Showing papers on "Pulsatile flow published in 1978"

Fluid dynamics of coronary artery stenosis.

Abstract: A large-scale model of the coronary circulation, instrumented to permit detailed pressure and velocity measurements, has been used to study flow through isolated stenotic elements in large coronary arteries. Pulsatile aortic and instantaneous peripheral resistance were stimulated with servovalves. A variety of axisymmetric and asymmetric stenoses were studied and flow separation was found to occur for all but very mild stenoses. Pressure recovery downstream of the stenosis throat was limited and, in some cases, no recovery was observed. Pressure drop was primarily dependent upon the minimum area of the stenosis and relatively independent of stenosis geometry. Flow was quasi-steady at normal heart rates, and simple steady flow theory proved adequate to describe the pressure drop through the stenosis. The theory yielded results that agreed well with published data for dogs and appears promising for predicting effects of hemodynamic variables on a given stenotic lesion. Thus, principal findings of the study are that a relatively severe stenosis behaves essentially like an orifice and that a simple quasi-steady theory appears adequate to predict effects of a stenosis on coronary flow.

Aortic input impedance in heart failure.

Abstract: The input impedance of the systemic circulation was calculated from recordings of pulsatile pressure and flow in the ascending aorta of 20 patients. Ten patients had clinical and hemodynamic evidence of heart failure. The other 10 subjects had no clinical evidence of heart failure and were used as a control group. In the heart failure patients, both input resistance and characteristic impedance (index of aortic distensibility) were significantly increased compared to pressure- and age-matched control subjects. Oscillations of impedance moduli, represented by the difference between maximum and minimum moduli, were also significantly increased in the heart failure patients compared with the control subjects. The increased characteristic input impedance in these heart failure patients suggests that the human aorta is stiffer in heart failure, and the larger oscillations in the impedance spectrum indicate an increase in pressure and flow wave reflections. From reflected wave theory in elastic tubes, reflected pressure waves add to the amplitude of incident pressure waves at the entrance of the system, whereas reflected flow waves subtract from the magnitude of the forward flow. Thus, changes in aortic distensibility could have an important influence on the pulsatile function of the failing left ventricle.

Acute effects of adrenergic receptor blocking drugs and neuroleptic agents on pulsatile discharges of luteinizing hormone in the ovariectomized rat.

Abstract: Blood samples were taken every 5 min for a 3-h period from ovariectomized (OVX) adult rats bearing chronic venous catheters. After 1 h of sampling, an experimental drug was injected through the sampling catheter. The neuroleptics, chlorpromazine and haloperidol, blocked pulsatile discharges of luteinizing hormone (LH) in some animals, for periods of 65–120 min, as did the α-adrenergic receptor blockers, phenoxybenzamine and phentolamine. Pimozide, a more specific dopaminergic blocking agent, had less effect, while neither the β-adrenergic receptor blocker, propranolol, nor the control treatments had any influence on the pulsatile LH patterns. The temporal pattern of inhibition of pulsatile discharges of LH by these drugs is more rapid than the inhibition caused by estrogen treatment in the OVX rat. These results suggest the presence of α, but not β, adrenergic elements in the pulsatile mode of LH release in the OVX rat. They do not support the presence of dopaminergic elements, but neither do they conclusively deny it.

The Sites of Action of Estradiol and Phentolamine in the Inhibition of the Pulsatile, Circhoral Discharges of LH in the Rhesus Monkey (Macaca mulatto)*

Abstract: Pulsatile LH secretion was re-established in ovariectomized monkeys bearing hypothalamic lesions by an intermittent infusion of LHRH. The administration of estradiol to such animals resulted in a prompt cessation of these pulsatile discharges of LH and a resultant decline in the mean plasma concentration of the gonadotropin. The time course of this inhibition of LH secretion was indistinguishable from that observed after estrogen administration to ovariectomized animals with intact nervous systems. In contrast, phentolamine did not interrupt the pulsatile LH discharges occasioned by the hourly administration of exogenous LHRH to the lesioned animals. These results are consistent with the conclusion that the acute negative feedback action of estradiol on circhoral LH release in the monkey is at the level of the pituitary gland, whereas the inhibitory action of phentolamine on this mode of LH secretion is at a neural site. (Endocrinology 102: 1015, 1978)

Ontogeny of pulsatile luteinizing hormone and testosterone secretion in male lambs.

