Showing papers on "Pulsatile flow published in 2021"

Porous effects on the fractional modeling of magnetohydrodynamic pulsatile flow: an analytic study via strong kernels

Abstract: An accurate measurement of pulsatile flow is frequently encountered in exhaust and intake manifolds of internal combustion and Stirling engines. Keeping this view, a mathematical modeling of magnetohydrodynamic pulsatile flow is proposed on the basis of modern fractional differentiations (Atangana–Baleanu and Caputo–Fabrizio fractional operators) in the presence of porosity. The modeling of magnetohydrodynamic pulsatile flow is based on non-integer-order partial differential equation of velocity field. The solvability of fractional differential equation of velocity field is tackled via Hankel and Laplace transform techniques. The proposed fractional modeling is verified from general fractional solutions of velocity field of pulsatile flow on the imposed initial and boundary conditions for sinusoidal oscillation. The general fractional solutions of velocity field of pulsatile flow have been retrieved for porous and non-porous velocity field and magnetized and non- magnetized velocity field as well. Finally, our results suggest that time-dependent pulsatile flow of velocity field needs accurate and reproducible generation of pulsatile flow as a function of time.

Aortic Stiffness, Central Blood Pressure, and Pulsatile Arterial Load Predict Future Thoracic Aortic Aneurysm Expansion.

Abstract: Thoracic aortic aneurysm is a disease associated with high morbidity and mortality. Clinically useful strategies for medical management of thoracic aortic aneurysm are critically needed. To address this need, we sought to determine the role of aortic stiffness and pulsatile arterial load on future aneurysm expansion. One hundred five consecutive, unoperated subjects with thoracic aortic aneurysm were recruited and prospectively followed. By combining arterial tonometry with echocardiography, we estimated measures of aortic stiffness, central blood pressure, steady, and pulsatile arterial load at baseline. Aneurysm size was measured at baseline and follow-up with imaging; growth was calculated in mm/y. Stepwise multivariable linear regression assessed associations of arterial stiffness and load measures with aneurysm growth after adjusting for potential confounders. Mean±SD age, baseline aneurysm size, and follow-up time were 62.6±11.4 years, 46.24±3.84 mm, and 2.92±1.01 years, respectively. Aneurysm growth rate was 0.43±0.37 mm/y. After correcting for multiple comparisons, higher central systolic (β±SE: 0.026±0.009, P=0.007), and pulse pressures (β±SE: 0.032±0.009, P=0.0002), carotid-femoral pulse wave velocity (β±SE: 0.032±0.011, P=0.005), amplitudes of the forward (β±SE: 0.044±0.012, P=0.0003) and reflected (β±SE: 0.060±0.020, P=0.003) pressure waves, and lower total arterial compliance (β±SE: -0.086±0.032, P=0.009) were independently associated with future aneurysm growth. Measures of aortic stiffness and pulsatile hemodynamics are independently associated with future thoracic aortic aneurysm growth and provide novel insights into disease activity. Our findings highlight the role of central hemodynamic assessment to tailor novel risk assessment and therapeutic strategies to patients with thoracic aortic aneurysm.

Bulk flow of cerebrospinal fluid observed in periarterial spaces is not an artifact of injection

Abstract: Cerebrospinal fluid (CSF) flowing through periarterial spaces is integral to the brain's mechanism for clearing metabolic waste products. Experiments that track tracer particles injected into the cisterna magna (CM) of mouse brains have shown evidence of pulsatile CSF flow in perivascular spaces surrounding pial arteries, with a bulk flow in the same direction as blood flow. However, the driving mechanism remains elusive. Several studies have suggested that the bulk flow might be an artifact, driven by the injection itself. Here, we address this hypothesis with new in vivo experiments where tracer particles are injected into the CM using a dual-syringe system, with simultaneous injection and withdrawal of equal amounts of fluid. This method produces no net increase in CSF volume and no significant increase in intracranial pressure. Yet, particle-tracking reveals flows that are consistent in all respects with the flows observed in earlier experiments with single-syringe injection.

Torrents of torment: turbulence as a mechanism of pulsatile tinnitus secondary to venous stenosis revealed by high-fidelity computational fluid dynamics.

Abstract: Background Pulsatile tinnitus (PT) is a debilitating condition that can be caused by a vascular abnormality, such as an arterial or venous lesion. Although treatment of PT-related venous lesions has been shown to successfully cure patients of the associated ‘tormenting’ rhythmical sound, much controversy still exists regarding their role in the etiology of PT. Methods A patient presented with a history of worsening, unilateral PT. A partial venous sinus obstruction related to the large arachnoid granulation was detected on the right side, and subsequently stented at the right transverse sinus. High-fidelity computational fluid dynamics (CFD) was performed on a 3D model digitally segmented from the pre-stent venogram, with assumed pulsatile flow rates. A post-stent CFD model was also constructed from this. Data-driven sonification was performed on the CFD velocity data, blinded to the patient’s self-reported sounds. Results The patient reported that the PT was completely resolved after stenting, and has had no recurrence of the symptoms after more than 2 years. CFD simulation revealed highly disturbed, turbulent-like flow at the sigmoid sinus close to auditory structures, producing a sonified audio signal that reproduced the subjective sonance of the patient’s PT. No turbulence or sounds were evident at the stenosis, or anywhere in the post-stent model. Conclusions For the first time, turbulence generated distal to a venous stenosis is shown to be a cause of PT. High-fidelity CFD may be useful for identifying patients with such ‘torrents’ of flow, to help guide treatment decision-making.

