Showing papers on "Pulsatile flow published in 1968"

The Physiologic Role of Pulsatile and Nonpulsatile Blood Flow: III. Effects of Unilateral Renal Artery Depulsation

Abstract: A REVIEW of the physiologic disturbances encountered in nonpulsatile perfusion suggests a far greater importance to pulsatile blood flow than has heretofore been accorded. Although there is some evidence that blood flow through organs may be affected by nonpulsatile perfusion, it is now generally accepted that it is not. However, considerable evidence is available favoring the view that nonpulsatile perfusion may impair organ function in a number of ways. 1 That kidney function might be affected by the arterial pulse is suggested by several studies. Hamel 2 and Hooker, 3 studying the isolated kidney, found that a reduction in pulse pressure resulted in a drop in urine output. Gasell, 4 studying the intact kidney, confirmed this. Judson and Rausch 5 demonstrated a direct correlation between pulse pressure and urine output in humans undergoing aortic surgery. Senning et al 6 showed that nonpulsatile perfusion resulted in a depression in renal function

Transmission of Pulsatile Blood Pressure and Flow through the Isolated Lung

Abstract: A horizontal isolated lung preparation has been used to examine the transmission of pulsatile blood pressure and flow. Arterial and venous pressure and flows were measured with pressure transducers and electromagnetic flowmeters. After a sudden increase in pulmonary arterial pressure, delays of several seconds were observed before venous flow began to increase. Flow then increased slowly over a period of 1 to 9 seconds to a new steady level. The transmission of pulsatile flow was independent of the outlet pressure and identical for perfusion in the forward and reverse directions. Flow transmission fell from about 75% at a frequency of 0.03 cps to approximately 10% at a frequency of 1 cps. Pressure transmission down to the collapsible vessels was measured when alveolar pressure exceeded venous pressure. At 0.1 cps approximately 50% of the incident pressure wave was transmitted, and at 1 cps this was reduced to 30%. It was concluded that the lung passed well only the low-frequency components of the applied input and that in a vertical lung only about 30% of the mean to peak pressure pulse would be transmitted down to the small vessels and therefore affect the distribution of blood flow.

The Pressure Gradient in Ventricular Outflow Obstruction: Influence of Peripheral Resistance

Abstract: When flow of fluid in elastic tubing is pulsatile, as in the cardiovascular system, the magnitude of the pressure gradient across a fixed stenosis can be substantially decreased by an increase in the downstream resistance. This is possibly due to an uneven transfer of energy. Clinical implications are cited.

Erythrocyte Destruction by Prosthetic Heart Valves

Abstract: Immediate hemolysis induced by eight aortic and five mitral valve prostheses was measured in in vitro steady- and pulsatile-flow systems. The mean index of hemolysis (IH) for the aortic valves ranged from 0.010 to 0.031 and 0.012 to 0.035 with steady and pulsatile flow, respectively. The IH for the mitral valves ranged from 0.004 to 0.021 in the steady-flow system, and from 0.011 to 0.021 in the pulsatile system. The Barnard-UCT aortic valve and the Kay-Shiley and Portex-Hammersmith mitral valves produced the least hemolysis in each group. The graphite-benzalkonium-heparin-coated Gott-Daggett valve was the most hemolytic valve in both the mitral and the aortic groups. The degree of hemolysis demonstrated in these experiments appears to be important, particularly since several factors which are likely to have minimized these data have been cited. The calculated daily hemoglobin released from a single prosthetic valve represents a substantial fraction of a human's total hemoglobin clearance capacity and red...

Pulmonary venous blood flow.

Abstract: : Pulsatile characteristics of blood flow in major pulmonary veins were determined from chronically implanted dogs. From these data, five distinct positive flow maxima or waves are proposed to describe the variety of waveforms observed over a cardiac cycle. These five waves appear to change in amplitude and relative position among dogs, with respiration and under physiologic stress, and thereby permit an explanation of the different patterns that have been reported by other investigators. The general appearance of the flow waveform is particularly sensitive to heart rate. Four of the five flow waves are attributed to left heart action. One wave corresponds to the effects of right ventricular ejection transmitted through the pulmonary vascular bed. Limited data from respiration maneuvers and pharmacologic intervention provide changing waveform patterns which support these conclusions. Dissimilar waveforms were recorded simultaneously from some pairs of lobar veins. (Author)

Aortic baroreceptor activity during permanent distension of the receptor area.

Abstract: Aortic baroreceptor activity is known to be reduced in cases of persisting hypertension, the resetting probably resulting from changes in the aortic wall. The present investigation is an attempt to study the effects of permanent, localized dilatation of the aortic baroreceptor area on receptor activity. Ascending aortic stenosis was produced in 24 rabbits, and aortic diameters and aortic nerve activity were compared with results obtained in 10 normal rabbits. Aortograms four weeks after production of the stenosis showed diameters in the upper part of the ascending aorta and the aortic arch to be on average 16 % and 13 % greater than normal. Whereas an acute dilatation of this degree would have given marked increases of aortic nerve activity, the relationship between pressure and receptor activity was normal in animals with a permanent dilatation, both at pulsatile and steady pressures. The load-length relationship of aortic strips from normal and dilated receptor area was also equal, indicating that the uniformity of the relationship between pressure and activity in the two situations, at least in steady states, was due to adaptation of the aortic wall. It thus seems that chronic increases of neither pressure nor receptor area diameter will have consequences for aortic baroreceptor activity.