Showing papers on "Pulsatile flow published in 2003"
TL;DR: It appears likely that the totality of the BP curve, not simply 2 specific and arbitrary points, should be considered to act mechanically on the arterial wall and therefore should be used to propose an adequate definition of high BP.
Abstract: Blood pressure (BP) is a powerful cardiovascular (CV) risk factor that acts on the arterial wall and is responsible in part for various CV events, such as cerebrovascular accidents and ischemic heart disease. In clinical practice, 2 specific and arbitrary points of the BP curve, peak systolic BP (SBP) and end-diastolic BP (DBP), are used to define the CV risk factor. Because the goal of drug treatment of hypertension is to prevent CV complications, it appears likely that the totality of the BP curve, not simply 2 specific and arbitrary points, should be considered to act mechanically on the arterial wall and therefore should be used to propose an adequate definition of high BP.
A current approach consists of considering the BP curve as the summation of a steady component, mean blood pressure (MBP), and a pulsatile component, pulse pressure (PP).1 MBP, the product of cardiac output multiplied by total peripheral resistance, is the pressure for the steady flow of blood and oxygen to peripheral tissues and organs. The pulsatile component, PP, is the consequence of intermittent ventricular ejection from the heart. PP is influenced by several cardiac and vascular factors, but it is the role of large conduit arteries, mainly the aorta, to minimize pulsatility. In addition to the pattern of left ventricular ejection, the determinants of PP (and SBP) are the cushioning capacity of arteries and the timing and intensity of wave reflections.1 The former is influenced by arterial stiffness, usually expressed in the quantitative terms of compliance and distensibility.1 The latter result from the summation of a forward wave coming from the heart and propagating at a given speed (pulse wave velocity, or PWV) toward the origin of resistance vessels and a backward wave returning toward the heart from particular sites characterized by specific …
1,121 citations
TL;DR: An ultra-high-speed spectral domain optical Doppler tomography system is used to acquire images of blood flow in a human retina in vivo, at 29,000 depth profiles per second and with data acquisition over 99% of the measurement time.
Abstract: An ultra-high-speed spectral domain optical Doppler tomography (SD-ODT) system is used to acquire images of blood flow in a human retina in vivo, at 29,000 depth profiles (A-lines) per second and with data acquisition over 99% of the measurement time. The phase stability of the system is examined and image processing algorithms are presented that allow accurate determination of bi-directional Doppler shifts. Movies are presented of human retinal flow acquired at 29 frames per second with 1000 A-lines per frame over a time period of 3.28 seconds, showing accurate determination of vessel boundaries and time-dependent bi-directional flow dynamics in artery-vein pairs. The ultra-high-speed SD-ODT system allows visualization of the pulsatile nature of retinal blood flow, detects blood flow within the choroid and retinal capillaries, and provides information on the cardiac cycle. In summary, accurate video rate imaging of retinal blood flow dynamics is demonstrated at ocular exposure levels below 600 microW.
587 citations
TL;DR: In this paper, four different turbulence models were employed to study their influence on the results of pulsatile turbulent flow in axisymmetric stenoses and 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
Abstract: 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.
201 citations
TL;DR: PVR falls with exogenous NO late after Fontan-type operation, suggesting pulmonary endothelial dysfunction, related in some part to lack of pulsatility in the pulmonary circulation because of altered flow characteristics, may have a role in these patients.
Abstract: Background— The pulsatile nature of pulmonary blood flow is important for shear stress–mediated release of endothelium-derived nitric oxide (NO) and lowering pulmonary vascular resistance (PVR) by passive recruitment of capillaries Normal pulsatile flow is lost or markedly attenuated after Fontan-type operations, but to date, there are no data on basal pulmonary vascular resistance and its responsiveness to exogenous NO at late follow-up in these patients Methods and Results— We measured indexed PVR (PVRI) using Fick principle to calculate pulmonary blood flow, with respiratory mass spectrometry to measure oxygen consumption, in 15 patients (median age, 12 years; range, 7 to 17 years; 12 male, 3 female) at a median of 9 years after a Fontan-type operation (6 atriopulmonary connections, 7 lateral tunnels, 2 extracardiac conduits) The basal PVRI was 211±079 Wood unit (WU) times m2 (mean±SD) and showed a significant reduction to 161±048 (P=0016) after 20 ppm of NO for 10 minutes The patients with no
196 citations
TL;DR: The hemodynamic effects of RCA motion can be ignored as a first approximation in modeling studies because it has little effect on time-averaged WSS patterns, and even this effect is overshadowed by the variations in WSS due to flow pulsation.
