Longitudinal Tethering of Arteries in Dogs

Abstract

The magnitude and properties of longitudinal vascular tethering were studied in the thoracic aorta, abdominal aorta, and femoral artery of 23 dogs. The tethering was found to consist of a dominant viscoelastic restraining element that demonstrated a moderate degree of stress relaxation and a significant inertial component that was related to the mass of the vessel and its surrounding tissues (the "added mass"). Static and dynamic studies of these properties showed them to be surprisingly linear. The simplest linear model that could simulate these experimental data consisted of two elastic components, two frictional components and a lumped inertial component. Within the physiologic range of frequencies (1 to 20 cycles/sec), the two elastic components became dynamically coupled so that they appeared to act as a single spring, the stiffness of which could be characterized by a "dynamic spring constant." The mean value of the dynamic spring constant was 12 g/cm³ for the thoracic aorta; it increased along the aorta toward the femoral artery to almost 70 times that value. Contrary to the simple tethering model assumed by Womersley, these data showed that the mechanical behavior of the system is strongly influenced by frictional components.