PURPOSE: The objective of the present study is to investigate the steady and pulsatile flow phenomena of the blood substitute fluids in the circular and bifurcated vessels numerically and experimentally. METHODS: The particle image velocimetry (PIV) is adopted to visualize the flow fields in the circular and bifurcated vessels. In order to analyse the complex flow phenomena of the blood substitute fluids in the bifurcated vessel, the constitutive equations which are suitable to describe the rheological properties of the non-Newtonian fluids are determined and the steady and unsteady momentum equations are solved by the finite volume prediction. RESULTS AND CONCLUSION: Velocity vectors of the steady flow in the bifurcated tube obtained by the PIV system are in good agreement with those obtained by the numerical analysis. The experimental and numerical results show the recirculation zone in the outer wall distal to bifurcation.
Blood Substitutes* ; Pulsatile Flow* ; Rheology*

PURPOSE: Characteristics of pulsatile flow in 3-dimensional arterial geometry and elastic vessel wall should be investigated in order to understand the physiological blood flow in human body. In this study, the modelling of the physiological blood flow in the elastic blood vessel is proposed. METHODS: The finite volume predictions are used to analyse the pulsatile flow characteristics in the elastic blood vessel. RESULTS AND CONCLUSION: Variations of the pressure and the velocity waveforms are obtained using the proposed modelling. The magnitudes of the pressure waveforms in the elastic blood vessel model are bigger than those of the rigid blood vessel model.
Blood Vessels* ; Human Body ; Pulsatile Flow*

This article introduces a new method using the servo motor which is controlled by ARM microcontroller to provide power for a pulsatile blood pump to beat. This method is featured with straightforward structure, accurate control, excellent timeliness, stable performance and small noise. And it can adjust the rate of beat, the rate of flow and the compression ratio according to actual demand.
Algorithms ; Heart-Assist Devices ; Models, Cardiovascular ; Pulsatile Flow

The parallel-plate flow chamber (PPFC) with rectangular shape, of which the height is far smaller than its own length and width, is one of the main apparatus for in vitro studies of the mechanical behavior of the cells. Considering that the Reynolds numbers of flows in the usually used PPFCs are small, a perturbation solution of laminar pulsatile Casson fluid in the PPFC is presented using Reynolds number as perturbation parameter. Furthermore, the velocities and shear stresses in the PPFC are given. The numerical results demonstrate that under the same pressure gradient the shear stresses are almost identical between Casson fluid and Newtonian fluid, whereas under the same flux the shear stresses are obviously different between Casson fluid and Newtonian fluid. The results in this paper provide a theoretical way to determine the shear stresses in the parallel-plate flow chamber under pulsatile Casson fluid.
Algorithms ; In Vitro Techniques ; Models, Cardiovascular ; Pulsatile Flow ; Stress, Mechanical

PURPOSE: To determine the effect of anglulation between aorta the and renal artery on signal loss in theproximal renal artery, as seen on magnetic resonance angiography by phantom study using a pulsatile flow model. MATERIALS AND METHODS: Three phantoms of aorta and renal artery with angulation of 90 degree, 60 degree, and 30 degree wereobtained. Pulsatile recirculating flow (44%W/W glycerin, 60bpm) was used for MR angiography. First, axial 3D-TOFimages were obtained and reconstructed. MIP images were analyzed for the presence, area, and location of signalloss. 2D-PC images were obtained perpendicularly to the renal artery at a distance of 0, 4, 8 and 12mm from theostium. To calculate mean signal intensity of the renal artery, a ROI was drawn on 2D-PC images. To correlatesignal loss in 3D-TOF images with signal decrease in 2D-PC, we analyzed changes in signal intensity during onepulse cycle according to change of angulation and distance from the ostium of the renal artery by the calculatedvalues of relative signal decrease and ratio of signal decrease. RESULTS: A signal loss was observed up to 4mmfrom the ostium of the renal artery only in the case of the 90 degree phantom. Because the signal intensity measured inthe 2D-PC image of the 90 degree phantom was higher than that of the 60 degree phantom the signal loss observed in the3D-TOF images of the 90 degree phantom could not be explained by the magnitude of measured signal intensity alone.Relative signal decrease only at a distance of 0 and 4mm in the 90 degree phantom was evenly increased through a pulsecycle and the ratio of signal decrease at the same location was more than 50%. In contrast to the results of the90 degree phantom, those of 60 degree and 30 degree showed decreased of signal intensity mainly during the diastolic phase.CONCLUSION: Signal loss should become apparent at a certain angle between 60 degree and 90 degree. Decreased signalintensity causing signal loss in 3D-TOF was maintained throughout the systolic and diastolic phase of a pulsatilecycle and correlated with the ratio of signal decrease.
Angiography ; Aorta* ; Glycerol ; Magnetic Resonance Angiography ; Pulsatile Flow ; Renal Artery*

