Comparison of rat aortic, carotid & femoral artery viscoelastic properties using harmonic analysis.

Viscoelastic properties of rat (Wistar Kyota) large (6 aorta), medium (12 carotid) and small (8 femoral) in vitro artery segments, were contrasted over a wide range of static and dynamic pressures. Relationship of change in static pressure (delta dyne/mm2) to diameter (delta mm) was used to estimate a segment's incremental elasticity (KD) at each pressure level. Dynamic intravascular pressure response (Po) was recorded during swept frequency pressure (2-200 Hz; +/- 10 mm Hg) inputs as superimposed on mean pressure steps of 40, 80, 120, 160 and 200 mm Hg (P(i)). Analysis of dynamic data included Fast Fouier Transform of Po/P(i) with FANSIM (TUTSIM Products) curve fit to Bode plots. Curve fit coefficients were used to estimate properties of natural frequency (omega n) damping, viscosity and inertia. Statistical analysis employed ANOVA and SNK multiple comparison procedures. Results indicated that as step-pressure was increased diameter, KD and omega n increased proportionately in all segments. Values of KD and omega n were always highest in femoral and lowest in aortic segments. In all segments damping decreased inversely with increasing pressure while, viscosity and inertia were lowest between 80 and 160 mm Hg. These results documented distinct viscoelastic properties for the three arteries as well as, differences in their response characteristics.