Abstract
This study has been attempted to evaluate the parallel conductor hypothesis (Nyboer, 1950) for the measurement of limb blood flow by electrical impedance or admittance plethysmography using a compensation technique. The principle of this technique is based on the theory that the admittance change in a limb segment immersed in an electrolyte solution disappears when the resistivity of the solution is equal to that of the blood flowing into the segment (ρb), if the segment is regarded as a parallel conductor model. The relationship between the admittance change and volume of the blood flow in the segment can be precisely analyzed by this technique.
In the forearms of 10 healthy subjects, ρb values have been compared with the resistivity of the electrolyte solution (ρs0), when the admittance variation following venous occlusion almost completely disappeared. These two values showed only a slight difference. From the difference between ρb and ρs0, the error which will be caused by modelling a limb segment as a parallel conductor was calculated to be within ±2%. This suggests that the parallel conductor hypothesis would be acceptable for the measurement of blood flow in the limb segment. Using the results the resistivity constant (k=ΔV/V0 vs. ΔY/Y0) and the form factor (x) in each limb segment have also been calculated. Based on these data the difference between the parallel and the random-pooling model is discussed.
