Pulsatile Flow Rate Research Articles

Aortic Doppler velocity measurement and cardiac function in the fetal lamb

Aortic haemodynamic parameters, and Doppler waveforms in particular, were investigated in acute experiments with fetal lambs. Cardiovascular changes were produced by central infusion of the drugs esmolol and dopamine. Pulsed Doppler waveforms were obtained from the descending thoracic aorta, simultaneous with recordings of pulsatile aortic volume flow rate, diameter and blood pressure. The relation between Doppler-derived velocities and the corresponding full vessel lumen velocities was shown to be fairly linear and consistent across different animals. The aortic volume flow per beat decreased with esmolol ( p < 0.003, repeated measures ANOVA); the Doppler and vessel lumen mean velocities also decreased, whether measured only at peak systole or over the full cardiac cycle (at most p < 0.003). With dopamine the aortic flow per beat increased ( p < 0.001), as did the Doppler and vessel lumen mean velocities (at most p < 0.02). An inverse relation between the aortic flow per beat and the peripheral resistance was observed. To identify inotropic changes in the presence of vascular effects, a theoretical model based on cardiac power output changes was implemented. The data were divided into three groups, according to whether the model did or did not identify a definite inotropic effect (positive or negative). The Doppler velocity changes for these three groups were different ( p < 0.0001). The mean Doppler velocity increased by 7 cm s −1 in the positive inotropic effect group, and decreased by 4 cm s −1 in the negative group. The aortic flow parameters of the human fetus are very similar to those of the fetal lamb. Decreased aortic velocities have been reported in human fetal compromise, and the results of this study support the hypothesis that this can be evidence of impaired fetal cardiac function.

Pulsatile flow visualization in a model of the human abdominal aorta and aortic bifurcation

The infrarenal abdominal aorta and aortic bifurcation are frequent sites of atherosclerosis. The local hemodynamics are considered to be atherogenetic factors; a detailed description of these flow fields is, therefore, essential to understand their relationship to atherosclerosis. The aim of this study was, therefore, to provide such detailed information using a flow visualization technique in an anatomically realistic flow model of the abdominal aorta and its main branches in which the complex pulsatile flow waveforms and flow rates were simulated for two physiologic flow conditions (rest and exercise). At rest, the particle path lines in the suprarenal abdominal aorta were straight with no visible signs of flow reversal. Vortices were initiated opposite to the main branches. In the infrarenal aorta, large flow separation zones formed at the posterior aortic wall and at the lateral walls in the aortic bifurcation during systolic deceleration, and flow reversal was present during diastole. Under exercise conditions, the particle path lines were straight, and only slight flow reversal was seen. This study emphasizes, that rather than being a straight tube with forward-moving fluid, the abdominal aorta has to be considered as a complex part of the arterial tree. Distinct local hemodynamic qualities of importance for explaining atherogenesis were pointed out. At rest, the suprarenal abdominal aorta had much less complicated flow characteristics than the infrarenal abdominal aorta where the distal, posterior vessel wall and the lateral walls of the bifurcation were sites of flow patterns thought to be associated with atherosclerosis. During exercise, the infrarenal flow patterns changed dramatically away from the flow patterns associated with the induction of atherosclerosis.

Clinical studies of cranial and spinal compliance and the craniospinal flow of cerebrospinal fluid.

The cranial compartment contributed 37% and the spinal compartment 63% to the total compliance of the craniospinal space in the horizontal body position. In the erect position the values were almost reversed, the cranial compartment contributing 66% and the spinal compartment 34%. The total compliance was almost unaffected by body position. The pulsatile volume of cerebrospinal fluid (CSF) moving between the cranial and spinal compartments was about 1 ml in the horizontal position. The corresponding pulsatile change in cerebral blood volume was calculated to be 1.6 ml. A craniospinal block increased the intracranial pressure amplitude by 110% in the horizontal position. The volume of CSF moving between the cranial and spinal compartments when sitting up and lying down, was about 3 ml. The pulsatile and postural flow rate of CSF may reach about 200 ml/min. High CSF flow velocity may impair the protective coating of CSF around the brain and thus contribute to herniation.

A Comparative Flow Study of the Omniscience and the Björk-Shiley Cardiac Valve Prostheses

The pressure-flow rate characteristics of two new convex-concave pivoting disc prosthetic heart valves are evaluated in vitro. The Omniscience and Björk-Shiley prostheses are chosen since both use curved occluders with similar dynamic function, but with different occluder curvature and eccentricity. The Omniscience prosthesis is shown to have consistently less pressure loss, and therefore less energy loss, over a range of steady state and pulsatile flow rates. The enhanced flow characteristics of the Omniscience valve are attributed to the larger opening angle of the occluder, the method of retaining the occluder, in the valve frame, the smaller curvature of the occluder, the smaller pivot-axis eccentricity, and the smaller profile thickness of the occluder. The valves are also tested in the closed position, with steady state pressure gradients causing leakage or backflow. This data is compared with the pulsatile pressure-flow rate data to gain insight into the nature of regurgitation. The total regurgitation of the pivoting disc valves are thought to be strongly dependent upon both the maximal opening angle of the occluder and the radial clearance between the disc and the valve orifice. Both the Omniscience valve and the Björk-Shiley valve are found to have nearly equal volumes of total regurgitation.

Laser anemometry measurements of pulsatile flow past aortic valve prostheses

Experimental results are presented on physiological pulsatile flow past caged ball and tilting disc aortic valve prostheses mounted in an axisymmetric chamber incorporated in a mock circulatory system. The measurements of velocity profiles and turbulent normal stresses during several times in a cardiac cycle were obtained using laser-Doppler anemometry. Our results show that with increased angle of opening for the tilting disc valves, a large but locally confined vortex is observed along the wall in the minor flow region throughout most of the cardiac cycle. The turbulent normal stresses measured downstream to the tilting disc in the minor flow region parallel to the tilt axis were found to be larger than those measured downstream to the caged ball valves. Comparison of measurements with steady flow at flow rates comparable to peak pulsatile flow rate show that the turbulent normal stresses are larger by a factor of two in pulsatile flow with a frequency of 1.2 Hz.

Myocardial contract ity:non-invasive assessment after cardiac surgery

The shape of the carotid blood-flow signal in the assessment of myocardial contractility is important. The non-invasive electromagnetic method permits the measurement of the pulsatile carotid flow rate and thus to estimate the maximum blood flow acceleration (max. dF/dt), which is directly related to myocardial contractility. The electromagnetic flowmeter method, routinely used in the superficial arteries of arteriosclerotic patients, has been modified to record the blood flow rate in the carotid artery. Two ECG electrodes on both sides of the common carotid artery record the signal given by a small magnet located above the electrodes. Using this method, we have studied the effects of isoprenaline infusion in a normal subject. In patients after cardiac surgery we measured max. dF/dt in the region of the carotid artery and compared changes in it with parameters obtained by invasive methods such as the cardiac index, and the pulmonary and systemic pressures. The first results of blood flow recordings in the ascending aorta are presented here.

Determination of pulsatile flow rates by indicator-dilution methods

A new method is proposed for measuring nonsteady flow rates when this flow is pulsatile in nature. This method involves the use of indicators and does not require direct access to the vessel carrying the fluid. No knowledge of the associated mathematics is required for its application. The investigator infuses indator into the vessel leading into a capillary or similar labyrinth at a time-varying rate such that the indicator concentration at the outflow from the labyrinth remains constant in time. When this condition at the outflow has been achieved, the pulsatile flow rate at the inflow is given simply as the ratio of the varying infusion rate to the constant outflow indicator concentration.