The relation between arterial viscoelasticity and wave propagation in the canine femoral artery in vivo.

The influence of arterial dimensions and viscoelasticity on pulse wave propagation has been expressed in many theoretical models of blood flow in arteries, but few experimental tests of these theories in vivo have been reported. The measurements required for such tests include not only the arterial viscoelasticity, diameter, and wall thickness, but also the true propagation coefficients and impedances, for comparison with the values "predicted" by solution of the model equations. We made such measurements in 16 experiments on the femoral artery in nine anesthetized dogs. A two-point pressure and flow technique was used to measure wave propagation, and an ultrasonic micrometer was used to measure vessel diameter as a function of time and pressure. Measured attenuation constants ranged from 0.010 at 1.3 Hz to 0.075 at 12.7 Hz, and were more than twice as large as those predicted by two representative linear models. True phase velocity, which increased from 6.71 m/sec at 1.3 Hz to 10.54 m/sec at 12.7 Hz, agreed closely with the values computed by the Cox model but were lower than those given by the Jager model. The resistive, but not the reactive, component of longitudinal impedance was significantly greater than predicted by the models at all frequencies. The experiments do not identify the source of these discrepancies. The use of linear models to calculate pulsatile blood flow from pressure gradients in relatively small vessels, or to calculate attenuation and characteristic impedance from arterial viscoelasticity in vessels of any size, produces significant errors.