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PubMed1975

[New basic considerations and theories for improving angio-cine-densitometry. IV. The effect of discontinuous, pulsatile flow on angio-cine-densitometric measurements (author's transl)].

Various expressions of the speed of flow of blood in arteries are discussed, such as instantaneous speed, integral speed, pulse wave speed (phase speed) and velocity of a moving front. The flow profile of the abdominal aorta was obtained by cine-densitometry, bearing in mind the above considerations, and the densitometric curves have been analysed. Differences of the flow velocities in different persons have been interpreted as a result of these theoretical considerations. The effects of the point of measurement, the distance over which the measurement was carried out and the pulse wave length on velocity were examined. In order to obtain a median blood stream velocity by angio-cine-densitometry, repeated injections of small volumes of contrast medium (random sampling method) are recommended.

Blood Flow Velocity↗
PubMed1985

A circle of Willis simulation using distensible vessels and pulsatile flow.

The development of a one-dimensional numerical (finite-difference) model of the arterial network surrounding the circle of Willis is described based on the full Navier-Stokes and conservation of mass equations generalized for distensible vessels. The present model assumes an elastic wall defined by a logarithmic pressure-area relation obtained from the literature. The viscous term in the momentum equation is evaluated using the slope of a Karman-Pohlhausen velocity profile at the vessel boundary. The afferent vessels (two carotids and two vertebrals) are forced with a canine physiologic pressure signature corresponding to an aortic site. The network associated with each main efferent artery of the circle is represented by a single vessel containing an appropriate amount of resistance so that the mean flow through the system is distributed in accordance with the weight of brain irrigated by each vessel as determined from a steady flow model of the same network. This resistance is placed a quarter wave-length downstream from the heart to insure proper reflection from the terminations, where the quarter wavelength is determined using the frequency corresponding to the first minimum on an input impedance-frequency diagram obtained at the heart. Computer results are given as time histories of pressure and flow at any model nodal point starting from initial conditions of null flow and constant pressure throughout the model. Variations in these pressure and flow distributions caused by the introduction of pathologic situations into the model illustrate the efficacy of the simulation and of the circle in equalizing and redistributing flows in abnormal situations.

Cerebrovascular Circulation↗
PubMed1986

Phasic and spatial pressure measurements in a femoral artery branch model for pulsatile flow.

Phasic and spatial time-averaged pressure distributions were measured in a 60-deg femoral artery branch model over a large range of branch flow ratios and at physiological Reynolds numbers of about 120 and 700. The results obtained with an in-vivo like flow wave form indicated spatial adverse time average pressure gradients in the branch vicinity which increased in magnitude with branch flow ratio, and the importance of the larger inertial effects at the higher Reynolds numbers. Pressure losses in the branch entrance region were relatively large, and corresponding flow resistances may limit branch flow, particularly at higher Reynolds numbers. The effect of branch flow was to reduce the pressure loss in the main lumen.

Blood Pressure↗