Showing papers on "Pulsatile flow published in 2010"
TL;DR: Pb, a transit time–independent measure of reflected wave magnitude, predicted long-term cardiovascular mortality in men and women independent of arterial stiffness.
Abstract: The value of increased arterial wave reflection, usually assessed by the transit time-dependent augmentation index and augmented pressure (Pa), in the prediction of cardiovascular events may have been underestimated. We investigated whether the transit time-independent measures of reflected wave magnitude predict cardiovascular outcomes independent of arterial stiffness indexed by carotid-femoral pulse wave velocity. A total of 1272 participants (47% women; mean age: 52+/-13 years; range: 30 to 79 years) from a community-based survey were studied. Carotid pressure waveforms derived by tonometry were decomposed into their forward wave amplitudes, backward wave amplitudes (Pb), and a reflection index (=[Pb/(forward wave amplitude+Pb)]), in addition to augmentation index, Pa, and reflected wave transit time. During a median follow-up of 15 years, 225 deaths occurred (17.6%), including 64 cardiovascular origins (5%). In univariate Cox proportional hazard regression analysis, pulse wave velocity, Pa, and Pb predicted all-cause and cardiovascular mortality in both men and women, whereas augmentation index, reflected wave transit time, and reflection index were predictive only in men. In multivariate analysis accounting for age, height, and heart rate, Pb predicted cardiovascular mortality in both men and women, whereas Pa was predictive only in men. Per 1-SD increment (6 mm Hg), Pb predicted 15-year cardiovascular mortality independent of brachial but not central pressure, pulse wave velocity, augmentation index, Pa, and conventional cardiovascular risk factors with hazard ratios of approximately 1.60 (all P<0.05). In conclusion, Pb, a transit time-independent measure of reflected wave magnitude, predicted long-term cardiovascular mortality in men and women independent of arterial stiffness.
343 citations
TL;DR: This work proposes that this continuous oscillatory activity is crucial for optimal responsiveness of glucocorticoid-sensitive neural processes in this neuroendocrine system.
Abstract: Lightman and Conway-Campbell review findings showing that, superimposed on its well-known circadian rhythm, the HPA axis shows ultradian, oscillatory activity. They describe how the resulting pulsatile release of glucocorticoids maintains optimal responsiveness of the HPA axis and the brain processes regulated by these hormones.
328 citations
TL;DR: Echocardiographic particle image velocimetry offers new insights into cardiac function and might be of importance to optimize valve replacement therapy.
171 citations
TL;DR: It is concluded that pulsatile shear patterns may be central for supporting arterial identity, and that arterial Gja5 expression plays a functional role in flow-driven arteriogenesis.
Abstract: In the developing chicken embryo yolk sac vasculature, the expression of arterial identity genes requires arterial hemodynamic conditions. We hypothesize that arterial flow must provide a unique signal that is relevant for supporting arterial identity gene expression and is absent in veins. We analyzed factors related to flow, pressure and oxygenation in the chicken embryo vitelline vasculature in vivo. The best discrimination between arteries and veins was obtained by calculating the maximal pulsatile increase in shear rate relative to the time-averaged shear rate in the same vessel: the relative pulse slope index (RPSI). RPSI was significantly higher in arteries than veins. Arterial endothelial cells exposed to pulsatile shear in vitro augmented arterial marker expression as compared with exposure to constant shear. The expression of Gja5 correlated with arterial flow patterns: the redistribution of arterial flow provoked by vitelline artery ligation resulted in flow-driven collateral arterial network formation and was associated with increased expression of Gja5. In situ hybridization in normal and ligation embryos confirmed that Gja5 expression is confined to arteries and regulated by flow. In mice, Gja5 (connexin 40) was also expressed in arteries. In the adult, increased flow drives arteriogenesis and the formation of collateral arterial networks in peripheral occlusive diseases. Genetic ablation of Gja5 function in mice resulted in reduced arteriogenesis in two occlusion models. We conclude that pulsatile shear patterns may be central for supporting arterial identity, and that arterial Gja5 expression plays a functional role in flow-driven arteriogenesis.
165 citations
TL;DR: Understanding the pulsatile arterial hemodynamics that elevate cardiovascular risk has led to the use of pharmacological therapies, which prevent arterial stiffness and reduce wave reflections, and improve cardiovascular morbidity and mortality.
