Showing papers on "Pulsatile flow published in 1970"

Hydrodynamic Forces in Dissecting Aneurysms In-Vitro Studies in a Tygon Model and in Dog Aortas

Abstract: It has been argued that pulse wave characteristics are important factors in extension and rupture of acute dissecting aneurysms. To test this, a standard model of an aorta was constructed, consisting of an outer layer of Tygon tubing and an inner layer of rubber cement. An "intimal tear" was produced and the "aorta" was subjected to nonpulsatile and pulsatile flow with increasing increments of pressure. With nonpulsatile flow alone (97 experiments) no dissection occurred at pressures up to 400 mm Hg. Pulsatile flow produced rapid and usually complete dissection with a maximum systolic pressure of 120 mm Hg. The extent of dissection per pulse was related to dp/dtmax in the fluid. No dissection occurred until a critical value of dp/dtmax (790 mm Hg/sec) was reached. Dog aortas were then used in place of the Tygon tube "aorta" with similar results; i.e., dissection did not occur with nonpulsatile flow, but did occur with pulsatile flow (3800 mm Hg/sec). The dissecting dog aorta ruptured to the outside or reentered the vessel lumen. It was concluded that pulse wave characteristics, particularly dp/dtmax, are important in the propagation of dissection.

Comparison of the reflex vasomotor responses to separate and combined stimulation of the carotid sinus and aortic arch baroreceptors by pulsatile and non-pulsatile pressures in the dog.

Abstract: 1. In the anaesthetized dog the carotid sinuses and aortic arch were isolated from the circulation and separately perfused with blood by a method which enabled the mean pressure, pulse pressure and pulse frequency to be varied independently in each vasosensory area. The systemic circulation was perfused at constant blood flow by means of a pump and the systemic venous blood was oxygenated by an extracorporeal isolated pump-perfused donor lung preparation.2. When the vasosensory areas were perfused at non-pulsatile pressures within the normal physiological range of mean pressures, the reflex reduction in systemic vascular resistance produced by a given rise in mean carotid sinus pressure was significantly greater than that resulting from the same rise of aortic arch pressure.3. On the other hand, when the vasosensory areas were perfused at normal pulsatile pressures and within the normal physiological range of mean pressures, there was no difference in the size of the reflex vascular responses elicited by the same rise in mean pressure in the carotid sinuses and in the aortic arch.4. Whereas the vasomotor responses elicited reflexly by changes in mean carotid sinus pressure are modified by alterations in pulse pressure, those evoked by the aortic arch baroreceptors through changes of mean pressure are only weakly affected by modifications in pulse pressure. Evidence for this was obtained from single stepwise changes of mean pressure in each vasosensory area during pulsatile and non-pulsatile perfusion, and from curves relating the mean pressure in the carotid sinuses or aortic arch and systemic arterial perfusion pressure.5. The vasomotor response elicited by combined stimulation of the carotid sinus and aortic arch baroreceptors was greater than either response resulting from their separate stimulation.6. When the mean perfusion pressures in the two vasosensory areas are changed together, the curve relating mean pressure to systemic arterial pressure during pulsatile perfusion of the areas is considerably flatter than that for non-pulsatile perfusion.7. Increasing the pulse pressure in the carotid sinuses or aortic arch caused a decrease in systemic vascular resistance, the response elicited from the carotid sinuses being the larger.8. Altering the phase angle between the pulse pressure waves in the carotid sinuses and aortic arch had no effect on systemic vascular resistance.9. In both vasosensory areas, increasing the pulse frequency caused a reduction in systemic vascular resistance.

Mechanism for control pulsatile fluid flow

Abstract: This application relates to an apparatus for imparting a pulsatile flow to fluid in a conduit, which has pumping means for providing the pulsatile flow of fluid therein. The apparatus includes an elastic tubular section defining a portion of the conduit and located downstream of the pulsatile flow providing means. The tubular section is surrounded by a sealed sleeve to define a pressurizable space about the tubular section. The space is pressurizable so that the pulsatile flow pattern of fluid passing through the tubular section is controlled in a manner responsive to the pressure within said space. If desired, a portion of the flow conduit upstream of the pumping means is of enlarged transverse dimension and sealed within a second sleeve to define a second pressurizable space to provide a means for increasing the flow of fluid into the pulsatile pumping means.

Pulsatile pressure and flow in the mesenteric vascular bed of the cat.

