Age dependent changes of arterial wall viscoelasticity. 
Viscoelastic characteristics (VEC) of old rat aorta (Wistar, 10 months) were obtained by sinusoidal excitation of intraluminal pressure (p) in cylindrical arterial preparations.  The pressure excitation frequency (f(exc)) was swept in the range 3-30 Hz up and down at several mean-pressure levels while response volume oscillations were recorded and resonance curves were plotted.  Natural frequency (f(0)), dynamic modulus of elasticity (E') and coefficient of viscosity (beta) were estimated from resonance curves and the dependences of VEC on p were drawn.  The results showed that f(0) decreased linearly with p whereas our previous data for young rat aorta (Wistar, 4 months) showed independence of f(0) on p. E' increased nonlinearly with p with the values being higher in comparison to young rat aorta.  This means stiffening of rat aorta with age in accordance with the known literature data.  beta-values increased linearly with p being higher in comparison to young rat aorta, demonstrative of raised intrinsic friction in the wall.  VEC values were higher at decreasing f(exc) suggesting that the direction of excitation sweeping also determines the arterial wall biomechanical behaviour.  It could be concluded that blood vessels VEC worsen with age, which endangers the arterial wall integrity, especially at higher intraluminal pressure.