Series Elastic and Contractile Elements in Vascular Smooth Muscle

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Abstract
Segments of dog common carotid artery were excised, cannulated, and restored to in situ length. They were immersed in a Krebs-Ringer's bath and inflated with 100% O2 under nonoscillating pressure. Diameter was continuously monitored with a linear displacement transducer. The vessel segments were relaxed and then treated isometrically with norepinephrine to excite the muscle. These continuously contracted vessels were subjected to 10- or 25-mm Hg quick release steps to 0 mm Hg. Then the muscle was inactivated with potassium cyanide, and the quick releases were repeated to study the parallel elastic elements. Finally, vessel wall volumes were determined radiographically. Computations were performed to compute series elastic element stiffness for both the Maxwell and the Voigt model of the arterial wall. These experiments indicated that the series elastic element stiffness was dependent on the applied stress and independent of muscle length provided that the vessels were excited at initial strains less than 0.70. Vessels excited isometrically at various initial pressures up to 150 mm Hg yielded identical stress-series elastic element stiffness curves. The computed series elastic element extension at an applied stress of 1.0 x 106 dynes/cm was 18.9% for the Hill model and 14.7-17.9% for the Voigt model; these values are percents of the vessel diameter at 0 mm Hg after application of potassium cyanide. The values were reduced to 11.2% for the Maxwell model and 8.6-10.5% for the Voigt model when they were expressed as a percent of the circumferential length associated with the peak in the length-tension curve. Vessels excited isometrically at pressures higher than 150 mm Hg exhibited greater series elastic element extensibility.

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