Abstract: The ontogeny of pulsatile LH and testosterone (T) secretion was studied in the developing male sheep. Three variables of LH secretion (frequency of LH pulses, magnitude of LH pulses, and the levels between pulses) were determined during a 6-h period at each of 1, 2, 3, 5, 7, 8, 12, and 16 weeks of age in six male lambs. Pulsatile LH secretion was evident by 1-2 weeks of age in rapidly growing lambs and by 3-7 weeks of age in slowly growing lambs. Although mean height of LH discharges increased 2-fold after the onset of pulsatile release, levels between discharges remained constant throughout the entire study. The most striking change, however, occurred in the frequency of LH discharges. The frequency increased 20-fold between weeks 1 and 8 and then decreased 3-fold between weeks 8 and 16. In each lamb, a brief (less than 3 h), but marked rise (greater than 2 ng/ml) in levels of circulating T occurred after the first observed pulse of LH. Thereafter, as the lambs became older, increased concentrations of serum T were observed only during periods of pulsatile LH secretion, the highest mean level of T occurring about 1 h after each LH peak. Administration of human chorionic gonadotropin (hCG) iv to 2-day-old males resulted in a marked increase in circulating T. A greater increment in concentrations of serum T occurred after the same absolute dose (50 IU) of hCG at 8 weeks of age than at 2 days of age. These results indicate that in the male lamb 1) pulsatile secretion of LH is initiated shortly after birth and changes in mean levels of LH are primarily a reflection of changes in frequency of LH discharges; 2) before the onset of pulsatile LH secretion, the testes are capable of responding to an exogenous LH-like gonadotropin with increased secretion of T; 3) after the onset of pulsatile LH secretion, a rise in circulating T follows each pulse of LH; and 4) an increase in capacity of the testes to secret T occurs during the first 8 weeks of postnatal life. It is concluded that the pattern of LH secretion, coupled with the capacity of the testes to secrete T, determines the pattern and magnitude of T secretion in the developing male sheep.

Pulsatile blood pumping apparatus and method

Abstract: An intracorporeal, extracorporeal, cardiac assist, perfusion device or other pulsatile blood pumping system for circulating blood within living tissue under automatic control. Plural physiologic parameters of the tissue are monitored and utilized to control plural operating parameters of the pump during succeeding cycles of its operation so as to restore the monitored physiologic parameters to desired predetermined (but adjustable) values.

Elastic and inertial effects in pulsatile flow of polymeric liquids in circular tubes

Abstract: In the earlier theoretical work of Barnes, Townsend, and Walters on pulsatile flow of viscoelastic fluids, it was found that an Oldroyd model predicted that flow enhancement should decrease with increasing frequency of pulsation, whereas their experimental data showed an increase . Their calculations have been repeated for the Goddard—Miller model using two different expressions for the relaxation modulus; it is found that the Goddard—Miller model leads to the same discrepancy between theory and experiment. It is tentatively concluded that secondary-flow effects are playing an important role. The role of the elastic and inertial effects and the role of the shape of the viscosity vs. shear rate curve are discussed.

Influence of erythrocyte velocity on impedance plethysmographic measurements

Abstract: Impedance plethysmography has been widely used clinically. However, uncertainty exists concerning the source of the impedance signal. The present study was designed to indicate the relative contributions made by blood volume changes and blood flow changes. Anin vitro flow system containing a pulsatile pump, a bovine carotid artery, a rigid tube, and a terminal resis tance was assembled. Impedance recordings were made on both the expansile artery and the rigid tube. The impedance signal from the rigid tube was taken as the flow-related component. The signal from the expansile artery represented the combined effects of volume changes and flow changes. The recordings were made over the full physiological range of pulse pressures and peak flow values, using both normal saline and blood (haematocrit =26±4%). No impedance change was detected in the rigid vessel using saline as the perfusate. When blood was used, the impedance signal from the rigid tube averaged about 10% of that from the expansile vessel and its morphology was different. Changes in erthrocyte velocity produced a small but definite change in the impedance signal recorded from the artery.

The effect of distension of the pulmonary vein‐atrial junction on activity of left atrial receptors

Abstract: 1. In anaesthetized dogs, the activity from left atrial receptors with vagal afferent fibres has been examined during distension of small balloons in the pulmonary veins or the application of pulsatile pressures to an isolated perfused pouch of the left atrium. 2. Eleven fibres were found in nineteen dogs. The receptors discharging into these fibres were located, post mortem, to the atrial endocardium and reasons are given for believing that these fibres were myelinated and the receptors were B or Intermediate. 3. Distension of small balloons induced significant increases in the discharge of action potentials from the receptors, the increases were similar to those after infusions of saline or dextran. 4. In the perfused pouch the ‘dynamic’ thresholds for pulsatile pressure were high as were the mean and pulsatile pressures required to induce bursts of action potentials similar to those observed from atrial receptors in the atrium of normal size. Restoration of the atrium to its normal size resulted in ‘dynamic’ thresholds and responses to changes in pressure within the normal range. The changes could be explained assuming the Laplace relationship. 5. This evidence supports the conclusion from previous investigations in which these techniques were used, that the increase in discharge in atrial receptors with myelinated vagal fibres could be the cause of the increase in heart rate and urine flow.

Hemodynamics of arterial stenosis.

Abstract: In order to derive a better understanding of the effect of varying degrees of stenosis on arterial pulsatile waveforms, an in vitro model was constructed and in vivo studies were done in dogs to observe and record the changes in the pulsatile and steady arterial blood flow components. Blood flow measurements were made using the electromagnetic blood flowmeter proximal and distal to the stenosis. The data show that as the degree of stenosis increases, the decreases in the pulsatile components of flow and distal pressure occur earlier and to a much greater degree than changes in mean flow.

