Rheological properties of arteries under normal and experimental hypertension conditions.

Abstract Rheological properties of rabbit aortas in vitro were studied under control and hypertensive conditions by subjecting small segments of the aorta to uniaxial stress relaxation tests for various constant strain values ranging from 0.2 to 1.5 and stress-strain tests for deformation rates ranging from 8 to 40 mm/min. An examination of experimental results indicates that below a strain value ϵ0, which depends upon the location of aortic segment within the aorta, the arterial tissue essentially displays pure elastic response. For strains above this strain value, the tissue displays time dependent response. Based upon a nonlinear viscoelasticity theory, a constitutive relation involving six material constants for the characterization of the observed stress relaxation behavior has been developed. Results indicate that the material constants for normotensive and hypertensive aortas differ significantly. It is found that the effect of hypertension is to increase the in vitro stiffness of the aortas. The paper suggests the observed increase of stiffness to an increase in collagen fiber density and water absorption in the arterial wall.