The results demonstrate the ease of IVC filter modeling with the Overture software framework. Flow conditions caused by the tilted Celect filter may elevate the risk of intrafilter thrombosis and facilitate vascular remodeling. This latter condition also increases the risk of penetration and potential incorporation of the hook of the filter into the vena caval wall, thereby complicating filter retrieval. Consequently, severe tilt at the time of filter deployment may warrant early clinical intervention.

  20. 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.

  1. 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.

  2. High Order Filter Methods for Shock/Turbulence MHD Flows

    NASA Technical Reports Server (NTRS)

    Yee, H. C.; Sjoegreen, Bjoern

    2003-01-01

    Low-dissipative high order filter finite difference methods for shock/turbulence/combustion compressible viscous MHD flows has been constructed. Several variants of the filter approach that cater to different flow types are proposed. These filters provide a natural and efficient way for the minimization of the divergence of the magnetic field (del (raided dot) B) numerical error in the sense that no standard divergence cleaning is required. For certain 2-D MHD test problems, divergence free preservation of the magnetic fields of these filter schemes has been achieved.

  3. 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.

  4. Particle flow for nonlinear filters with log-homotopy

    NASA Astrophysics Data System (ADS)

    Daum, Fred; Huang, Jim

    2008-04-01

    We describe a new nonlinear filter that is vastly superior to the classic particle filter. In particular, the computational complexity of the new filter is many orders of magnitude less than the classic particle filter with optimal estimation accuracy for problems with dimension greater than 2 or 3. We consider nonlinear estimation problems with dimensions varying from 1 to 20 that are smooth and fully coupled (i.e. dense not sparse). The new filter implements Bayes' rule using particle flow rather than with a pointwise multiplication of two functions; this avoids one of the fundamental and well known problems in particle filters, namely "particle collapse" as a result of Bayes' rule. We use a log-homotopy to derive the ODE that describes particle flow. This paper was written for normal engineers, who do not have homotopy for breakfast.

  5. Method of producing monolithic ceramic cross-flow filter

    DOEpatents

    Larsen, D.A.; Bacchi, D.P.; Connors, T.F.; Collins, E.L. III

    1998-02-10

    Ceramic filter of various configuration have been used to filter particulates from hot gases exhausted from coal-fired systems. Prior ceramic cross-flow filters have been favored over other types, but those previously have been assemblies of parts somehow fastened together and consequently subject often to distortion or delamination on exposure hot gas in normal use. The present new monolithic, seamless, cross-flow ceramic filters, being of one-piece construction, are not prone to such failure. Further, these new products are made by a novel casting process which involves the key steps of demolding the ceramic filter green body so that none of the fragile inner walls of the filter is cracked or broken. 2 figs.

  6. Method of producing monolithic ceramic cross-flow filter

    DOEpatents

    Larsen, David A.; Bacchi, David P.; Connors, Timothy F.; Collins, III, Edwin L.

    1998-01-01

    Ceramic filter of various configuration have been used to filter particulates from hot gases exhausted from coal-fired systems. Prior ceramic cross-flow filters have been favored over other types, but those previously horn have been assemblies of parts somehow fastened together and consequently subject often to distortion or delamination on exposure hot gas in normal use. The present new monolithic, seamless, cross-flow ceramic filters, being of one-piece construction, are not prone to such failure. Further, these new products are made by novel casting process which involves the key steps of demolding the ceramic filter green body so that none of the fragile inner walls of the filter is cracked or broken.

  7. Granular flow in Dorfan Impingo filter for gas cleanup

    SciTech Connect

    Hsiau, S.S.; Smid, J.; Tsai, H.H.; Kuo, J.T.; Chou, C.S.

    1999-07-01

    Inside a two-dimensional model of the louvered Drofan Impingo panel with transparent front and rear walls, the velocity fields of filter granules without gas cross flow were observed. The PE beads with diameter of 6 mm were used as filter granules. The filter bed was filled with beads continuously and circulated until the granular flows inside the panel reached the steady state condition. In the moving granular bed, there is a central fast flowing core of filter granules surrounded by large quasi-stagnant zones located close to the louver walls. The existence of quasi-stagnant zones may result in the dust plugging problems. The velocity fields of filter granules are plotted for three different louver geometries.

  8. SITE TECHNOLOGY CAPSULE: FILTER FLOW TECHNOLOGY, INC. - COLLOID POLISHING FILTER METHOD

    EPA Science Inventory

    The Filter Flow Technology, Inc. (FFT) Coloid Polishing Filter Method (CPFM) was demonstrated at the U.S Department of Energy's (DOE) Rock Flats Plant (RFP) as part of the U.S. Environmental Protection Agency's (EPA) Superfund and Innovative Technology Evaluation (SITE) program. ...

  9. SITE TECHNOLOGY CAPSULE: FILTER FLOW TECHNOLOGY, INC. - COLLOID POLISHING FILTER METHOD

    EPA Science Inventory

    The Filter Flow Technology, Inc. (FFT) Coloid Polishing Filter Method (CPFM) was demonstrated at the U.S Department of Energy's (DOE) Rock Flats Plant (RFP) as part of the U.S. Environmental Protection Agency's (EPA) Superfund and Innovative Technology Evaluation (SITE) program. ...

  10. Method and apparatus for measuring flow velocity using matched filters

    SciTech Connect

    Raptis, A.C.

    1981-07-17

    An apparatus and method for measuring the flow velocities of individual phase flow components of a multiphase flow is disclosed. Signals arising from flow noise disturbance are extracted from the flow, at upstream and downstream locations. The signals are processed through pairs of matched filters which are matched to the flow disturbance frequency characteristics of the phase flow component to be measured. The processed signals are then cross-correlated to determine the transit delay time of the phase flow component between sensing positions.

  11. Filtered Rayleigh Scattering Measurements in a Buoyant Flow Field

    DTIC Science & Technology

    2008-03-01

    John William Strutt , the third Baron of Rayleigh , or more commonly known as Lord Rayleigh , was the first to offer a correct explanation of the...FILTERED RAYLEIGH SCATTERING MEASUREMENTS IN A BUOYANT FLOW FIELD         THESIS       Steven Michael Meents, Captain, USAF...AFIT/GAE/ENY/08-M22 FILTERED RAYLEIGH SCATTERING MEASUREMENTS IN A BUOYANT FLOW FIELD THESIS Presented to the Faculty Department of Aeronautics

  12. 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.

  13. 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

  14. Adaptive clutter filtering for ultrasound color flow imaging.

    PubMed

    Yoo, Yang Mo; Managuli, Ravi; Kim, Yongmin

    2003-09-01

    In this article, we present an adaptive clutter rejection method for selecting different clutter filters in ultrasound color flow imaging. A single clutter filter is typically used to reject the clutter. Because the clutter characteristics vary in both space and time, the single clutter filter approach has difficulty in providing optimum clutter rejection in ultrasound images. To achieve more accurate velocity estimation, we have developed a method to select a clutter filter adaptively at each location in an image from a set of predefined filters. Selection criteria have been developed based on the underlying clutter characteristics and the properties of various filters (e.g., minimum-phase finite impulse response, projection-initialized infinite impulse response and polynomial regression). We have incorporated our adaptive clutter rejection method in an ultrasound system. We have found that our adaptive method can reduce the mean absolute error between the estimated and true flow velocities significantly compared with the conventional methods, in which a single clutter filter is used throughout the entire image. With in vivo abdominal data, we obtained an average gain of 5.0 dB in signal-to-clutter ratio (SCR), compared with the conventional method. These preliminary results indicate that the proposed adaptive method could improve the accuracy of flow velocity estimation in ultrasound color flow imaging through the improvement in SCR and the reduction in bias.

  15. 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.

  16. 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.

  17. Mathematical modeling of flow field in ceramic candle filter

    NASA Astrophysics Data System (ADS)

    Seo, Taewon; Kim, Heuy-Dong; Choi, Joo-Hong; Chung, Jae Hwa

    1998-06-01

    Integrated gasification combined cycle (IGCC) is one of the candidates to achieve stringent environmental regulation among the clean coal technologies. Advancing the technology of the hot gas cleanup systems is the most critical component in the development of the IGCC. Thus the aim of this study is to understand the flow field in the ceramic filter and the influence of ceramic filter in removal of the particles contained in the hot gas flow. The numerical model based on the Reynolds stress turbulence model with the Darcy’s law in the porous region is adopted. It is found that the effect of the porosity in the flowfield is negligibly small while the effect of the filter length is significant. It is also found as the permeability decreases, the reattachment point due to the flow separation moves upstream. This is because the fluid is sucked into the filter region due to the pressure drop before the flow separation occurs. The particle follows well with the fluid stream and the particle is directly sucked into the filter due to the pressure drop even in the flow separation region.

  18. Electrically heated particulate filter with zoned exhaust flow control

    DOEpatents

    Gonze, Eugene V [Pinckney, MI

    2012-06-26

    A system includes a particulate matter (PM) filter that includes X zones. An electrical heater includes Y heater segments that are associated with respective ones of the X zones. The electrical heater is arranged upstream from and proximate with the PM filter. A valve assembly includes Z sections that are associated with respective ones of the X zones. A control module adjusts flow through each of the Z sections during regeneration of the PM filter via control of the valve assembly. X, Y and Z are integers.

  19. Direction of fluid flow and the properties of fibrous filters

    SciTech Connect

    Pich, J.; Spurny, K.

    1991-01-01

    The influence of the fluid flow direction (downflow and upflow) on the filtration properties of filters that have a fibrous structure is investigated. It is concluded that selectivity of these filters (dependence of the filter efficiency on the particle size) in the case of upflow is changed - in comparison with the case of downflow - in three ways: the position of the minimum of this dependence is shifted to larger particle sizes, and the whole selectivity is decreased and simultaneously deformed. Corresponding equations for this shift and changes are derived and analyzed. Theoretical predictions are compared with available experimental data. In all cases qualitative agreement and in some cases quantitative agreement is found.

  20. Development of a monolithic ceramic cross flow filter

    SciTech Connect

    Larsen, D.A.

    1995-12-01

    High-temperature, high-pressure particulate control is required to protect turbine equipment and to meet environmental stack emissions standards in coal-fueled power systems. Ceramic cross flow filters have high surface area per unit volume for removing particulates from these hot gas streams. A one-piece monolithic ceramic cross flow filter is needed. Mullite bonded, porous, permeable alumina ceramics were made on a lab scale with the Blasch injection forming process. Permeability and other initial targeted property requirements were achieved: >200 cd (<1 iwg/fpm), room temperature modulus of rupture >1000 psi, particle size 100/200 mesh, pore size 20 microns. It is concluded that it is feasible to use the proprietary Blasch process to form cross flow filters.

  1. Cross flow filter for AEPSC: TIDD slipstream HGCU project preliminary design package for Westinghouse cross flow filter system. Final submittal

    SciTech Connect

    Haldipur, G.B.; Lippert, T.E.

    1989-06-16

    The Westinghouse ceramic cross-flow filter element is constructed of multiple layers of thin, porous ceramic plates that contain ribs to form gas flow channels. Consecutive layers of the ceramic plates are oriented such that the channels of alternating plates are at an angle of 90 degrees (``cross flow``) to each other. The current size of a ceramic cross flow filter element is 12 in. {times} 12 in. {times} 14 in. Both sides of the short channels (4 in.) are exposed to the particle-laden coal gas. One end of the long (12 in.) channels is sealed while the other end of the long channel is mounted to the clean gas plenum. The particle-laden coal gas flows through the ``roof and floor`` of the porous ceramic plates that comprise the short, ``dirty side`` channels. The gas flows through the porous plates to the long, ``clean side`` channels. The gas flows through the porous plates to the long, ``clean side`` channels and finally to the clean gas plenum. The dust cake on the ``dirty side`` channels is periodically removed by applying a high-pressure reverse pulse of dry, clean gas through the clean gas plenum. For the TIDD plant filter slipstream, air will be utilized for filter cleaning.

  2. Cross flow filter for AEPSC: TIDD slipstream HGCU project preliminary design package for Westinghouse cross flow filter system

    SciTech Connect

    Haldipur, G.B.; Lippert, T.E.

    1989-06-16

    The Westinghouse ceramic cross-flow filter element is constructed of multiple layers of thin, porous ceramic plates that contain ribs to form gas flow channels. Consecutive layers of the ceramic plates are oriented such that the channels of alternating plates are at an angle of 90 degrees ( cross flow'') to each other. The current size of a ceramic cross flow filter element is 12 in. {times} 12 in. {times} 14 in. Both sides of the short channels (4 in.) are exposed to the particle-laden coal gas. One end of the long (12 in.) channels is sealed while the other end of the long channel is mounted to the clean gas plenum. The particle-laden coal gas flows through the roof and floor'' of the porous ceramic plates that comprise the short, dirty side'' channels. The gas flows through the porous plates to the long, clean side'' channels. The gas flows through the porous plates to the long, clean side'' channels and finally to the clean gas plenum. The dust cake on the dirty side'' channels is periodically removed by applying a high-pressure reverse pulse of dry, clean gas through the clean gas plenum. For the TIDD plant filter slipstream, air will be utilized for filter cleaning.

  3. 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.

  4. 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

  5. Transverse high gradient magnetic filter cell with bounded flow field

    SciTech Connect

    Badescu, V.; Rotariu, O.; Murariu, V.; Rezlescu, N.

    1997-11-01

    The capture of fine paramagnetic particles from a fluid suspension in a magnetic filter element of a novel design is analyzed. Unlike the systems previously analyzed, in the model the flow is bounded by two by two parallel planar plates, and the ferromagnetic wires are installed outside these spaces, within planes parallel with the plates. The analysis is based on the study of particle trajectories, considering the laminar flow of carrier fluid. From these the authors establish the conditions for the maximum recovery of the particles in suspension. This study is useful in designing magnetic filter batteries with corrosion-protected ferromagnetic wires.

  6. 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).

  7. 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

  8. 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

  9. Application of velocity filtering to optical-flow passive ranging

    NASA Technical Reports Server (NTRS)

    Barniv, Yair

    1992-01-01

    The performance of the velocity filtering method as applied to optical-flow passive ranging under real-world conditions is evaluated. The theory of the 3-D Fourier transform as applied to constant-speed moving points is reviewed, and the space-domain shift-and-add algorithm is derived from the general 3-D matched filtering formulation. The constant-speed algorithm is then modified to fit the actual speed encountered in the optical flow application, and the passband of that filter is found in terms of depth (sensor/object distance) so as to cover any given range of depths. Two algorithmic solutions for the problems associated with pixel interpolation and object expansion are developed, and experimental results are presented.

  10. Absorption Filter Based Optical Diagnostics in High Speed Flows

    NASA Technical Reports Server (NTRS)

    Samimy, Mo; Elliott, Gregory; Arnette, Stephen

    1996-01-01

    Two major regimes where laser light scattered by molecules or particles in a flow contains significant information about the flow are Mie scattering and Rayleigh scattering. Mie scattering is used to obtain only velocity information, while Rayleigh scattering can be used to measure both the velocity and the thermodynamic properties of the flow. Now, recently introduced (1990, 1991) absorption filter based diagnostic techniques have started a new era in flow visualization, simultaneous velocity and thermodynamic measurements, and planar velocity measurements. Using a filtered planar velocimetry (FPV) technique, we have modified the optically thick iodine filter profile of Miles, et al., and used it in the pressure-broaden regime which accommodates measurements in a wide range of velocity applications. Measuring velocity and thermodynamic properties simultaneously, using absorption filtered based Rayleigh scattering, involves not only the measurement of the Doppler shift, but also the spectral profile of the Rayleigh scattering signal. Using multiple observation angles, simultaneous measurement of one component velocity and thermodynamic properties in a supersonic jet were measured. Presently, the technique is being extended for simultaneous measurements of all three components of velocity and thermodynamic properties.

