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

Abstract

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.

Large Artery Calcification on Dialysis Patients Is Located in the Intima and Related to Atherosclerosis

“…First, large arteries (carotid, femoral, brachial, aorta) are "elastic" arteries because their function is merely being a driver of the blood stroke. It implies a poor VSMC content in the media of these arteries (20,21). On the contrary, small, peripheral arteries are aimed at the regulation of blood flow in the tissue according to metabolic demands, and they present a dense layer of VSMCs.…”

Elements of Vascular Mechanics

“…Force-bearing histological elements of the wall A substantial part of the periodic stress due to the pulsatile component of the blood pressure will be met by the elastic membranes (Apter 1966). Their amount is high in arteries close to the heart, decreasing toward the periphery and diminishing in the smallest arteries with inner diameters below about 120 m (true arterioles).…”

“…After several decades of systemic investigations now we have a fairly good if not final picture how the histological composition of the vascular wall affects its elasticity (Apter 1966, Bergel 1961, 1964, Cox 1975a, 1978, Dobrin 1978, Fung 1984, 1995, Gow 1972, Greenwald 2007, Koens 2010, Oxlund 1986, Roach 1957, VanDijk 1984, Vidik 1982. The endothelium will not much contribute to the mechanical properties with the exception of capillaries and maybe, of the smallest other vessels.…”

“…Collagen lends rigidity and high tensile strength to the vascular wall, again, at high distending forces, while very moderate forces are sufficient to strengthen the coiled up collagenous bundles in the vessel wall. More collagen in the wall usually means higher rigidity (Apter 1966, Bergel 1961, 1964, Cox 1978, Dobrin 1978, Gow 1972, Greenwald 2007, Hegedus 1984, Oxlund 1986, Vidik 1982, but usually only at higher stresses. Collagen accumulation is typical in many types of diseased vessels ("sick vessel syndrome", Heistad 1995).…”

“…In addition to reduce inner radius (and to increase wall thickness) vascular smooth muscle contraction substantially alters the elastic properties of vessels (Apter 1966, Busse 1981,Cox 1975a, Dobrin 1969, 1978, Gow 1972, Greenwald 1982, Hudetz 1980, Monos 1979, Nadasy 1987, vanDijk 1984 , Fig 4a.). In case of large arteries, where the lumen reducing effect practically will not affect flow-resistance, the setting of the elastic modulus can be considered one of the main functions of the smooth muscle in the wall.…”