Abstract: Arterial aging can be attributed to two different pathophysiological changes--increase in arterial stiffness and disturbed wave reflections The capacity of the aorta to absorb the force exerted by the left ventricular ejection and dampen pulsatile flow becomes diminished with advancing age, owing to the progressive hardening of the arterial wall These changes contribute to increase blood pressure, mainly systolic blood pressure and pulse pressure, which can trigger cardiovascular events Understanding the pulsatile arterial hemodynamics that elevate cardiovascular risk has led to the use of pharmacological therapies, which prevent arterial stiffness and reduce wave reflections, and improve cardiovascular morbidity and mortality Antifibrotic agents, such as those that block the renin-angiotensin-aldosterone pathway, are often given in association with diuretics, calcium-channel blockers, or both, but not with standard beta-blockers Consistent reductions in cardiovascular outcomes obtained using these agents can be predicted through noninvasive measurements of central systolic blood pressure and pulse pressure
142 citations
TL;DR: Pulmonary hypertension that is secondary to congestive heart failure, as defined by a TPG > 15 mm Hg can be reversed by the use of pulsatile and axial-flow LVADs; furthermore, post-transplant survival for patients with secondary pulmonary hypertension treated with an LVAD was no different than for those without pulmonary hypertension who received LVAD support.
Abstract: Background Pulmonary hypertension associated with chronic congestive heart failure posses a significant risk of morbidity and death after heart transplantation. Isolated observations suggest that chronic ventricular unloading may lead to normalization of pulmonary pressures and thus render a patient likely to be a heart transplant candidate. Methods This study is a retrospective analysis of 9 heart failure patients with secondary pulmonary hypertension (transpulmonary gradient [TPG] > 15 mm/Hg). Two were treated with a pulsatile left ventricular assist device (LVAD) and 7 with an axial-flow LVAD. Results After LVAD support, mean pulmonary artery pressure decreased from 39 ± 7 to 31 ± 5 mm Hg, and the TPG decreased from 19 ± 3 to 13 ± 4 mm Hg ( p 15 mm Hg vs those with TPG p = 0.6). This finding was supported by analysis of a large multi-institutional cohort obtained from the Organ Procurement and Transplantation Network database, where no differences in survival were found in the same groups. Conclusions Pulmonary hypertension that is secondary to congestive heart failure, as defined by a TPG > 15 mm Hg can be reversed by the use of pulsatile and axial-flow LVADs; furthermore, post-transplant survival for patients with secondary pulmonary hypertension treated with an LVAD was no different than for those without pulmonary hypertension who received LVAD support.
89 citations
TL;DR: The initial in vitro testing of the CFTAH with a single, valveless, continuous-flow pump demonstrated its passive self-regulation of flows and atrial pressures and a new automatic control mode.
Abstract: The clinical use of left ventricular assist devices (LVADs) is becoming more widely accepted, due in large part to the introduction of continuous-flow blood pumps.1-6 These newer devices show significant improvements in size, simplicity, reliability, durability, and clinical results. However, 20-50% of patients undergoing LVAD implantation also have significant right ventricular failure, which limits the utility of implantable LVAD therapy.7-11 Existing total artificial hearts (TAHs) are either a temporary pneumatic system (CardioWest™, SynCardia, Tucson, AZ) with an externalized pneumatic driver or a permanent pulsatile implantable system (AbioCor™, Abiomed®, Danvers, MA). To date, they have demonstrated significant limitations in initial clinical trials because of their large size, limited durability, and incidence of thrombus formation and embolization.12 The inherent design characteristics of these pulsatile systems prevent significant reductions in size.
The feasibility of native heart replacement with two separate continuous-flow pumps has recently been demonstrated at the Texas Heart Institute (Houston, TX)13 and Tohoku University (Sendai, Japan).14 These systems require duplication of pump components, increasing the potential for component failure and necessitating the development of complex algorithms to appropriately coordinate the outputs of the two pumps. We are developing a continuous-flow TAH (CFTAH) that is extremely innovative, exploring radical new concepts in TAH design. The proposed concept involves the use of a valveless, sensorless, continuous-flow pump and automatic control system. This double-pump concept comprises a single, continuously rotating, brushless DC motor and a pump assembly with a centrifugal pump on both ends. Pump speed will be modulated to create pulsatile flow and pressure. This report details the CFTAH design concept and our initial in vitro data in a mock circulatory loop.
84 citations
TL;DR: The numerical results suggest that the effects of low WSS and high OSI tend to cause wall thickening occurred along the inferior wall of the aortic arch and the anterior wall ofThe brachiocephalic artery, similar implication reported in a number of previous studies.
