Pulsatile flow

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

Further investigations on pulsatile movements in the cerebrospinal fluid pathways.

Abstract: In 1966 some radiologic observations of pulsatile movements in the cerebrospinal fluid pathways were described by DU BOULAY who was working upon O'CONNELL'S idea of a CSF pump. Now, as a result of further work, the earlier conclusions have been modified and widened. The present findings throw light upon the CSF circulation and possibly, as will be reported separately, upon the aetiology of hydromyelia, some forms of hydrocephalus and of arachnoid cysts. The work to be described here is intended to put the whole subject into perspective. A brief review of the literature may be helpful. Leaving aside early observations establishing the existence of pulsatile pressure changes, most published work is concerned with the following main topics: (1) If the source of the pulsatile pressure waves coincident with heart rate is (a) arterial in the head, (b) arterial in the spine, or (c) venous. (2) Granted that a large part of the pulse pressure wave derives from the head, the question arises if it comes from (a) expansion of arteries at the base, (b) expansion of the vessels within the brain, or (c) expansion of the choroid plexuses. (3) The means by which the respiratory fluctuation of CSF pressure is brought about. (4) The relationship of alterations in cerebral blood flow to CSF pressure changes. (There are also

Integrated microfluidic chip for endothelial cells culture and analysis exposed to a pulsatile and oscillatory shear stress.

Abstract: For a comprehensive understanding of cells or tissues, it is important to enable multiple studies under the controllable microenvironment of a chip. In this report, we present an integrated microfluidic cell culture platform in which endothelial cells (ECs) are under static conditions or exposed to a pulsatile and oscillatory shear stress. Through the integration of a microgap, self-contained flow loop, pneumatic pumps, and valves, the novel microfluidic chip achieved multiple functions: pulsatile and oscillatory fluid circulation, cell trapping, cell culture, the formation of ECs barrier, and adding shear stress on cells. After being introduced into the chip by gravity, the ECs arranged along the microgap with the help of hydrodynamic forces and grew in the microchannel for more than 7 days. The cells proliferated and migrated to form a barrier at the microgap to mimic the vessel wall, which separated the microenvironment into two compartments, microchannel and microchamber. An optimized pneumatic micropump was embedded to actuate flow circulation in a self-contained loop that induced a pulsatile and oscillatory shear stress at physiological levels on the ECs in the microchannel. All the analyses were performed under either static or dynamic conditions. The performance of the barrier was evaluated by the diffusion and distribution behaviors of fluorescently labeled albumin. The permeability of the barrier was comparable to that in traditional in vitro assays. The concentration gradients of the tracer formed in the microchamber can potentially be used to study cell polarization, migration and communications in the future. Additionally, the morphology and cytoskeleton of the ECs response to the pulsatile and oscillatory shear stress were analyzed. The microfluidic chip provided a multifunctional platform to enable comprehensive studies of blood vessels at the cell or tissue level.

Amplitude and phase of cerebrospinal fluid pulsations: Experimental studies and review of the literature

Abstract: Object A recently developed model of communicating hydrocephalus suggests that ventricular dilation may be related to the redistribution of pulsations in the cranium from the subarachnoid spaces (SASs) into the ventricles. Based on this model, the authors have developed a method for analyzing flow pulsatility in the brain by using the ratio of aqueductal to cervical subarachnoid stroke volume and the phase of cerebrospinal fluid (CSF) flow, which is obtained at multiple locations throughout the cranium, relative to the phase of arterial flow. Methods Flow data were collected in a group of 15 healthy volunteers by using a series of images acquired with cardiac-gated, phase-contrast magnetic resonance imaging. The stroke volume ratio was 5.1 ± 1.8% (mean ± standard deviation). The phase lag in the aqueduct was −52.5 ± 16.5° and the phase lag in the prepontine cistern was −22.1 ± 8.2°. The flow phase at the level of C-2 was +5.1 ± 10.5°, which was consistent with flow synchronous with the arterial pulse. The...

The effect of the pulse upon the formation and flow of lymph

Abstract: The ears of rabbits were perfused with defibrinated rabbit's blood in such a way that pulsation could be imparted to the perfusate or withheld from it at will. In the absence of pulsation there was almost no lymph flow, whereas when it was present lymph flow was rapid despite the fact that the "systolic" pressure of the perfusate never exceeded the constant pressure in the non-pulsatile instances and the volume flow was far less. Non-pulsatile perfusion led to a slight flow of lymph in ears that were becoming edematous, whereas when it was pulsatile the lymph flow was enormous. The pulse exercises an influence to move fluid into the lymphatics and along them.

Direct numerical simulation of the pulsatile flow through an aortic bileaflet mechanical heart valve

Abstract: This work focuses on the direct numerical simulation of the pulsatile flow through a bileaflet mechanical heart valve under physiological conditions and in a realistic aortic root geometry. The motion of the valve leaflets has been computed from the forces exerted by the fluid on the structure both being considered as a single dynamical system. To this purpose the immersed boundary method, combined with a fluid–structure interaction algorithm, has shown to be an inexpensive and accurate technique for such complex flows. Several complete flow cycles have been simulated in order to collect enough phase-averaged statistics, and the results are in good agreement with experimental data obtained for a similar configuration. The flow analysis, strongly relying on the data accessibility provided by the numerical simulation, shows how some features of the leaflets motion depend on the flow dynamics and that the criteria for the red cell damages caused by the valve need to be formulated using very detailed analysis. In particular, it is shown that the standard Eulerian computation of the Reynolds stresses, usually employed to assess the risk of haemolysis, might not be adequate on several counts: (i) Reynolds stresses are only one part of the solicitation, the other part being the viscous stresses, (ii) the characteristic scales of the two solicitations are very different and the Reynolds stresses act on lengths much larger than the red cells diameter and (iii) the Eulerian zonal assessment of the stresses completely misses the information of time exposure to the solicitation which is a fundamental ingredient for the phenomenon of haemolysis. Accordingly, the trajectories of several fluid particles have been tracked in a Lagrangian way and the pointwise instantaneous viscous stress tensor has been computed along the paths. The tensor has been then reduced to an equivalent scalar using the von Mises criterion, and the blood damage index has been evaluated following Grigioni et al. (Biomech. Model Mechanobiol., vol. 4, 2005, p. 249).