A Method for Estimation of Intensity of Wave Reflection in an Elastic Tube

Abstract

The wave reflection coefficient, Γ, distinguishes the effect of aging, arterial disease and vasoactive agents on arterial hemodynamics. Despite its obvious appeal, Γ was not widely used in clinical situations because its computation requires complex and invasive arterial pressure and flow waveforms. A more useful alternate method for estimation of Γ is developed. The method uses the phase velocity spectrum derived from the phase of the pressure transfer function. In an elastic tube both the separating distance between the input and measurement sites and the distance to the termination site were changed. Pressure waveforms that were input to the system were obtained from a human subject. Results indicate that the phase velocity spectrum at lower frequencies (<5 Hz) was affected only by the distance to the termination site. The estimated wave reflection coefficients were found to be independent of the distance to the measurement site at specific termination distances if terminations were less than quarter wavelength. This method could be used to estimate the wave reflection coefficient from pressure measurements that have accurate phase information but otherwise limited amplitude information, such as applanation tonometry and photoplethysmography.