The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
Joseph L. Bull - One of the best experts on this subject based on the ideXlab platform.
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an investigation of Pulsatile Flow past two cylinders as a model of blood Flow in an artificial lung
International Journal of Heat and Mass Transfer, 2011Co-Authors: Khalil Khanafer, Robert H Bartlett, Ronald B Hirschl, Joseph L. BullAbstract: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.
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Pulsatile Flow past an oscillating cylinder
Physics of Fluids, 2011Co-Authors: Adnan Qamar, Robinson Seda, Joseph L. BullAbstract: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
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Pulsatile Flow past an oscillating cylinder
Physics of Fluids, 2011Co-Authors: Adnan Qamar, Robinson Seda, Joseph L. BullAbstract: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 ω(c) and ω, respectively. The Keulegan-Carpenter number (K(c)=U(o)∕Dω(c)) was used to describe the frequency of the oscillating cylinder while the Pulsatile free-stream velocity was fixed by imposing ω∕K(c)=1 for all cases investigated. The parameters of interest and their values were amplitude (0.5D
Tony Walshe - One of the best experts on this subject based on the ideXlab platform.
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the role of Pulsatile Flow in controlling microvascular retinal endothelial and pericyte cell apoptosis and proliferation
Cardiovascular Research, 2011Co-Authors: Tony Walshe, Paul Connell, Lorna M Cryan, Gail Ferguson, Colm Obrien, Paul A. CahillAbstract:Aims Aberrant retinal blood Flow is a hallmark of various retinopathies and may be a causative factor in the pathology associated with these conditions. We examined the effects of Pulsatile Flow on bovine retinal endothelial cell (BREC) and bovine retinal pericyte (BRP) apoptosis and proliferation. Methods and results Co-cultured BRECs and BRPs were exposed to low (0.3 mL/min) or high (25 mL/min) Pulsatile Flow for 72 h using a perfused transcapillary culture system. Pulsatile Flow increased BREC nitric oxide synthase (eNOS) and cyclooxygenase-2 (COX-2) expression and activity concomitant with a significant decrease in pre-pro-endothelin-1 (ET-1) mRNA and peptide. BREC apoptosis was significantly attenuated following exposure to high Flow. The inhibition of NOS, COX, and ET receptors significantly reduced the pro-survival effects of Flow on BREC. In contrast, BRP apoptosis was significantly enhanced following exposure to high Flow. The inhibition of COX and ET receptors significantly attenuated the high Flow-induced increase in BRP apoptosis when compared with untreated controls. Treatment of static BREC with NO donor ( S -nitroso- N -acetylpenicillamine, SNAP), ET-1, or iloprost inhibited serum deprivation-induced apoptosis, whereas treatment of BRP with ET-1 and iloprost, but not SNAP, was ineffective. High Pulsatile Flow decreased BRP proliferation, in the absence of any changes in BREC proliferation. Conclusion Increased Pulsatile Flow promotes BREC survival and enhances BRP apoptosis through the activation of endothelial-derived vasoactive substances. Altered Pulsatile Flow does not alter BREC proliferation in co-culture with BRP, whereas BRP proliferation was significantly decreased at high Flow rates. These interactions have important implications for vessel growth and regression during retinal vascular pathogenesis.
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The effect of Pulsatile Flow on co-cultured retinal endothelial & pericyte cells
2005Co-Authors: Tony WalsheAbstract:Microvascular cell fate decisions are hallmarks of the microvascular cell response to injury and play a crucial role in the pathogenesis of retinal disease. Abnormalities in retinal blood Flow play a critical role in remodeling of the retinal vasculature by altering microvascular endothelial and pericyte cell fate (proliferation, apoptosis and migration). Retinal blood Flow is controlled locally by vasodilators such as nitric oxide, prostacyclin and the vasoconstrictor endothelin-1 , with considerable evidence linking retinal pathologies such as Normal Tension Glaucoma and Diabetic Retinopathy to altered retinal blood Flow Shear stress has previously been shown to modulate EC production of these vasoactive agents in macrovascular cells. Therefore, using a perfused transcapillary coculture of bovine microvascular retinal endothelial cells (BRECs) and bovine retinal pericytes (BRPs), we examined the acute and chronic effect of Pulsatile Flow on the release of these vasoactive mediators and their subsequent role in modulating retinal vascular cell fate. Acute exposure to Pulsatile Flow increased BREC NO, PGI2 & ET-1 formation and release Similarly, chronic exposure to Pulsatile Flow enhanced NO and PGI2 release while concomitantly inhibiting ET-1 in these cells In parallel studies, there was an increase in BRP apoptosis following exposure to high Pulsatile Flow, whereas BREC apoptosis decreased. Furthermore, the Pulsatile Flow-induced increases in BRP apoptosis is dependent on increased PGI2 , whereas both ET-1 and NO mediate the protective effect of increased Flow on BRECs survival. Notch receptor-hgand interactions and the Hedgehog signalling pathway have been strongly implicated in vascular morphogenesis and remodelling of the embryonic vasculature, with Hedgehog acting upstream of Notch signalling during development. We therefore tested the hypothesis that Hedgehog (Hh) and Notch pathway interact to promote changes in vascular cell fate in BRECs and BRPs in vitro in response to changes in Pulsatile Flow.
Aaron S. Goldstein - One of the best experts on this subject based on the ideXlab platform.