  11. An overland flow sampler for use in vegetative filters

    Treesearch

    D. Eisenhauer; M. Helmers; J. Brothers; M. Dosskey; T. Franti; A. Boldt; B. Strahm

    2002-01-01

    Vegetative filters (VF) are used to remove contaminants from agricultural runoff and improve surface water quality. Techniques are needed to quantify the performance of VF in realistic field settings. The goal of this project was to develop and test a relatively simple and low cost method for sampling overland flow in a VF. The 0.3 m wide sampler has the capacity to...

  12. Efficiency of subsurface flow constructed wetland with trickling filter.

    PubMed

    Vucinic, Aleksandra Anic; Hrenovic, Jasna; Tepes, Predrag

    2012-06-01

    Effective wastewater purification in subsurface flow constructed wetlands must include adequate pretreatment and ensure a sufficient amount of dissolved oxygen. In a pilot-scale operation, a subsurface flow constructed wetland (CW) consisted of a primary settlement tank, a trickling filter for pretreatment and two serially assembled basins. The trickling filter was added to ensure sufficient aeration, increase purification of the wastewater and shorten the wastewater purification time. The estimated nominal flow was 0.7 m3/d. The experiments were conducted using the wastewater from the municipal sewage canal of the city of Zagreb, with utilization of three different flows: 0.72 (A), 1.44 (B) and 2.88 (C) m3/d. The efficiency of the purification process was monitored over a period of three years (TSS, BOD5, COD, NH4-N, NO2-N, PO4-P, dissolved oxygen, temperature and pH). The experimental results showed an increase in the removal efficiency with a doubling of the nominal flow from 0.7 to 1.44 m3/d, which could be related to the implementation of the trickling filter where high removal rates were achieved.

  13. Information and Entropy Flow in the Kalman?Bucy Filter

    NASA Astrophysics Data System (ADS)

    Mitter, Sanjoy K.; Newton, Nigel J.

    2005-01-01

    We investigate the information theoretic properties of Kalman-Bucy filters in continuous time, developing notions of information supply, storage and dissipation. Introducing a concept of energy, we develop a physical analogy in which the unobserved signal describes a statistical mechanical system interacting with a heat bath. The abstract `universe' comprising the signal and the heat bath obeys a non-increase law of entropy; however, with the introduction of partial observations, this law can be violated. The Kalman-Bucy filter behaves like a Maxwellian demon in this analogy, returning signal energy to the heat bath without causing entropy increase. This is made possible by the steady supply of new information. In a second analogy the signal and filter interact, setting up a stationary non-equilibrium state, in which energy flows between the heat bath, the signal and the filter without causing any overall entropy increase. We introduce a rate of interactive entropy flow that isolates the statistical mechanics of this flow from marginal effects. Both analogies provide quantitative examples of Landauer's Principle.

  14. 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

  15. 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.

  16. 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.

  17. 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.

  18. Treatment of a synthetic waste water with a two-direction-flow anaerobic filter

    SciTech Connect

    Li, Y.

    1987-01-01

    This study was undertaken to improve the treatment efficiency of the anaerobic filter treatment of domestic and industrial waste waters. Two laboratory scale anaerobic filters were constructed. The filters were made of PVC pipe, six inches in diameter and six feet high. Activated charcoal was used as packing media. The first filter was operated as an upflow anaerobic filter. The second filter was operated as a two direction flow anaerobic filter. The substrate was fed into the bottom of the reactor, withdrawn after flowing upward approximately one foot, pumped to the top of the filter, and then flowed downward through the remainder of the filter. The treated effluent discharged opposite the port where the first section effluent was pumped to the top of the filter. The two filters were operated in parallel, using the same substrate, glucose, and the same hydraulic detention time of 32 hours. Three phases of operation were conducted: 1) pulsed operation, 2) continuous feed operation, and 3) continuous feed operation with twice the flow of number 2. The two direction flow filter produced better treatment than the up-flow filter because the hydrogen concentration in the methane phase of the filter was reduced, mixing was enhanced and a more uniform bacteria distribution occurred throughout the filter. All of these improvements over the upflow filter, and the resulting improved treatment efficiency, can be attributed to the two direction flow configuration.

  19. 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

  20. 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.

  1. Ultrasonic Mastering of Filter Flow and Antifouling of Renewable Resources.

    PubMed

    Radziuk, Darya; Möhwald, Helmuth

    2016-04-04

    Inadequate access to pure water and sanitation requires new cost-effective, ergonomic methods with less consumption of energy and chemicals, leaving the environment cleaner and sustainable. Among such methods, ultrasound is a unique means to control the physics and chemistry of complex fluids (wastewater) with excellent performance regarding mass transfer, cleaning, and disinfection. In membrane filtration processes, it overcomes diffusion limits and can accelerate the fluid flow towards the filter preventing antifouling. Here, we outline the current state of knowledge and technological design, with a focus on physicochemical strategies of ultrasound for water cleaning. We highlight important parameters of ultrasound for the delivery of a fluid flow from a technical perspective employing principles of physics and chemistry. By introducing various ultrasonic methods, involving bubbles or cavitation in combination with external fields, we show advancements in flow acceleration and mass transportation to the filter. In most cases we emphasize the main role of streaming and the impact of cavitation with a perspective to prevent and remove fouling deposits during the flow. We also elaborate on the deficiencies of present technologies and on problems to be solved to achieve a wide-spread application.

  2. 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

  3. 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

  4. Adaptive probabilistic collocation based Kalman filter for unsaturated flow problem

    NASA Astrophysics Data System (ADS)

    Man, J.; Li, W.; Zeng, L.; Wu, L.

    2015-12-01

    The ensemble Kalman filter (EnKF) has gained popularity in hydrological data assimilation problems. As a Monte Carlo based method, a relatively large ensemble size is usually required to guarantee the accuracy. As an alternative approach, the probabilistic collocation based Kalman filter (PCKF) employs the Polynomial Chaos to approximate the original system. In this way, the sampling error can be reduced. However, PCKF suffers from the so called "cure of dimensionality". When the system nonlinearity is strong and number of parameters is large, PCKF is even more computationally expensive than EnKF. Motivated by recent developments in uncertainty quantification, we propose a restart adaptive probabilistic collocation based Kalman filter (RAPCKF) for data assimilation in unsaturated flow problem. During the implementation of RAPCKF, the important parameters are identified and active PCE basis functions are adaptively selected. The "restart" technology is used to alleviate the inconsistency between model parameters and states. The performance of RAPCKF is tested by unsaturated flow numerical cases. It is shown that RAPCKF is more efficient than EnKF with the same computational cost. Compared with the traditional PCKF, the RAPCKF is more applicable in strongly nonlinear and high dimensional problems.

  5. Thermal/chemical stability of ceramic cross flow filter materials

    SciTech Connect

    Alvin, M.A.; Bahovchin, D.M.; Lippert, T.E.; Tressler, R.E.; McNerney, K.B.

    1992-01-01

    Westinghouse has undertaken a two phase program to determine possible long-term, high temperature influence that advanced coal-based power system environments may have on the stability of the ceramic cross flow filter elements. During the past year, we have principally focused our efforts on developing an understanding of the stability of the alumina/mullite filter material at high temperature (i.e., 870, 980, and 1100[degrees]C) under oxidizing conditions which contain gas phase alkali species. The alumina/mullite cross flow liter material that has consistently been used throughout the flow-through gas phase alkali testing segment of this program, consists of mullite rods or needles that are embedded within an amorphous phase which contains corundum (Al[sub 2]O[sub 3]) and anorthite (CaAl[sub 2]Si[sub 2]O[sub 8]). Due to the rapid cooling rate that was used to produce the alumina/mullite filter disc material from high fire, the matrix consists of 59.6 wt% mullite, 30.5 wt% amorphous, 5.1 wt% anorthite, and 4.8 wt% alumina. The relatively low, as-fabricated, hot strength of this material (841[plus minus]259 psi at 870[degrees]C) is a direct result of the high amorphous content which softens at temperatures of 870[degrees]C. Load versus deflection curves as a function of temperature indicate that this material is relatively brittle up to temperatures of 600[degrees]C. Both a loss of strength, as well as plastic deformation of the matrix occurs at [approximately]700[degrees]C. If cross flow filters are manufactured from an alumina/mullite matrix that contains an [approximately]30.5 wt% amorphous content, we suspect that the plastic nature of the glass phase could potentially serve as a substrate for fines collection during initial filter operation at 700[degrees]C. Similarly the plastic nature could potentially cause deformation of the liter under load.

  6. Thermal/chemical stability of ceramic cross flow filter materials

    SciTech Connect

    Alvin, M.A.; Bahovchin, D.M.; Lippert, T.E.; Tressler, R.E.; McNerney, K.B.

    1992-11-01

    Westinghouse has undertaken a two phase program to determine possible long-term, high temperature influence that advanced coal-based power system environments may have on the stability of the ceramic cross flow filter elements. During the past year, we have principally focused our efforts on developing an understanding of the stability of the alumina/mullite filter material at high temperature (i.e., 870, 980, and 1100{degrees}C) under oxidizing conditions which contain gas phase alkali species. The alumina/mullite cross flow liter material that has consistently been used throughout the flow-through gas phase alkali testing segment of this program, consists of mullite rods or needles that are embedded within an amorphous phase which contains corundum (Al{sub 2}O{sub 3}) and anorthite (CaAl{sub 2}Si{sub 2}O{sub 8}). Due to the rapid cooling rate that was used to produce the alumina/mullite filter disc material from high fire, the matrix consists of 59.6 wt% mullite, 30.5 wt% amorphous, 5.1 wt% anorthite, and 4.8 wt% alumina. The relatively low, as-fabricated, hot strength of this material (841{plus_minus}259 psi at 870{degrees}C) is a direct result of the high amorphous content which softens at temperatures of 870{degrees}C. Load versus deflection curves as a function of temperature indicate that this material is relatively brittle up to temperatures of 600{degrees}C. Both a loss of strength, as well as plastic deformation of the matrix occurs at {approximately}700{degrees}C. If cross flow filters are manufactured from an alumina/mullite matrix that contains an {approximately}30.5 wt% amorphous content, we suspect that the plastic nature of the glass phase could potentially serve as a substrate for fines collection during initial filter operation at 700{degrees}C. Similarly the plastic nature could potentially cause deformation of the liter under load.

  7. Filter-matrix lattice Boltzmann model for microchannel gas flows.

    PubMed

    Zhuo, Congshan; Zhong, Chengwen

    2013-11-01

    The lattice Boltzmann method has been shown to be successful for microscale gas flows, and it has attracted significant research interest. In this paper, the recently proposed filter-matrix lattice Boltzmann (FMLB) model is first applied to study the microchannel gas flows, in which a Bosanquet-type effective viscosity is used to capture the flow behaviors in the transition regime. A kinetic boundary condition, the combined bounce-back and specular-reflection scheme with the second-order slip scheme, is also designed for the FMLB model. By analyzing a unidirectional flow, the slip velocity and the discrete effects related to the boundary condition are derived within the FMLB model, and a revised scheme is presented to overcome such effects, which have also been validated through numerical simulations. To gain an accurate simulation in a wide range of Knudsen numbers, covering the slip and the entire transition flow regimes, a set of slip coefficients with an introduced fitting function is adopted in the revised second-order slip boundary condition. The periodic and pressure-driven microchannel flows have been investigated by the present model in this study. The numerical results, including the velocity profile and the mass flow rate, as well as the nonlinear pressure distribution along the channel, agree fairly well with the solutions of the linearized Boltzmann equation, the direct simulation Monte Carlo results, the experimental data, and the previous results of the multiple effective relaxation lattice Boltzmann model. Also, the present results of the velocity profile and the mass flow rate show that the present model with the fitting function can yield improved predictions for the microchannel gas flow with higher Knudsen numbers in the transition flow regime.

  8. 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.

  9. 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

  10. Coupled continuum and molecular model of flow through fibrous filter

    NASA Astrophysics Data System (ADS)

    Zhao, Shunliu; Povitsky, Alex

    2013-11-01

    A coupled approach combining the continuum boundary singularity method (BSM) and the molecular direct simulation Monte Carlo (DSMC) is developed and validated using Taylor-Couette flow and the flow about a single fiber confined between two parallel walls. In the proposed approach, the DSMC is applied to an annular region enclosing the fiber and the BSM is employed in the entire flow domain. The parameters used in the DSMC and the coupling procedure, such as the number of simulated particles, the cell size, and the size of the coupling zone are determined by inspecting the accuracy of pressure drop obtained for the range of Knudsen numbers between zero and unity. The developed approach is used to study flowfield of fibrous filtration flows. It is observed that in the partial-slip flow regime, Kn ⩽ 0.25, the results obtained by the proposed coupled BSM-DSMC method match the solution by BSM combined with the heuristic partial-slip boundary conditions. For transition molecular-to-continuum Knudsen numbers, 0.25 < Kn ⩽ 1, the difference in pressure drop and velocity between these two approaches is significant. This difference increases with the Knudsen number that confirms the usefulness of coupled continuum and molecular methods in numerical modeling of transition low Reynolds number flows in fibrous filters.

  11. 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.

  12. 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.

  13. Modeling of two-dimensional overland flow in a vegetative filter

    Treesearch

    Matthew J. Helmers; Dean E. Eisenhauer; Thomas G. Franti; Michael G. Dosskey

    2002-01-01

    Water transports sediment and other pollutants through vegetative filters. It is often assumed that the overland flow is uniformly distributed across the vegetative filter, but this research indicates otherwise. The objective of this study was to model the two-dimensional overland water flow through a vegetative filter, accounting for variation in microtopography,...

  14. Flow Characteristics of Pulse Cleaning System in Ceramic Filter

    SciTech Connect

    Zhongli, J.; Peng, S.; Chen, H.; Shi, M.

    2002-09-19

    The rigid ceramic filters have been recognized to be a most promising kind of equipment for the gas-solid separation and the cleaning of hot gases due to their unique properties and higher separation efficiency for larger than 5 {micro}m particles, which will well meet downstream system component protection and environmental standards. They have potential for increased efficiency in advanced coal-fired power generation systems like pressurized fluidized bed combustion (PFBC) and integrated gasification combined cycle (IGCC) process, and petrochemical process such as fluid catalyst cracking (FCC) Process. In the commercial utilization of rigid ceramic filters, the performance of pulse cleaning systems has crucial effects on the long-term structural durability and reliability of the entire design. In order to get a clear insight into the nature of this cleaning process and provide a solid basis for the industrial applications, the transient flow characteristics of the rigid ceramic candle filter during the whole pulse cleaning process should be completely analyzed.

  15. Replacement of fluid-filter elements without interruption of flow

    NASA Technical Reports Server (NTRS)

    Kotler, R. A.; Ward, J. B.

