MEASUREMENT OF OSCILLATORY FLOW PRESSURE-GRADIENT IN AN ELASTIC ARTERY MODEL

In vitro experiments were conducted to measure the oscillatory flow pr essure gradient along an elastic tube in order to assess the recent no nlinear theory of Wang and Tarbell, According to this theory, in an el astic tube with oscillatory flow, the mean (time-averaged) pressure gr adient cannot be calculated using Poiseuille's law, The effect of wall motion creates a nonlinear convective acceleration, and an induced me an pressure gradient is required to balance the convective acceleratio n, The induced mean pressure gradient depends on the diameter variatio n over a cycle, the pulsatility and unsteadiness of the flow, and the phase difference between the pressure wave form and the flow wave form , The amplitude of the pressure gradient also depends on these paramet ers and may deviate significantly from Womersley's rigid tube theory, A flow loop was constructed to produce oscillatory flow in an elastic tube, Flow wave forms were measured with an ultrasonic flow probe, and ultrasonic diameter crystals were used to measure wall movement, A sp ecial device for pressure drop measurement was constructed using Milla r catheter tip transducers to obtain both forward and backward pressur e drops that were then averaged, This averaging method eliminated the static error of the pressure transducers. The pressure-flow phase angl e was varied by clamping a distal elastic section at various locations , Pressure gradients were obtained for a range of phase angles between -55 degrees and +49 degrees, The mean and amplitude of the measured p ressure gradient were compared to theoretical values, Both positive an d negative induced mean pressure gradients were measured over the rang e of phase angles, The measured pressure gradient amplitudes were alwa ys lower than predicted by Womersley's rigid tube theory, The experime ntal means and amplitudes are in good agreement with the elastic tube theoretical values, Thus, the experiments verify the theory of Wang an d Tarbell.