Producing accurate pulsatile flow rates is essential for many in vitro experimental studies in biofluid dynamics research. A controller system was developed to control a flow loop to produce easily adjustable pulsatile flow rates with sufficient accuracy. An Arduino board is used as a micro-controller to control a pump to produce various pulsatile flow rates, and an open-source proportional-integral-derivative (PID) control algorithm is developed for this purpose. Four non-trivial pulsatile waveforms were produced by the PID controller, as well as an iterative controller, and the performance of both controllers was evaluated. Both the PID and iterative controllers were able to successfully produce slowly-varying signals (single and multi-harmonic low frequency sine waves), but for high frequency signals where the flow has strong acceleration/deceleration (e.g. for physiological waveforms) the iterative controller exhibited significant undershoot. The comparison of PID and iterative controllers suggests that if the desired flow rate is a low frequency, simple waveform then the iterative controller is preferred due to simplicity of implementation. However, if the desired signal is rapidly changing and more complicated then the PID controller achieves better results. This system can be implemented in many flow loops due to its simplicity and low cost, and does not require a mathematical model of the system.
Carotid Artery, Common ; In Vitro Techniques* ; Models, Theoretical ; Pulsatile Flow*

In this paper the theory of autocorrelation algorithm for color flow mapping is analyzed and a new way for ultrasound color flow velocity estimation and real-time display is proposed. The method sets up a mapping table which directly relates to the dynamic display range and has only 256 entries using an inverse mapping method instead of calculating the arctangent value directly. This method is ideal for software implementation and offers an interactive way to the user for changing the dynamic range of flow velocity and thus to increasing the display resolution.
Algorithms ; Blood Flow Velocity ; Humans ; Pulsatile Flow ; physiology ; Rheology ; instrumentation ; Ultrasonography, Doppler, Color ; instrumentation ; methods

Pulsatile blood flow plays an important role in maintaining normal vascular endothelial function. Quantitative measurement of pulsatility of artery blood pressure and blood flow in dogs and effects of enhanced external counterpulsation (EECP) on the pulsatility were taken in this study. Common carotid artery blood pressure and blood flow were measured in 6 beagle dogs that had suffered from an acute myocardial infarction 6 weeks before. A 6F tip transducer catheter was inserted into the right common carotid artery to measure blood pressure, and blood flow was measured in the left common carotid artery by an electromagnetic blood flow probe under anesthesia before and during EECP. Blood pulse pressure, pulsatility index (ratio of peak pressure to end diastolic pressure) and standard deviation of blood pressure were calculated to evaluate the pulsatility of arterial blood pressure. Blood pulse flow, pulsatility index (ratio of peak flow to trough flow) and standard deviation of blood flow were calculated to evaluate the pulsatility of blood flow. Mean vascular resistance (MVR) was calculated as MVR = mean blood pressure/mean blood flow. Blood pulse pressure, pulsatility index and standard deviation of blood pressure were elevated from 30 +/- 9 mmHg, 1.26 +/- 0.05 and 8.7 +/- 2.5 mmHg to 43 +/- 8 mmHg (P < 0.05), 1.54 +/- 0.13 and 12.4 +/- 2.0 mmHg (P < 0.05) before and during EECP, respectively. Blood pulse flow, pulsatility index and standard deviation of blood flow were elevated from 317 +/- 48 ml/min, 2.85 +/- 0.21 and 96 +/- 21 ml/min to 447 +/- 88 ml/min, 4.56 +/- 0.90 and 131 +/- 39 ml/min before and during EECP (P < 0.05). MVR was decreased from 578 +/- 72 before EECP to 476 +/- 85 Wood units during EECP(P < 0.05). These data demonstrate that EECP gives an elevation of pulsatility to blood pressure and blood flow, thus it may lead to the decrease of vascular resistance.
Animals ; Blood Pressure ; Carotid Arteries ; physiology ; Counterpulsation ; Dogs ; Hemodynamics ; Pulsatile Flow ; Regional Blood Flow ; Vascular Resistance