    1969-01-01

    Gatling-type filter assembly, preloaded with several filter elements enables filter replacement without breaking into the operative fluid system. When the filter element becomes contaminated, a unit inner subassembly is rotated 60 degrees to position a clean filter in the line.

  16. 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.

  17. 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.

  18. Performance evaluation of eigendecomposition-based adaptive clutter filter for color flow imaging.

    PubMed

    Song, Fuxian; Zhang, Dong; Gong, Xiufen

    2006-12-22

    In this paper, a newly developed eigendecomposition-based adaptive filter is applied in flow velocity estimation and its performance is evaluated and compared with the static polynomial regression filter. Results demonstrate that the eigendecomposition-based filter is the fully-adaptive and can not only suppress the clutter signals with minimal loss of low-flow signal, but also give less influence on the flow velocity estimation especially under the circumstance of high clutter velocity.

  19. Particle filter based on thermophoretic deposition from natural convection flow

    SciTech Connect

    Sasse, A.G.B.M.; Nazaroff, W.W. ); Gadgil, A.J. )

    1994-04-01

    We present an analysis of particle migration in a natural convection flow between parallel plates and within the annulus of concentric tubes. The flow channel is vertically oriented with one surface maintained at a higher temperature than the other. Particle migration is dominated by advection in the vertical direction and thermophoresis in the horizontal direction. From scale analysis it is demonstrated that particles are completely removed from air flowing through the channel if its length exceeds L[sub c] = (b[sup 4]g/24K[nu][sup 2]), where b is the width of the channel, g is the acceleration of gravity, K is a thermophoretic coefficient of order 0.5, and [nu] is the kinematic viscosity of air. Precise predictions of particle removal efficiency as a function of system parameters are obtained by numerical solution of the governing equations. Based on the model results, it appears feasible to develop a practical filter for removing smoke particles from a smoldering cigarette in an ashtray by using natural convection in combination with thermophoresis. 22 refs., 8 figs., 1 tab.

  20. 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.

  1. 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

  2. Flow regions of granules in Dorfan Impingo filter for gas cleanup

    SciTech Connect

    Kuo, J.T.; Smid, J.; Hsiau, S.S.; Tsai, S.S.; Chou, C.S.

    1999-07-01

    Inside a two-dimensional model of the louvered Dorfan Impingo panel with transparent front and rear walls the flow region of filter granules without gas cross flow were observed. The white PE beads were used as filter granules. Colored PE beads served as tracers. Filter granules were discharged and circulated to the bed. The flow rate of filter medium was controlled by the belt conveyor. The image processing system including a Frame Grabber and JVC videocamera was used to record the granular flow. Every image of motion was digitized and stored in a file. The flow patterns and the quasi-stagnant zones history in the moving granular bed were evaluated. The experiment showed fast central moving region (flowing core) of filter granules and quasi-stagnant zones close to louver walls.

  3. 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.

  4. Improvement of hemodynamic performance using novel helical flow vena cava filter design

    PubMed Central

    Chen, Ying; Zhang, Peng; Deng, Xiaoyan; Fan, Yubo; Xing, Yubin; Xing, Ning

    2017-01-01

    We propose a vena cava filter in which helical flow is created in the filter’s working zone to minimize filter blockage by trapped clots and facilitate the lysis of trapped clots. To validate this new design, we compared five helical flow inducers with different thread pitches in terms of blood flow patterns in the filter. The vena cava was reconstructed based on computed tomography images. Both the numerical simulation and in vitro experiment revealed that the helical flow inducer can effectively create a helical flow in the vessel, thereby subduing the filter structure’s adverse disruption to blood flow, and increasing flow-induced shear stress in the filter center. In addition, the smaller thread pitch helical flow inducer reduced the oscillating shear index and relative residence time on the vessel wall. Moreover, we observed that the helical flow inducer in the vena cava could induce flow rotation both in clockwise and counterclockwise directions. In conclusion, the new design of the filter with the smaller thread pitch inducer is advantageous over the traditional filter in terms of improving local hemodynamics, which may reduce thrombosis build-up after deployment. PMID:28112186

  5. 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.

  6. The effect of flow on the filtration performance of paediatric breathing system filters.

    PubMed

    Wilkes, A R; Malan, C A; Hall, J E

    2008-01-01

    The effect of flow on the filtration performance of six different types of filter intended for use in paediatric anaesthesia was measured by challenging the filters with sodium chloride particles at five different flows: 6, 10, 15, 20 and 30 l x min(-1). Twenty-five unused samples of each filter type were evaluated. The pressure drop across each filter was measured at the same flows as those used to measure penetration. The pressure drop varied both between and within the types of filter. Mean pressure drop varied between 89 and 262 Pa at a flow of 15 l x min(-1) for the six different filters. Penetration of sodium chloride particles varied from 1.9 to 18% at 15 l x min(-1) for the six filters. Allowing for the variation in pressure drop, the penetration of particles increased fairly linearly as flow increased for all six filter types. The increase in penetration per unit increase in flow varied from 0.11 to 0.82% per litre per minute. Over the range of flows studied, the increase in penetration with flow is fairly predictable.

  7. A Graphical Filter/Flow Representation of Boolean Queries: A Prototype Implementation and Evaluation.

    ERIC Educational Resources Information Center

    Young, Degi; Shneiderman, Ben

    1993-01-01

    Literature showing the disadvantages of Boolean logic in online searching is reviewed, and research comparing the Filter/Flow visual interface (i.e., a graphical representation of Boolean operators) with a text-only interface is described. A significant difference in the total number of correct queries is reported that favored Filter/Flow. (16…

  8. Filter-based modeling of unsteady turbulent cavitating flow computations

    NASA Astrophysics Data System (ADS)

    Wu, Jiongyang

    Cavitation plays an important role in the design and operation of fluid machinery and devices because it causes performance degradation, noise, vibration, and erosion. Cavitation involves complex phase-change dynamics, large density ratio between phases, and multiple time scales. Noticeable achievements have been made in employing homogeneous two-phase Navier-Stokes equations for cavitating computations in computational and modeling strategies. However, these issues pose challenges with respect to accuracy, stability, efficiency and robustness because of the complex unsteady interaction associated with cavitation dynamics and turbulence. The present study focuses on developing and assessing computational modeling techniques to provide better insight into unsteady turbulent cavitation dynamics. The ensemble-averaged Navier-Stokes equations, along with a volume fraction transport equation for cavitation and turbulence closure, are employed. To ensure stability and convergence with good efficiency and accuracy, the pressure-based Pressure Implicit Splitting of Operators (PISO) algorithm is adopted for time-dependent computations. The merits of recent transport equation-based cavitation models are first re-examined. To account for the liquid-vapor mixture compressibility, different numerical approximations of speed-of-sound are further investigated and generalized. To enhance the generality and capability of the recent interfacial dynamics-based cavitation model (IDM), we present an improved approximation for the interfacial velocity via phase transformation. In turbulence modeling, a filter-based model (FBM) derived from the k-epsilon two-equation model, an easily deployable conditional averaging method aimed at improving unsteady simulations, is introduced. The cavitation and turbulence models are assessed by unsteady simulations in various geometries including square cylinder, convergent-divergent nozzle, Clark-Y hydrofoil, and hollow-jet valve. The FBM reduces eddy

  9. 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.

  10. Non-resonant parametric amplification in biomimetic hair flow sensors: Selective gain and tunable filtering

    NASA Astrophysics Data System (ADS)

    Droogendijk, H.; Bruinink, C. M.; Sanders, R. G. P.; Krijnen, G. J. M.

    2011-11-01

    We demonstrate that the responsivity of flow sensors for harmonic flows can be improved significantly by non-resonant parametric amplification. Using electrostatic spring softening by AC-bias voltages, increased responsivity and sharp filtering are achieved in our biomimetic flow sensors. Tunable filtering is obtained for non-resonant electromechanical parametric amplification, applicable at a wide range of non-resonant frequencies while achieving highly selective gain of up to 20 dB.

  11. Hollywood log-homotopy: movies of particle flow for nonlinear filters

    NASA Astrophysics Data System (ADS)

    Daum, Fred; Huang, Jim

    2011-06-01

    In this paper we show five movies of particle flow to provide insight and intuition about this new algorithm. The particles flow solves the well known and important problem of particle degeneracy. Bayes' rule is implemented by particle flow rather than as a pointwise multiplication. This theory is roughly seven orders of magnitude faster than standard particle filters, and it often beats the extended Kalman filter by two orders of magnitude in accuracy for difficult nonlinear problems.

  12. Computational Modeling of Blood Flow in the TrapEase Inferior Vena Cava Filter

    SciTech Connect

    Singer, M A; Henshaw, W D; Wang, S L

    2008-02-04

    To evaluate the flow hemodynamics of the TrapEase vena cava filter using three dimensional computational fluid dynamics, including simulated thrombi of multiple shapes, sizes, and trapping positions. The study was performed to identify potential areas of recirculation and stagnation and areas in which trapped thrombi may influence intrafilter thrombosis. Computer models of the TrapEase filter, thrombi (volumes ranging from 0.25mL to 2mL, 3 different shapes), and a 23mm diameter cava were constructed. The hemodynamics of steady-state flow at Reynolds number 600 was examined for the unoccluded and partially occluded filter. Axial velocity contours and wall shear stresses were computed. Flow in the unoccluded TrapEase filter experienced minimal disruption, except near the superior and inferior tips where low velocity flow was observed. For spherical thrombi in the superior trapping position, stagnant and recirculating flow was observed downstream of the thrombus; the volume of stagnant flow and the peak wall shear stress increased monotonically with thrombus volume. For inferiorly trapped spherical thrombi, marked disruption to the flow was observed along the cava wall ipsilateral to the thrombus and in the interior of the filter. Spherically shaped thrombus produced a lower peak wall shear stress than conically shaped thrombus and a larger peak stress than ellipsoidal thrombus. We have designed and constructed a computer model of the flow hemodynamics of the TrapEase IVC filter with varying shapes, sizes, and positions of thrombi. The computer model offers several advantages over in vitro techniques including: improved resolution, ease of evaluating different thrombus sizes and shapes, and easy adaptation for new filter designs and flow parameters. Results from the model also support a previously reported finding from photochromic experiments that suggest the inferior trapping position of the TrapEase IVC filter leads to an intra-filter region of recirculating

  13. Adaptive Low Dissipative High Order Filter Methods for Multiscale MHD Flows

    NASA Technical Reports Server (NTRS)

    Yee, H. C.; Sjoegreen, Bjoern

    2004-01-01

    Adaptive low-dissipative high order filter finite difference methods for long time wave propagation of shock/turbulence/combustion compressible viscous MHD flows has been constructed. Several variants of the filter approach that cater to different flow types are proposed. These filters provide a natural and efficient way for the minimization of the divergence of the magnetic field [divergence of B] numerical error in the sense that no standard divergence cleaning is required. For certain 2-D MHD test problems, divergence free preservation of the magnetic fields of these filter schemes has been achieved.

  14. Divergence Free High Order Filter Methods for Multiscale Non-ideal MHD Flows

    NASA Technical Reports Server (NTRS)

    Yee, H. C.; Sjoegreen, Bjoern

    2003-01-01

    Low-dissipative high order filter finite difference methods for long time wave propagation of shock/turbulence/combustion compressible viscous MHD flows has been constructed. Several variants of the filter approach that cater to different flow types are proposed. These filters provide a natural and efficient way for the minimization of the divergence of the magnetic field (Delta . B) numerical error in the sense that no standard divergence cleaning is required. For certain 2-D MHD test problems, divergence free preservation of the magnetic fields of these filter schemes has been achieved.

  15. Adaptive Low Dissipative High Order Filter Methods for Multiscale MHD Flows

    NASA Technical Reports Server (NTRS)

    Yee, H. C.; Sjoegreen, Bjoern

    2004-01-01

    Adaptive low-dissipative high order filter finite difference methods for long time wave propagation of shock/turbulence/combustion compressible viscous MHD flows has been constructed. Several variants of the filter approach that cater to different flow types are proposed. These filters provide a natural and efficient way for the minimization of the divergence of the magnetic field [divergence of B] numerical error in the sense that no standard divergence cleaning is required. For certain 2-D MHD test problems, divergence free preservation of the magnetic fields of these filter schemes has been achieved.

  16. 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.

  17. 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.

  18. Low frequency filtering of nasal pressure channel causes loss of flow limitation.

    PubMed

    Walter, Robert N; Vaughn, Bradley V

    2013-03-01

    The objective of this clinical vignette is to explore whether changes in low filter settings for respiratory waveforms have a clinically significant effect on patient management of obstructive sleep apnea (OSA). This is a case report. We collected data from a continuous positive airway pressure (CPAP) titration polysomnogram (PSG) performed in our university based sleep laboratory. We reviewed the flow signal using low frequency filter settings of 0.0, 0.1, 0.3, and 0.5 Hz. We noted that a change in the low frequency filter for respiratory flow caused a change in the appearance of an otherwise flattened waveform indicating flow limitation to no longer appear flat. We noted that indiscriminate use of the low frequency filter for nasal pressure and flow estimate channels may lead to greater difficulty recognizing respiratory flow limitation.

  19. 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.

  20. Modeling sediment trapping in a vegetative filter accounting for converging overland flow

    Treesearch

    M. J. Helmers; D. E. Eisenhauer; T. G. Franti; M. G. Dosskey

    2005-01-01

    Vegetative filters (VF) are used to remove sediment and other pollutants from overland flow. When modeling the hydrology of VF, it is often assumed that overland flow is planar, but our research indicated that it can be two-dimensional with converging and diverging pathways. Our hypothesis is that flow convergence will negatively influence the sediment trapping...

  1. Eigen-based clutter filter design for ultrasound color flow imaging: a review.

    PubMed

    Yu, Alfred; Lovstakken, Lasse

    2010-05-01

    Proper suppression of tissue clutter is a prerequisite for visualizing flow accurately in ultrasound color flow imaging. Among various clutter suppression methods, the eigen-based filter has shown potential because it can theoretically adapt its stopband to the actual clutter characteristics even when tissue motion is present. This paper presents a formative review on how eigen-based filters should be designed to improve their practical efficacy in adaptively suppressing clutter without affecting the blood flow echoes. Our review is centered around a comparative assessment of two eigen-filter design considerations: 1) eigen-component estimation approach (single-ensemble vs. multi-ensemble formulations), and 2) filter order selection mechanism (eigenvalue-based vs. frequencybased algorithms). To evaluate the practical efficacy of existing eigen-filter designs, we analyzed their clutter suppression level in two in vivo scenarios with substantial tissue motion (intra-operative coronary imaging and thyroid imaging). Our analysis shows that, as compared with polynomial regression filters (with or without instantaneous clutter downmixing), eigen-filters that use a frequency-based algorithm for filter order selection generally give Doppler power images with better contrast between blood and tissue regions. Results also suggest that both multi-ensemble and single-ensemble eigen-estimation approaches have their own advantages and weaknesses in different imaging scenarios. It may be beneficial to develop an algorithmic way of defining the eigen-filter formulation so that its performance advantages can be better realized.

