Influence of Flow and Pressure on Wave Propagation in the Canine Aorta

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Abstract
Data on wave speed acquired from 20 anesthetized dogs showed that the thoracic aorta was essentially nondispersive for small artificially generated pressure waves traveling in the downstream or the upstream direction and having frequencies between 40 and 120 Hz. The amplitude of these waves decayed exponentially with the distance traveled. The attenuation was independent of frequency and pressure if the distance was measured in wavelengths. The logarithmic decrement of the downstream waves ranged between 0.7 and 1.0, whereas that of the retrograde waves was between 1.3 and 1.5. The discrepancy in the attenuation for the two directions appeared to be due to the taper of the thoracic aorta. Simultaneous measurements of the transmission times of waves traveling downstream and upstream indicated that small pressure perturbations were convected with a speed that was approximately equal to the mean flow velocity. The speed of such perturbations depended strongly on the aortic pressure level at which they were generated. For normal pressure pulses generated by the heart, the speed of small perturbations at systole might be 30% higher than that at diastole. Theoretical studies have shown that such changes in wave speed due to variations in pressure and flow produce marked nonlinear effects in hemodynamics.