The effect of distributed flow leakage on pulse propagation in viscoelastic arteries.

Abstract

The effects of distributed flow leakage on the transmission of pressure and flow waves along a viscoelastic tube was studied, to determine if current models of the arterial system could be improved by including this effect. A series of experiments were conducted using water-filled latex tubes. The results from the experiment were compared to a theoretical model based on a modified transmission line model, which included the effects of viscoelasticity and frequency dependent friction. The model showed very good agreement with the experimental results. Viscoelasticity was included in the model using a new concept: complex compliance. Using the complex compliance, dimensionless parameters were found which could be used to determine the importance of the viscoelasticity on the propagation coefficient and on the characteristic impedance. Other dimensionless parameters were found, which can be used to determine the effects of the flow leakage on the propagation parameters. It was found that the leakage greatly increased the attenuation and the characteristic reactance, however the effects on the phase coefficient and characteristic resistance were negligible. It was found that, for low-loss lines (such as the large arteries), the leakage caused a very small reduction in the pressure and flow transfer functions. The reduction of the pressure transfer functions was larger at the serial resonant frequencies, and the reduction of the flow transfer functions was greater at parallel resonant frequencies. The results of this study indicate that current models for the arterial system would not be substantially improved by the addition of a distributed leakage term.