Abstract: The transmission of arterial pressure and flow pulse through the mesenteric vascular bed was studied in 18 experiments on cats. Pressures were measured in the superior mesenteric artery and in small mesenteric veins, red blood cell flow velocities in mesenteric microvessels smaller than 60 μ diameter. Venous pressures were found to show heart beat synchronous oscillatory components of 0.2–0.5mmHg amplitude. Venous pressure pulses were delayed in time in comparison to the arterial pressure pulses: mean transit times varied between 85 and 110 msec. Blood flow velocities in arterioles and venules were generally pulsatile, the amplitude of the arteriolar pulses averaging 52.5% of mean velocity, of the venular pulses 32.5%. The velocity pulses were found to be similar in shape as flow pulses in larger arteries. Infusion of vasoactive drugs showed transmission of arterial pulses to be inversely dependent upon vascular resistance. It is concluded that the concept of complete damping of the arterial pulse during the passage of blood through the intestinal vascular bed cannot be maintained. Two different mechanisms of pulse transmission are discussed: direct hydraulic transmission through the capillary network and transmission across the vascular wall from the arteriole to the venule.

Instantaneous lung capillary blood flow in patients with heart disease

Abstract: The instantaneous pattern of pulmonary capillary blood flow was recorded by the nitrous oxide-body-plethysmograph method in 36 patients with heart disease. It was found to be abnormal in the presence of significant pulmonary arterial or pulmonary venous hypertension. Tachycardia, a low cardiac output, and right ventricular failure also contributed to converting a normally pulsatile capillary blood flow pattern to a more uniform one.

A new regional perfusion system.

Abstract: The development of an in situ perfusion system utilizing a new pulsatile pneumatic pump (Starling-Fields pump) is described Experiments with dogs demonstrated that kidneys perfused in situ for 4–6 hr by this system maintained life when transplanted into bilaterally nephrectomized recipients The pump is automatic and incapable of pumping a gas A technician is not required for its operation Hemolysis is less than with roller or peristaltic pumps The pulsatile flow provided is in the physiologic range Chemotherapeutic agents may be added easily and directly into the pump The pump's small size, inability to pump air emboli, autoregulation, low hemolysis, and ease of operation offer advantages that make it especially suitable for regional perfusion use

Pulsatile velocity of blood in the pulmonary artery of dogs: measurement by an ultrasound gauge.

Abstract: An advanced model of an ultrasound flow gauge, mounted on a N7 catheter was used to measure flow velocity in the pulmonary artery of closed-chest dogs. The recorded flow signals were calibrated in cm/sec by determining stroke volume (by dye dilution) and diameter of the pulmonary artery (by angiography). The influence of positive and negative inotropic drugs on velocity and acceleration is reported.

Variations of transthoracic electrical impedance in relation with hemodynamic changes of pulmonary circulation.

Abstract: Applying electrodes on bilateral chest walls, variations of electrical impedance were recorded during breath holding under various manipulations of the pulmonary hemodynamics with dogs. Pulsatile variations of the impedance recorded either directly from lobe surfaces or chest walls were in constant coupling with ECG and pressure waves in the pulmonary artery. These impedance pulses and their first differential derivatives decreased their height and area when the pulmonary blood flow was decreased, and increased those when the flow was increased. These changes disappeared when the manipulations were released and they returned to the original shapes. These results suggest that the impedance measurement on the chest wall gives informations concerning changes of pulmonary circulatory dynamics and can possibly be employed as a non-traumatic and continuous monitoring techninque for the pulmonary blood flow both experimentally and clinically.

A Pulsatile Roller Pump for Cardiac Bypass

Abstract: This short communication describes a cardiac bypass pump which produces a pulsatile flow. By driving a roller pump with a dc torque motor, it has been possible to provide electronic control of pulse rate and stroke volume. Flow and pressure recordings in dogs undergoing left-heart bypass are nearly physiological.

Mechanical Support of the Circulation: A New Approach

Abstract: A new technique of circulatory support by total left ventricular bypass is presented. Ten large, conditioned dogs had total circulatory support for four hours with pulsatile flow. Since the right ventricle and lungs were not bypassed, no oxygenator was needed. The various physiologic parameters measured changed very little. The arterial and venous pressures, vascular resistance, and flow from the pump remained constant. Arterial pH, oxygen pressure (PO2), carbon dioxide pressure, and lactate, and the venous PO2stayed within the normal range. Average hemolysis was only 14.5 mg/100 cc/hr and the urine output was 19 cc/hr. The technique was used successfully in one patient.

High‐resolution laser doppler velocity measurement of bidirectional pulsatile fluid flow

Abstract: A laser Doppler heterodyning system has been developed for localized measurement of the magnitude and direction of time‐varying fluid flow velocity. Directional sensitivity is achieved by shifting the frequency of the reference laser beam by an acoustical diffraction cell. A Doppler frequency shift proportional to fluid flow velocity is obtained by heterodyning the scattered laser light with a frequency‐shifted reference laser beam. Experimental results for time‐varying flow velocity in perturbed flow sections are presented.

