Pressure-diameter relations of the in vivo aorta

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Abstract
Simultaneous pressure and diameter (using a Peterson transformer coil) pulses were recorded from the aorta, carotid, and femoral arteries of the dog. The pressure-diameter loop showed many points of similarity with that given by excised vessels. Thus the loop was modified by changes in pulse pressure, heart rate, and the number of successive pulses covering the same pressure range. The in vivo loops showed a greater rate of diameter return during stretch-release. Any effect of vasoactive drugs on extensibility was obscured by changes in one or more of the passive factors. Attempts to stimulate the muscle of the aorta directly were ineffectual. A wall stiffening was produced, in a minority of cases, with muscular arteries. As one means of evaluating the physiological significance of the distensibility changes, modifications of the pulse contour technique for calculating stroke indexes were made, based on the usual dimensions of the hysteresis loops. Recalculation of a large number of pulses showed a better fit of derived stroke indexes with those obtained by the Fick procedure.

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