Abstract: Cardiovascular disease is the primary cause of morbidity and mortality in the western world. Complex hemodynamics plays a critical role in the development of aortic dissection and atherosclerosis, as well as many other diseases. Since fundamental fluid mechanics are important for the understanding of the blood flow in the cardiovascular circulatory system of the human body aspects, a joint experimental and numerical study was conducted in this study to determine the distributions of wall shear stress and pressure and oscillatory WSS index, and to examine their correlation with the aortic disorders, especially dissection. Experimentally, the Phase-Contrast Magnetic Resonance Imaging (PC-MRI) method was used to acquire the true geometry of a normal human thoracic aorta, which was readily converted into a transparent thoracic aorta model by the rapid prototyping (RP) technique. The thoracic aorta model was then used in the in vitro experiments and computations. Simulations were performed using the computational fluid dynamic (CFD) code ACE+® to determine flow characteristics of the three-dimensional, pulsatile, incompressible, and Newtonian fluid in the thoracic aorta model. The unsteady boundary conditions at the inlet and the outlet of the aortic flow were specified from the measured flowrate and pressure results during in vitro experiments. For the code validation, the predicted axial velocity reasonably agrees with the PC-MRI experimental data in the oblique sagittal plane of the thoracic aorta model. The thorough analyses of the thoracic aorta flow, WSSs, WSS index (OSI), and wall pressures are presented. The predicted locations of the maxima of WSS and the wall pressure can be then correlated with that of the thoracic aorta dissection, and thereby may lead to a useful biological significance. The numerical results also suggest that the effects of low WSS and high OSI tend to cause wall thickening occurred along the inferior wall of the aortic arch and the anterior wall of the brachiocephalic artery, similar implication reported in a number of previous studies.
83 citations
TL;DR: Because of the inverse (peripheral-to-aortic) pressure gradient, pulse pressure amplification normally produces a substantial reversal of the femoral flow, the degree of which is determined by the aortic distensibility and peripheral wave reflection.
Abstract: Aortic stiffness, peripheral wave reflection, and aorta-to-peripheral pulse pressure amplification all predict cardiovascular risk. However, the pathophysiological mechanism behind it is unknown. Tonometric pressure waveforms were recorded on the radial, carotid, and femoral arteries in 138 hypertensive patients (age: 56±13 years) to estimate aorta-to-peripheral amplifications, aortic augmentation index, and aortic (carotid-femoral) pulse wave velocity. The femoral Doppler velocity waveform was recorded to calculate the reverse/forward flow index and diastolic/systolic forward flow ratio. The aorta-to-femoral and aorta-to-radial amplifications correlated inversely with the aortic augmentation index and pulse wave velocity. The femoral flow waveform was triphasic, composed of systolic forward, subsequent reverse, and diastolic forward phases in 129 patients, whereas it was biphasic and lacked a diastolic forward flow in 9 patients. Both the femoral reverse index (30±10%) and diastolic forward ratio (12±4%) correlated positively with the aorta-to-femoral amplification and inversely with the aortic augmentation index and pulse wave velocity; these correlations were independent of age, sex, diastolic pressure, and femoral artery diameter. Patients with biphasic (versus triphasic) flow were older, shorter, included more diabetics, had smaller femoral diameters, and showed greater aortic pulse wave velocity even when adjusted for all of these covariates. In conclusion, because of the inverse (peripheral-to-aortic) pressure gradient, pulse pressure amplification normally produces a substantial reversal of the femoral flow, the degree of which is determined by the aortic distensibility and peripheral wave reflection. Arteriosclerosis (increased stiffness, increased augmentation, and reduced amplification) decreases both the reverse and diastolic forward flows, potentially causing circulatory disturbance of truncal organs and lower extremities.
82 citations
TL;DR: Steady simulations are valid for an assessment of time-averaged WSS distributions and side-branches must not be neglected in numerical flow simulation (steady and transient) studies.
80 citations
TL;DR: Continuous unloading deranged the physiologic profile of myocardial and vascular hemodynamic energy utilization, whereas pulsatile unloading preserved more normal physiologic values, which may have important implications for chronic LVAD therapy.