In vitro investigation of the impact of pulsatile blood flow on the vascular architecture of decellularized porcine kidneys.

Abstract: A method was established using a scaffold-bioreactor system to examine the impact pulsatile blood flow has on the decellularized porcine kidney vascular architecture and functionality. These scaffolds were subjected to continuous arterial perfusion of whole blood at normal physiological (650 ml/min and 500 ml/min) and pathophysiological (200 ml/min) rates to examine dynamic changes in venous outflow and micro-/macrovascular structure and patency. Scaffolds subjected to normal arterial perfusion rates observed drops in venous outflow over 24 h. These reductions rose from roughly 40% after 12 h to 60% after 24 h. There were no apparent signs of clotting at the renal artery, renal vein, and ureter. In comparison, venous flow rates decreased by 80% to 100% across the 24 h in acellular scaffolds hypoperfused at a rate of 200 ml/min. These kidneys also appeared intact on the surface after perfusion. However, they presented several arterial, venous, and ureteral clots. Fluoroscopic angiography confirmed substantial alterations to normal arterial branching patterns and patency, as well as parenchymal damage. Scanning electron microscopy revealed that pulsatile blood perfusion significantly disrupted glomerular microarchitecture. This study provides new insight into circumstances that limit scaffold viability and a simplified model to analyze conditions needed to prepare more durable scaffolds for long-term transplantation.

Transitional pulsatile flows with stenosis in a two-dimensional channel

Abstract: Although blood flows are mostly laminar, transition to turbulence and flow separations are observed at curved vessels, bifurcations, or constrictions. It is known that wall-shear stress plays an important role in the development of atherosclerosis as well as in arteriovenous grafts. In order to help understand the behavior of flow separation and transition to turbulence in post-stenotic blood flows, an experimental study of transitional pulsatile flow with stenosis was carried out using time-resolved particle image velocimetry and a microelectromechanical systems wall-shear stress sensor at the mean Reynolds number of 1750 with the Womersley number of 6.15. At the start of the pulsatile cycle, a strong shear layer develops from the tip of the stenosis, increasing the flow separation region. The flow at the throat of the stenosis is always laminar due to acceleration, which quickly becomes turbulent through a shear-layer instability under a strong adverse pressure gradient. At the same time, a recirculation region appears over the wall opposite to the stenosis, moving downstream in sync with the movement of the reattachment point. These flow behaviors observed in a two-dimensional channel flow are very similar to the results obtained previously in a pipe flow. We also found that the behavior in a pulsating channel flow during the acceleration phase of both 25% and 50% stenosis cases is similar to that of the steady flow, including the location and size of post-stenotic flow separation regions. This is because the peak Reynolds number of the pulsatile flow is similar to that of the steady flow that is investigated. The transition to turbulence is more dominant for the 50% stenosis as compared to the 25% stenosis, as the wavelet spectra show a greater broadening of turbulence energy. With an increase in stenosis to 75%, the accelerating flow is directed toward the opposite wall, creating a wall jet. The shear layer from the stenosis bifurcates as a result of this, one moving with the flow separation region toward the upper wall and the other with the wall jet toward the bottom wall. Low wall-shear stress fluctuations are found at two post-stenotic locations in the channel flow – one immediately downstream of the stenosis over the top wall (stenosis side) inside the flow separation region, and the other in the recirculation region on the bottom wall (opposite side of the stenosis).

Pulsatile flow dynamics in symmetric and asymmetric bifurcating vessels

Abstract: Bifurcating vessel is a characteristic feature of biological systems such as arteries in the cardiovascular system and pulmonary airways. In cardiovascular system, the bifurcations are often asymmetric, flow is pulsatile, and the fluid, blood, shows a complex rheology. In this work, we study computationally pulsatile flow in planar symmetric and asymmetric, three-dimensional bifurcating vessels. The fluid is considered to be Newtonian as well as non-Newtonian following Carreau's model, and the results are compared. While the flow divides in the two daughter tubes equally in symmetric bifurcations, the flow distribution is time-dependent during a cardiac cycle in asymmetric bifurcations. The flow pattern changes significantly during a cardiac cycle. The secondary flow caused by a turning streamline is analyzed in terms of secondary velocity, vorticity, and helicity. Significant variation is observed in the secondary flow in a cardiac cycle. The secondary flow is observed to be stronger at the start of the diastole despite reduced flow rate. The separated flow on the outer wall causes a significant reduction in time-averaged wall shear stress, a biomarker to assess the possibility of atherosclerotic plaque development. While no significant difference is observed in the results obtained for Newtonian and non-Newtonian fluids at high shear rates, for example, during systole, significant differences are observed when the shear rate is low, during diastole or in the separation region. The velocity profile for the non-Newtonian fluid is observed to be flatter than that for Newtonian fluid. Further oscillatory shearing index, relative residence time, the parameters used as biomarkers are presented.