Abstract: The purpose of this work was to investigate the effects of physiologically realistic cardiac-induced motion on hemodynamics in human right coronary arteries. The blood flow patterns were numerically simulated in a modeled right coronary artery (RCA) having a uniform circular cross section of 2.48 mm diam. Arterial motion was specified based on biplane cineangiograms, and incorporated physiologically realistic bending and torsion. Simulations were carried out with steady and pulsatile inflow conditions (mean ReD=233, α =1.82) in both fixed and moving RCA models, to evaluate the relative importance of RCA motion, flow pulsation, and the interaction between motion and flow pulsation. RCA motion with a steady inlet flow rate caused variations in wall shear stress (WSS) magnitude up to 150% of the inlet Poiseuille value. There was significant spatial variability in the magnitude of this motion-induced WSS variation. However, the time-averaged WSS distribution was similar to that predicted in a static model representing the time-averaged geometry. Furthermore, the effects of flow pulsatility dominated RCA motion-induced effects; specifically, there were only modest differences in the WSS history between simulations conducted in fixed and moving RCA models with pulsatile inflow. RCA motion has little effect on time-averaged WSS patterns. It has a larger effect on the temporal variation of WSS, but even this effect is overshadowed by the variations in WSS due to flow pulsation. The hemodynamic effects of RCA motion can, therefore, be ignored as a first approximation in modeling studies. © 2003 Biomedical Engineering Society.
180 citations
TL;DR: Pulsatile flow in a planar channel with a one-sided semicircular constriction with Reynolds numbers greater than 1000 is simulated and the presence of a characteristic shear-layer frequency which increases monotonically with Reynolds number is found.
Abstract: 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.
140 citations
TL;DR: The hemodynamics of pulsatile blood flow is examined in hypothetical three-dimensional models of abdominal aortic aneurysms (AAAs) using the finite element method and the effect of asymmetry in hypothetically shaped AAAs is to increase the maximum wall shear stress at peak flow and to induce the appearance of secondary flows in late diastole.
Abstract: In the abdominal segment of the human aorta under a patient's average resting conditions, pulsatile blood flow exhibits complex laminar patterns with secondary flows induced by adjacent branches and irregular vessel geometries. The flow dynamics becomes more complex when there is a pathological condition that causes changes in the normal structural composition of the vessel wall, for example, in the presence of an aneurysm. This work examines the hemodynamics of pulsatile blood flow in hypothetical three-dimensional models of abdominal aortic aneurysms (AAAs). Numerical predictions of blood flow patterns and hemodynamic stresses in AAAs are performed in single-aneurysm, asymmetric, rigid wall models using the finite element method. We characterize pulsatile flow dynamics in AAAs for average resting conditions by means of identifying regions of disturbed flow and quantifying the disturbance by evaluating flow-induced stresses at the aneurysm wall, specifically wall pressure and wall shear stress. Physiologically realistic abdominal aortic blood flow is simulated under pulsatile conditions for the range of time-average Reynolds numbers 50 < or = Rem < or = 300, corresponding to a range of peak Reynolds numbers 262.5 < or = Repeak < or = 1575. The vortex dynamics induced by pulsatile flow in AAAs is depicted by a sequence of four different flow phases in one period of the cardiac pulse. Peak wall shear stress and peak wall pressure are reported as a function of the time-average Reynolds number and aneurysm asymmetry. The effect of asymmetry in hypothetically shaped AAAs is to increase the maximum wall shear stress at peak flow and to induce the appearance of secondary flows in late diastole.
138 citations
TL;DR: Analytical expressions for axial velocity, fluid acceleration, flow rate and shear stress have been obtained inulsatile flow of blood through a stenosed porous medium under the influence of body acceleration.
108 citations
TL;DR: PC-MRI for flow quantitation may be combined with SENSE to achieve a substantive reduction of scanning time in children with left-to-right shunt, and Qp/Qs quantification is possible by PC-MRI+SF-3 in <60 seconds.