Abstract: Debate exists regarding the merits and limitations of continuous versus pulsatile flow mechanical circulatory support. To characterize the hemodynamic differences between each mode of support, we investigated the acute effects of continuous versus pulsatile unloading of the failing left ventricle in a bovine model. Heart failure was induced in male calves (n = 14). During an acute study, animals were instrumented through thoracotomy for hemodynamic measurement. A continuous flow (n = 8) and/or pulsatile flow (n = 8) left ventricular assist device (LVAD) was implanted and studied during maximum support ( approximately 5 L/min) and moderate support ( approximately 2-3 L/min) modes. Pulse pressure (PP), surplus hemodynamic energy (SHE), and (energy equivalent pressure [EEP]/mean aortic pressure (MAP) - 1) x 100% were derived to characterize hemodynamic energy profiles during the different support modes. Standard hemodynamic parameters of cardiac performance were also derived. Data were analyzed by repeated measures one-way analysis of variance within groups and unpaired Student's t-tests across groups. During maximum and moderate continuous unloading, PP, SHE, and (EEP/MAP - 1) x 100% were significantly decreased compared with baseline and compared with pulsatile unloading. As a result, continuous unloading significantly altered left ventricular peak systolic pressure, aortic systolic and diastolic pressure, +/-dP/dt, and rate x pressure product, whereas pulsatile unloading preserved a normal profile of physiologic values. As continuous unloading increased, the pressure-volume relationship collapsed, and the aortic valve remained closed. In contrast, as pulsatile unloading increased, a comparable decrease in left ventricular volumes was noted. However, a normal range of left ventricular pressures was preserved. Continuous unloading deranged the physiologic profile of myocardial and vascular hemodynamic energy utilization, whereas pulsatile unloading preserved more normal physiologic values. These findings may have important implications for chronic LVAD therapy.
TL;DR: Five different coronary stent designs are taken, used in clinical practice, and the hemodynamic differences arising due to the difference in their design are explored, of particular interest is the design of the segments (connectors) that connect two struts.
Abstract: The design of coronary stents has evolved significantly over the past two decades. However, they still face the problem of in-stent restenosis, formation of neointima within 12 months of the implant. The biological response after stent implantation depends on various factors including the stent geometry which alters the hemodynamics. This study takes five different coronary stent designs, used in clinical practice, and explores the hemodynamic differences arising due to the difference in their design. Of particular interest is the design of the segments (connectors) that connect two struts. Pulsatile blood flow analysis is performed for each stent, using 3-D computational fluid dynamics (CFD), and various flow features viz. recirculation zones, velocity profiles, wall shear stress (WSS) patterns, and oscillatory shear indices are extracted for comparison. Vessel wall regions with abnormal flow features, particularly low, reverse, and oscillating WSS, are usually more susceptible to restenosis. Unlike previous studies, which have tried to study the effect of design parameters such as strut thickness and strut spacing on hemodynamics, this work investigates the differences in the flow arising purely due to differences in stent-shape, other parameters being similar. Two factors, the length of the connectors in the cross-flow direction and their alignment with the main flow, are found to affect the hemodynamic performance. This study also formulates a design index (varying from 18.81% to 24.91% for stents used in this study) that quantifies the flow features that could affect restenosis rates and which, in future, could be used for optimization studies.
TL;DR: This work considers the decoding of hormone pulsatility by taking the HPG axis as a model system and focussing on molecular mechanisms of frequency decoding by pituitary gonadotrophs, which involves steroid feedback‐dependent endogenous rhythmic activity throughout the HPA axis.
Abstract: Ultradian pulsatile hormone secretion underlies the activity of most neuroendocrine systems, including the hypothalamic-pituitary adrenal (HPA) and gonadal (HPG) axes, and this pulsatile mode of signalling permits the encoding of information through both amplitude and frequency modulation. In the HPA axis, glucocorticoid pulse amplitude increases in anticipation of waking, and, in the HPG axis, changing gonadotrophin-releasing hormone pulse frequency is the primary means by which the body alters its reproductive status during development (i.e. puberty). The prevalence of hormone pulsatility raises two crucial questions: how are ultradian pulses encoded (or generated) by these systems, and how are these pulses decoded (or interpreted) at their target sites? We have looked at mechanisms within the HPA axis responsible for encoding the pulsatile mode of glucocorticoid signalling that we observe in vivo. We review evidence regarding the 'hypothalamic pulse generator' hypothesis, and describe an alternative model for pulse generation, which involves steroid feedback-dependent endogenous rhythmic activity throughout the HPA axis. We consider the decoding of hormone pulsatility by taking the HPG axis as a model system and focussing on molecular mechanisms of frequency decoding by pituitary gonadotrophs.
TL;DR: It is suggested that pulsatile as well as non-pulsatile left ventricular assist devices are equally able to treat chronic heart failure and might thus offer a greater advantage when recovery of left Ventricular function is expected.
