Pulsatile flow

About: Pulsatile flow is a research topic. Over the lifetime, 6278 publications have been published within this topic receiving 149638 citations.

CHOROIDAL BLOOD FLOW: Review and Potential Explanation for the Choroidal Venous Anatomy Including the Vortex Vein System.

Abstract: Purpose To review control mechanisms for blood flow in the choroid, propose a system by which venous outflow is controlled by a Starling resistor, and propose an explanation for the choroidal venous architectural anatomy. Methods The main blood flow control mechanisms were reviewed including autoregulation, neurovascular coupling, and myogenic regulation. Applicable blood flow control mechanisms in the brain, a high flow organ in a low compliance outer shell, were used to examine analogous processes that may be occurring in the choroid. Results There does not seem to be effective autoregulation in the choroid, although myogenic mechanisms may be present. There is a sophisticated neural innervation that provides partial control. Like the brain, the eye has a high pulsatile blood flow rate and is encased in a noncompliant casing. As part of modulating pulsatile pressure in the cranium, the brain uses venous storage and a Starling resistor effect to modulate venous outflow. An analogous function in the eye could be provided by the choroid, which contains fascicles of large veins that converge in vortices to drain out of the eye. This vortex area seems to be where the Starling resistor effect is possible. This mechanism would have important impact on theories of many ocular diseases including central serous chorioretinopathy and spaceflight-associated neuroocular syndrome. Conclusion Control of blood flow is critical in the choroid, and this control seems to extend to the venous outflow system. Abnormalities in venous outflow may critically affect function in predictable pathogenic mechanisms.

Pulsatile pressure-flow relations and pulse-wave propagation in the umbilical circulation of fetal sheep.

Abstract: The relations between pulsatile pressures and flows in the umbilico-placental circulation have been investigated using chronically instrumented fetal sheep. Under resting conditions, mean arterial pressure fell by 30 +/- 6%, from 44 +/- 2 to 31 +/- 2 mm Hg between the aortic termination and the arteries feeding the cotyledons, and pressure waves were substantially damped during propagation between the two recording sites. This high flow resistance and wave attenuation are attributed to the very thick walls and extreme length of the umbilical arteries. Unique relations between pulsatile components of pressure and flow, characterized as vascular impedance spectra, were also observed. At rest, impedance to pulsatile flow was only slightly below resistance to steady flow, and impedance phase was positive at low frequencies. Pulse-wave reflections had more modest effects in this bed than others. Thus, oscillations in impedance spectra and percent wave transmission with increasing frequency, which are widely accepted manifestations of wave reflections, were relatively small. Positive impedance phases at low frequencies indicated that novel mechanisms influence phase relations between pressure and flow. A significant vascular compliance residing in the peripheral vascular beds could account for this findings. The vasodilator nitroprusside enhanced wave-reflection effects, whereas the vasoconstrictor angiotensin II reduced these effects. These changes were opposite to the effects of vasoactive substances in other systems, probably because these drugs act predominantly on the supply (umbilical) arteries rather than on the peripheral placental vasculature. When peripheral vascular resistance was selectively elevated by infusing 50-microns microspheres, reflection effects were enhanced: the pressure pulse in the umbilical artery was transmitted without attenuation, or was amplified, and impedance spectra more closely resembled patterns typical of other vascular beds. Specifically, impedance modulus fell sharply with increasing frequency, and impedance phase was negative at low frequency. In addition, we observed coordinated oscillations in impedance modulus and phase that are characteristic of beds that exhibit wave-reflection effects. These findings indicate that the specialized anatomy and control mechanisms observed in the umbilical circulation result in unique hemodynamic function, in which wave-propagation effects exert influences not readily predictable from studies on other systems.

Effect of trabeculectomy on pulsatile ocular blood flow.

Abstract: Trabeculectomy, despite producing an effective reduction in intraocular pressure, may not prevent continued visual field loss. This may be because of the presence of other factors in the pathogenesis of glaucoma. Vascular factors have been suggested as being particularly important. To study the effect of trabeculectomy on ocular blood flow the technique of ocular pulse analysis has been used to derive a measure of pulsatile ocular blood flow in 17 patients (average age 65.6 (SD 1.8) years) undergoing trabeculectomy. A significant increase in pulsatile ocular blood flow of 29% was observed in the group as a whole in the standing position following operation but in some individuals blood flow changed only slightly despite a large reduction in intraocular pressure. The significance of these findings in relation to the prognosis of visual field preservation following trabeculectomy is discussed.

Cardiopulmonary bypass with physiological flow and pressure curves: pulse is unnecessary!

Abstract: Objective: Advocates of pulsatile flow postulate that the flow pattern during extracorporeal circulation (ECC) should be similar to the physiological one. However, the waveforms generated by clinically used pulsatile pumps are by far different from the physiological ones. Therefore, we constructed a new computer-controlled pulsator which can provide nearly physiological perfusion patterns during ECC. We compared its effect (group 1) with pulsatile (group 2) and non-pulsatile (group 3) perfusion generated by a conventional roller pump. Methods: Thirty pigs (10 per group) underwent 180 min ECC with an aortic cross-clamp time of 120 min. Pulse pressure, peak aortic flow, dp/dtmax, pulsatility index and energy-equivalent pressure were measured online. Renal and intestinal blood flow was calculated by fluorescent microspheres. The inflammatory response was assessed by the level of interleukin 6/1ra, the haemolysis by the free haemoglobin, and the escape rate of plasma protein by the disappearance rate of Evans Blue dye. Results: When compared to the preoperative curves, pulsatile waveforms during ECC were similar in group 1 and severely damped in group 2. Inflammatory response increased without significant differences between the groups. There were no differences between groups in renal and bowel blood flow. Free haemoglobin after ECC was higher in the pulsatile groups (group 1 = 43 � 144 mg dl � 1 , group 2 = 40 � 164 mg dl � 1 , group 3 = 11 � 4m g dl � 1 ; group 1 vs 2 (ns); group 1 or 2 vs 3 (p < 0.001)). The escape rate of Evans Blue increased after ECC in group 1 1.8-fold (p < 0.05), in group 2 1.45-fold (p < 0.05) and in group 3 1.27-fold (ns). Conclusion: Even when using pulsatile flow patterns which mimic closely the physiological waveforms, there is no advantage concerning organ perfusion or inflammatory response. Moreover, the extent of haemolysis and capillary leak is higher compared to non-pulsatile perfusion. Efforts to optimise pulsatility are not justified.