Behavior Of Pulsatile Flow Research Articles

Experimental and theoretical analysis of pulsatile flow in elastic tubes: Wave propagation and attenuation

The objective of this study was to comprehensively examine the pulsatile flow behavior within an elastic tube using experimental and theoretical approaches. This work is an extension of our earlier report [Roknujjaman et al., Phys. Fluids, 34, 123612 (2022)]. In this paper, we adapted a quasi-one-dimensional model to elucidate the wave propagation and pulse attenuation phenomena in an elastic tube and compared with experimental findings. According to our investigation, the key findings were as follows: the experimental and predicted flow wave propagation trend agreed well. Additionally, because of the silicon tubes greater deformation than the urethane tubes, the pulsation was decreased farther in the silicon tubes than in the urethane ones. Furthermore, because of the reflected wave near the tube exit, the pulsations amplitude significantly increased, but it did not enlarge when the resistance was installed at the exit. Finally, we infer that the quasi-one-dimensional model is a better fit for experimental results compared to the two-dimensional model.

Optimization and extraction of functional information fromin vitroflow models using dual-beam spectral-domain optical coherence tomography cross-correlation analysis

As in vivo flow behavior can be pulsatile, intermittent, and/or otherwise changeable with time, the ability to provide clinicians with a means of real-time visualization and functional assessment of structures is of particular importance. The discernment of pulsatile flow behavior using a dual-beam spectral domain optical coherence tomography system (db-SdOCT) by quasi-simultaneous measurement by two planes of illumination is demonstrated. By cross-correlation analysis, it is possible to compute velocity metrics pertaining to flowing particle motion, without a priori angular knowledge. This is the first application of cross-correlation-based dynamic assessment for the extraction of pulsatile behavior in an in vitro environment using an optimized db-SdOCT system. The experimental results outlined have shown the db-SdOCT system and its associated algorithms to be successful in the discernment of intermittent pulsatile flow behavior in in vitro models, concurrent to yielding velocity values in good agreement with that of the applied flow rate.

B110 脳動脈瘤内血流動態の数値解析と実験的検証

This paper presents CFD results of steady and pulsatile flow behavior in a cerebral aneurysm and their comparison with in vitro measurements taken with a stereoscopic PIV technique and a miniature pressure probe. A commercial CFD code based on FVM is utilized with a computational grid system that is defined from a 3-D shape of a patient's cerebral aneurysm. The aneurysm considered here has experienced the rapture in the tip of the main body of the aneurysm. Both a long entrance region and a fine mesh near the aneurysm wall are defined in the computational grid system in order to permit a direct comparison with the measurement. The CFD results obtained thus for steady and pulsatile flows show good agreement with the measurements. The CFD results are analyzed and discussed in detail to reveal the flow behaviors that are responsible for the wall shear stress and the wall pressure inside the aneurysm.

B222 Dynamic PIVを用いた血管モデル内拍動流の時系列計測

This paper aims to investigate behavior of pulsatile blood flow in a curved pipe that emulates the Internal Carotid Artery (ICA), which is the frequent occurrence site of an aneurysm. Due to the limit of in vivo experiment, the PIV (Particle Image Velocimetry) is applied to obtain detailed flow information such as complicated secondary flow created by curvature of in vitro experiment. However, the blood flow in the artery is pulsatile, and time-resolution of the conventional PIV is not enough to capture transient behavior of pulsatile flow. Thus, the dynamic PIV is applied to measure unsteady flow. Since the dynamic PIV can provide good resolution in space as well as in time.As a result of measurement, even with the same Reynolds number, flow characteristics at systole are drastically different from those at diastole. Especially at the time of diastole, the large recirculation flow, which is not seen in steady flow, is observed in the separation region. The secondary flow in the cross section changes according to changes of flow rate in time.

Numerical simulation of steady flow fields in a model of abdominal aorta with its peripheral branches

In the present study, a numerical calculation procedure based on a finite volume method was developed to simulate steady flow fields in a model of abdominal aorta with its peripheral branches. The study focused on the steady baseline flow fields and the wall shear stress (WSS) distribution as well as the localization of the reversed flow regions and results were compared to those obtained by other investigators. In the case of resting conditions, the existence of a region of reversed flow of about one to two diameters in size and next to the renal arteries and along the posterior wall as observed by other researchers was confirmed. However, under the exercise conditions this region could be wiped out. The flow reversal along the lateral walls proximal to the bifurcation persisted in both rest and exercise conditions. The WSS distribution and the wall shear stress gradient distribution were obtained. The lowest WSS occurred near the ostia of the renal arteries and the lateral walls of the iliac arteries. And the highest is always at the turn to the branch. The results were generally consistent with those obtained experimentally and numerically by other investigators. It was also shown that the steady flow might be used to depict the averaged behavior of pulsatile flow. The present computer code provides a platform for the future more realistic simulations.

Comparison of physiological and simple pulsatile flows through stenosed arteries

Most experimental and numerical studies of pulsatile flow through stenosed arteries have been performed for a first harmonic oscillatory flow. In this paper, numerical solutions are presented for a physiological pulsatile flow as well as for an equivalent simple pulsatile flow, having the same stroke volume as the physiological flow, and the differences in their flow behavior are discussed. The analysis is restricted to laminar flow, Newtonian fluid and axisymmetric rigid stenosis. Comparison of results shows that the behaviors of the two flows are similar at some instances of time, however, important observed differences indicate that for thorough understanding of pulsatile flow behavior in stenosed arteries, the actual physiological flow should be simulated.

Laminar and turbulent flow in the mammalian aorta: Reynolds number

Laminar to turbulent flow transition in the mammalian aorta is generally characterized by Reynolds number. When dimensional analysis is applied to obtain the Reynolds number in allometric form, it is found that this number is not invariant of body weight but is approximately proportional to body length dimensions. This implies that flow in the aorta of large mammals is turbulent and laminar in smaller mammals during most of ventricular ejection. Since Reynolds number is defined for steady flow through rigid tubes, it may not reflect the actual fluid behavior of pulsatile flow in compliant vessels such as the aorta. In addition, turbulence is frequency dependent. The larger compliance of the aorta and the slower heart rate in larger mammals and the shorter entrance length and higher heart rate in smaller mammals lead to equal prevalence of turbulence. The consequence is that the aortic flow waveforms remain similar in all mammals.

Rheology and hemodynamics.

The mechanisms of red cell aggregation and cell deformation can impart viscoelastic behavior to blood: at very high hematocrits, the cell deformation mechanism dominates; at physiological and low hematocrits, red cell aggregation dominates at low shear rates. At physiological hematocrits, the viscoelastic behavior may be linear at low shear rates, where the elastic component of the complex viscosity may be comparable in magnitude to the viscous component; in the higher shear rate region, where red cell aggregation is less extensive or absent, blood behavior is nonlinear, and the elastic component becomes less significant. The nonadditivity of steady and oscillatory flow data for prediction of pulsatile flow behavior is indicative of the importance of the mean shear rate and the kinetics of the red cell aggregation-disaggregation processes in governing pulsatile blood flow. While oscillatory measurements will be useful in assessing rheological parameters that may give insight into the fundamental aspects of flow of normal and pathological bloods, it is not clear that the elastic component of the complex viscosity of blood will be of significance in physiological pulsatile flow. Many interesting questions remain to be answered, such as the question raised by the finding that normal stress differences were not detectablemore » for blood under low shear rates. Judging from the number of papers presented at the Third International Congress of Biorheology, we can look forward to considerable activity in this area.« less