To understand the local hemodynamics of modified TF-AHCB carotid bifurcation model, using particle image velocimetry technique to measure the instantaneous velocity distribution of the model attatched to a circuit. The velocity was controlled by regulating the height of the reservoir. The working fluid consists of glycerine and water mixture with viscosity of 3.75 mPa.s similar to human blood. Instantaneous velocity fields were obtained by PIV and the shear stresses were calculated according to the velocity. The results showed that inside the model, there were a large flow separation and an anticlockwise rotating vortex on the lateral wall of ICA, The location and distance of the vortex changed with the flow velocity. The higher the flow velocity, the smaller the vortex distance, and the farther the location. The shear stresses on the lateral wall were significantly lower in all work condition. And there a low shear stress kernel when the velocity was lower than 0.839 m/s. The location of the low shear stress was just the position of atherosclerosis. The flow pattern inside the model consists of large flow separation and vortex zones. And there are low shear stress zones at the lateral wall of ICA, Where are thought to be associated with the genesis of atherosclerosis.
Blood Flow Velocity ; Carotid Arteries ; physiology ; Models, Cardiovascular ; Pulsatile Flow ; Regional Blood Flow ; physiology ; Rheology ; methods ; Stress, Mechanical

PURPOSE: The image quality of magnetic resonance angiography (MRA) varies according to the imaging techniques applied and the parameters affected by blood flow patterns, as well as by the shape of the blood vessels. This study was designed to assess the influence on signal intensity and its distribution of the geometry of these vessels, the imaging parameters, and the concentration of contrast media in MRA of stenosis and aneurysm models. MATERIALS AND METHODS: MRA was performed in stenosis and aneurysm models made of glass tubes, using pulsatile flow with viscosity and flow profile similar to those of blood. Slice and maximum intensity projection (MIP) images were obtained using various imaging techniques and parameters ; there was variation in repetition time, flip angle, imaging planes, and concentrations of contrast media. On slice images of three-dimensional (3D) time-of-flight (TOF) techniques, flow signal intensity was measured at five locations in the models, and contrast ratio was calculated as the difference between flow signal intensity (SI) and background signal intensity (SIb) divided by background signal intensity or (SI-SIb)/SIb. MIP images obtained by various techniques and using various parameters were also analyzed, with emphasis in the stenosis model on demonstrated degree of stenosis, severity of signal void and image distortion, and in the aneurysm model, on degree of visualization, distortion of contour and distribution of signals. RESULTS: In 3D TOF, the shortest TR (36 msec) and the largest FA (50 degree) resulted in the highest contrast ratio, but larger flip angles did not effectively demonstrate the demonstration of the peripheral part of the aneurysm . Loss of signal was most prominent in images of the stenosis model obtained with parallel or oblique planes to the flow direction. The two-dimensional TOF technique also caused signal void in stenosis, but precisely demonstrated the aneurysm, with dense opacification of the peripheral part. The phase contrast technique showed some distortions in the imaging of stenosis, and partial opacification of ananeurysm. Contrast enhanced imaging offered no advantages in the imaging of the stenosis, but was excellent for demonstration of the aneurysm. CONCLUSION: This study demonstrates a spectrum of MRA images of stenosis and aneurysm model according to variation in imaging parameters and the concentration of contrast media.
Aneurysm* ; Angiography* ; Blood Vessels ; Constriction, Pathologic* ; Contrast Media* ; Glass ; Magnetic Resonance Angiography ; Pulsatile Flow* ; Viscosity