Pulsatile Flow Patterns in Distensible Tubes

Abstract

Pulsatile flow patterns in polyvinyl tubes were visualized by means of streaming birefringence and compared with those obtained using an electromagnetic flowmeter. At low flow rates the frequency spectrum of the birefringence pattern is similar to that of volume flow. As the flow rates are progressively increased, irregular eddies appear, particularly during deceleration of flow, first in the central core and later spreading into the peripheral sleeve. They are characterized by a wide frequency spectrum. The concepts of laminar and turbulent flow are reviewed and evidence is presented which indicates that the power losses associated with the observed eddies are negligible with respect to the losses due to the average flow and its pulsatile components of low frequency. Flow disturbances observed in the arterial tree appear to be similar in character to those found in the present study. It is unlikely that they can account for significant discrepancies between experimental and theoretically predicted pressure-flow relations.