Noninvasive measurements of nonlinear arterial elasticity

To describe fully the compliance characteristics of an artery with nonlinear elastic properties, measurements must be obtained over a wide range of pressures. Furthermore, repeated measurements, as required in temporal studies of arterial implants, require that the measuring technique be noninvasive. The application of a pulsed ultrasound echo-tracking device is described, which fulfills both criteria. Nonlinear compliance-pressure (CP) curves were obtained from the femoral arteries of dogs, with the use of halothane anesthesia to vary systemic pressure, and were used to compare the gross elastic properties of different vessels. Studies using controlled hemorrhage or the vasoactive drugs, nitroprusside and levarterenol (norepinephrine), were used to verify that the CP curves obtained during halothane anesthesia did not reflect varying degrees of smooth muscle activation. However, surgical exposure did temporarily reduce arterial compliance at pressures between 60 and 140 mmHg. The effect of vasoactive intervention and of postsurgical changes in arterial or graft compliance can thus be quantitated by use of CP curves or by comparing incremental elastic moduli, which can also be estimated from the noninvasively derived measurements.