Abstract: INTRODUCTION Left ventricular assist devices have been successfully used as a bridge to cardiac transplantation. Because many patients exhibit marked clinical improvement of their heart failure after LVAD implantation, we studied the physiological effect of pulsatile and non-pulsatile devices on the neurohormonal axis and exercise capacity. METHODS We prospectively included 20 patients (17 men, 3 women) undergoing LVAD implantation between November 2001 and January 2004. Ten patients (1 woman and 9 men) were treated with the non-pulsatile INCOR-LVAD (Berlin Heart(c)) and ten patients received the pulsatile EXCOR LVAD (Berlin Heart(c)). Blood samples for plasma renin activity (PRA) were taken once a week over a period of ten weeks. All blood samples were collected in the morning before mobilization. Blood pressure, body weight, fluid intake and urine production were measured once a day. All patients received standard hospital diet with no limitation in fluid intake. RESULTS Body weight remained constant in both groups throughout the ten weeks' examination, and fluid intake and urine production were balanced in all patients. Although there was no significant difference in mean blood pressure (INCOR: 70 +/- 10 mmHg; EXCOR: 73 +/- 10 mmHg), plasma renin activity was substantially elevated in patients with non-pulsatile left ventricular support (INCOR: 94.68 +/- 33.97 microU/ml; EXCOR: 17.06 +/- 15.94 microU/ml; P < 0.05). Furthermore plasma aldosterone levels were significantly higher in patients supported by non-pulsatile INCOR LVAD (INCOR: 73.4 +/- 9.6 microg/ml; EXCOR: 20.6 +/- 4.6 microg/ml; P < 0.05). CONCLUSIONS Our data suggest that pulsatile as well as non-pulsatile left ventricular assist devices are equally able to treat chronic heart failure. However pulsatile devices seem to have a greater impact on reversing the changes in plasma renin activity and might thus offer a greater advantage when recovery of left ventricular function is expected.
TL;DR: These results validated CFTAH self-balancing of left and right circulation, induced arterial flow and pressure pulsatility, accurate calculated flow and SVR parameters, and the performance of an automatic active control mode in an acute, in vivo setting in response to a wide range of imposed physiologic perturbations.
Abstract: Background The purpose of this study was to evaluate the acute in vivo pump performance of a unique valveless, sensorless, pulsatile, continuous-flow total artificial heart (CFTAH) that passively self-balances left and right circulations without electronic intervention. Methods The CFTAH was implanted in two calves, with pump and hemodynamic data recorded at baseline over the full range of pump operational speeds (2,000 to 3,000 rpm) in 200-rpm increments, with pulsatility variance, and under a series of induced hemodynamic states created by varying circulating blood volume and systemic and pulmonary vascular resistance (SVR and PVR). Results Sixty of the 63 induced hemodynamic states in Case 1 and 73 of 78 states in Case 2 met our design goal of a balanced flow and maximum atrial pressure difference of 10 mm Hg. The correlation of calculated vs measured flow and SVR was high (R2 = 0.857 and 0.832, respectively), allowing validation of an additional level of automatic active control. By varying the amplitude of sinusoidal modulation of the speed waveform, 9 mm Hg of induced pulmonary and 18 mm Hg of systemic arterial pressure pulsation were achieved. Conclusions These results validated CFTAH self-balancing of left and right circulation, induced arterial flow and pressure pulsatility, accurate calculated flow and SVR parameters, and the performance of an automatic active control mode in an acute, in vivo setting in response to a wide range of imposed physiologic perturbations.
TL;DR: In this paper, an experimental and numerical study of pulsated Dean flow, three-dimensional pulsatile flow in a curved pipe, is performed by CFD code (Fluent 6) in which a pulsated velocity field is imposed as an inlet condition.
TL;DR: The UA-PAM system, capable of real-time B-scan imaging at 50 Hz and high-speed 3-D imaging, is validated by imaging the subcutaneous microvasculature in rats and humans and demonstrates the feasibility of noninvasive in vivo imaging of human pulsatile dynamics.
Abstract: With a refined ultrasound-array-based real-time photoacoustic microscopy (UA-PAM) system, we demonstrate the feasibility of noninvasive in vivo imaging of human pulsatile dynamics. The system, capable of real-time B-scan imaging at 50 Hz and high-speed 3-D imaging, is validated by imaging the subcutaneous microvasculature in rats and humans. After the validation, a human artery around the palm-wrist area is imaged, and its pulsatile dynamics, including the arterial pulsatile motion and changes in hemoglobin concentration, is monitored with 20-ms B-scan imaging temporal resolution. To our knowledge, this is the first demonstration of real-time photoacoustic imaging of human physiological dynamics. Our results show that UA-PAM can potentially enable many new possibilities for studying functional and physiological dynamics in both preclinical and clinical imaging settings.