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Effect of Low-Frequency Pulsatile Flow on Expression of Osteoblastic Genes by Bone Marrow Stromal Cells
Annals of Biomedical Engineering, 2009Co-Authors: Lindsay A. Sharp, Aaron S. GoldsteinAbstract:Perfusion culture of osteoprogenitor cells is a promising means to form a bone-like extracellular matrix for tissue engineering applications, but the mechanism by which hydrodynamic shear stimulates expression of bone extracellular matrix (ECM) proteins is not understood. Osteoblasts are mechanosensitive and respond differently to steady and Pulsatile Flow. Therefore, to probe the effect of Flow, bone marrow stromal cells (BMSCs)—cultured under osteogenic conditions—were exposed to steady or Pulsatile Flow at frequencies of 0.015, 0.044, or 0.074 Hz. Following 24 h of stimulus, cells were cultured statically for an additional 13 days and then analyzed for the expression of bone ECM proteins collagen 1α1 (Col1α1), osteopontin, osteocalcin (OC), and bone sialoprotein (BSP). All mRNA levels were elevated by Flow, but OC and BSP were enhanced modestly with Pulsatile Flow. To determine if these effects were related to gene induction during Flow, BMSCs were again exposed to steady or Pulsatile Flow for 24 h, but then analyzed immediately for expression of growth and differentiation factors bone morphogenetic proteins (BMP)-2, -4, and -7, transforming growth factor (TGF)-β1, and vascular endothelial growth factor-A. All growth and differentiation factors were significantly elevated by Flow, except BMP-4 which was suppressed. In addition, expression of BMP-2 and -7 were enhanced and TGF-β1 suppressed by Pulsatile Flow relative to steady Flow. These results demonstrate that Pulsatile Flow modulates expression of BMP-2, -7, and TGF-β1 and suggest that enhanced expression of bone ECM proteins by Pulsatile Flow may be mediated through the induction of BMP-2 and -7.
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Effect of low-frequency Pulsatile Flow on expression of osteoblastic genes by bone marrow stromal cells
Annals of Biomedical Engineering, 2009Co-Authors: Lindsay A. Sharp, Yong W. Lee, Aaron S. GoldsteinAbstract:Perfusion culture of osteoprogenitor cells is a promising means to form a bone-like extracellular matrix for tissue engineering applications, but the mechanism by which hydrodynamic shear stimulates expression of bone extracellular matrix (ECM) proteins is not understood. Osteoblasts are mechanosensitive and respond differently to steady and Pulsatile Flow. Therefore, to probe the effect of Flow, bone marrow stromal cells (BMSCs)--cultured under osteogenic conditions--were exposed to steady or Pulsatile Flow at frequencies of 0.015, 0.044, or 0.074 Hz. Following 24 h of stimulus, cells were cultured statically for an additional 13 days and then analyzed for the expression of bone ECM proteins collagen 1alpha1 (Col1alpha1), osteopontin, osteocalcin (OC), and bone sialoprotein (BSP). All mRNA levels were elevated by Flow, but OC and BSP were enhanced modestly with Pulsatile Flow. To determine if these effects were related to gene induction during Flow, BMSCs were again exposed to steady or Pulsatile Flow for 24 h, but then analyzed immediately for expression of growth and differentiation factors bone morphogenetic proteins (BMP)-2, -4, and -7, transforming growth factor (TGF)-beta1, and vascular endothelial growth factor-A. All growth and differentiation factors were significantly elevated by Flow, except BMP-4 which was suppressed. In addition, expression of BMP-2 and -7 were enhanced and TGF-beta1 suppressed by Pulsatile Flow relative to steady Flow. These results demonstrate that Pulsatile Flow modulates expression of BMP-2, -7, and TGF-beta1 and suggest that enhanced expression of bone ECM proteins by Pulsatile Flow may be mediated through the induction of BMP-2 and -7.
Hiroo Takayama - One of the best experts on this subject based on the ideXlab platform.
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effects of continuous Flow versus Pulsatile Flow left ventricular assist devices on myocardial unloading and remodeling
Circulation-heart Failure, 2011Co-Authors: Tomoko S Kato, Aalap Chokshi, Parvati Singh, Tuba Khawaja, Faisal H Cheema, Hirokazu Akashi, Khurram Shahzad, Shinichi Iwata, Shunichi Homma, Hiroo TakayamaAbstract:Background—Continuous-Flow left ventricular assist devices (LVAD) are increasingly used for patients with end-stage heart failure (HF). We analyzed the effects of ventricular decompression by continuous-Flow versus Pulsatile-Flow LVADs on myocardial structure and function in this population. Methods and Results—Sixty-one patients who underwent LVAD implantation as bridge-to-transplant were analyzed (Pulsatile-Flow LVAD: group P, n=31; continuous-Flow LVAD: group C, n=30). Serial echocardiograms, serum levels of brain natriuretic peptide (BNP), and extracellular matrix biomarkers (ECM) were compared between the groups. Myocardial BNP and ECM gene expression were evaluated in a subset of 18 patients. Postoperative LV ejection fraction was greater (33.2±12.6% versus 17.6±8.8%, P<0.0001) and the mitral E/E′ was lower (9.9±2.6 versus 13.2±3.8, P=0.0002) in group P versus group C. Postoperative serum levels of BNP, metalloproteinases (MMP)-9, and tissue inhibitor of MMP (TIMP)-4 were significantly lower in grou...
Adnan Qamar - One of the best experts on this subject based on the ideXlab platform.
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Pulsatile Flow past an oscillating cylinder
Physics of Fluids, 2011Co-Authors: Adnan Qamar, Robinson Seda, Joseph L. BullAbstract: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
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Pulsatile Flow past an oscillating cylinder
Physics of Fluids, 2011Co-Authors: Adnan Qamar, Robinson Seda, Joseph L. BullAbstract: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 ω(c) and ω, respectively. The Keulegan-Carpenter number (K(c)=U(o)∕Dω(c)) was used to describe the frequency of the oscillating cylinder while the Pulsatile free-stream velocity was fixed by imposing ω∕K(c)=1 for all cases investigated. The parameters of interest and their values were amplitude (0.5D
