Passive mechanical properties of the guinea pig aorta and portal vein: a comparison in the low-frequency range.

The study was carried out to determine the differences in the low-frequency dynamic mechanical properties of the guinea pig aorta and portal vein. Experiments were performed at five passive load levels in the aorta and at four levels in the portal vein. Sudden stretches 65 s in duration were imposed on the muscles, and the resulting force responses were recorded. After the experiments, the Fourier transformations of the force responses and the length perturbations were calculated. The results of the transformation were used to find the dynamic stiffness values in the range of 0-3 Hz. The quotient of the dynamic to the static stiffness (Ed/Es) obtained for the aorta and portal vein was the higher the higher was the frequency. At a given frequency and load level, the quotient Ed/Es was significantly greater for the portal vein than that for the aorta. Furthermore, the quotient value obtained for the portal vein varied with the passive load, whereas the same quotient obtained for the aorta did not vary significantly with the load levels. The phase difference between force and length was small and constant over the frequency range of 0-3 Hz, in both vessels. The differences in the dynamic characteristics are discussed in relation to the shortening capacity of the muscle cells in the two vessels.