TL;DR: Hemodynamic load provoked by isometric exercise strongly predicts LVMI in hypertension, suggesting that provoked testing captures important arterial properties that are not apparent at rest and is advantageous to assess dynamic arterial load in hypertension.
Abstract: Although resting hemodynamic load has been extensively investigated as a determinant of left ventricular (LV) hypertrophy, little is known about the relationship between provoked hemodynamic load a...
TL;DR: Pulsatile flow of blood through mild stenosed narrow arteries is analyzed by treating the blood in the core region as a Casson fluid and the plasma in the peripheral layer as a Newtonian fluid, finding that the pressure drop, plug core radius, wall shear stress and resistance to flow increase with the increase of the yield stress or stenosis size while all other parameters held constant.
TL;DR: Findings indicate that the SBP2, an estimate of central SBP, is significantly associated with the presence of SVD in an apparently healthy general population.
TL;DR: This investigation tested the hypothesis that pulsatile left ventricular assist synchronized to the cardiac cycle provides superiorleft ventricular unloading and circulatory support compared with continuous-flow left Ventricular assist devices at the same level of ventricular assistance device flow.
TL;DR: Next-generation MCS device development should ideally implement designs that offer the benefits of rotary pump technology while providing the physiologic benefits of pulsatile end-organ perfusion.
Abstract: A growing population experiencing heart failure (100 000 patients/year), combined with a shortage of donor organs (less than 2200 hearts/year), has led to increased and expanded use of mechanical circulatory support (MCS) devices. MCS devices have successfully improved clinical outcomes, which are comparable with heart transplantation and result in better 1-year survival than optimal medical management therapies. The quality of perfusion provided during MCS therapy may play an important role in patient outcomes. Despite demonstrated physiologic benefits of pulsatile perfusion, continued use or development of pulsatile MCS devices has been widely abandoned in favor of continuous flow pumps owing to the large size and adverse risks events in the former class, which pose issues of thrombogenic surfaces, percutaneous lead infection, and durability. Next-generation MCS device development should ideally implement designs that offer the benefits of rotary pump technology while providing the physiologic benefits of pulsatile end-organ perfusion.
TL;DR: In vitro investigation with pulsed Doppler ultrasound using the complete spectral data to investigate the three-dimensional distribution of advanced parameters that may have potential for making a more specific in vivo diagnosis of carotid disease and stroke risk demonstrated the importance of plaque shape, which is typically not considered in standard diagnosis, in addition to stenosis severity.
Abstract: Hemodynamics play a significant role in stroke risk, where thrombus formation may be accelerated in regions of slow or recirculating flow, high shear and increased turbulence. An in vitro investigation was performed with pulsed Doppler ultrasound (DUS) using the complete spectral data to investigate the three-dimensional (3-D) distribution of advanced parameters that may have potential for making a more specific in vivo diagnosis of carotid disease and stroke risk. The effect of stenosis symmetry and the potential of DUS spectral parameters for visualizing regions of recirculation or turbulence were explored. DUS was used to map pulsatile flow in four model geometries representing two different plaque symmetries (eccentricity) and two stenosis severities (mild, severe). Qualitative comparisons were made with flow patterns visualized using digital particle imaging. Color-encoded maps of DUS spectral parameters (mean velocity, spectral-broadening index and turbulence intensity) clearly distinguished regions of slow or recirculating flow and disturbed or turbulent flow. Distinctly different flow patterns resulted from stenoses of equal severity but different eccentricity. Noticeable differences were seen in both the size and location of recirculation zones and in the paths of high-velocity jets. Highly elevated levels of turbulence intensity were seen distal to severe stenosis. Results demonstrated the importance of plaque shape, which is typically not considered in standard diagnosis, in addition to stenosis severity.
TL;DR: Speed modulation in the CFTAH could enable physicians to obtain desired pressure waveforms by simple manual adjustment of speed control input waveforms, including pulsatile pulmonary arterial waveform.
Abstract: This study demonstrated the concept of using speed modulation in a continuous-flow total artificial heart (CFTAH) to shape arterial pressure waveforms and to adjust pressure pulsatility. A programmable function generator was used to determine the optimum pulsatile speed profile. Three speed profiles [sinusoidal, rectangular, and optimized (a profile optimized for generation of a physiologic arterial pressure waveform)] were evaluated using the CFTAH mock circulatory loop. Hemodynamic parameters were recorded at average pump speeds of 2,700 rpm and a modulation cycle of 60 beats per minute. The effects of varying physiologically relevant vascular resistance and lumped compliance on the hemodynamics were assessed. The feasibility of using speed modulation to manipulate systemic arterial pressure waveforms, including a physiologic pressure waveform, was demonstrated in vitro. The additional pump power consumption needed to generate a physiologic pulsatile pressure was 16.2% of the power consumption in nonpulsatile continuous-flow mode. The induced pressure waveforms and pulse pressure were shown to be very responsive to changes in both systemic vascular resistance and arterial compliance. This system also allowed pulsatile pulmonary arterial waveform. Speed modulation in the CFTAH could enable physicians to obtain desired pressure waveforms by simple manual adjustment of speed control input waveforms.
