Rheological Properties of Major Arteries and Veins

Abstract

Rheological properties were investigated of longitudinal and circumferential strips excised from various portions along the aortic tree and venous trunk. The properties of smooth muscle, elastin and collagen fibers were also studied in order to elucidate the respective contribution of the corresponding vascular components to the rheological properties of vascular walls.1) In the proximal aorta, longitudinal and circumferential strips exhibited only a slight viscoelasticity. In the remaining aortic portions, the more distal the portion, the more elastic the longitudinal strips and the more viscoelastic the circumferential ones. In all the venous segments, longitudinal strips were highly elastic, but the circumferential ones were apparently viscoelastic. 2) Elastin fibers could be regarded as an almost entirely elastic component, whereas smooth muscle fibers exhibited remarkable viscoelasticity. Collagen fibers were characterized by an extremely high elastic modulus. Comparison of rheological properties between vascular walls and components revealed that the characteristic behavior of walls seemed to be determined mainly by the elastin and smooth muscle fibers involved. On the other hand, participation of the collagen fibers in tension development can be ruled out, at least, under the present experimental conditions.3) The following inferences could be derived in relation to the contribution of the elastin and smooth muscle fibers to the region- and direction-dependent differences in rheological properties of the aortic and venous walls. In the proximal aorta, no direction-dependent difference was observed. The elastin fibers may play a leading role and the smooth muscle fibers a complimentary role in determining the wall properties. Below the middle aorta, the contribution of the smooth muscle fibers increases circumferentially, whereas the longitudinal properties approach those of the elastin fibers. In large veins, the longitudinal behaviors are chiefly determined by the elastin fibers and the circumferential ones by the smooth muscle fibers. 4) The inferences were supported by histological findings. Architectural models for the vascular walls were proposed on the basis of these rheological and histological observations.