Wave Reflection at the Origin of a First-Generation Branch Artery and Target Organ Protection: The AGES-Reykjavik Study.

Abstract: Excessive pressure and flow pulsatility in first-generation branch arteries are associated with microvascular damage in high-flow organs like brain and kidneys. However, the contribution of local wave reflection and rereflection to microvascular damage remains controversial. Aortic flow, carotid pressure, flow and hydraulic power, brain magnetic resonance images, and cognitive scores were assessed in AGES-Reykjavik study participants without history of stroke, transient ischemic attack, or dementia (N=668, 378 women, 69-93 years of age). The aorta-carotid interface was generalized as a markedly asymmetrical bifurcation, with a large parent vessel (proximal aorta) branching into small (carotid) and large (distal aorta) daughter vessels. Local reflection coefficients were computed from aortic and carotid characteristic impedances. The bifurcation reflection coefficient, which determines pressure amplification in both daughter vessels, was low (0.06 +/- 0.03). The carotid flow transmission coefficient was low (0.11 +/- 0.04) and associated with markedly lower carotid versus aortic flow pulsatility (waveform SD, 7.2 +/- 2.0 versus 98.7 +/- 21.8 mL/s, P<0.001), pulsatility index (1.8 +/- 0.5 versus 4.5 +/- 0.6, P<0.001), and pulsatile power percentage (10 +/- 4% versus 25 +/- 5%, P<0.001). Transmitted as compared to incident pulsatile power (19.0 +/- 9.8 versus 35.9 +/- 17.8 mW, P<0.001) was further reduced by reflection (-4.3 +/- 2.7 mW) and rereflection (-12.5 +/- 8.1 mW) within the carotid. Higher carotid flow pulsatility correlated with lower white matter volume (R=-0.130, P<0.001) and lower memory scores (R=-0.161, P<0.001). Marked asymmetry of characteristic impedances at aorta-branch artery bifurcations limits amplification of pressure, markedly reduces absolute and relative pulsatility of transmitted flow and hydraulic power into first-generation branch arteries, and thereby protects the downstream local microcirculation from pulsatile damage.

The Pulsatile Modification Improves Hemodynamics and Attenuates Inflammatory Responses in Extracorporeal Membrane Oxygenation

Abstract: Background: COVID-19 is still a worldwide pandemic and extracorporeal membrane oxygenation (ECMO) is vital for extremely critical COVID-19 patients Pulsatile flow impacts greatly on organ function and microcirculation, however, the effects of pulsatile flow on hemodynamics and inflammatory responses during ECMO are unknown An in vivo study was launched aiming at comparing the two perfusion modes in ECMO Methods: Fourteen beagles were randomly allocated into two groups: the pulsatile group (n=7) and the non-pulsatile group (n=7) ECMO was conducted using the i-Cor system for 24 hours Hemodynamic parameters including surplus hemodynamic energy (SHE), energy equivalent pressure (EEP), oxygenator pressure drop (OPD), and circuit pressure drop (CPD) were monitored To assess inflammatory responses during ECMO, levels of tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), IL-6, IL-8, and transforming growth factor-beta1 (TGF-beta1) were measured Results: EEP and SHE were markedly higher in pulsatile circuits when compared with the conventional circuits Between-group differences in both OPD and CPD reached statistical significance Significant decreases in TNF-alpha were seen in animals treated with pulsatile flows at 2 hours, 12 hours, and 24 hours as well as a decrease in IL-1beta at 24 hours during ECMO The TGF-beta1 levels were significantly higher in pulsatile circuits from 2 hours to 24 hours The changes in IL-6 and IL-8 levels were insignificant Conclusion: The modification of pulsatility in ECMO generates more hemodynamic energies and attenuates inflammatory responses as compared to the conventional non-pulsatile ECMO

Pulsation of anastomotic vortex veins in pachychoroid spectrum diseases.

Abstract: Accumulating evidence points to pachychoroid possibly being caused by vortex vein congestion which results in remodeling of choroidal drainage routes via intervortex vein anastomosis. This hypothesis prompted us to investigate vortex vein hemodynamics by studying videos of indocyanine green angiography (ICGA) in a retrospective case series of 295 eyes with pachychoroid spectrum diseases. In the early phase of the video-ICGA, pulsatile vortex venous flow was observed in 76 eyes (25.8%) at the vortex veins connected with anastomosis between superior and inferior vortex veins. The patients with pulsatile vortex venous flow were significantly older than those without pulsatile vortex venous flow (67.8 ± 13.2 vs. 63.9 ± 14.5 years, P < 0.05). Pulsatile vortex venous flow was 1.84 times more common in the inferior quadrants than in the superior quadrants. Interestingly, 14 of 76 eyes (18.4%) with pulsatile vortex venous flow showed retrograde pulsatile blood flow in the vortex veins. This retrograde pulsatile blood flow was 2.50 times more common in the inferior than in the superior quadrants. These findings indicate altered vortex vein hemodynamics due to vortex vein congestion in pachychoroid spectrum diseases.

