Determination of wave speed and distensibility of flexible tubes using diameter and velocity

It is well accepted that wave speed is one of the key factors describing wave propagation in arteries [1]. Local wave speed is directly related to the mechanical properties of the arterial wall [2] and is widely used to determine the arterial distensibility [3]. Several methods have been proposed for determining wave speed in arteries, such as foot-to-foot and PU-loop methods. In this paper, we suggest a new method for the determination of wave speed and wall distensibility, using noninvasive measurements. The theoretical foundation of this method is based on the 1-D conservation of mass and momentum equations of flow in flexible tubes. We simultaneously measured pressure, diameter and velocity at the same site, sequentially along silicon and latex tubes which are 1m in length and of different diameters. We compared the results of the new method, ln(D)U-loop, with those determined by the PU-loop method. Wave speeds determined by both methods are comparable, although wave speeds determined by the new technique are slightly smaller than those determined by PU-loop method. We also compared distensibility calculated by the new method with those calculated using the traditional method (D(t)), D(t) = dP/AdA, where A and dA are the cross sectional area and its change respectively, and dP is the change in pressure. The results of both methods are in agreement. We conclude that the new technique has the advantage of using only noninvasive parameters which is of clinical relevance.