Abstract: Background— Parallel imaging by sensitivity encoding (SENSE) may considerably reduce scan time in MRI. For rapid flow quantification in children with congenital heart disease, we evaluated phase-contrast MRI (PC-MRI) techniques combined with SENSE. Methods and Results— In 22 pediatric patients (mean age, 7.2±6.2 years) with cardiac left-to-right shunt, blood flow rate in the pulmonary artery (Qp) and ascending aorta (Qs) and flow ratio Qp/Qs were determined by PC-MRI with SENSE reduction-factor 2 and 3 (SF-2 and SF-3). Additionally, we used PC-MRI with higher spatial in-plane resolution (1.6×2.1 versus 2.3×3.1 mm) with and without SF-3. Results were compared with a recently validated standard PC-MRI protocol and tested in vitro using a pulsatile flow phantom. Reduction of signal averages from 2 to 1 and application of SENSE accelerated flow measurements by a factor of 3.5 (5.2) using PC-MRI with SF-2 (SF-3) compared with standard PC-MRI. For blood flow rate through the pulmonary artery and aorta, as well ...
98 citations
TL;DR: It seems that the radial artery dilates in such a way as to maintain the peak wallShear stress constant, suggesting that endothelial cells sense the maximum rather than the time-averaged wall shear stress.
Abstract: It is known that changes in blood flow induce vascular remodeling and that shear stress, the tractive force acting on the vessel wall due to blood flowing, influences endothelial cell function. The aim of the present study was to investigate the relation between changes in pulsatile shear forces and arterial remodeling in response to chronic elevation in blood flow within the radial artery. The authors studied vessel diameter, flow rate, and shear stress in the radial artery of uremic patients before and after surgical creation of a native arteriovenous fistula for hemodialysis access. For this purpose, the authors used echo-color-Doppler ultrasound to perform diameter and blood velocity measurements. Time-function blood flow rate and wall shear stress were calculated based on arterial diameter, center-line velocity wave-form, and blood viscosity, using a numerical method developed according to Womersley's theory for unsteady flow in tubes. The results confirmed that the radial artery diameter increases i...
85 citations
TL;DR: It is argued that for relatively thin blood layers the light diffraction on aggregates becomes the dominant phenomenon and this dependence may serve as a basis for an alternative approach to noninvasive blood tests: occlusion spectroscopy.
Abstract: The influence of red blood cell (RBC) aggregation on transparency of blood in the red-near infrared spectral range is investigated. We argue that for relatively thin blood layers the light diffraction on aggregates becomes the dominant phenomenon. The nature of pulsatile changes of blood transparency is explained by pulsations of RBC aggregate size. For another case of over-systolic vessel occlusion the following time evolution of blood transparency strongly depends on light wavelength. This dependence may serve as a basis for an alternative approach to noninvasive blood tests: occlusion spectroscopy. Theoretical results well correspond to both in vivo and in vitro measurements reproducing pulsatile blood flow and long occlusion as well.
TL;DR: The regurgitant flow field of the St. Jude Medical bileaflet mechanical heart valve was assessed using PIV under physiologic pulsatile flow conditions and suggested little potential for hemolysis when the hinge jets collided, however, the vortex motion near the occluder tips potentially provides a low-pressure environment for cavitation.
Abstract: The regurgitant flow fields of clinically used mechanical heart valves have been traditionally studied in vitro using flow visualization, ultrasound techniques, and laser Doppler velocimetry under steady and pulsatile flow. Detailed investigation of the forward and regurgitant flow fields of these valves can elucidate a valve's propensity for blood element damage, thrombus formation, or cavitation. Advances in particle image velocimetry (PIV) have allowed its use in the study of the flow fields of prosthetic valves. Unlike other flow field diagnostic systems, recent work using PIV has been able to relate particular regurgitant flow field characteristics of the Bjork-Shiley Monostrut valve to a propensity for cavitation. In this study, the regurgitant flow field of the St. Jude Medical bileaflet mechanical heart valve was assessed using PIV under physiologic pulsatile flow conditions. Data collected at selected time points prior to and after valve closure demonstrated the typical regurgitant jet flow patterns associated with the St. Jude valve, and indicated the formation of a strong regurgitant jet, in the B-datum plane, along with twin vortices near the leaflets. Estimated ensemble-average viscous shear rates suggested little potential for hemolysis when the hinge jets collided. However, the vortex motion near the occluder tips potentially provides a low-pressure environment for cavitation.
TL;DR: The results suggest that the interstitial fluid flow is unlikely to cause the periosteal bone formation in venous stasis.