The effect of entrance flow development on vortex formation and wall shear stress in a curved artery model

Abstract: We numerically investigate the effect of entrance condition on the spatial and temporal evolution of multiple three-dimensional vortex pairs and the wall shear stress distribution in a curved artery model. We perform this study using a Newtonian blood-analog fluid subjected to a pulsatile flow with two inflow conditions. The first flow condition is fully developed while the second condition is undeveloped (i.e., uniform). We discuss the connection along the axial direction between regions of organized vorticity observed at various cross sections of the model and compare results between the different entrance conditions. We model a human artery with a simple, rigid 180° curved pipe with a circular cross section and constant curvature, neglecting the effects of taper, torsion, and elasticity. Numerical results are computed from a discontinuous high-order spectral element flow solver. The flow rate used in this study is physiological. We observe differences in secondary flow patterns, especially during the deceleration phase of the physiological waveform where multiple vortical structures of both Dean-type and Lyne-type coexist. The results indicate that decreased axial velocities under an undeveloped condition produce smaller secondary flows that ultimately inhibit growth of any interior flow vortices. We highlight the effect of the entrance condition on the formation of these structures and subsequent appearance of abnormal inner wall shear stresses, which suggest there may be a lower prevalence of cardiovascular disease in curved arteries where the flow is rather undeveloped—a potentially physiologically significant result to help understand the influence of blood flow development on disease.

The pulsatile flow of thermally developed non-Newtonian Casson fluid in a channel with constricted walls

Abstract: This article presents a numerical investigation of the pulsatile flow of non-Newtonian Casson fluid through a rectangular channel with symmetrical local constriction on the walls. The objective is to study the heat transfer characteristics of the said fluid flow under an applied magnetic field and thermal radiation. Such a study may find its application in devising treatments for stenosis in blood arteries, designing biomechanical devices, and controlling industrial processes with flow pulsation. Using the finite difference approach, the mathematical model is solved and is converted into the vorticity-stream function form. The impacts of the Hartman number, Strouhal number, Casson fluid parameter, porosity parameter, Prandtl number, and thermal radiation parameter on the flow profiles are argued. The effects on the axial velocity and temperature profiles are observed and argued. Some plots of the streamlines, vorticity, and temperature distribution are also shown. On increasing the values of the magnetic field parameter, the axial flow velocity increases, whereas the temperature decreases. The flow profiles for the Casson fluid parameter have a similar trend, and the profiles for the porosity parameter have an opposite trend to the flow profiles for the magnetic field parameter. The temperature decreases with an increase in the Prandtl number. The temperature increases with an increase in the thermal radiation parameter. The profile patterns are not perfectly uniform downstream of the constriction.

Acute Response of Human Aortic Endothelial Cells to Loss of Pulsatility as Seen during Cardiopulmonary Bypass.

Abstract: Cardiopulmonary bypass (CPB) results in short-term (3-5 h) exposure to flow with diminished pulsatility often referred to as "continuous flow". It is unclear if short-term exposure to continuous flow influences endothelial function, particularly, changes in levels of pro-inflammatory and pro-angiogenic cytokines. In this study, we used the endothelial cell culture model (ECCM) to evaluate if short-term (≤5 h) reduction in pulsatility alters levels of pro-inflammatory/pro-angiogenic cytokine levels. Human aortic endothelial cells (HAECs) cultured within the ECCM provide a simple model to evaluate endothelial cell function in the absence of confounding factors. HAECs were maintained under normal pulsatile flow for 24 h and then subjected to continuous flow (diminished pulsatile pressure and flow) as observed during CPB for 5 h. The ECCM replicated pulsatility and flow morphologies associated with normal hemodynamic status and CPB as seen with clinically used roller pumps. Levels of angiopoietin-2 (ANG-2), vascular endothelial growth factor-A (VEGF-A), and hepatocyte growth factor were lower in the continuous flow group in comparison to the pulsatile flow group whereas the levels of endothelin-1 (ET-1), granulocyte colony stimulating factor, interleukin-8 (IL-8) and placental growth factor were higher in the continuous flow group in comparison to the pulsatile flow group. Immunolabelling of HAECs subjected to continuous flow showed a decrease in expression of ANG-2 and VEGF-A surface receptors, tyrosine protein kinase-2 and Fms-related receptor tyrosine kinase-1, respectively. Given that the 5 h exposure to continuous flow is insufficient for transcriptional regulation, it is likely that pro-inflammatory/pro-angiogenic signaling observed was due to signaling molecules stored in Weible-Palade bodies (ET-1, IL-8, ANG-2) and via HAEC binding/uptake of soluble factors in media. These results suggest that even short-term exposure to continuous flow can potentially activate pro-inflammatory/pro-angiogenic signaling in cultured HAECs and pulsatile flow may be a successful strategy in reducing the undesirable sequalae following continuous flow CPB.

