Comparison between theoretical and directly measured pulse propagation velocities in the aorta of the anaesthetised dog

The propagation velocity (Cm) of the flow and pressure pulse has been measured in the abdominal aorta of anaesthetised dogs under vasoconstricted and vasodilated conditions. Simultaneously, measurements of the pressure strain elastic modulus (Ep) were obtained using a mercury in silastic strain gauge. These values of Ep were used to estimate a calculated propagation velocity (Cc) derived from the Moens Korteweg relationship. After Fourier analysing the pressure, flow and radius data it was found that Cc showed very little frequency dependence and that during vasodilatation Cm ≈ Cc to within a few percent for all harmonics above the first; whilst during vasoconstriction close agreement was observed at harmonics ≥ 6th. The mean values of Cm for these higher harmonics, and Cc for all harmonics, together with the mean propagation velocity (Cff) obtained from foot-to-foot time delays were, during vasodilation :Cm = 5.88 ± 1.2 (SD), Cc = 6.00 ± 1.04 and Cff = 5.79 ± 1.03 and during vasoconstriction Cm = 8.04 ± 1.27, Cc = 8.10 ± 1.04 and Cff = 8.00 ± 1.16. (units ms−1) Measurements in one dog of the impedance (ratio of pressure to flow) demonstrated that the contribution of peripheral reflections was negligible for the 6th and subsequent harmonics during vasoconstriction and above the first harmonic during vasodilatation, suggesting that the lack of agreement at lower frequencies between measured and calculated velocities was due to the presence of reflected waves. We conclude that within the frequency range in which reflected waves are negligible the Moens Korteweg equation in conjunction with measurements of pulse propagation velocity may be used to obtain accurate information on the elastic properties of the aorta.