TL;DR: The approach described herein might offer a new way towards an improved assessment of detailed in vivo flow conditions and alterations of blood flow associated with heart valve prostheses in particular.
Abstract: Blood flow through the ascending aorta of two individuals is studied numerically. Realistic flow simulation is enabled by the combination of MRI and CFD. The aim of this study is the validation of the calculated flow field and, on the other hand, a comparison between flow distal to an artificial heart valve and native flow of a healthy volunteer. Three-dimensional, time-dependent computer models of the human ascending aorta were reconstructed from three-directional data sets acquired by MRI in the subjects studied. MRI velocity measurements downstream of the aortic valve provided the inflow conditions for the computational study. The pulsatile flow is described by the ALE-modified Navier-Stokes equations with respect to the time-varying flow domain. The numerical approach applies our own developed finite-element solver. During systolic acceleration the flow patterns distal to the valves do not show major differences between the two configurations. During flow deceleration, however, a significant influence of the disturbed inflow conditions can be found in the whole segment. Using the methods proposed, simulation of blood flow in the ascending aorta of the two subjects could be successfully performed. There was good qualitative agreement of blood velocities predicted by CFD and velocity data measured by MRI. In conclusion, the approach described herein might offer a new way towards an improved assessment of detailed in vivo flow conditions and alterations of blood flow associated with heart valve prostheses in particular. Combining CFD and MRI potentially extends the quantification of hemodynamic variables in vivo at a scale beyond the resolution limit inherent to MRI.
Journal Article•
TL;DR: The results presented confirm that the model developed is suitable for calculation of the wall shear stress that develops in the radial artery of patients before and after surgical creation of an arteriovenous fistula for hemodialysis.
TL;DR: The combined MRI/CFD is expected to provide more reliable information about the full three-dimensional velocity field and to further explore the potential for in vivo applications.
Abstract: A combined magnetic resonance imaging (MRI) and computational fluid dynamics (CFD) modeling study was carried out for pulsatile flow in a carotid bifurcation phantom. The aim of the study was to quantify differences in flow patterns between MRI measurement and MRI-based CFD simulations and to further explore the potential for in vivo applications. The computational model was reconstructed from high resolution magnetic resonance (MR) scans. Velocities derived from phase-contrast MR measurements were used as boundary conditions for the CFD calculation. Detailed comparisons of velocity patterns were made between the CFD results and MRI measurements. Good agreement was achieved for the main velocity component in both well-behaved flow (in the common carotid) and disturbed region (in the carotid sinus). Comparison of in-plane velocity vectors showed less satisfactory consistency and revealed that the MR measurements obtained were inadequate to depict the secondary flow pattern as expected. It can be concluded that the combined MRI/CFD is expected to provide more reliable information about the full three-dimensional velocity field. © 2003 Biomedical Engineering Society.
PAC2003: 8761Lh, 8719Uv, 8385Pt, 8710+e
TL;DR: Although aging affects scleral rigidity and systemic blood pressure, multiple regression analysis indicates that the most influential factor affecting POBF is aging.
Abstract: :Purpose.Pulsatile ocular blood flow (POBF) assessment measures the choroidal circulation and provides diagnostic value to certain ocular diseases such as glaucoma. This technique assumes a constant ocular rigidity and is influenced by axial length, diurnal variation, and age. This study inv
Journal Article•
TL;DR: To evaluate the local hemodynamics in flow limiting coronary lesions, computational hemodynamics was applied to a group of patients previously reported by Wilson et al. (1988) and found the pulsatile flow field was principally quasi-steady before flow separation occurred.
TL;DR: For correct understanding of the pathophysiology of hypertensive disease, its risks for target-organ damage and its effective treatment, both the pulsatile and steady components of the blood pressure curve must be considered.
Abstract: Epidemiological studies in the past decade have stressed the importance of both pulse pressure and mean arterial pressure (MAP) as important risk factors in hypertension-related cardiovascular disease. Pulse pressure and MAP are determined by different segments of the cardiovascular system. Pulse pressure is the pulsatile component of the blood pressure curve. It is determined by left ventricular ejection, the cushioning capacity (compliance) of the large arteries, and the timing and intensity of wave reflections from the microcirculation. MAP is the steady component; it is determined by cardiac output and peripheral (micro)vascular resistance. To a large degree, the structural design of the heart and vascular tree determine the pulse pressure and MAP, in addition to the propagation of the pressure wave through the vasculature. Pressure and flow, in contrast, influence the composition and geometry of the heart and vasculature. Hypertensive disease is associated with important structural alterations of the heart, such as hypertrophy and fibrosis, and of the vasculature, such as large artery stiffening, small artery remodelling and microvascular rarefaction. Recent basic research has revealed some of the molecular pathways involved in the remodelling of the cardiovascular system under the influence of physical forces. For correct understanding of the pathophysiology of hypertensive disease, its risks for target-organ damage and its effective treatment, both the pulsatile and steady components of the blood pressure curve must be considered.
