Pulsatile Flow Patterns in Distensible Tubes

• During the last fifty years a number of physical theories have been proposed in an attempt to describe analytically the behavior of pulsatile flow in the mammalian arterial system. In order to make such an approach to a system of nonuniform, viscoelastic vessels containing a non-Newtonian fluid at all possible, it becomes necessary to introduce simplifying assumptions, the judicious selec-tion of which represents one of the most critical points of departure for any analysis and requires considerable insight into bio-logical phenomena. Womersley's1 theory, al-though similar to those developed earlier by Witzig2 and Lambossy,3 has been the most widely applied because of its refinements and because he provided the tables necessary for a solution of the linearized Navier-Stokes equations with minimal labor. Due mainly to the unavailability of adequate instrumentation for accurate measurement of blood pressure and flow, experimental verifi-cation of these theories and their underlying assumptions has become possible only during recent years. In a careful study,4 comparing experimental data with those predicted by theory, evidence was presented that Womers-ley's theory underestimates the viscous losses associated with pulsatile blood flow by a factor of three or more. In view of the assumptions underlying the theory, the authors suggested that this discrepancy may be due either to nonlaminar flow characteris-tics or to convective acceleration associate