  2. An evaluation of the filtration performance of paediatric breathing system filters at low flows.

    PubMed

    Malan, C A; Wilkes, A R; Hall, J E; Gildersleve, C

    2007-05-01

    The filtration performance of five different types of filter intended for use in paediatric anaesthesia was measured. A total of 120 unused filters (24 samples of each filter type) were evaluated. The pressure drop and filtration performance, using challenges of sodium chloride particles, were measured for each filter at 3 l min(-1) and 15 l min(-1). The pressure drop was less at the lower flow; there was a wide variation in the pressure drop across some filters. The filtration performance of all filter types showed an improvement at 3 l min(-1) compared to 15 l min(-1). Four filter types had filtration efficiencies greater than 95% at 15 l min(-1) and greater than 99% at 3 l min(-1). The remaining filter type had a filtration efficiency less than 90% at 15 l min(-1) and greater than 95% at 3 l min(-1). These levels of performance are comparable to that of breathing system filters intended for use in adult anaesthesia using flows representing mean inspiratory flow.

  3. Design and Initial Development of Monolithic Cross-Flow Ceramic Hot-Gas Filters

    SciTech Connect

    Barra, C.; Limaye, S.; Stinton, D.P.; Vaubert, V.M.

    1999-06-06

    Advanced, coal-fueled, power generation systems utilizing pressurized fluidized bed combustion (PFBC) and integrated gasification combined cycle (IGCC) technologies are currently being developed for high-efficiency, low emissions, and low-cost power generation. In spite of the advantages of these promising technologies, the severe operating environment often leads to material degradation and loss of performance in the barrier filters used for particle entrapment. To address this problem, LoTEC Inc., and Oak Ridge National Laboratory are jointly designing and developing a monolithic cross-flow ceramic hot-gas filter. The filter concept involves a truly monolithic cross-flow design that is resistant to delamination, can be easily fabricated, and offers flexibility of geometry and material make-up. During Phase I of the program, a thermo-mechanical analysis was performed to determine how a cross-flow filter would respond both thermally and mechanically to a series of thermal and mechanical loads. The cross-flow filter mold was designed accordingly, and the materials selection was narrowed down to Ca{sub 0.5}Sr{sub 0.5}Zr{sub 4}P{sub 6}O{sub 24} (CS-50) and 2Al{sub 2}O{sub 3}-3SiO{sub 2} (mullite). A fabrication process was developed using gelcasting technology and monolithic cross-flow filters were fabricated. The program focuses on obtaining optimum filter permeability and testing the corrosion resistance of the candidate materials.

  4. 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.

  5. 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

  6. Analysis of nitrogen removal processes in a subsurface flow carbonate sand filter treating municipal wastewater.

    PubMed

    Kløve, Bjørn; Søvik, Anne-Kristine; Holtan-Hartwig, Liv

    2005-01-01

    Controlled experiments were carried out in a mesoscale subsurface flow sand filter treating municipal wastewater from a single household. The system consisted of a 50 cm high vertical flow column (pre-filter) with unsaturated flow and a 3 m long horizontal subsurface flow unit (main filter) with saturated flow. Fluxes of nitrogen and carbon were analyzed in 4 different operating conditions (low and high loading, with and without the prefilter unit). Water samples were taken from the inlet, the outlet and within the sand filter at different depths and locations and analysed for water quality (Tot N, NO3-N, NH4-N, TOC, DOC, CODcr, BOD5, SS, pH, and EC) and dissolved gas content (N2O, CH4, and CO2). Emissions of N2O, CH4, and CO2 were measured with the closed-chamber technique adjacent to water quality sampling points. The results show that prefiltering in a vertical, unsaturated flow column changed the incoming ammonium to nitrate during low loading. During high loading part of the ammonium nitrified in the pre-filter was lost by denitrification. Within the horizontal main filter there were two pathways for the incoming nitrate: denitrification and dissimilatory nitrate reduction to ammonium (DNRA).

  7. 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

  8. Robust scale-up of dead end filtration: impact of filter fouling mechanisms and flow distribution.

    PubMed

    Laska, Michael E; Brooks, Ralph P; Gayton, Marshall; Pujar, Narahari S

    2005-11-05

    Robust design of a dead end filtration step and the resulting performance at manufacturing scale relies on laboratory data collected with small filter units. During process development it is important to characterize and understand the filter fouling mechanisms of the process streams so that an accurate assessment can be made of the filter area required at manufacturing scale. Successful scale-up also requires integration of the lab-scale filtration data with an understanding of flow characteristics in the full-scale filtration equipment. A case study is presented on the development and scale-up of a depth filtration step used in a 2nd generation polysaccharide vaccine manufacturing process. The effect of operating parameters on filter performance was experimentally characterized for a diverse set of process streams. Filter capacity was significantly reduced when operating at low fluxes, caused by both low filtration pressure and high stream viscosity. The effect of flux on filter capacity could be explained for a variety of diverse streams by a single mechanistic model of filter fouling. To complement the laboratory filtration data, the fluid flow and distribution characteristics in manufacturing-scale filtration equipment were carefully evaluated. This analysis identified the need for additional scale-up factors to account for non-uniform filter area usage in large-scale filter housings. This understanding proved critical to the final equipment design and depth filtration step definition, resulting in robust process performance at manufacturing scale. Copyright (c) 2005 Wiley Periodicals, Inc.

  9. Performance Evaluation of Axial Flow AG-1 FC and Prototype FM (High Strength) HEPA Filters - 13123

    SciTech Connect

    Giffin, Paxton K.; Parsons, Michael S.; Wilson, John A.; Waggoner, Charles A.

    2013-07-01

    High efficiency particulate air (HEPA) filters are routinely used in DOE nuclear containment activities. The Nuclear Air Cleaning Handbook (NACH) stipulates that air cleaning devices and equipment used in DOE nuclear applications must meet the American Society of Mechanical Engineers (ASME) Code on Nuclear Air and Gas Treatment (AG-1) standard. This testing activity evaluates two different axial flow HEPA filters, those from AG-1 Sections FC and FM. Section FM is under development and has not yet been added to AG-1 due to a lack of qualification data available for these filters. Section FC filters are axial flow units that utilize a fibrous glass filtering medium. The section FM filters utilize a similar fibrous glass medium, but also have scrim backing. The scrim-backed filters have demonstrated the ability to endure pressure impulses capable of completely destroying FC filters. The testing activities presented herein will examine the total lifetime loading for both FC and FM filters under ambient conditions and at elevated conditions of temperature and relative humidity. Results will include loading curves, penetration curves, and testing condition parameters. These testing activities have been developed through collaborations with representatives from the National Nuclear Security Administration (NNSA), DOE Office of Environmental Management (DOE-EM), New Mexico State University, and Mississippi State University. (authors)

  10. Application of Micropore Filter Technology: Exploring the Blood Flow Path in Arterial-Line Filters and Its Effect on Bubble Trapping Functions

    PubMed Central

    Herbst, Daniel P.

    2017-01-01

    Abstract: Conventional arterial-line filters commonly use a large volume circular shaped housing, a wetted micropore screen, and a purge port to trap, separate, and remove gas bubbles from extracorporeal blood flow. Focusing on the bubble trapping function, this work attempts to explore how the filter housing shape and its resulting blood flow path affect the clinical application of arterial-line filters in terms of gross air handling. A video camera was used in a wet-lab setting to record observations made during gross air-bolus injections in three different radially designed filters using a 30–70% glycerol–saline mixture flowing at 4.5 L/min. Two of the filters both had inlet ports attached near the filter-housing top with bottom oriented outlet ports at the bottom, whereas the third filter had its inlet and outlet ports both located at the bottom of the filter housing. The two filters with top-in bottom-out fluid paths were shown to direct the incoming flow downward as it passed through the filter, placing the forces of buoyancy and viscous drag in opposition to each other. This contrasted with the third filter's bottom-in bottom-out fluid path, which was shown to direct the incoming flow upward so that the forces of buoyancy and viscous drag work together. The direction of the blood flow path through a filter may be important to the application of arterial-line filter technology as it helps determine how the forces of buoyancy and flow are aligned with one another. PMID:28298665

  11. Application of Micropore Filter Technology: Exploring the Blood Flow Path in Arterial-Line Filters and Its Effect on Bubble Trapping Functions.

    PubMed

    Herbst, Daniel P

    2017-03-01

    Conventional arterial-line filters commonly use a large volume circular shaped housing, a wetted micropore screen, and a purge port to trap, separate, and remove gas bubbles from extracorporeal blood flow. Focusing on the bubble trapping function, this work attempts to explore how the filter housing shape and its resulting blood flow path affect the clinical application of arterial-line filters in terms of gross air handling. A video camera was used in a wet-lab setting to record observations made during gross air-bolus injections in three different radially designed filters using a 30-70% glycerol-saline mixture flowing at 4.5 L/min. Two of the filters both had inlet ports attached near the filter-housing top with bottom oriented outlet ports at the bottom, whereas the third filter had its inlet and outlet ports both located at the bottom of the filter housing. The two filters with top-in bottom-out fluid paths were shown to direct the incoming flow downward as it passed through the filter, placing the forces of buoyancy and viscous drag in opposition to each other. This contrasted with the third filter's bottom-in bottom-out fluid path, which was shown to direct the incoming flow upward so that the forces of buoyancy and viscous drag work together. The direction of the blood flow path through a filter may be important to the application of arterial-line filter technology as it helps determine how the forces of buoyancy and flow are aligned with one another.

  12. Comparison of NOM removal and microbial properties in up-flow/down-flow BAC filter.

    PubMed

    Han, Lineng; Liu, Wenjun; Chen, Mo; Zhang, Minglu; Liu, Shuming; Sun, Ruilin; Fei, Xiangqin

    2013-09-15

    The removal of natural organic matter (NOM) in term of CODMn by up-flow biologically activated carbon filter (UBACF) and down-flow biologically activated carbon filter (DBACF) was investigated in a pilot-scale test. The impacts of the molecular weight distribution of NOM on its degradation by the UBACF and DBACF were evaluated. The relationship between biodegradation and the microbial properties in the UBACF and DBACF were approached as well. The feed water of the UBACF and DBACF were pumped from the effluent of the rapid sand filtration (RSF) of Chengnan Drinking Water Treatment Plant (CDWTP), Huaian, Jiangsu Province, China. When the adsorption was the dominant mechanism of NOM removal at the initial stage of operation, the CODMn removal efficiency by the UBACF was lower than the DBACF. However, with the microbes gradually accumulated and biofilm formed, the removal of CODMn by the UBACF increased correspondingly to 25.3%, at the steady-state operation and was approximately 10% higher than that by the DBACF. Heterotrophy plate count (HPC) in the finished water of the UBACF was observed 30% higher than that of the DBACF. The UBACF effluent had higher concentration of detached bacteria whereas the DBACF harbored more attached biomass. The highest attached biomass concentration of the UBACF was found in the middle of the GAC bed. On the contrary, the highest attached biomass concentration of the DBACF was found on the top of the GAC bed. Furthermore, a total of 9479 reads by pyrosequencing was obtained from samples of the UBACF and DBACF effluents. The UBACF effluent had a more diverse microbial community and more even distribution of species than the DBACF effluent did. Alphaproteobacteria and Betaproteobacteria were the dominant groups in the finished water of the UBACF and DBACF. The higher organic matter removal by the UBACF was attributed to the presence of its higher biologically activity.

  13. N95 and p100 respirator filter efficiency under high constant and cyclic flow.

    PubMed

    Eshbaugh, Jonathan P; Gardner, Paul D; Richardson, Aaron W; Hofacre, Kent C

    2009-01-01

    This study investigated the effect of high flow conditions on aerosol penetration and the relationship between penetration at constant and cyclic flow conditions. National Institute for Occupational Safety and Health (NIOSH)-approved N95 and P100 filtering facepiece respirators and cartridges were challenged with inert solid and oil aerosols. A combination of monodisperse aerosol and size-specific aerosol measurement equipment allowed count-based penetration measurement of particles with nominal diameters ranging from 0.02 to 2.9 microm. Three constant flow conditions (85, 270, and 360 L/min) were selected to match the minute, inhalation mean, and inhalation peak flows of the four cyclic flow conditions (40, 85, 115, and 135 L/min) tested. As expected, penetration was found to increase under increased constant and cyclic flow conditions. The most penetrating particle size (MPPS) generally ranged from 0.05 to 0.2 microm for P100 filters and was approximately 0.05 microm for N95 filters. Although penetration increased at the high flow conditions, the MPPS was relatively unaffected by flow. Of the constant flows tested, the flows equivalent to cyclic inhalation mean and peak flows best approximated the penetration measurements of the corresponding cyclic flows.

  14. Molecular filter-based diagnostics in high speed flows

    NASA Technical Reports Server (NTRS)

    Elliott, Gregory S.; Samimy, MO; Arnette, Stephen A.

    1993-01-01

    The use of iodine molecular filters in nonintrusive planar velocimetry methods is examined. Detailed absorption profiles are obtained to highlight the effects that determine the profile shape. It is shown that pressure broadening induced by the presence of a nonabsorbing vapor can be utilized to significantly change the slopes bounding the absorbing region while remaining in the optically-thick regime.

  15. Effects of Purge-Flow Rate on Microbubble Capture in Radial Arterial-Line Filters.

    PubMed

    Herbst, Daniel P

    2016-09-01

    The process of microbubble filtration from blood is complex and highly dependent on the forces of flow and buoyancy. To protect the patient from air emboli, arterial-line filters commonly use a micropore screen, a large volume housing with purpose-built shape, and a purge port to trap, separate, and remove circulating microbubbles. Although it has been proposed that an insufficient buoyancy force renders the purge port ineffective at removing microbubbles smaller than 500 μm, this research attempts to investigate the purge flow of an arterial-line filter to better understand the microbubble removal function in a typical radial filter design. As its primary objective, the study aims to determine the effect of purge-flow rate on bubble capture using air bolus injections from a syringe pump with 22-gauge needle and Doppler ultrasound bubble detection. The measureable bubble size generated in the test circuit ranged between 30 and 500 μm, while purge flow was varied between .1 and .5 L/min for testing. Statistical analysis of the test data was handled using a repeated measures design with significance set at p < .05 level. Outcomes demonstrated that higher purge flows yielded higher bubble counts, but the effect of purge-flow rate on bubble capture decreased as bubble size increased. Results also showed that purge flow from the test filter was capable of capturing all bubble sizes being generated over the entire flow range tested, and confirms utility of the purge port in removing microbubbles smaller than 500 μm. By analyzing bubble counts in the purge flow of a typical radial-filter design, this study demonstrates that currently available micropore filter technology is capable of removing the size range of bubbles that commonly pass through modern pump-oxygenator systems and should continue to be considered during extracorporeal circulation as a measure to improve patient safety.

  16. Effects of Purge-Flow Rate on Microbubble Capture in Radial Arterial-Line Filters

    PubMed Central

    Herbst, Daniel P.