Quantifying the non-Newtonian effects of pulsatile hemodynamics in tubes

Abstract: We investigate in silico the pulsatile blood flow in straight, rigid tubes using an elasto-viscoplastic, constitutive model coupled with thixotropy (TEVP) (Varchanis et al., 2019; Giannokostas et al., 2020). In addition to blood viscoelasticity, our model accounts for RBC aggregation through a kinetic equation that describes the level of blood structure at any instance and the viscoplasticity at stasis conditions. We evaluate the model parameters using steady, simple shear, and transient multi-shear rheometric experiments for human physiological subjects with normal blood aggregation. Then, we accurately reproduce previous experimental results (Thurston, 1975; Bugliarello and Sevilla, 1970; Thurston, 1976; Womersley, 1955) and provide reliable predictions for the pressure, stress, and velocity fields. We also investigate blood flow under sinusoidal and experimentally determined waveforms of the pressure-gradient with different frequencies, amplitudes, and patterns, providing a thorough parametric study. We find that the streamwise normal stress is of considerable magnitude. This stress component stretches the RBCs and their aggregates in the flow direction. Commonly used inelastic hemorheological models (e.g., Casson and Newtonian) cannot predict this. Typical values of the time-averaged wall normal-stress are found in the range of 2 Pa − 30 Pa , which are an order of magnitude larger than the corresponding wall shear-stress for the same hemodynamic conditions. The inelastic models systematically underestimate the shear-stress and overestimate the mean velocity. Finally, the TEVP model accurately predicts the phase-lags between the pressure-gradient and the flow-rate, and between the pressure-gradient and the structure-parameter for the whole range of the frequencies expressed in terms of the Womersley number, indicating its physical completeness and robustness.

Brain blood and cerebrospinal fluid flow dynamics during rhythmic handgrip exercise in young healthy men and women

Abstract: KEY POINTS The cerebral fluid response to exercise, including the arterial and venous cerebral blood flow (CBF) and cerebrospinal fluid (CSF), currently remains unknown. We used time-resolved phase-contrast magnetic resonance imaging to assess changes in CBF and CSF flow dynamics during moderate-intensity rhythmic handgrip (RHG) exercise in young healthy men and women. Our data demonstrated that RHG increases the cerebral arterial inflow and venous outflow while decreasing the pulsatile CSF flow during RHG. Furthermore, changes in blood stroke volume at the measured arteries, veins, and sinuses and CSF stroke volume at the cerebral aqueduct were positively correlated with each other during RHG. Male and female participants exhibited distinct blood pressure responses to RHG, but their cerebral fluid responses were similar. These results collectively suggest that RHG influences both CBF and CSF flow dynamics in a way that is consistent with the Monro-Kellie hypothesis to maintain intracranial volume-pressure homeostasis in young healthy adults. ABSTRACT Cerebral blood flow (CBF) increases during exercise, but its impact on cerebrospinal fluid (CSF) flow remains unknown. This study investigated CBF and CSF flow dynamics during moderate-intensity rhythmic handgrip (RHG) exercise in young healthy men and women. Twenty-six participants (12 women) underwent the RHG and resting control conditions in random order. Participants performed 3 sets of RHG, during which cine phase-contrast magnetic resonance imaging (PC-MRI) was performed to measure blood stroke volume (SV) and flow rate in the internal carotid (ICA) and vertebral (VA) arteries, the internal jugular vein (IJV), the superior sagittal (SSS) and straight sinuses (SRS), and CSF SV and flow rate in the cerebral aqueduct of Sylvius. Blood pressure, end-tidal CO2 (EtCO2 ), heart rate (HR), and respiratory rate were simultaneously measured during cine PC-MRI scans. Compared with control conditions, RHG showed significant elevations of HR, mean arterial pressure, and respiratory rate with a mild reduction of EtCO2 (all P < 0.05). RHG decreased blood SV in the measured arteries, veins, and sinuses and CSF SV in the aqueduct (all P < 0.05). Conversely, RHG increased blood flow in the ICA, VA, and IJV (all P < 0.05). At the aqueduct, RHG decreased the absolute CSF flow rate (P = 0.0307), which was calculated as a sum of the caudal and cranial CSF flow rates. Change in the ICA SV was positively correlated with changes in the IJV, SSS, SRS, and aqueductal SV during RHG (all P < 0.05). These findings demonstrate a close coupling between the CBF and CSF flow dynamics during RHG in young healthy adults.

Measurement of Pulsatile Insulin Secretion: Rationale and Methodology.

