Hydraulic impedance in occlusive arterial disease of the leg

An investigation has been made of hydraulic impedance in occlusive arterial disease in vivo and in a laboratory model. Pressure and flow are inseparable variables of the arterial network. Since hydraulic impedance combines these variables and is a parameter of the arteries themselves it was thought that measurement of hydraulic impedance might be used to describe the extent of disease and the ability of a diseased artery, or its replacement, to conduct the pulsatile flow required. Measurements on dogs with simulated occlusive disease gave support to this idea. In order to study each of the relevant parameters independently a rubber tube model of the superficial femoral artery was developed. The diseased condition was simulated by rigid obstructions of known dimensions. Pulsatile flow of sinusoidal form was produced by a piston assembly. The effect of the degree of obstruction on hydraulic impedance and other indices of pressure and flow was determined using fluids of different viscosities. It was confirmed that impedance was dependent on both the radial and axial dimensions of a constriction simulating arterial disease. Comparison with other indices showed impedance to be a sensitive index of obstruction. Hydraulic impedance was investigated in patients undergoing reconstructive arterial surgery of the leg. The impedance measured in the common femoral artery of subjects with occlusive arterial disease was significantly higher than normal. Reconstructive surgery lowered the impedance. Though there was a significant difference in the impedance measured before reconstruction between patients who had a successful operation and those who did not, it was not possible to accurately predict the outcome of an operation. The factor determining the success of a reconstructive procedure in the leg may be the state of the collateral circulation.