Determination of wave speed and wave separation in the arteries

Considering waves in the arteries as infinitesimal wave fronts rather than sinusoidal wavetrains, the change in pressure across the wave front, dP, is related to the change in velocity, dU, that it induces by the 'water hamme r' equation, dP = +/- rho cdU, where rho is the density of blood and c is t he local wave speed, When only unidirectional waves are present, this relat ionship corresponds to a straight line when P is plotted against U with slo pe rhoc. When both forward and backward waves are present, the PU-loop is n o longer linear. Measurements in latex tubes and systemic and pulmonary art eries exhibit a linear range during early systole and this provides a way o f determining the local wave speed from the slope of the linear portion of the loop. Once the wave speed is known, it is also possible to separate the measured P and U into their forward and backward components. In cases wher e reflected waves are prominent, this separation of waves can help clarify the pattern of waves in the arteries throughout the cardiac cycle. (C) 2001 Elsevier Science Ltd. All rights reserved.