Abstract: Pancreatic β-cells are responsible for the synthesis and exocytosis of insulin in response to an increase in circulating glucose. Insulin secretion occurs in a pulsatile manner, with oscillatory pulses superimposed on a basal secretion rate. Insulin pulses are a marker of β-cell health, and secretory parameters, such as pulse amplitude, time interval and frequency distribution, are impaired in obesity, aging and type 2 diabetes. In this review, we detail the mechanisms of insulin production and β-cell synchronization that regulate pulsatile insulin secretion, and we discuss the challenges to consider when measuring fast oscillatory secretion in vivo. These include the anatomical difficulties of measuring portal vein insulin noninvasively in humans before the hormone is extracted by the liver and quickly removed from the circulation. Peripheral concentrations of insulin or C-peptide, a peptide cosecreted with insulin, can be used to estimate their secretion profile, but mathematical deconvolution is required. Parametric and nonparametric approaches to the deconvolution problem are evaluated, alongside the assumptions and trade-offs required for their application in the quantification of unknown insulin secretory rates from known peripheral concentrations. Finally, we discuss the therapeutical implication of targeting impaired pulsatile secretion and its diagnostic value as an early indicator of β-cell stress.

Unsteady pulsatile fractional Maxwell viscoelastic blood flow with Cattaneo heat flux through a vertical stenosed artery with body acceleration

Abstract: In the current problem, we aim to discuss the heat transfer of pulsatile unsteady fractional Maxwell fluid (blood) flow through a vertical stenosed artery with body acceleration. The concept of fractional Cattaneo model will modify the energy equation. We will get the solutions using Laplace and finite Hankel transformations. The inverse of the transformed functions will be calculated numerically. It is observed that, the heat relaxation time causes a delay in the heat transfer until a critical time. In addition, the heat transfer increases sharply to take its maximum value at a critical value of time then it decreases to reach the steady state. Moreover, the blood velocity, the flow rate, and the shear stress continue to fluctuate during the time period due to the pulsatile phenomenon and body acceleration.

Reversal of renal tissue hypoxia during experimental cardiopulmonary bypass in sheep by increased pump flow and arterial pressure

Abstract: Aim: Renal tissue hypoxia during cardiopulmonary bypass could contribute to the pathophysiology of acute kidney injury. We tested whether renal tissue hypoxia can be alleviated during cardiopulmonary bypass by the combined increase in target pump flow and mean arterial pressure. Methods: Cardiopulmonary bypass was established in eight instrumented sheep under isoflurane anaesthesia, at a target continuous pump flow of 80 mL·kg min and mean arterial pressure of 65 mmHg. We then tested the effects of simultaneously increasing target pump flow to 104 mL·kg min and mean arterial pressure to 80 mmHg with metaraminol (total dose 0.25-3.75 mg). We also tested the effects of transitioning from continuous flow to partially pulsatile flow (pulse pressure ~15 mmHg). Results: Compared with conscious sheep, at the lower target pump flow and mean arterial pressure, cardiopulmonary bypass was accompanied by reduced renal blood flow (6.8 ± 1.2 to 1.95 ± 0.76 mL·min kg ) and renal oxygen delivery (0.91 ± 0.18 to 0.24 ± 0.11 mL·O min kg ). There were profound reductions in cortical oxygen tension (PO ) (33 ± 13 to 6 ± 6 mmHg) and medullary PO (31 ± 12 to 8 ± 8 mmHg). Increasing target pump flow and mean arterial pressure increased renal blood flow (to 2.6 ± 1.0 mL·min kg ) and renal oxygen delivery (to 0.32 ± 0.13 mL·O min kg ) and returned cortical PO to 58 ± 60 mmHg and medullary PO to 28 ± 16 mmHg; levels similar to those of conscious sheep. Partially pulsatile pump flow had no significant effects on renal perfusion or oxygenation. Conclusions: Renal hypoxia during experimental CPB can be corrected by increasing target pump flow and mean arterial pressure within a clinically feasible range. −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 2 2 2 2 2 2

Vortex dynamics of veno-arterial extracorporeal circulation: A computational fluid dynamics study

Abstract: Veno-arterial extra corporeal membrane oxygenation (VA-ECMO) is a modified heart lung machine used for patients with both heart and lung failure. This results in retrograde supply of oxygenated blood through the femoral artery in which the unsteady pulsating antegrade flow from the aorta interacts with a steady, uniform, and retrograde flow from the femoral artery, creating a mixing zone. This work aims to provide a mechanistic interpretation of VA-ECMO by developing an in-silico framework using computational fluid dynamics. We performed several numerical simulations to investigate the effects of aortic geometry on VA-ECMO by implementing two idealized full aorta models and studied the formation of secondary flow features and vortices. We used vortex identification methods to capture the three-dimensional vortical structures formed under various ECMO support levels. Our results show that under pulsatile aortic flow and 80% of ECMO support, the streamwise vorticity and aortic arch geometry strongly influence the mixing zone. Furthermore, we found that pulsatility at the aortic inlet causes oscillation in secondary flow structures at the abdominal aorta leading to unsteadiness in ECMO flow and differential wall shear stress. We also examined the effects of VA-ECMO flow rates on secondary flow and vortical structures. We show that the location and complexity of secondary flows and vortical structures are affected by ECMO support levels and geometry of aortic segments. Together, we believe that this computational framework is a crucial step in understanding flow features and vortical structures formed during VA-ECMO administration, which can improve patient care and ECMO management.

