NEW EXPERIMENTS ON SHEAR MODULUS OF ELASTICITY OF ARTERIES

Although the mechanical properties of blood vessels have been studied extensively, the shear modulus of the blood vessel wall is still unkno wn. New data on the shear modulus of elasticity of rat arteries and it s variation with axial stretch and blood pressure are presented. The d ata were obtained from a new instrument designed and constructed by us to perform simultaneous torsion, inflation, and longitudinal stretchi ng tests. It was found under physiological conditions (pressure = 120 mmHg or 16 kPa; longitudinal stretch = 1.2 relative to zero-stress sta te), the shear modulus of normal rat thoracic aorta is G = 137+/-18 kP a. The difference of shear modulus at body temperature (37 degrees C) and room temperature (25 degrees C) is within 10%. The shear modulus v aries significantly with changing longitudinal and circumferential str ains in proportion to the strain energy due to these strains. A consti tutive equation based on a pseudo strain energy function is proposed. The vessel wall is not transversely isotropic in the incremental sense . When the rat was subjected to high blood pressure due to constrictio n of its aorta, the shear modulus does not vary significantly with the length of time the animal was subjected to hypertension.