TL;DR: Three-dimensional pulsatile flow simulations through the hinge of a BMHV under aortic conditions reveal the presence of flow patterns known to be detrimental to blood elements, underscores the need to conduct three-dimensional simulations throughout the cardiac cycle.
Abstract: Thromboembolic complications of bileaflet mechanical heart valves (BMHV) are believed to be due to detrimental stresses imposed on blood elements by the hinge flows. Characterization of these flows is thus crucial to identify the underlying causes for complications. In this study, we conduct three-dimensional pulsatile flow simulations through the hinge of a BMHV under aortic conditions. Hinge and leaflet geometries are reconstructed from the Micro-Computed Tomography scans of a BMHV. Simulations are conducted using a Cartesian sharp-interface immersed-boundary methodology combined with a second-order accurate fractional-step method. Physiologic flow boundary conditions and leaflet motion are extracted from the Fluid–Structure Interaction simulations of the bulk of the flow through a BMHV. Calculations reveal the presence, throughout the cardiac cycle, of flow patterns known to be detrimental to blood elements. Flow fields are characterized by: (1) complex systolic flows, with rotating structures and slow reverse flow pattern, and (2) two strong diastolic leakage jets accompanied by fast reverse flow at the hinge bottom. Elevated shear stresses, up to 1920 dyn/cm2 during systole and 6115 dyn/cm2 during diastole, are reported. This study underscores the need to conduct three-dimensional simulations throughout the cardiac cycle to fully characterize the complexity and thromboembolic potential of the hinge flows.
TL;DR: A numerical model is constructed for the simulation of the cardiovascular response in the heart failure condition under representative cases of pulsatile impeller pump support and results show that a constant pump speed is the most efficient work mode for the rotary pump.
Abstract: There is significant interest in the development and application of variable speed impeller-pump type ventricular assist devices designed to generate pulsatile blood flow. However, no study has so far been carried out to investigate the systemic cardiovascular response to various aspects of pump motion. In this article, a numerical model is constructed for the simulation of the cardiovascular response in the heart failure condition under representative cases of pulsatile impeller pump support. The native cardiovascular model is based on a previously validated model, and the impeller pump is modeled by directly fitting the pressure-flow curves that describe the pump characteristics. The model developed is applied to study circulatory dynamics under different degrees of phase shift and pulsation ratio in the pump motion profile. The characteristic variables are discussed as criteria for the evaluation of system response for comparison of the pulsatile flows. Simulation results show that a constant pump speed is the most efficient work mode for the rotary pump, and with the application of either a phase shift of 75% and a pulsation ratio of 0.5, or a phase shift of 42% and a pulsation ratio of 0.55, it is possible to generate arterial pulse pressure with the maximal magnitude of about 28 mmHg. However, this is achieved at the cost of reduced cardiac output and pump efficiency.
TL;DR: The results show that the flow downstream of a dysfunctional valve was characterized by abnormally elevated velocities and shear stresses as well as large scale vortices which can predispose to blood components damage.
TL;DR: The data gave no support to the hypothesis that pulsatile ICP is higher within the CSF of the cerebral ventricles (ICPIV) than within the subdural (ICPSD) compartment or the brain parenchyma (ICPPAR) in iNPH patients.