Pulsatile flow of a dusty fluid through a constricted channel

Abstract: The problem of pulsatile flow of a fluid, containing small solid particles, through a two-dimensional constricted channel is studied in view of its importance in arteriosclerosis. A perturbation solution is sought in terms of the slope of the channel. The effects of mass concentration of dust particles on the streamline pattern, axial velocities of the fluid and solid particles, shear stress and pressure distribution are studied.

Aortic input impedance and left ventricular energetics in acute isovolumic anaemia

Abstract: Ascending aortic impedance spectra and left ventricular energetics were studied before and for one hour following the rapid induction of anaemia in seven dogs anaesthetised with halothane N2O/O2. A control group of five dogs were similarly studied, using the same protocol, but mimicking the induction of anaemia by bleeding and immediate replacement of the shed blood. Anaemia (Hb 6.6 g·dl−1), induced by an isovolumic exchange-transfusion with Dextran 70, resulted in a significant decrease in the impedance modulus at zero frequency, and a slight reduction in the characteristic impedance (Z). No consistent changes were observed in the phase angle of impedance. The reduction in systemic vascular resistance after the induction of anaemia was associated with a significant rise in the heart rate and stroke volume, and significant increases were observed in both the steady and pulsatile components of left ventricular work. The administration of propranolol (0.2 mg·kg−1) 60 min after dextran-exchange resulted in a reversion of these indices to the pre-exchange control values. No significant changes were observed in the pulsatile to total work ratio. The absence of any significant increase in this ratio demonstrates that the efficiency with which the heart is ‘decoupled’ from the peripheral vascular bed by the impedance characteristics of the aorta is not compromised by the hyperdynamic circulatory state that is the consequence of an acutely induced anaemia. The reversion of the indices of left ventricular energetics to the pre-anaemia control values is interpreted as corroborative evidence for the existence of increased cardiac sympathetic drive during acute isovolumic anaemia.

A Method To Determine The Instantaneous Blood-Flow Using Cine- Or Video-Densitometric Data

Abstract: A new method for determining the time distribution of blood-flow within a vessel using x-ray imaging is presented. The method has been validated by both stationary and pulsatile flow experiments. The method is capable of determining average flow values under conditions of high pulsatile flow. The application of this method to cine-recorded data of aortic blood flow in dogs is in good agreement with the known shape of the aortic flow distribution. An application of this method to evaluate aortic regurgitation is shown.© (1978) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Pulsatile cerebral echo in diagnosis of brain death

Abstract: ✓ Conclusive diagnosis of brain death can be made by the demonstration of prolonged cessation of cerebral blood flow. This report describes a simple method to determine the presence or absence of the blood flow in the brain by recording the pulsatile midline echo on one channel of the electroencephalogram (EEG) or on any four-channel monitoring system in the intensive care unit. A firm transducer holder has been developed to eliminate artifacts caused by transducer motion. The pulsations of the midline echo are assumed to be the result of displacement of the midline structures by the arterial injection of each cardiac systole. Thus, the absence of these midline pulsatile echoes correlates with the absence of cerebral blood flow and, if the absence persists over 30 minutes in the presence of normal blood pressure, then the result is brain death. Twenty-eight cases of clinical brain death with electrocerebral silence of EEG and 18 obtunded patients with various types of cerebral pathology were examined by t...

Non-invasive electromagnetic measurement of the peripheral pulsatile blood flow: experimental study and clinical applications.

Abstract: The non-invasive electromagnetic blood flowmeter described in this paper allows us to measure pulsatile flow through a limb. The limb is placed in a magnetic field and the blood flow rate induces electromagnetic forces which are detected at the skin surface with ECG electrodes (Faraday's law). A special computer technique is necessary to isolate the signal from artefacts (local ECG, BCG, EMG). In vitro calibration is performed using a circulatory model and in vivo using mongrel dogs. Its validity is assessed by comparing the results with the responses obtained from the invasive electromagnetic flowmeter. Sources of error in the measurement such as blood composition (Na+, K+), haematocrit (45% to 29%), and venous flow are reported here. The results indicate that the method is reliable, easy to utilise and offers a unique non-invasive way of measuring true pulsatile blood flow rate in humans. Various clinical applications are discussed for possible use of the device.

Ultrasonic evaluation of pulsatile abdominal masses.

Abstract: Gray scale ultrasound B-mode scanning provides a rapid and safe method for evaluating the origin of a pulsatile midline abdominal mass. In those patients who do not have an aortic aneurysm, ultrasound will frequently provide another explanation. Tortuous aortas, pancreatic pseudocysts, metastatic cancers, lymphomas, and low-lying livers may all present as pulsatile masses clinically mimicking an aortic aneurysm. Visualization of the para-aortic soft tissues as well as the aorta allows these conditions to be distinguished by abdominal ultrasound. ( JAMA 239:419-422, 1978)