TL;DR: It is possible to effectively estimate flow in a rotary blood pump without implanting additional invasive sensors, and an average flow estimation algorithm was derived from root mean square (RMS) pump impeller speed and RMS input power.
Abstract: Non-invasive estimation of flow was investigated in an implantable rotary blood pump (iRBP) with a hydrodynamic bearing. The effects of non-pulsatile and pulsatile flows were studied using in vitro mock loops, and acute (N = 3) and chronic (N = 6) ovine experiments. Using the non-pulsatile and pulsatile mock loops an average flow estimation algorithm was derived from root mean square (RMS) pump impeller speed and RMS input power. These algorithms were programmed into the iRBP controller for subsequent validation in vivo. In the acute experiments, venous return and systemic vascular resistance were adjusted through pharmacological intervention and exsanguination to produce an average range of pump flows from 0.0 to 2.6 l min(-1). Over this range the RMS estimation error was 88 +/- 12 ml, with a linear correlation slope of 0.992 +/- 0.006 (R2 = 0.986 +/- 0.004). In the chronic experiments, animals were monitored daily for up to three months and an average range of flows from 2.8 to 4.8 l min(-1) recorded. A linear correlation between the estimated and measured pump flows yielded a slope of 1.005 +/- 0.006 (R2 = 0.966 +/- 0.004). The RMS estimation error was 120 +/- 11 ml. Using this algorithm it is possible to effectively estimate flow in a rotary blood pump without implanting additional invasive sensors.
TL;DR: The hypotensive effect of exercise on intraocular pressure is confirmed and shows that exercise significantly increases pulsatile ocular blood flow.
Abstract: Purpose. The hypotensive effect of exercise on intraocular pressure is well documented, however, little is known about the effect of exercise on pulsatile ocular blood flow. This study examines this effect and follows the recovery of intraocular pressure and pulsatile ocular blood flow after a standard exercise period. Methods. Eighteen visually normal subjects participated in a 4-min period of bicycle ergometry. Intraocular pressure and pulsatile ocular blood flow were measured by pneumotonometry before, immediately after exercise, and at regular intervals during the recovery period. Results. Intraocular pressure was found to decrease significantly with strenuous exercise and recovered gradually toward baseline over a period of 30 min. Pulsatile ocular blood flow increased significantly immediately after exercise then returned to baseline levels between 5 and 10 min after stopping exercise. Conclusions. This study confirms the hypotensive effect of exercise on intraocular pressure and shows that exercise significantly increases pulsatile ocular blood flow.
TL;DR: The authors' data indicate a small, but significant increase in choroidal blood flow with increasing blood pressure, which is similar to that seen in treated hypertension.
Abstract: Purpose Untreated hypertension is associated with ocular complications and is a risk factor for the development and progression of vascular ocular pathologies. We set out to investigate the association between systemic blood pressure and choroidal blood flow. Methods All subjects were male non-smokers, who did not receive any medication and had normal or slightly elevated blood pressure (systolic blood pressure ≤160 mmHg; diastolic blood pressure ≤100 mmHg). The association between systemic blood pressure and fundus pulsation amplitude, a measure of pulsatile choroidal blood flow, was investigated in 318 volunteers. In addition, the association between systemic blood pressure and blood flow velocities in the posterior ciliary arteries supplying the choroid was investigated in these subjects. Results Ocular fundus pulsation amplitude (r=0.252; P<0.001) and mean flow velocity in the posterior ciliary arteries (r=0.346, P<0.001) were significantly associated with mean arterial pressure. The correlation of ocular haemodynamic variables with systolic and diastolic blood pressure was in the same range. Conclusions Our data indicate a small, but significant increase in choroidal blood flow with increasing blood pressure.
TL;DR: The data indicate that the effectiveness of unloading in continuous mode depends on the contractility of the native ventricle, and in pulsatile mode, the pump timing is an important determinant of pump/cardiovascular system interaction, with a counterpulsation setting yielding the best unloading.