Abstract: In patients with idiopathic normal pressure hydrocephalus (iNPH) and ventriculomegaly, examine whether there is a gradient in pulsatile intracranial pressure (ICP) from within the cerebrospinal fluid (CSF) of cerebral ventricles (ICPIV) to the subdural (ICPSD) compartment. We hypothesized that pulsatile ICP is higher within the ventricular CSF. The material includes 10 consecutive iNPH patients undergoing diagnostic ICP monitoring as part of pre-operative work-up. Eight patients had simultaneous ICPIV and ICPSD signals, and two patients had simultaneous signals from the lateral ventricle (ICPIV) and the brain parenchyma (ICPPAR). Intracranial pulsatility was characterized by the wave amplitude, rise time, and rise time coefficient; static ICP was characterized by mean ICP. None of the patients demonstrated gradients in pulsatile ICP, that is, we found no evidence of higher pulsatile ICP within the CSF of the cerebral ventricles (ICPIV), as compared to either the subdural (ICPSD) compartment or within the brain parenchyma (ICPPAR). During ventricular infusion testing in one patient, the ventricular ICP (ICPIV) was artificially increased, but this increase in ICPIV produced no gradient in pulsatile ICP from the ventricular CSF (ICPIV) to the parenchyma (ICPPAR). In this cohort of iNPH patients, we found no evidence of transmantle gradient in pulsatile ICP. The data gave no support to the hypothesis that pulsatile ICP is higher within the CSF of the cerebral ventricles (ICPIV) than within the subdural (ICPSD) compartment or the brain parenchyma (ICPPAR) in iNPH patients.
TL;DR: A new computer-controlled pulsator is constructed which can provide nearly physiological perfusion patterns during ECC and shows no advantage concerning organ perfusion or inflammatory response, even when using pulsatile flow patterns which mimic closely the physiological waveforms.
Abstract: Objective: Advocates of pulsatile flow postulate that the flow pattern during extracorporeal circulation (ECC) should be similar to the physiological one. However, the waveforms generated by clinically used pulsatile pumps are by far different from the physiological ones. Therefore, we constructed a new computer-controlled pulsator which can provide nearly physiological perfusion patterns during ECC. We compared its effect (group 1) with pulsatile (group 2) and non-pulsatile (group 3) perfusion generated by a conventional roller pump. Methods: Thirty pigs (10 per group) underwent 180 min ECC with an aortic cross-clamp time of 120 min. Pulse pressure, peak aortic flow, dp/dtmax, pulsatility index and energy-equivalent pressure were measured online. Renal and intestinal blood flow was calculated by fluorescent microspheres. The inflammatory response was assessed by the level of interleukin 6/1ra, the haemolysis by the free haemoglobin, and the escape rate of plasma protein by the disappearance rate of Evans Blue dye. Results: When compared to the preoperative curves, pulsatile waveforms during ECC were similar in group 1 and severely damped in group 2. Inflammatory response increased without significant differences between the groups. There were no differences between groups in renal and bowel blood flow. Free haemoglobin after ECC was higher in the pulsatile groups (group 1 = 43 � 144 mg dl � 1 , group 2 = 40 � 164 mg dl � 1 , group 3 = 11 � 4m g dl � 1 ; group 1 vs 2 (ns); group 1 or 2 vs 3 (p < 0.001)). The escape rate of Evans Blue increased after ECC in group 1 1.8-fold (p < 0.05), in group 2 1.45-fold (p < 0.05) and in group 3 1.27-fold (ns). Conclusion: Even when using pulsatile flow patterns which mimic closely the physiological waveforms, there is no advantage concerning organ perfusion or inflammatory response. Moreover, the extent of haemolysis and capillary leak is higher compared to non-pulsatile perfusion. Efforts to optimise pulsatility are not justified.
TL;DR: The ratio between the characteristic time scale of transport by the mean flow across the neck and the time Scale of vortex ring formation can be used to predict for a given sidewall aneurysm model the critical value of the waveform PI for which the hemodynamics will transition from the cavity mode to the vortex ring mode.
Abstract: High-resolution numerical simulations are carried out to systematically investigate the effect of the incoming flow waveform on the hemodynamics and wall shear stress patterns of an anatomic sidewall intracranial aneurysm model. Various wave forms are constructed by appropriately scaling a typical human waveform such that the waveform maximum and time-averaged Reynolds numbers, the Womersley number (α), and the pulsatility index (PI) are systematically varied within the human physiologic range. We show that the waveform PI is the key parameter that governs the vortex dynamics across the aneurysm neck and the flow patterns within the dome. At low PI, the flow in the dome is similar to a driven cavity flow and is characterized by a quasi-stationary shear layer that delineates the parent artery flow from the recirculating flow within the dome. At high PI, on the other hand, the flow is dominated by vortex ring formation, transport across the neck, and impingement and breakdown at the distal wall of the aneurysm dome. We further show that the spatial and temporal characteristics of the wall shear stress field on the aneurysm dome are strongly correlated with the vortex dynamics across the neck. We finally argue that the ratio between the characteristic time scale of transport by the mean flow across the neck and the time scale of vortex ring formation can be used to predict for a given sidewall aneurysm model the critical value of the waveform PI for which the hemodynamics will transition from the cavity mode to the vortex ring mode.