ABSTRACT

24The measurement of physiologic flows is of interest both from the viewpoint of clinical diagnostics and in order to gain a better understanding of the various organ systems for both physiologic and pathologic conditions. Such measurements may range from that of quantifying the general flow rate in a system to documenting the nature of very specific, local, detailed, fluid dynamic events. In either case, the extreme complexities of such flows are a limiting factor on the measurements which one can perform. Physiologic flows are, in general, not simple. The flow complexities that can arise include asymmetric velocity profiles or flow patterns due to branching and curvature effects, turbulence, secondary flows which manifest themselves as a corkscrew, helical motion associated with streamline curvature, flow separation in which the downstream moving fluid separates from the wall and subsequently reattaches resulting in a dead water region, and the pulsatile or time-varying nature of a flow. In this presentation, these flow features will be discussed using, primarily, the cardiovascular system as an example. The measurement of physiologic flows is also limited by instrumentation characteristics, and the interaction between the nature of physiologic flows and instrumentation currently in use also will be discussed.