Abstract: Due to the increased appeal of rotary blood pumps for long-term cardiac assist, we conducted a study of their capacity to unload the left ventricle (LV). We used a validated mathematical model of the cardiovascular system and implemented the pump characteristics of an investigational microdiagonal pump (Medos). The influence of the pump on systemic hemodynamics, LV energetic parameters, and wall stress was evaluated in continuous and synchronous pulsatile modes of operation. For the continuous mode simulations, the influence of heart rate, LV contractility, and pump speed was assessed in a parametric study. For the pulsatile mode, different onsets of a synchronous time-varying pump speed pattern were tested. Our data indicate that the effectiveness of unloading in continuous mode depends on the contractility of the native ventricle. Hypocontractile ventricles are most easily unloaded, while ventricles with moderate contractility require high continuous pump speeds to achieve notable unloading. In pulsatile mode, the pump timing is an important determinant of pump/cardiovascular system interaction, with a counterpulsation setting yielding the best unloading.
TL;DR: A novel fourfold ensemble construct is formulated and implemented, wherein systemic GH pulses stimulate long-latency, concentration-dependent secretion of periventricular-nuclear SRIF and a basis for the paradoxical GH-inhibiting action of centrally delivered GHRH is explained.
Abstract: Growth hormone (GH) secretion is vividly pulsatile in all mammalian species studied. In a simplified model, self-renewable GH pulsatility can be reproduced by assuming individual, reversible, time-...
TL;DR: Considering the pulsatile nature of subendocardial flow and the vulnerability of this layer, pharmacological manipulation of the balance between NO and O2− may improve sub endocardial perfusion.
Abstract: Coronary blood vessels are compressed by the contracting myocardium. This leads to oscillations in flow in especially the subendocardium. We examined the effects of steady and oscillating flow on isolated, cannulated subendocardial and subepicardial porcine arterioles. Steady flow-induced dilation in both vessel types, up to 12.9+/-0.8% of the passive diameter in subendocardials and 9.6+/-1.4% in subepicardials at 40 dyne/cm2. Dilation was completely abolished after treatment with 10 micromol/L L-NNA. Sinusoidal modulation of steady flow at 1.5 Hz and 50% to 200% amplitude did not affect dilation. Oscillating flow without a net forward component with peak-peak shear values up to 100 dyne/cm2 caused no dilation at all in these vessels. However, in the presence of 100 U/mL superoxide dismutase (SOD), oscillating flow induced dilation up to 19.5+/-2.3% in subendocardial vessels and 11.5+/-4.3% in subepicardials. LNNA (10 micromol/L) blocked this dilation by approximately 50%. SOD did not affect the magnitude of steady flow-induced dilation, but the response time after onset of steady flow shortened from 23.4+/-1.5 to 14.3+/-2.1 seconds. Diphenyleneiodinium, an inhibitor of NAD(P)H oxidase, uncovered dilation to oscillating flow in subendocardial vessels up to 9.5+/-1.6%. Flow causes production of both NO and O2-. During steady flow, the bioavailability of NO is sufficient to cause vasodilation. During oscillating flow, NO is quenched by the O2-, suppressing vasodilation. Considering the pulsatile nature of subendocardial flow and the vulnerability of this layer, pharmacological manipulation of the balance between NO and O2- may improve subendocardial perfusion.
TL;DR: The blood flow to the acetabular fragment is of some concern in juxtaarticular pelvic osteotomies used for the treatment of hip dysplasia but no direct measurements have determined the effect of the Bernese periacetabular osteotomy (PAO) on acetABular perfusion.
TL;DR: It has been determined that pGz, a novel method of increasing shear stress on the vascular endothelium, attenuates the vasoactive response to L-NAME.