Flow Pattern in Central and Peripheral Human Veins:A Pilot Study

Abstract: A short survey is given on exploratory work in venous flowmetry. The normal flow pattern in the human superior vena cava is described from our own recordings achieved with conventional cuff type electromagnetic probes. The retrograde transfer and delay of the central flow pattern to extratboracic peripheral veins is shown, demonstrating a pulsatile venous return to the right heart, created by the hearts own action. A catheter tip electromagnetic velocity flow probe is demonstrated and its advantages presented. A comparison of the central venous flow pattern in man recorded with a conventional probe and the catheter tip probe simultaneously shows a close conformity of the patterns.

Spatially Resolved Simulation Of CoronaryHemodynamics

Abstract: Computer-generated "realistic" structures of arterial trees consisting of 8000 segments have been used as a basis for computer simulations of coronary hemodynamics. For the perfusion pressure, a synthesized wave form typical of the aortic pressure was used, while the temporally varying intramyocardial pressure was related to the (also) synthesized left ventricular pressure. The elastic properties of the vessel segments were derived from a simple adhoc model of arterial compliance. The model yields the typical wave form of pulsatile coronary flow. The variability of coronary flow patterns resulting from variations in the way intramyocardial squeezing is applied has been investigated in detail.

Haemodynamics of the small arterial region in the femoral vascular bed.

Abstract: Based on experimental measurements of femoral arterial blood pressure and flow and the assumption that for peripheral haemodynamics the vascular bed can be lumped into functional sections, the effect of the small arterial region on femoral artery blood pressure-flow dynamics has been formulated. An analogue computer model has been developed to represent the dynamics for both pulsatile as well as non-pulsatile components of pressure and flow. Each section of the model has been identified with definite physiological analogue. The performance of the model corresponds closely to experimental data obtained from the dog, both for normal situations as well as for induced vasoconstriction and vasodilatation. Therefore the conclusion has been drawn that the assumptions made are empirically valid and the model can be used to describe the role of the small arterial region in peripheral haemodynamics.

Open chest pulsatile left-heart bypass without anticoagulation. An experimental study.

Abstract: A nonthrombogenic left-heart bypass system employing a pulsatile pump, porcine aortic valves, and polyurethan-polyvinyl-graphite-tetrahydrofuran-coated tubing to bypass the cross clamped thoracic aorta was evaluated in animal experiments. This system provided accurate control of proximal and distal aortic pressures and better tissue perfusion than nonpulsatile bypass techniques. Intraoperative and postoperative hemorrhage was markedly reduced because heparinization was not required. This nonthrombogenic pulsatile bypass would appear to be the method of choice to permit prolonged cross clamping of the thoracic aorta.

Pulsatile cerebral impedance measured with permanent electrodes implanted in the human brain

Abstract: Impedance measurement was first applied to neurosurgery in 1921, when the German surgeon A. W. Meyerl tried to locate cerebral tumors by this means. The technique was further developed by Steinke and Buchholtz,2 and quite recently Organ and co-workers3 reported a series of patients with brain tumors, in whom the tumor margins had been fairly accurately located by means of a roving electrode moved through the tumor. Another way to use impedance measurements in neurosurgery was developed by Freygang and Landau4 in 1955. These workers found that the impedance of the cerebral gray matter differed from that of the white matter. Robinson and Tompkins5 were the first to show, in animal experiments, that deep cerebral structures could be located by means of a roving impedance electrode. This new method offered welcome help to stereotaxic neurosurgery, in which it was important to make certain that the electrode inserted into various deep cerebral structures lay in the correct site in each individual patient. In 1965, in our stereotaxic laboratory, we started a fairly similar impedance recording during stereotaxic operations in man. We found that the impedance in the cerebral gray matter was approximately 25% lower than that of the capsular white matter.6 By this method we could estimate the frontier between the capsula interna and the thalamus with an accuracy of approximately 1 mm, and we could also record whether the electrode went via the thalamus to the subthalamic white matter. A monopolar electrode gave a better localization curve than a bipolar coaxial one. The reason for this difference is, in all probability, that when bipolar coaxial electrodes are used, free cerebral tissue gathers or an electrolyte bridge develops on the electrode surface between the two poles. During these locating measurements we observed that the cerebral impedance pulsated synchronously with the heart. Similar observations had been made earlier by Sugano and Inanaga in 1961' and by Birzis and Tachibana in 1962.8 The latter subsequently carried out comprehensive animal experiments on the pulsatile cerebral impedance. In this paper I shall report some observations made during the last four years through permanent impedance electrodes implanted in human brains. Some of the observations were made during acute investigations in the course of stereotaxic operations.