Pulsatile Bi-Directional Aerosol Flow Affects Aerosol Delivery to the Intranasal Olfactory Region: A Patient-Specific Computational Study

Abstract: The nasal olfactory region is a potential route for non-invasive delivery of drugs directly from the nasal epithelium to the brain bypassing the often impermeable blood-brain barrier. However, efficient aerosol delivery to the olfactory region is challenging due to its location in the nose. Here we explore aerosol delivery with bi-directional pulsatile flow conditions for targeted drug delivery to the olfactory region using a computational fluid dynamics (CFD) model on the patient-specific nasal geometry. Aerosols with aerodynamic diameter of 1 µm, which is large enough for delivery of large enough drug doses and yet potentially small enough for non-inertial aerosol deposition due to e.g. particle diffusion and flow oscillations, is inhaled for 1.98 s through one nostril and exhaled through the other one. The bi-directional aerosol delivery with steady flow rate of 4 L/min results in deposition efficiencies (DEs) of 50.9% and 0.48% in the nasal cavity and olfactory region, respectively. Pulsatile flow with average flow rate of 4 L/min (frequency: 45 Hz) reduces these values to 34.4% and 0.12%, respectively, and it mitigates the non-uniformity of right-left deposition in both the cavity (from 1.77- to 1.33-fold) and the olfactory region (from 624- to 53.2-fold). The average drug dose deposited in the nasal cavity and the olfactory epithelium region is very similar in the right nasal cavity independent of pulsation conditions (inhalation side). In contrast, the local aerosol dose in the olfactory region of the left side is at least 100-fold lower than that in the nasal cavity independent of pulsation condition. Hence, while pulsatile flow reduces the right-left (inhalation-exhalation) imbalance, it is not able to overcome it. However, on the inhalation side (even with pulsation) allows for relatively high olfactory epithelium drug doses per area reaching the same level as in the total nasal cavity. Due to the relatively low drug deposition in olfactory region on the exhalation side, this allows either very efficient targeting of the inhalation side, or uniform drug delivery by performing bidirectional flow first from the one and then from the other side of the nose.

Cu and Cu-SWCNT Nanoparticles’ Suspension in Pulsatile Casson Fluid Flow via Darcy–Forchheimer Porous Channel with Compliant Walls: A Prospective Model for Blood Flow in Stenosed Arteries

Abstract: The use of experimental relations to approximate the efficient thermophysical properties of a nanofluid (NF) with Cu nanoparticles (NPs) and hybrid nanofluid (HNF) with Cu-SWCNT NPs and subsequently model the two-dimensional pulsatile Casson fluid flow under the impact of the magnetic field and thermal radiation is a novelty of the current study. Heat and mass transfer analysis of the pulsatile flow of non-Newtonian Casson HNF via a Darcy–Forchheimer porous channel with compliant walls is presented. Such a problem offers a prospective model to study the blood flow via stenosed arteries. A finite-difference flow solver is used to numerically solve the system obtained using the vorticity stream function formulation on the time-dependent governing equations. The behavior of Cu-based NF and Cu-SWCNT-based HNF on the wall shear stress (WSS), velocity, temperature, and concentration profiles are analyzed graphically. The influence of the Casson parameter, radiation parameter, Hartmann number, Darcy number, Soret number, Reynolds number, Strouhal number, and Peclet number on the flow profiles are analyzed. Furthermore, the influence of the flow parameters on the non-dimensional numbers such as the skin friction coefficient, Nusselt number, and Sherwood number is also discussed. These quantities escalate as the Reynolds number is enhanced and reduce by escalating the porosity parameter. The Peclet number shows a high impact on the microorganism’s density in a blood NF. The HNF has been shown to have superior thermal properties to the traditional one. These results could help in devising hydraulic treatments for blood flow in highly stenosed arteries, biomechanical system design, and industrial plants in which flow pulsation is essential.

Non-modal transient growth of disturbances in pulsatile and oscillatory pipe flows

Abstract: Laminar flows through pipes driven at steady, pulsatile or oscillatory rates undergo a subcritical transition to turbulence. We carry out an extensive linear non-modal stability analysis of these flows and show that for sufficiently high pulsation amplitudes the stream-wise vortices of the classic lift-up mechanism are outperformed by helical disturbances exhibiting an Orr-like mechanism. In oscillatory flow, the energy amplification depends solely on the Reynolds number based on the Stokes-layer thickness, and for sufficiently high oscillation frequency and Reynolds number, axisymmetric disturbances dominate. In the high-frequency limit, these axisymmetric disturbances are exactly similar to those recently identified by Biau (J. Fluid Mech., vol. 794, 2016, R4) for oscillatory flow over a flat plate. In all regimes of pulsatile and oscillatory pipe flow, the optimal helical and axisymmetric disturbances are triggered in the deceleration phase and reach their peaks in typically less than a period. Their maximum energy gain scales exponentially with Reynolds number of the oscillatory flow component. Our numerical computations unveil a plausible mechanism for the turbulence observed experimentally in pulsatile and oscillatory pipe flow.