    2016-01-01

    Abstract: The process of microbubble filtration from blood is complex and highly dependent on the forces of flow and buoyancy. To protect the patient from air emboli, arterial-line filters commonly use a micropore screen, a large volume housing with purpose-built shape, and a purge port to trap, separate, and remove circulating microbubbles. Although it has been proposed that an insufficient buoyancy force renders the purge port ineffective at removing microbubbles smaller than 500 μm, this research attempts to investigate the purge flow of an arterial-line filter to better understand the microbubble removal function in a typical radial filter design. As its primary objective, the study aims to determine the effect of purge-flow rate on bubble capture using air bolus injections from a syringe pump with 22-gauge needle and Doppler ultrasound bubble detection. The measureable bubble size generated in the test circuit ranged between 30 and 500 μm, while purge flow was varied between .1 and .5 L/min for testing. Statistical analysis of the test data was handled using a repeated measures design with significance set at p < .05 level. Outcomes demonstrated that higher purge flows yielded higher bubble counts, but the effect of purge-flow rate on bubble capture decreased as bubble size increased. Results also showed that purge flow from the test filter was capable of capturing all bubble sizes being generated over the entire flow range tested, and confirms utility of the purge port in removing microbubbles smaller than 500 μm. By analyzing bubble counts in the purge flow of a typical radial-filter design, this study demonstrates that currently available micropore filter technology is capable of removing the size range of bubbles that commonly pass through modern pump-oxygenator systems and should continue to be considered during extracorporeal circulation as a measure to improve patient safety. PMID:27729703

  17. Thermal/chemical degradation of ceramic cross-flow filter materials

    SciTech Connect

    Alvin, M.A.; Lane, J.E.; Lippert, T.E.

    1989-11-01

    This report summarizes the 14-month, Phase 1 effort conducted by Westinghouse on the Thermal/Chemical Degradation of Ceramic Cross-Flow Filter Materials program. In Phase 1 expected filter process conditions were identified for a fixed-bed, fluid-bed, and entrained-bed gasification, direct coal fired turbine, and pressurized fluidized-bed combustion system. Ceramic cross-flow filter materials were also selected, procured, and subjected to chemical and physical characterization. The stability of each of the ceramic cross-flow materials was assessed in terms of potential reactions or phase change as a result of process temperature, and effluent gas compositions containing alkali and fines. In addition chemical and physical characterization was conducted on cross-flow filters that were exposed to the METC fluid-bed gasifier and the New York University pressurized fluidized-bed combustor. Long-term high temperature degradation mechanisms were proposed for each ceramic cross-flow material at process operating conditions. An experimental bench-scale test program is recommended to be conducted in Phase 2, generating data that support the proposed cross-flow filter material thermal/chemical degradation mechanisms. Papers on the individual subtasks have been processed separately for inclusion on the data base.

  18. A baker's dozen of new particle flows for nonlinear filters, Bayesian decisions and transport

    NASA Astrophysics Data System (ADS)

    Daum, Fred; Huang, Jim

    2015-05-01

    We describe a baker's dozen of new particle flows to compute Bayes' rule for nonlinear filters, Bayesian decisions and learning as well as transport. Several of these new flows were inspired by transport theory, but others were inspired by physics or statistics or Markov chain Monte Carlo methods.

  19. An explicit filtering method for large eddy simulation of compressible flows

    NASA Astrophysics Data System (ADS)

    Mathew, Joseph; Lechner, Richard; Foysi, Holger; Sesterhenn, Joern; Friedrich, Rainer

    2003-08-01

    A method for large eddy simulation (LES) is presented in which the sub-grid-scale modeling is achieved by filtering procedures alone. The procedure derives from a deconvolution model, and provides a mathematically consistent approximation of unresolved terms arising from any type of nonlinearity. The formal steps of primary filtering to obtain LES equations, approximate deconvolution to construct the subgrid model term and regularization are combined into an equivalent filter. This filter should be an almost perfect low pass filter below a cut-off wavenumber and then fall off smoothly. The procedure has been applied to a pressure-velocity-entropy formulation of the Navier-Stokes equations for compressible flow to perform LES of two fully developed, turbulent, supersonic channel flows and has been assessed by comparison against direct numerical simulation (DNS) data. Mach numbers are 1.5 and 3.0, and Reynolds numbers are 3000 and 6000, respectively. Effects of filter cut-off location, choice of differentiation scheme (a fifth-order compact upwind formula and a symmetric sixth-order compact formula were used), and grid refinement are examined. The effects are consistent with, and are readily understood by reference to, filtering characteristics of the differentiation and the LES filter. All simulations demonstrate a uniform convergence towards their respective DNS solutions.

  20. Adaptive clutter filtering based on sparse component analysis in ultrasound color flow imaging.

    PubMed

    Li, Peng; Yang, Xiaofeng; Zhang, Dalong; Bian, Zhengzhong

    2008-07-01

    An adaptive method based on the sparse component analysis is proposed for stronger clutter filtering in ultrasound color flow imaging (CFI). In the present method, the focal underdetermined system solver (FOCUSS) algorithm is employed, and the iteration of the algorithm is based on weighted norm minimization of the dependent variable with the weights being a function of the preceding iterative solutions. By finding the localized energy solution vector representing strong clutter components, the FOCUSS algorithm first extracts the clutter from the original signal. However, the different initialization of the basis function matrix has an impact on the filtering performance of FOCUSS algorithms. Thus, 2 FOCUSS clutter- filtering methods, the original and the modified, are obtained by initializing the basis function matrix using a predetermined set of monotone sinusoids and using the discrete Karhunen-Loeve transform (DKLT) and spatial averaging, respectively. Validation of 2 FOCUSS filtering methods has been performed through experimental tests, in which they were compared with several conventional clutter filters using simplistic simulated and gathered clinical data. The results demonstrate that 2 FOCUSS filtering methods can follow signal varying adaptively and perform clutter filtering effectively. Moreover, the modified method may obtain the further improved filtering performance and retain more blood flow information in regions close to vessel walls.

  1. Flow and fouling in membrane filters: Effects of membrane morphology

    NASA Astrophysics Data System (ADS)

    Sanaei, Pejman; Cummings, Linda J.

    2015-11-01

    Membrane filters are widely-used in microfiltration applications. Many types of filter membranes are produced commercially, for different filtration applications, but broadly speaking the requirements are to achieve fine control of separation, with low power consumption. The answer to this problem might seem obvious: select the membrane with the largest pore size and void fraction consistent with the separation requirements. However, membrane fouling (an inevitable consequence of successful filtration) is a complicated process, which depends on many parameters other than membrane pore size and void fraction; and which itself greatly affects the filtration process and membrane functionality. In this work we formulate mathematical models that can (i) account for the membrane internal morphology (internal structure, pore size & shape, etc.); (ii) fouling of membranes with specific morphology; and (iii) make some predictions as to what type of membrane morphology might offer optimum filtration performance.

  2. 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.

  3. 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.

  4. 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

  5. Modeling Flow Past a TrapEase Inferior Vena Cava Filter

    NASA Astrophysics Data System (ADS)

    Singer, Michael; Henshaw, William; Wang, Stephen

    2008-11-01

    This study uses three-dimensional computational fluid dynamics to evaluate the efficacy of the TrapEase inferior vena cava (IVC) filter. Hemodynamics of the unoccluded and partially occluded filter are examined, and the clinical implications are assessed. The IVC, which is the primary vein that drains the legs, is modeled as a straight pipe, and a geometrically accurate model of the filter is constructed using computer aided design. Blood is modeled as a homogeneous, incompressible, Newtonian fluid, and the method of overset grids is used to solve the Navier-Stokes equations. Results are corroborated with in-vitro studies. Flow around the unoccluded filter demonstrates minimal disruption, but spherical clots in the downstream trapping position lead to regions of stagnant and recirculating flow that may promote further clotting. The volume of stagnant flow and the peak wall shear stress increase with clot volume. For clots trapped in the upstream trapping position, flow is disrupted along the cava wall downstream of the clot and within the filter. The shape and location of trapped clots also effect the peak wall shear stress and may impact the efficacy of the filter.

  6. Cross-flow, filter-sorbent catalyst for particulate, SO sub 2 and NO sub x control

    SciTech Connect

    Benedek, K. , Inc., Cambridge, MA ); Flytzani-Stephanopoulos, M. )

    1991-08-01

    This report describes a new concept for integrated pollutant control: a cross-flow filter comprised of layered, gas permeable membranes that act a particulate filter, an SO{sub 2} sorbent, and a NO{sub x} reduction catalyst.

  7. 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.

  8. Syringe Pump Performance Maintained with IV Filter Use During Low Flow Rate Delivery for Pediatric Patients.

    PubMed

    Chau, Destiny F; Vasilopoulos, Terrie; Schoepf, Miriam; Zhang, Christina; Fahy, Brenda G

    2016-09-01

    Complex surgical and critically ill pediatric patients rely on syringe infusion pumps for precise delivery of IV medications. Low flow rates and in-line IV filter use may affect drug delivery. To determine the effects of an in-line filter to remove air and/or contaminants on syringe pump performance at low flow rates, we compared the measured rates with the programmed flow rates with and without in-line IV filters. Standardized IV infusion assemblies with and without IV filters (filter and control groups) attached to a 10-mL syringe were primed and then loaded onto a syringe pump and connected to a 16-gauge, 16-cm single-lumen catheter. The catheter was suspended in a normal saline fluid column to simulate the back pressure from central venous circulation. The delivered infusate was measured by gravimetric methods at predetermined time intervals, and flow rate was calculated. Experimental trials for initial programmed rates of 1.0, 0.8, 0.6, and 0.4 mL/h were performed in control and filter groups. For each trial, the flow rate was changed to double the initial flow rate and was then returned to the initial flow rate to analyze pump performance for titration of rates often required during medication administration. These conditions (initial rate, doubling of initial rate, and return to initial rate) were analyzed separately for steady-state flow rate and time to steady state, whereas their average was used for percent deviation analysis. Differences between control and filter groups were assessed using Student t tests with adjustment for multiplicity (using n = 3 replications per group). Mean time from 0 to initial flow (startup delay) was <1 minute in both groups with no statistical difference between groups (P = 1.0). The average time to reach steady-state flow after infusion startup or rate changes was not statistically different between the groups (range, 0.8-5.5 minutes), for any flow rate or part of the trial (initial rate, doubling of initial rate, and

  9. 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

  10. Flow of Viscoelastic Polymer Solutions through Filter Screens

    NASA Astrophysics Data System (ADS)

    Machač, Ivan; Surý, Alexander; Šiška, Bedřich

    2011-07-01

    In this contribution, the measurements are presented of the pressure drop in the creeping flow of viscoelastic solution of polyacrylamides through metal wire screens, differing in wire diameter, aperture dimension, and type of weaving. In this flow, a strong elastic pressure drop excess manifest itself. Analysing the extensive set of experimental data, it was verified that for engineering estimation of the pressure drop excess, a simple form of the corrective Deborah number function can be used.

  11. Construction of Low Dissipative High Order Well-Balanced Filter Schemes for Non-Equilibrium Flows

    NASA Technical Reports Server (NTRS)

    Wang, Wei; Yee, H. C.; Sjogreen, Bjorn; Magin, Thierry; Shu, Chi-Wang

    2009-01-01

    The goal of this paper is to generalize the well-balanced approach for non-equilibrium flow studied by Wang et al. [26] to a class of low dissipative high order shock-capturing filter schemes and to explore more advantages of well-balanced schemes in reacting flows. The class of filter schemes developed by Yee et al. [30], Sjoegreen & Yee [24] and Yee & Sjoegreen [35] consist of two steps, a full time step of spatially high order non-dissipative base scheme and an adaptive nonlinear filter containing shock-capturing dissipation. A good property of the filter scheme is that the base scheme and the filter are stand alone modules in designing. Therefore, the idea of designing a well-balanced filter scheme is straightforward, i.e., choosing a well-balanced base scheme with a well-balanced filter (both with high order). A typical class of these schemes shown in this paper is the high order central difference schemes/predictor-corrector (PC) schemes with a high order well-balanced WENO filter. The new filter scheme with the well-balanced property will gather the features of both filter methods and well-balanced properties: it can preserve certain steady state solutions exactly; it is able to capture small perturbations, e.g., turbulence fluctuations; it adaptively controls numerical dissipation. Thus it shows high accuracy, efficiency and stability in shock/turbulence interactions. Numerical examples containing 1D and 2D smooth problems, 1D stationary contact discontinuity problem and 1D turbulence/shock interactions are included to verify the improved accuracy, in addition to the well-balanced behavior.

  12. 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.

  13. 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.

  14. 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

  15. File-Based Data Flow in the CMS Filter Farm

    SciTech Connect

    Andre, J.M.; et al.

    2015-12-23

    During the LHC Long Shutdown 1, the CMS Data Acquisition system underwent a partial redesign to replace obsolete network equipment, use more homogeneous switching technologies, and prepare the ground for future upgrades of the detector front-ends. The software and hardware infrastructure to provide input, execute the High Level Trigger (HLT) algorithms and deal with output data transport and storage has also been redesigned to be completely file- based. This approach provides additional decoupling between the HLT algorithms and the input and output data flow. All the metadata needed for bookkeeping of the data flow and the HLT process lifetimes are also generated in the form of small “documents” using the JSON encoding, by either services in the flow of the HLT execution (for rates etc.) or watchdog processes. These “files” can remain memory-resident or be written to disk if they are to be used in another part of the system (e.g. for aggregation of output data). We discuss how this redesign improves the robustness and flexibility of the CMS DAQ and the performance of the system currently being commissioned for the LHC Run 2.

  16. Contribution of breathing frequency and inhalation flow rate on performance of N95 filtering facepiece respirators.

    PubMed

    Mahdavi, Alireza; Bahloul, Ali; Haghighat, Fariborz; Ostiguy, Claude

    2014-03-01

    The investigation of particle penetration through filtering facepiece respirators under cyclic flows is very necessary because cyclic flows represent actual breathing flow patterns. This article reports the development of a procedure to investigate the individual impact of breathing frequency and flow rate on the performance of N95 filtering facepiece respirators. Experiments were performed for two peak inhalation flows (PIFs; 135 and 360 l min(-1)) and two breathing frequencies [24 and 42 breaths per minute (BPM)] for a total of four cyclic flows (Flow A: 135 l min(-1) and 24 BPM; Flow B: 135 l min(-1) and 42 BPM; Flow C: 360 l min(-1) and 24 BPM; and Flow D: 360 l min(-1) and 42 BPM). Each experiment was performed using two different set-ups: the first set-up included both inhalations and exhalations through the filter media and test chamber, while with the second set-up, only inhalation flows were considered. The results showed that, for the most penetrating particle size range, an increase in both PIF and breathing frequency could potentially enhance the penetration with both set-ups; however, the effect of PIF was observed to be much more pronounced than that of frequency. The results indicated that with both set-ups, when the PIF was increased from 135 to 360 l min(-1) (for the given frequency: 24 or 42 BPM), an increase of up to 139-152% in penetration was observed. On the other hand, only a 10-16% increase in penetration occurred when the frequency was changed from 24 to 42 BPM (for a given PIF: 135 or 360 l min(-1)). This suggests that, from low to high respiratory efforts, a huge portion of penetration enhancement is due to PIF variations and only a small portion is contributed by frequency variations.

  17. CFD simulation of an internal spin-filter: evidence of lateral migration and exchange flow through the mesh.

    PubMed

    Figueredo-Cardero, Alvio; Chico, Ernesto; Castilho, Leda R; Medronho, Ricardo A

    2009-11-01

    In the present work Computational Fluid Dynamics (CFD) was used to study the flow field and particle dynamics in an internal spin-filter (SF) bioreactor system. Evidence of a radial exchange flow through the filter mesh was detected, with a magnitude up to 130-fold higher than the perfusion flow, thus significantly contributing to radial drag. The exchange flow magnitude was significantly influenced by the filter rotation rate, but not by the perfusion flow, within the ranges evaluated. Previous reports had only given indirect evidences of this exchange flow phenomenon in spin-filters, but the current simulations were able to quantify and explain it. Flow pattern inside the spin-filter bioreactor resembled a typical Taylor-Couette flow, with vortices being formed in the annular gap and eventually penetrating the internal volume of the filter, thus being the probable reason for the significant exchange flow observed. The simulations also showed that cells become depleted in the vicinity of the mesh due to lateral particle migration. Cell concentration near the filter was approximately 50% of the bulk concentration, explaining why cell separation achieved in SFs is not solely due to size exclusion. The results presented indicate the power of CFD techniques to study and better understand spin-filter systems, aiming at the establishment of effective design, operation and scale-up criteria.