Abstract: Periodic acceleration (pGz), a novel method of ventilatory support, is achieved using a platform that moves cyclically in the headward-footward direction. PGz has been shown to increase vascular shear stress and regional blood flows, as well as decrease pulmonary and systemic vascular resistances. PGz also increases nitric oxide (NO) production. This study was undertaken to determine the effects of pGz on the NO inhibiting effects of N-w-nitro-L-arginine (L-NAME) in vivo, and to determine if increased NO production due to pGz could be reproduced in vitro with isolated arteries. Pigs were assigned to conventional ventilation (CV), or pGz, with no additional breathing assistance. L-NAME was infused in cumulative doses of 1, 3, 10, 30, and 100 mg/kg. Cardiac output decreased in both groups by 50%. There was also a dose-dependent increase in blood pressure, pulmonary artery pressure, and vascular resistances. However, pGz attenuated the vascular response of L-NAME. Isolated porcine aortas exposed to nonpulsatile, pulsatile, and pulsatile flow plus pGz exhibited an increase in nitrites with the addition of pulsatile flow (300%, relative to steady flow), and a further increase with pGz (1000%, relative to steady flow). It has been determined that pGz, a novel method of increasing shear stress on the vascular endothelium. attenuates the vasoactive response to L-NAME. The in vitro experiments demonstrated that increases in NO production in vivo could be reproduced in vitro, which provides the opportunity to investigate the mechanisms of cardiovascular pGz effects.
TL;DR: When the flow pattern was changed from pulsatile to nonpulsatile, the velocity of erythrocytes in many capillaries dropped and remained at a low level, and the number of perfused capillary decreased.
Abstract: This study has three purposes, as follows. The first is to develop a microscopic system to observe the microcirculation of animals implanted with an artificial heart. The second is to investigate the influence of flow pattern change from pulsatile to nonpulsatile on the microcirculation. The third is to study the effects of pulsatility in blood flow on endothelium-derived nitric oxide release in the microvasculature. When the flow pattern was changed from pulsatile to nonpulsatile, the velocity of erythrocytes in many capillaries dropped and remained at a low level, and the number of perfused capillaries decreased. After the flow pattern was returned to pulsatile, the velocity of erythrocytes recovered to the initial level. In many cases, the flow of nonperfused capillaries recovered to the initial level as well. Also, the pulsatile flow enhances the basal and flow-stimulated endothelium-derived nitric oxide release in microvessels.
TL;DR: Reverse flow in the LPV correlated significantly with an elevated resistance index of the umbilical arteries, which could have major physiological implications: Deoxygenated blood may be added via theLPV to the blood shifted through the DV and ultimately reach critical fetal organs.
Abstract: Critical fetal organs are preferentially supplied with oxygenated blood from the umbilical vein (UV) by way of the ductus venosus (DV). Under normal conditions a significant part of UV-blood flows steadily forward through the left portal vein (LPV). Blood flow through the LPV could reverse, however, in cases of absent or reversed endodiastolic flow in the umbilical arteries. We tested when fetal blood flow reversal occurs by studying 28 cases with pathological flow in the umbilical artery. In the LPV we observed normal nonpulsatile forward flow in 9 cases, pulsatile forward flow in 10 cases, and reversed flow in 9 cases. Reverse flow in the LPV correlated significantly with an elevated resistance index of the umbilical arteries. This reversal could have major physiological implications: Deoxygenated blood may be added via the LPV to the blood shifted through the DV and ultimately reach critical fetal organs. In extremis there could be a waterhose effect, whereby more blood flows through the DV than the UV that supplies it. The LPV is thus the watershed of the venous circulation of the fetus.
TL;DR: Changes in the local hemodynamics due to mild exercise may be relatively small in the carotid artery, according to the results of a fully coupled fluid-structure three-dimensional finite element model of acarotid bifurcation.
Abstract: The important influence of hemodynamic factors in the initiation and progression of arterial disease has led to numerous studies to computationally simulate blood flow at sites of disease and examine potential correlative factors. This study considers the differences in hemodynamics produced by varying heart rate in a fully coupled fluid-structure three-dimensional finite element model of a carotid bifurcation. Two cases with a 50% increase in heart rate are considered: one in which peripheral resistance is uniformly reduced to maintain constant mean arterial pressure, resulting in an increase in mean flow, and a second in which cerebral vascular resistance is held constant so that mean carotid artery flow is nearly unchanged. Results show that, with increased flow rate, the flow patterns are relatively unchanged, but the magnitudes of mean and instantaneous wall shear stress are increased roughly in proportion to the flow rate, except at the time of minimum flow (and maximum flow separation) when shear stress in the carotid bulb is increased in magnitude more than threefold. When cerebral peripheral resistance is held constant, the differences are much smaller, except again at end diastole. Maximum wall shear stress temporal gradient is elevated in both cases with elevated heart rate. Changes in oscillatory shear index are minimal. These findings suggest that changes in the local hemodynamics due to mild exercise may be relatively small in the carotid artery.