Modeling of pulsatile EMHD flow of Au-blood in an inclined porous tapered atherosclerotic vessel under periodic body acceleration

Abstract: A theoretical study on the pulsatile flow of Sutterby nanofluid in an inclined porous tapered arterial stenosis under the simultaneous impact of electro-osmotic , magnetohydrodynamic and periodic body forces with slip effect at the arterial wall is presented. Gold (Au) nanoparticles with various shapes (spheres, bricks, cylinders, platelets and blades) are utilized in the analysis. Poisson–Boltzmann equation is used to encounter the phenomena of the applied electric field. By assuming the low zeta potential on the walls, Debye–Huckel approximation is adapted to linearize the Poisson–Boltzmann equation, and then closed-form solution for the electric potential function is obtained. Under the assumption of small Reynolds number and mild stenoses case, the equations that govern the flow are made non-dimensional, and a suitable radial coordinate transformation is used to convert the irregular boundary to a regular boundary. The analytical expression for temperature profile is obtained via Laplace and finite Hankel transforms, from which Nusselt number is derived while the velocity profile is computed numerically employing a Crank–Nicolson scheme with the appropriate boundary and initial conditions. The physical aspect of various emerging parameters is analyzed through various graphs and tables for profiles of dimensionless velocity, temperature, volumetric flow flux, flow impedance, skin-friction coefficient and Nusselt number. It is found that an upsurge in the electro-osmotic parameter serves to reduce the hemodynamic factors (skin-friction and impedance) substantially, whereas an adverse trend is noticed for the Hartmann number. It is also deduced that the utilization of the spherical shape nanoparticles shows the higher heat flux at the stenosed arterial wall compared to the other nanoparticle shapes, and hence, nanoparticles and their shapes play a prominent role in biomedical applications. In order to validate the current results, different comparisons have been made with earlier published studies in a limiting case and an excellent agreement was found.

Two-phase analysis of blood flow through a stenosed artery with the effects of chemical reaction and radiation

Abstract: The paper presents a study related to the two-phase analysis of pulsatile blood flow through a narrowed stenosed artery with radiation and the chemical effects. In the model, a vertical artery is considered in which the flow of blood is assumed vertical upward and the direction of an external applied magnetic is in the radial direction of the flow. To understand the behavior of blood flow, graphs of the velocity profile, wall shear stress, flow rate, flow impedance and concentration profile are portrayed with different values of the magnetic and radiation parameters. In order to validate the results, a comparative study is presented between the single-phase and two-phase model of the blood flow, which shows that the two-phase model fits more accurately with the experimental data than the single-phase model, as mean errors are $$0.3\%$$ for the two-phase model while it is $$1\%$$ for single-phase model. For pulsatile flow, the phase difference between the pressure gradient and the flow rate is displayed with the effects of the magnetic field and different heights of the stenosis.

Study of Magnetohydrodynamic Pulsatile Blood Flow through an Inclined Porous Cylindrical Tube with Generalized Time-Nonlocal Shear Stress

Abstract: The effects of pulsatile pressure gradient in the presence of a transverse magnetic field on unsteady blood flow through an inclined tapered cylindrical tube of porous medium are discussed in this article. The fractional calculus technique is used to provide a mathematical model of blood flow with fractional derivatives. The solution of the governing equations is found using integral transformations (Laplace and finite Hankel transforms). For the semianalytical solution, the inverse Laplace transform is found by means of Stehfest’s and Tzou’s algorithms. The numerical calculations were performed by using Mathcad software. The flow is significantly affected by Hartmann number, inclination angle, fractional parameter, permeability parameter, and pulsatile pressure gradient frequency, according to the findings. It is deduced that there exists a significant difference in the velocity of the flow at higher time when the magnitude of Reynolds number is small and large.

Non-Newtonian Casson pulsatile fluid flow influenced by Lorentz force in a porous channel with multiple constrictions: A numerical study

Abstract: In this paper, we investigate non-Newtonian Casson fluid flow with pulsation in a channel having symmetrical constriction bumps on the upper and lower walls. The medium is assumed to be porous, following Darcy’s law. The fluid is modeled as electrically low conducting, and the pulsatile flow is subjected to a transverse magnetic field of uniform strength to study the impact of the resulting Lorentz force. We transform the mathematical model using the vorticity-stream function form for obtaining the solution. We analyze influence of the Hartman, Strouhal, Casson fluid, and porosity parameters on various flow profiles. It is revealed that the region of flow separation in the wake of a constriction bump tends to vanish with increasing the magnetic field parameter as well as Casson fluid parameter. The wall shear stress has higher values at the first constriction bump than that at the second constriction bump on a wall. It is also noticed that wall shear stress decreases with increasing the value of the porosity parameter during the pulsation cycle.