  18. Performance of Improved High-Order Filter Schemes for Turbulent Flows with Shocks

    NASA Technical Reports Server (NTRS)

    Kotov, Dmitry Vladimirovich; Yee, Helen M C.

    2013-01-01

    The performance of the filter scheme with improved dissipation control ? has been demonstrated for different flow types. The scheme with local ? is shown to obtain more accurate results than its counterparts with global or constant ?. At the same time no additional tuning is needed to achieve high accuracy of the method when using the local ? technique. However, further improvement of the method might be needed for even more complex and/or extreme flows.

  19. Effects of Temperature, Humidity and Air Flow on Fungal Growth Rate on Loaded Ventilation Filters.

    PubMed

    Tang, W; Kuehn, T H; Simcik, Matt F

    2015-01-01

    This study compares the fungal growth ratio on loaded ventilation filters under various temperature, relative humidity (RH), and air flow conditions in a controlled laboratory setting. A new full-size commercial building ventilation filter was loaded with malt extract nutrients and conidia of Cladosporium sphaerospermum in an ASHRAE Standard 52.2 filter test facility. Small sections cut from this filter were incubated under the following conditions: constant room temperature and a high RH of 97%; sinusoidal temperature (with an amplitude of 10°C, an average of 23°C, and a period of 24 hr) and a mean RH of 97%; room temperature and step changes between 97% and 75% RH, 97% and 43% RH, and 97% and 11% RH every 12 hr. The biomass on the filter sections was measured using both an elution-culture method and by ergosterol assay immediately after loading and every 2 days up to 10 days after loading. Fungal growth was detected earlier using ergosterol content than with the elution-culture method. A student's t-test indicated that Cladosporium sphaerospermum grew better at the constant room temperature condition than at the sinusoidal temperature condition. By part-time exposure to dry environments, the fungal growth was reduced (75% and 43% RH) or even inhibited (11% RH). Additional loaded filters were installed in the wind tunnel at room temperature and an RH greater than 95% under one of two air flow test conditions: continuous air flow or air flow only 9 hr/day with a flow rate of 0.7 m(3)/s (filter media velocity 0.15 m/s). Swab tests and a tease mount method were used to detect fungal growth on the filters at day 0, 5, and 10. Fungal growth was detected for both test conditions, which indicates that when temperature and relative humidity are optimum, controlling the air flow alone cannot prevent fungal growth. In real applications where nutrients are less sufficient than in this laboratory study, fungal growth rate may be reduced under the same operating conditions.

  20. 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

  1. Radial Flow Fludized Filter Finds Niche as a Pretreatment System for Surface Water in Small Communities

    EPA Science Inventory

    An emerging technology called radial flow fluidized filter (R3f) has been developed as a low cost simplistic filtration technology for small communities of less than 10,000 people. Fouling is a major impediment to the sustainability of membrane technology particularly for small ...

  2. Radial Flow Fludized Filter Finds Niche as a Pretreatment System for Surface Water in Small Communities

    EPA Science Inventory

    An emerging technology called radial flow fluidized filter (R3f) has been developed as a low cost simplistic filtration technology for small communities of less than 10,000 people. Fouling is a major impediment to the sustainability of membrane technology particularly for small ...

  3. Flow pathways and sediment trapping in a field-scale vegetative filter

    Treesearch

    M. J. Helmers; D. E. Eisenhauer; Mike G. Dosskey; T. G. Franti; J. M. Brothers; M. C. McCullough

    2005-01-01

    Vegetative filters (VF) are a best management practive installed in many areas to control sediment movement to water bodies. It is commonly assumed that runoff proceeds perpendicularly across a VF as sheet flow. However, there is little research information on natural pathways of water movement and performance of field-scale VF. The objectives of this study were: (1)...

  4. 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.

  5. Demonstration and Analysis of Filtered Rayleigh Scattering Flow Field Diagnostic System

    NASA Technical Reports Server (NTRS)

    Forkey, Joseph N.; Lempert, Walter R.; Miles, Richard B.

    1996-01-01

    Filtered Rayleigh Scattering (FRS) is a diagnostic technique which measures velocity, temperature, and pressure by determining Doppler shift, total intensity, and spectral line shape of laser induced Rayleigh-Brillouin scattering. In the work reported here, this is accomplished by using a narrow line width, injection seeded Nd-YAG laser sheet to induce Rayleigh-Brillouin scattering from a gas flow. This light is passed through an optical notch filter, and transmitted light is imaged onto an intensified charge coupled display (CCD) camera. By monitoring the grayscale value at a particular pixel while the laser frequency is tuned, the convolution between the Rayleigh-Brillouin scattering profile and the filter transmission profile is attained. Since the filter profile can be independently measured, it can be deconvolved from the measuring signal, yielding the Rayleigh-Brillouin scattering profile. From this profile, flow velocity, temperature, and pressure are determined. In this paper the construction and characterization of the optical notch filter and a newly developed frequency apparatus are discussed.

  6. A particle filter to reconstruct a free-surface flow from a depth camera

    NASA Astrophysics Data System (ADS)

    Combés, Benoit; Heitz, Dominique; Guibert, Anthony; Mémin, Etienne

    2015-10-01

    We investigate the combined use of a kinect depth sensor and of a stochastic data assimilation (DA) method to recover free-surface flows. More specifically, we use a weighted ensemble Kalman filter method to reconstruct the complete state of free-surface flows from a sequence of depth images only. This particle filter accounts for model and observations errors. This DA scheme is enhanced with the use of two observations instead of one classically. We evaluate the developed approach on two numerical test cases: a collapse of a water column as a toy-example and a flow in an suddenly expanding flume as a more realistic flow. The robustness of the method to depth data errors and also to initial and inflow conditions is considered. We illustrate the interest of using two observations instead of one observation into the correction step, especially for unknown inflow boundary conditions. Then, the performance of the Kinect sensor in capturing the temporal sequences of depth observations is investigated. Finally, the efficiency of the algorithm is qualified for a wave in a real rectangular flat bottomed tank. It is shown that for basic initial conditions, the particle filter rapidly and remarkably reconstructs the velocity and height of the free surface flow based on noisy measurements of the elevation alone.

  7. 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.

  8. A GPU-Parallelized Eigen-Based Clutter Filter Framework for Ultrasound Color Flow Imaging.

    PubMed

    Chee, Adrian J Y; Yiu, Billy Y S; Yu, Alfred C H

    2017-01-01

    Eigen-filters with attenuation response adapted to clutter statistics in color flow imaging (CFI) have shown improved flow detection sensitivity in the presence of tissue motion. Nevertheless, its practical adoption in clinical use is not straightforward due to the high computational cost for solving eigendecompositions. Here, we provide a pedagogical description of how a real-time computing framework for eigen-based clutter filtering can be developed through a single-instruction, multiple data (SIMD) computing approach that can be implemented on a graphical processing unit (GPU). Emphasis is placed on the single-ensemble-based eigen-filtering approach (Hankel singular value decomposition), since it is algorithmically compatible with GPU-based SIMD computing. The key algebraic principles and the corresponding SIMD algorithm are explained, and annotations on how such algorithm can be rationally implemented on the GPU are presented. Real-time efficacy of our framework was experimentally investigated on a single GPU device (GTX Titan X), and the computing throughput for varying scan depths and slow-time ensemble lengths was studied. Using our eigen-processing framework, real-time video-range throughput (24 frames/s) can be attained for CFI frames with full view in azimuth direction (128 scanlines), up to a scan depth of 5 cm ( λ pixel axial spacing) for slow-time ensemble length of 16 samples. The corresponding CFI image frames, with respect to the ones derived from non-adaptive polynomial regression clutter filtering, yielded enhanced flow detection sensitivity in vivo, as demonstrated in a carotid imaging case example. These findings indicate that the GPU-enabled eigen-based clutter filtering can improve CFI flow detection performance in real time.

  9. A GPU-Parallelized Eigen-Based Clutter Filter Framework for Ultrasound Color Flow Imaging.

    PubMed

    Chee, Adrian; Yiu, Billy; Yu, Alfred

    2016-09-07

    Eigen-filters with attenuation response adapted to clutter statistics in color flow imaging (CFI) have shown improved flow detection sensitivity in the presence of tissue motion. Nevertheless, its practical adoption in clinical use is not straightforward due to the high computational cost for solving eigen-decompositions. Here, we provide a pedagogical description of how a real-time computing framework for eigen-based clutter filtering can be developed through a single-instruction, multiple data (SIMD) computing approach that can be implemented on a graphical processing unit (GPU). Emphasis is placed on the single-ensemble-based eigen-filtering approach (Hankel-SVD) since it is algorithmically compatible with GPU-based SIMD computing. The key algebraic principles and the corresponding SIMD algorithm are explained, and annotations on how such algorithm can be rationally implemented on the GPU are presented. Real-time efficacy of our framework was experimentally investigated on a single GPU device (GTX Titan X), and the computing throughput for varying scan depths and slow-time ensemble lengths were studied. Using our eigenprocessing framework, real-time video-range throughput (24 fps) can be attained for CFI frames with full-view in azimuth direction (128 scanlines), up to a scan depth of 5 cm (λ pixel axial spacing) for slow-time ensemble length of 16 samples. The corresponding CFI image frames, with respect to the ones derived from non-adaptive polynomial regression clutter filtering, yielded enhanced flow detection sensitivity in vivo, as demonstrated in a carotid imaging case example. These findings indicate that GPU-enabled eigen-based clutter filtering can improve CFI flow detection performance in real time.

  10. On the structural limitations of recursive digital filters for base flow estimation

    NASA Astrophysics Data System (ADS)

    Su, Chun-Hsu; Costelloe, Justin F.; Peterson, Tim J.; Western, Andrew W.

    2016-06-01

    Recursive digital filters (RDFs) are widely used for estimating base flow from streamflow hydrographs, and various forms of RDFs have been developed based on different physical models. Numerical experiments have been used to objectively evaluate their performance, but they have not been sufficiently comprehensive to assess a wide range of RDFs. This paper extends these studies to understand the limitations of a generalized RDF method as a pathway for future field calibration. Two formalisms are presented to generalize most existing RDFs, allowing systematic tuning of their complexity. The RDFs with variable complexity are evaluated collectively in a synthetic setting, using modeled daily base flow produced by Li et al. (2014) from a range of synthetic catchments simulated with HydroGeoSphere. Our evaluation reveals that there are optimal RDF complexities in reproducing base flow simulations but shows that there is an inherent physical inconsistency within the RDF construction. Even under the idealized setting where true base flow data are available to calibrate the RDFs, there is persistent disagreement between true and estimated base flow over catchments with small base flow components, low saturated hydraulic conductivity of the soil and larger surface runoff. The simplest explanation is that low base flow "signal" in the streamflow data is hard to distinguish, although more complex RDFs can improve upon the simpler Eckhardt filter at these catchments.

  11. The role of pressure drop and flow redistribution on modeling mercury control using sorbent injection in baghouse filters

    SciTech Connect

    Joseph R.V. Flora; Richard A. Hargis; William J. O'Dowd; Andrew Karash; Henry W. Pennline; Radisav D. Vidic

    2006-03-15

    A mathematical model based on simple cake filtration theory was coupled to a previously developed two-stage mathematical model for mercury (Hg) removal from coal combustion using powdered activated carbon injection upstream of a baghouse filter. Values of the average permeability of the filter cake and the filter resistance extracted from the model were 4.4 x 10{sup -13}m{sup 2} and 2.5 x 10{sup -4}m{sup -1}, respectively. The flow is redistributed during partial cleaning of the filter, with flows higher across the newly cleaned filter section. The calculated average Hg removal efficiency from the baghouse is lower because of the high mass flux of Hg exiting the filter in the newly cleaned section. The model shows that calculated average Hg removal is affected by permeability, filter resistance, fraction of the baghouse cleaned, and cleaning interval. 17 refs., 8 figs., 2 tabs.

  12. The role of pressure drop and flow redistribution on modeling mercury control using sorbent injection in baghouse filters.

    PubMed

    Flora, Joseph R V; Hargis, Richard A; O'Dowd, William J; Karash, Andrew; Pennline, Henry W; Vidic, Radisav D

    2006-03-01

    A mathematical model based on simple cake filtration theory was coupled to a previously developed two-stage mathematical model for mercury (Hg) removal using powdered activated carbon injection upstream of a baghouse filter. Values of the average permeability of the filter cake and the filter resistance extracted from the model were 4.4 x 10(-13) m2 and 2.5 x 10(-4) m(-1), respectively. The flow is redistributed during partial cleaning of the filter, with flows higher across the newly cleaned filter section. The calculated average Hg removal efficiency from the baghouse is lower because of the high mass flux of Hg exiting the filter in the newly cleaned section. The model shows that calculated average Hg removal is affected by permeability, filter resistance, fraction of the baghouse cleaned, and cleaning interval.

  13. 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.

  14. 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.

  15. Analysis of up-flow aerated biological activated carbon filter technology in drinking water treatment.

    PubMed

    Lu, Shaoming; Liu, Jincui; Li, Shaowen; Biney, Elizabeth

    2013-01-01

    Problems have been found in the traditional post-positioned down-flow biological activated carbon filter (DBACF), such as microorganism leakage and low biodegradability. A pilot test was carried out to place a BACF between the sediment tank and the sand filter; a new technology of dual media up-flow aerated biological activated carbon filter (UBACF) was developed. Results showed that in terms of the new process, the up-flow mode was better than the down-flow. Compared with the DBACF, the problem of microorganism leakage could be well resolved with the UBACF process by adding disinfectant before the sand filtration, and a similar adsorption effect could be obtained. For the tested raw water, the COD(Mn) and NH3-N removal rate was 54.6% and 85.0%, respectively, similar to the waterworks with the DBACF process. The UBACF greatly enhanced oxygen supply capability and mass transfer rate via aeration, and the NH3-N removal ability was significantly improved from 1.5 mg/L to more than 3 mg/L. Influent to the UBACF with higher turbidity could be coped with through the primary filtration of the ceramisite layer combined with fluid-bed technology, which gave the carbon bed a low-turbidity environment of less than 1.0 NTU. The backwashing parameters and carbon abrasion rate of the two processes were almost the same.

