Correlation of Visco-Elastic Properties with Microscopic Structure of Large Arteries

The media of eight regions of the aorta and three of the pulmonary artery of dogs, as well as isolated elastin, collagen, and smooth muscle obtained from vascular and other sources, were subjected to a step-function circumferential stretch at a variety of temperatures between 0° and 70°C. The tension rose to a peak synchronously with the stretch and then fell along an essentially exponential course to a steady tension. Suitable use of the peak tension, the steady-state tension, and the time required to go from peak to steady state, supplied three temperature-dependent parameters (one viscous and two elastic) characteristic of the material. The two crystalline polymers, collagen and smooth muscle, had higher constants at low temperatures, and the amorphous polymer, elastin, had higher constants at high temperatures. Collagen differed from smooth muscle in its inertness to autonomic drugs and in its elastic modulus. Intact arteries stretched slightly (2% to 20%) in the presence of phenylephrine behaved like smooth muscle; arteries stretched more (20% to 70%) behaved like elastin. At both strain levels, the tensions developed were compatible with in vivo pressures. Arteries stretched even more (> 100%), to tensions compatible with pressures of 300 mm Hg, behaved like collagen.