Comparison of different methods for the determination of the true wave propagation coefficient, in rubber tubes and the canine thoracic aorta

The results from studies of wave propagation in large arteries carried out over the last 25 years have shown that there is a good agreement among values of the imaginary part of the complex propagation coefficient, as expressed by pressure or flow rate wave propagation velocity. However; there is considerable disparity among estimations of the degree of wave attenuation, the real part of the;propagation coefficient. In order to determine whether this disparity; is due to differences inherent in the various methods used to measure true wave propagation coefficients or whether it is caused by differences in experimental conditions, toe have compared three techniques for determining true pulse wave propagation coefficients: the three-point method the occlusion method and a recently described iterative procedure. In addition, the results were compared to apparent propagation coefficients calculated without accounting for reflections. Measurements were carried out using each method in turn on a rubber tube of known transmission characteristics in which the magnitude of reflections war small. The iterative procedure were also compared under conditions of strong reflection. In the tube, the values of propagation velocity and attenuation coefficient determined by each method were similar. Although some discrepancies were noted, they did not amount to a systematic trend The iterative procedure and the occlusion method were also used to analyse measurements on the thoracic aorta of three anaesthetized greyhounds. In the animal experiments, in spite of increased scatter, partly due to the variation between dogs, the two methods for determining true pulse-wave propagation yielded similar results. Since the differences between our estimates of propagation coefficients obtained by the methods tested are small with respect to those found when comparing the results from several reports in the literature, we conclude that any discrepancies between studies cannot be due to problems associated with the methods themselves but must have been caused by variations in experimental conditions or by other unknown artefacts. (C) 1997 Elsevier Science Ltd for IPEM.