Effect of variation of transmural pressure on the frequency response of isolated segments of canine carotid arteries.

The frequency-response curve of isolated canine arterial segments at transmural pressures between 140 and 40 mm Hg showed an initial constant-amplitude portion over the lower frequency range followed by one or two major amplitude peaks (resonances) at higher frequencies. At lower transmural pressures, the response was more damped and resonances were infrequent. The amplitude of the flat portion of the curve increased as transmural pressure was decreased, and thus the dynamic modulus of elasticity calculated at 10 Hz decreased. The static modulus behaved in a similar fashion, but it was always lower than the dynamic modulus. The resonances shifted to lower frequencies as transmural pressure was decreased, and thus the dynamic modulus of elasticity calcuwall stiffness. Two series of five arteries each were examined; in one series the arteries were mounted with a fixed 50% longitudinal elongation and in the other series they were mounted with variable, mean 85%, longitudinal elongations. The difference between the two series suggests that increasing longitudinal elongation markedly increases the frequency shift induced by transmural pressure of one of the resonances and may result in coincidence of the two resonances at a given transmural pressure which varies from artery to artery.