  16. 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. (

  17. Performance evaluation of a dual-flow recharge filter for improving groundwater quality.

    PubMed

    Samuel, Manoj P; Senthilvel, S; Mathew, Abraham C

    2014-07-01

    A dual-flow multimedia stormwater filter integrated with a groundwater recharge system was developed and tested for hydraulic efficiency and pollutant removal efficiency. The influent stormwater first flows horizontally through the circular layers of planted grass and biofibers. Subsequently, the flow direction changes to a vertical direction so that water moves through layers of pebbles and sand and finally gets recharged to the deep aquifers. The media in the sequence of vegetative medium:biofiber to pebble:sand were filled in nine proportions and tested for the best performing combination. Three grass species, viz., Typha (Typha angustifolia), Vetiver (Chrysopogon zizanioides), and St. Augustine grass (Stenotaphrum secundatum), were tested as the best performing vegetative medium. The adsorption behavior of Coconut (Cocos nucifera) fiber, which was filled in the middle layer, was determined by a series of column and batch studies.The dual-flow filter showed an increasing trend in hydraulic efficiency with an increase in flowrate. The chemical removal efficiency of the recharge dual-flow filter was found to be very high in case of K+ (81.6%) and Na+ (77.55%). The pH normalizing efficiency and electrical conductivity reduction efficiency were also recorded as high. The average removal percentage of Ca2+ was moderate, while that of Mg2+ was very low. The filter proportions of 1:1 to 1:2 (plant:fiber to pebble:sand) showed a superior performance compared to all other proportions. Based on the estimated annual costs and returns, all the financial viability criteria (internal rate of return, net present value, and benefit-cost ratio) were found to be favorable and affordable to farmers in terms of investing in the developed filtration system.

  18. Model simulation and experiments of flow and mass transport through a nano-material gas filter

    SciTech Connect

    Yang, Xiaofan; Zheng, Zhongquan C.; Winecki, Slawomir; Eckels, Steve

    2013-11-01

    A computational model for evaluating the performance of nano-material packed-bed filters was developed. The porous effects of the momentum and mass transport within the filter bed were simulated. For the momentum transport, an extended Ergun-type model was employed and the energy loss (pressure drop) along the packed-bed was simulated and compared with measurement. For the mass transport, a bulk dsorption model was developed to study the adsorption process (breakthrough behavior). Various types of porous materials and gas flows were tested in the filter system where the mathematical models used in the porous substrate were implemented and validated by comparing with experimental data and analytical solutions under similar conditions. Good agreements were obtained between experiments and model predictions.

  19. Infrared species tomography of a transient flow field using Kalman filtering.

    PubMed

    Daun, Kyle J; Waslander, Steven L; Tulloch, Brandon B

    2011-02-20

    In infrared species tomography, the unknown concentration distribution of a species is inferred from the attenuation of multiple collimated light beams shone through the measurement field. The resulting set of linear equations is rank-deficient, so prior assumptions about the smoothness and nonnegativity of the distribution must be imposed to recover a solution. This paper describes how the Kalman filter can be used to incorporate additional information about the time evolution of the distribution into the reconstruction. Results show that, although performing a series of static reconstructions is more accurate at low levels of measurement noise, the Kalman filter becomes advantageous when the measurements are corrupted with high levels of noise. The Kalman filter also enables signal multiplexing, which can help achieve the high sampling rates needed to resolve turbulent flow phenomena.

  20. A Fast Network Flow Model is used in conjunction with Measurements of Filter Permeability to calculate the Performance of Hot Gas Filters

    SciTech Connect

    VanOsdol, J.G.; Chiang, T-K.

    2002-09-19

    Two different technologies that are being considered for generating electric power on a large scale by burning coal are Pressurized Fluid Bed Combustion (PFBC) systems and Integrated Gasification and Combined Cycle (IGCC) systems. Particulate emission regulations that have been proposed for future systems may require that these systems be fitted with large scale Hot Gas Clean-Up (HGCU) filtration systems that would remove the fine particulate matter from the hot gas streams that are generated by PFBC and IGCC systems. These hot gas filtration systems are geometrically and aerodynamically complex. They typically are constructed with large arrays of ceramic candle filter elements (CFE). The successful design of these systems require an accurate assessment of the rate at which mechanical energy of the gas flow is dissipated as it passes through the filter containment vessel and the individual candle filter elements that make up the system. Because the filtration medium is typically made of a porous ceramic material having open pore sizes that are much smaller than the dimensions of the containment vessel, the filtration medium is usually considered to be a permeable medium that follows Darcy's law. The permeability constant that is measured in the lab is considered to be a function of the filtration medium only and is usually assumed to apply equally to all the filters in the vessel as if the flow were divided evenly among all the filter elements. In general, the flow of gas through each individual CFE will depend not only on the geometrical characteristics of the filtration medium, but also on the local mean flows in the filter containment vessel that a particular filter element sees. The flow inside the CFE core, through the system manifolds, and inside the containment vessel itself will be coupled to the flow in the filter medium by various Reynolds number effects. For any given filter containment vessel, since the mean flows are different in different locations

  1. Enhancement of microfluidic particle separation using cross-flow filters with hydrodynamic focusing

    PubMed Central

    Chiu, Yun-Yen; Huang, Chen-Kang

    2016-01-01

    A microfluidic chip is proposed to separate microparticles using cross-flow filtration enhanced with hydrodynamic focusing. By exploiting a buffer flow from the side, the microparticles in the sample flow are pushed on one side of the microchannels, lining up to pass through the filters. Meanwhile a larger pressure gradient in the filters is obtained to enhance separation efficiency. Compared with the traditional cross-flow filtration, our proposed mechanism has the buffer flow to create a moving virtual boundary for the sample flow to actively push all the particles to reach the filters for separation. It further allows higher flow rates. The device only requires soft lithograph fabrication to create microchannels and a novel pressurized bonding technique to make high-aspect-ratio filtration structures. A mixture of polystyrene microparticles with 2.7 μm and 10.6 μm diameters are successfully separated. 96.2 ± 2.8% of the large particle are recovered with a purity of 97.9 ± 0.5%, while 97.5 ± 0.4% of the small particle are depleted with a purity of 99.2 ± 0.4% at a sample throughput of 10 μl/min. The experiment is also conducted to show the feasibility of this mechanism to separate biological cells with the sample solutions of spiked PC3 cells in whole blood. By virtue of its high separation efficiency, our device offers a label-free separation technique and potential integration with other components, thereby serving as a promising tool for continuous cell filtration and analysis applications. PMID:26858812

  2. Enhancement of microfluidic particle separation using cross-flow filters with hydrodynamic focusing.

    PubMed

    Chiu, Yun-Yen; Huang, Chen-Kang; Lu, Yen-Wen

    2016-01-01

    A microfluidic chip is proposed to separate microparticles using cross-flow filtration enhanced with hydrodynamic focusing. By exploiting a buffer flow from the side, the microparticles in the sample flow are pushed on one side of the microchannels, lining up to pass through the filters. Meanwhile a larger pressure gradient in the filters is obtained to enhance separation efficiency. Compared with the traditional cross-flow filtration, our proposed mechanism has the buffer flow to create a moving virtual boundary for the sample flow to actively push all the particles to reach the filters for separation. It further allows higher flow rates. The device only requires soft lithograph fabrication to create microchannels and a novel pressurized bonding technique to make high-aspect-ratio filtration structures. A mixture of polystyrene microparticles with 2.7 μm and 10.6 μm diameters are successfully separated. 96.2 ± 2.8% of the large particle are recovered with a purity of 97.9 ± 0.5%, while 97.5 ± 0.4% of the small particle are depleted with a purity of 99.2 ± 0.4% at a sample throughput of 10 μl/min. The experiment is also conducted to show the feasibility of this mechanism to separate biological cells with the sample solutions of spiked PC3 cells in whole blood. By virtue of its high separation efficiency, our device offers a label-free separation technique and potential integration with other components, thereby serving as a promising tool for continuous cell filtration and analysis applications.

  3. Oxygen profile and clogging in vertical flow sand filters for on-site wastewater treatment.

    PubMed

    Petitjean, A; Forquet, N; Boutin, C

    2016-04-01

    13 million people (about 20% of the population) use on-site wastewater treatment in France. Buried vertical sand filters are often built, especially when the soil permeability is not sufficient for septic tank effluent infiltration in undisturbed soil. Clogging is one of the main problems deteriorating the operation of vertical flow filters for wastewater treatment. The extent of clogging is not easily assessed, especially in buried vertical flow sand filters. We suggest examining two possible ways of detecting early clogging: (1) NH4-N/NO3-N outlet concentration ratio, and (2) oxygen measurement within the porous media. Two pilot-scale filters were equipped with probes for oxygen concentration measurements and samples were taken at different depths for pollutant characterization. Influent and effluent grab-samples were taken three times a week. The systems were operated using batch-feeding of septic tank effluent. Qualitative description of oxygen transfer processes under unclogged and clogged conditions is presented. NH4-N outlet concentration appears to be useless for early clogging detection. However, NO3-N outlet concentration and oxygen content allows us to diagnose the early clogging of the system.

  4. Alternative filter media for phosphorous removal in a horizontal subsurface flow constructed wetland.

    PubMed

    Vohla, Christina; Põldvere, Elar; Noorvee, Alar; Kuusemets, Valdo; Mander, Ulo

    2005-01-01

    During the study period from 1997 to 2002 the purification efficiency of phosphorus in the horizontal subsurface flow (HSSF) constructed wetland (CW) in Kodijärve, has been quite high (63-95%). However, slowly increasing trend in outlet P concentrations and decreasing annual P removal rate are obviously the indicators that show possible saturation processes in filter media. To search for potential filter media with high phosphorus sorption capacity, sorption characteristics and particle size distribution of several local sands, gravels, glauconite-sandstone, LWA, and calcareous waste products from oil-shale industry were investigated. The average P sorption capacity for best materials (crashed ash block, oil, shale fly ash and the sediment from oil shale ash plateau) was higher than 96% and estimated design capacity was around 4-5 g P kg(-1). According to results, sediment from oil shale ash plateau was considered as perspective filter media for P retention. In Summer 2002 experimental sedimentation filter, filled with the sediment from oil shale ash plateau, was installed in the outlet from the Kodijärve HSSF CW. According to preliminary results the average P removal in the sedimentation filter was 52%.

  5. Particle capture in axial magnetic filters with power law flow model

    NASA Astrophysics Data System (ADS)

    Abbasov, T.; Herdem, S.; Köksal, M.

    1999-05-01

    A theory of capture of magnetic particle carried by laminar flow of viscous non-Newtonian (power law) fluid in axially ordered filters is presented. The velocity profile of the fluid flow is determined by the Kuwabara-Happel cell model. For the trajectory of the particle, the capture area and the filter performance simple analytical expressions are obtained. These expressions are valid for particle capture processes from both Newtonian and non-Newtonian fluids. For this reason the obtained theoretical results make it possible to widen the application of high-gradient magnetic filtration (HGMF) to other industrial areas. For Newtonian fluids the theoretical results are shown to be in good agreement with the experimental ones reported in the literature.

  6. 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

  7. 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

  8. 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.

  9. Fibrous filter efficiency and pressure drop in the viscous-inertial transition flow regime.

    SciTech Connect

    Sanchez, Andres L.; Brockmann, John E.; Dellinger, Jennifer Gwynne; Lucero, Daniel A.; Hubbard, Joshua A.; Servantes, Brandon Lee

    2011-10-01

    Fibrous filter pressure drop and aerosol collection efficiency were measured at low air pressures (0.2 to 0.8 atm) and high face velocities (5 to 20 meters per second) to give fiber Reynolds numbers in the viscous-inertial transition flow regime (1 to 16). In this regime, contemporary filtration theory based on Kuwabara's viscous flow through an ensemble of fibers under-predicts single fiber impaction by several orders of magnitude. Streamline curvature increases substantially as inertial forces become dominant. Dimensionless pressure drop measurements followed the viscous-inertial theory of Robinson and Franklin rather than Darcy's linear pressure-velocity relationship (1972). Sodium chloride and iron nano-agglomerate test aerosols were used to evaluate the effects of particle density and shape factor. Total filter efficiency collapsed when plotted against the particle Stokes and fiber Reynolds numbers. Efficiencies were then fitted with an impactor type equation where the cutpoint Stokes number and a steepness parameter described data well in the sharply increasing portion of the curve (20% to 80% efficiency). The cutpoint Stokes number was a linearly decreasing function of fiber Reynolds number. Single fiber efficiencies were calculated from total filter efficiencies and compared to contemporary viscous flow impaction theory (Stechkina et al. 1969), and numerical simulations from the literature. Existing theories under-predicted measured single fiber efficiencies although the assumption of uniform flow conditions for each successive layer of fibers is questionable; the common exponential relationship between single fiber efficiency and total filter efficiency may not be appropriate in this regime.

  10. Nonuniform air flow in inlets: the effect on filter deposits in the fiber sampling cassette.

    PubMed

    Baron, P A; Chen, C C; Hemenway, D R; O'Shaughnessy, P

    1994-08-01

    Smoke stream studies were combined with a new technique for visualizing a filter deposit from samples used to monitor asbestos or other fibers. Results clearly show the effect of secondary flow vortices within the sampler under anisoaxial sampling conditions. The vortices observed at low wind velocities occur when the inlet axis is situated at angles between 45 degrees and 180 degrees to the motion of the surrounding air. It is demonstrated that the vortices can create a complex nonuniform pattern in the filter deposit, especially when combined with particle settling or electrostatic interactions between the particles and the sampler. Inertial effects also may play a role in the deposit nonuniformity, as well as causing deposition on the cowl surfaces. Changes in the sampler, such as its placement, may reduce these biases. The effects noted are not likely to occur in all sampling situations, but may explain some reports of high variability on asbestos fiber filter samples. The flow patterns observed in this study are applicable to straight, thin-walled inlets. Although only compact particles were used, the air flow patterns and forces involved will have similar effects on fibers of the same aerodynamic diameter.

  11. Echo motion imaging with adaptive clutter filter for assessment of cardiac blood flow

    NASA Astrophysics Data System (ADS)

    Takahashi, Hiroki; Hasegawa, Hideyuki; Kanai, Hiroshi

    2015-07-01

    Visualization of the vortex blood flow in the cardiac chamber is a potential diagnostic tool for the evaluation of cardiac function. In the present study, a method for automatic selection of the desirable cutoff frequency of a moving target indicator filter, namely, a clutter filter, was proposed in order to visualize complex blood flows by the ultrahigh-frame-rate imaging of echoes from blood particles while suppressing clutter echoes. In this method, the cutoff frequency was adaptively changed as a function of the velocity of the heart wall (clutter source) in each frame. The feasibility of the proposed method was examined through the measurement of a healthy volunteer using parallel receive beamforming with a single transmission of a non-steered diverging beam. Using the moving target indicator filter as above with the cutoff frequency determined by the proposed method, the vortex-like blood flow in the cardiac chamber was visualized as movements of echoes from blood particles at a very high frame rate of 6024 Hz while suppressing clutter echoes.

  12. Enhanced Kalman Filtering for a 2D CFD NS Wind Farm Flow Model

    NASA Astrophysics Data System (ADS)

    Doekemeijer, B. M.; van Wingerden, J. W.; Boersma, S.; Pao, L. Y.

    2016-09-01

    Wind turbines are often grouped together for financial reasons, but due to wake development this usually results in decreased turbine lifetimes and power capture, and thereby an increased levelized cost of energy (LCOE). Wind farm control aims to minimize this cost by operating turbines at their optimal control settings. Most state-of-the-art control algorithms are open-loop and rely on low fidelity, static flow models. Closed-loop control relying on a dynamic model and state observer has real potential to further decrease wind's LCOE, but is often too computationally expensive for practical use. In this paper two time-efficient Kalman filter (KF) variants are outlined incorporating the medium fidelity, dynamic flow model “WindFarmSimulator” (WFSim). This model relies on a discretized set of Navier-Stokes equations in two dimensions to predict the flow in wind farms at low computational cost. The filters implemented are an Ensemble KF and an Approximate KF. Simulations in which a high fidelity simulation model represents the true wind farm show that these filters are 101 —102 times faster than a regular KF with comparable or better performance, correcting for wake dynamics that are not modeled in WFSim (noticeably, wake meandering and turbine hub effects). This is a first big step towards real-time closed-loop control for wind farms.

