Background: A time-domain approach to couple the Windkessel effect and wave propagation has been recently introduced. The technique assumes that the measured pressure in the aorta (P) is the sum of a reservoir pressure (Pr), due to the storage of blood, and an excess pressure (Pe), due to the waves. Since the subtraction of Pr from P results in a smaller component of Pe, we hypothesized that using the reservoir-wave approach would produce smaller values of wave speed and intensities. Therefore, the aim of this study is to quantify the differences in wave speed and intensity using P, wave-only, and Pe, reservoir-wave techniques.
Method: Pressure and flow were measured in the canine aorta in the control condition and during total occlusion at four sites. Wave speed was determined using the PU-loop (c) and PeU-loop (ce) methods, and wave intensity analysis was performed using P and separately using Pe; the magnitude and time of the main waves and the reflection index were calculated.
Results: Both analyses produced similar wave intensity analysis curves, and no significant differences in the timing of the waves, except onset of the forward expansion wave, indicated that distal occlusions have little effect on haemodynamics in the ascending aorta. We consistently found lower values of wave speed and intensities when the reservoir-wave model was applied. In particular, the magnitude of the backward waves was markedly smaller, even during proximal occlusions.
Conclusion: In the absence of other independent techniques or evidence, it is not currently possible to decide which of the two models is more correct.