  13. Large particle penetration through N95 respirator filters and facepiece leaks with cyclic flow.

    PubMed

    Cho, Kyungmin Jacob; Reponen, Tiina; McKay, Roy; Shukla, Rakesh; Haruta, Hiroki; Sekar, Padmini; Grinshpun, Sergey A

    2010-01-01

    The aim of this study was to investigate respirator filter and faceseal penetration of particles representing bacterial and fungal spore size ranges (0.7-4 mum). First, field experiments were conducted to determine workplace protection factors (WPFs) for a typical N95 filtering facepiece respirator (FFR). These data (average WPF = 515) were then used to position the FFR on a manikin to simulate realistic donning conditions for laboratory experiments. Filter penetration was also measured after the FFR was fully sealed on the manikin face. This value was deducted from the total penetration (obtained from tests with the partially sealed FFR) to determine the faceseal penetration. All manikin experiments were repeated using three sinusoidal breathing flow patterns corresponding to mean inspiratory flow rates of 15, 30, and 85 l min(-1). The faceseal penetration varied from 0.1 to 1.1% and decreased with increasing particle size (P < 0.001) and breathing rate (P < 0.001). The fractions of aerosols penetrating through the faceseal leakage varied from 0.66 to 0.94. In conclusion, even for a well-fitting FFR respirator, most particle penetration occurs through faceseal leakage, which varies with breathing flow rate and particle size.

  14. A novel retinal vessel extraction algorithm based on matched filtering and gradient vector flow

    NASA Astrophysics Data System (ADS)

    Yu, Lei; Xia, Mingliang; Xuan, Li

    2013-10-01

    The microvasculature network of retina plays an important role in the study and diagnosis of retinal diseases (age-related macular degeneration and diabetic retinopathy for example). Although it is possible to noninvasively acquire high-resolution retinal images with modern retinal imaging technologies, non-uniform illumination, the low contrast of thin vessels and the background noises all make it difficult for diagnosis. In this paper, we introduce a novel retinal vessel extraction algorithm based on gradient vector flow and matched filtering to segment retinal vessels with different likelihood. Firstly, we use isotropic Gaussian kernel and adaptive histogram equalization to smooth and enhance the retinal images respectively. Secondly, a multi-scale matched filtering method is adopted to extract the retinal vessels. Then, the gradient vector flow algorithm is introduced to locate the edge of the retinal vessels. Finally, we combine the results of matched filtering method and gradient vector flow algorithm to extract the vessels at different likelihood levels. The experiments demonstrate that our algorithm is efficient and the intensities of vessel images exactly represent the likelihood of the vessels.

  15. Real-Time Flood Forecasting System Using Channel Flow Routing Model with Updating by Particle Filter

    NASA Astrophysics Data System (ADS)

    Kudo, R.; Chikamori, H.; Nagai, A.

    2008-12-01

    A real-time flood forecasting system using channel flow routing model was developed for runoff forecasting at water gauged and ungaged points along river channels. The system is based on a flood runoff model composed of upstream part models, tributary part models and downstream part models. The upstream part models and tributary part models are lumped rainfall-runoff models, and the downstream part models consist of a lumped rainfall-runoff model for hillslopes adjacent to a river channel and a kinematic flow routing model for a river channel. The flow forecast of this model is updated by Particle filtering of the downstream part model as well as by the extended Kalman filtering of the upstream part model and the tributary part models. The Particle filtering is a simple and powerful updating algorithm for non-linear and non-gaussian system, so that it can be easily applied to the downstream part model without complicated linearization. The presented flood runoff model has an advantage in simlecity of updating procedure to the grid-based distributed models, which is because of less number of state variables. This system was applied to the Gono-kawa River Basin in Japan, and flood forecasting accuracy of the system with both Particle filtering and extended Kalman filtering and that of the system with only extended Kalman filtering were compared. In this study, water gauging stations in the objective basin were divided into two types of stations, that is, reference stations and verification stations. Reference stations ware regarded as ordinary water gauging stations and observed data at these stations are used for calibration and updating of the model. Verification stations ware considered as ungaged or arbitrary points and observed data at these stations are used not for calibration nor updating but for only evaluation of forecasting accuracy. The result confirms that Particle filtering of the downstream part model improves forecasting accuracy of runoff at

  16. In Vitro Evaluation of a Rheolytic Thrombectomy System for Clot Removal from Five Different Temporary Vena Cava Filters

    SciTech Connect

    Buecker, Arno; Neuerburg, Joerg; Schmitz-Rode, Thomas; Vorwerk, Dierk; Guenther, Rolf W.

    1997-11-15

    Purpose: To evaluate the feasibility of thrombus removal from temporary vena cava filters using a rheolytic thrombectomy device and to assess the embolization rate of this procedure. Methods: Five temporary vena cava filters together with porcine thrombi were placed in a vena cava flow model (semitranslucent silicone tube of 23 mm diameter, pulsatile flow at a mean flow rate of 4 L/min). A rheolytic thrombectomy system (Hydrolyser) was used with a 9 Fr guiding catheter to remove the clots. The effluent was passed through filters of different size and the amount of embolized particles as well as the remaining thrombus were measured. Results: Thrombus removal rates ranged from 85% to 100%. Embolization rates between 47% and 60% were calculated for the different filters. Conclusion: The Hydrolyser is able to remove sufficiently high amounts of thrombus from temporary vena cava filters. However, the amount of embolized particles makes it impossible to utilize this method without special precautions against embolization.

  17. Models of hydrodynamic flow in the bowhead whale filter feeding apparatus.

    PubMed

    Werth, Alexander J

    2004-09-01

    Anatomical and behavioral analyses suggest that the filtration mechanism of bowhead and right whales (Balaenidae) is driven by hydrodynamic as well as ram hydraulic pressures. Complementary models were devised to investigate biomechanical aspects of water flow in the buccal cavity of the bowhead whale Balaena mysticetus during continuous filter feeding. A mathematical model was created to test and quantify water flow predictions with steady state hydromechanical equations; a physical model of the bowhead mouth (approximately 1/15 scale) was constructed to visualize flow processes. Both models rely on morphometric data obtained from whales harvested by Inupiat Eskimos for subsistence purposes along with information on foraging ecology (locomotor velocity, gape, etc.). Results indicate that unique features of balaenid oral construction and function (e.g. subrostral gap, orolabial sulcus, curvature of baleen, extensive mandibular rotation and lingual mobility) not only permit steady, unidirectional flow of water through the mouth, but also establish Bernoulli and Venturi effects during feeding. These hydrodynamic conditions allow balaenids to improve filtering efficiency and avoid creation of an anterior compressive wave (by increasing flow velocity and thereby reducing pressure) so that they may capture elusive prey even at slow swimming speeds.

  18. 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)

  19. Robust optical flow using adaptive Lorentzian filter for image reconstruction under noisy condition

    NASA Astrophysics Data System (ADS)

    Kesrarat, Darun; Patanavijit, Vorapoj

    2017-02-01

    In optical flow for motion allocation, the efficient result in Motion Vector (MV) is an important issue. Several noisy conditions may cause the unreliable result in optical flow algorithms. We discover that many classical optical flows algorithms perform better result under noisy condition when combined with modern optimized model. This paper introduces effective robust models of optical flow by using Robust high reliability spatial based optical flow algorithms using the adaptive Lorentzian norm influence function in computation on simple spatial temporal optical flows algorithm. Experiment on our proposed models confirm better noise tolerance in optical flow's MV under noisy condition when they are applied over simple spatial temporal optical flow algorithms as a filtering model in simple frame-to-frame correlation technique. We illustrate the performance of our models by performing an experiment on several typical sequences with differences in movement speed of foreground and background where the experiment sequences are contaminated by the additive white Gaussian noise (AWGN) at different noise decibels (dB). This paper shows very high effectiveness of noise tolerance models that they are indicated by peak signal to noise ratio (PSNR).

  20. Cross-flow, filter-sorbet catalyst for particulate, SO sub 2 and NO sub x control

    SciTech Connect

    Not Available

    1990-11-01

    This report describes a new concept for integrated pollutant control: A cross-flow filter comprised of layered, gas permeable membranes that act as a particulate filter, an SO{sub 2} sorbent, and a NO{sub x} reduction catalyst.

  1. Long-term durability testing of ceramic cross-flow filter. Final report, September 29, 1987--December 31, 1992

    SciTech Connect

    Lippert, T.E.; Smeltzer, E.E.; Alvin, M.A.; Bachovchin, D.M.

    1993-08-01

    Long term durability testing of the cross flow filter is described. Two high temperature, high pressure test facilities were built and operated. The facilities were designed to simulate dirty gas environments typical of Pressurized Fluidized Bed Combustion (PFBC) and coal gasification. Details of the design and operation of the test facilities and filter testing results are described.

  2. Cross-flow, filter-sorbent catalyst for particulate, SO sub 2 and NO sub x control

    SciTech Connect

    Not Available

    1990-03-01

    This synopsis describes a new concept for integrated pollutant control: a cross-flow filter comprised of layered, gas permeable membranes that act as a particulate filter, an SO{sub 2} sorbent, and a NO{sub x} reduction catalyst.

  3. A reduced order model based on Kalman filtering for sequential data assimilation of turbulent flows

    NASA Astrophysics Data System (ADS)

    Meldi, M.; Poux, A.

    2017-10-01

    A Kalman filter based sequential estimator is presented in this work. The estimator is integrated in the structure of segregated solvers for the analysis of incompressible flows. This technique provides an augmented flow state integrating available observation in the CFD model, naturally preserving a zero-divergence condition for the velocity field. Because of the prohibitive costs associated with a complete Kalman Filter application, two model reduction strategies have been proposed and assessed. These strategies dramatically reduce the increase in computational costs of the model, which can be quantified in an augmentation of 10%- 15% with respect to the classical numerical simulation. In addition, an extended analysis of the behavior of the numerical model covariance Q has been performed. Optimized values are strongly linked to the truncation error of the discretization procedure. The estimator has been applied to the analysis of a number of test cases exhibiting increasing complexity, including turbulent flow configurations. The results show that the augmented flow successfully improves the prediction of the physical quantities investigated, even when the observation is provided in a limited region of the physical domain. In addition, the present work suggests that these Data Assimilation techniques, which are at an embryonic stage of development in CFD, may have the potential to be pushed even further using the augmented prediction as a powerful tool for the optimization of the free parameters in the numerical simulation.

  4. 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

  5. Data assimilation for unsaturated flow models with restart adaptive probabilistic collocation based Kalman filter

    SciTech Connect

    Man, Jun; Li, Weixuan; Zeng, Lingzao; Wu, Laosheng

    2016-06-01

    The ensemble Kalman filter (EnKF) has gained popularity in hydrological data assimilation problems. As a Monte Carlo based method, a relatively large ensemble size is usually required to guarantee the accuracy. As an alternative approach, the probabilistic collocation based Kalman filter (PCKF) employs the polynomial chaos to approximate the original system. In this way, the sampling error can be reduced. However, PCKF suffers from the so-called "curse of dimensionality". When the system nonlinearity is strong and number of parameters is large, PCKF could be even more computationally expensive than EnKF. Motivated by most recent developments in uncertainty quantification, we propose a restart adaptive probabilistic collocation based Kalman filter (RAPCKF) for data assimilation in unsaturated flow problems. During the implementation of RAPCKF, the important parameters are identified and active PCE basis functions are adaptively selected. The "restart" technology is used to eliminate the inconsistency between model parameters and states. The performance of RAPCKF is tested with numerical cases of unsaturated flow models. It is shown that RAPCKF is more efficient than EnKF with the same computational cost. Compared with the traditional PCKF, the RAPCKF is more applicable in strongly nonlinear and high dimensional problems.

  6. Data assimilation for unsaturated flow models with restart adaptive probabilistic collocation based Kalman filter

    NASA Astrophysics Data System (ADS)

    Man, Jun; Li, Weixuan; Zeng, Lingzao; Wu, Laosheng

    2016-06-01

    The ensemble Kalman filter (EnKF) has gained popularity in hydrological data assimilation problems. As a Monte Carlo based method, a sufficiently large ensemble size is usually required to guarantee the accuracy. As an alternative approach, the probabilistic collocation based Kalman filter (PCKF) employs the polynomial chaos expansion (PCE) to represent and propagate the uncertainties in parameters and states. However, PCKF suffers from the so-called "curse of dimensionality". Its computational cost increases drastically with the increasing number of parameters and system nonlinearity. Furthermore, PCKF may fail to provide accurate estimations due to the joint updating scheme for strongly nonlinear models. Motivated by recent developments in uncertainty quantification and EnKF, we propose a restart adaptive probabilistic collocation based Kalman filter (RAPCKF) for data assimilation in unsaturated flow problems. During the implementation of RAPCKF, the important parameters are identified and active PCE basis functions are adaptively selected at each assimilation step; the "restart" scheme is utilized to eliminate the inconsistency between updated model parameters and states variables. The performance of RAPCKF is systematically tested with numerical cases of unsaturated flow models. It is shown that the adaptive approach and restart scheme can significantly improve the performance of PCKF. Moreover, RAPCKF has been demonstrated to be more efficient than EnKF with the same computational cost.

  7. Results from Evaluation of Representative ASME AG-1 Section FK Radial Flow Dimple Pleated HEPA Filters Under Elevated Conditions - 12002

    SciTech Connect

    Giffin, Paxton K.; Parsons, Michael S.; Rickert, Jaime G.; Waggoner, Charles A.

    2012-07-01

    The American Society of Mechanical Engineers (ASME) has recently added Section FK establishing requirements for radial flow HEPA filters to the Code on Nuclear Air and Gas Treatment (AG-1). Section FK filters are expected to be a major element in the HEPA filtration systems across the US Department of Energy (DOE) complex. Radial flow filters have been used in Europe for some time, however a limited amount of performance evaluation data exists with respect to these new AG-1 Section FK units. In consultation with a technical working group, the Institute for Clean Energy Technology (ICET) at Mississippi State University (MSU)has evaluated a series of representative AG-1 Section FK dimple pleated radial flow HEPA filters. The effects of elevated relative humidity and temperature conditions on these filters are particularly concerning. Results from the evaluation of Section FK filters under ambient conditions have been presented at the 2011 waste management conference. Additions to the previous test stand to enable high temperature and high humidity testing, a review of the equipment used, the steps taken to characterize the new additions, and the filter test results are presented in this study. Test filters were evaluated at a volumetric flow rate of 56.6 m{sup 3}/min (2000 cfm) and were challenged under ambient conditions with Alumina, Al(OH){sub 3}, until reaching a differential pressure of 1 kPa (4 in. w.c.), at which time the filters were tested, unchallenged with aerosol, at 54 deg. C (130 deg. F) for approximately 1 hour. At the end of that hour water was sprayed near the heat source to maximize vaporization exposing the filter to an elevated relative humidity up to 95%. Collected data include differential pressure, temperature, relative humidity, and volumetric flow rate versus time. (authors)

  8. 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