Impedance of a measure of flow velocity in salt solutions.

Abstract

A method of impedance plethysmography used for the detection of local cerebral blood flow changes has also been found to be valid in blood-free salt solutions. From quantitative experiments on steady-state flow under gravity and on pulsatile flow in a circulatory model, it was concluded that the impedance change is proportional to the linear flow velocity of the ionic solution. Factors such as temperature, salinity, and others, which reduce the basal interelectrode impedance, tend to increase the sensitivity of the impedance change with flow. The sign of the impedance change reverses with reversal of direction of flow. The impedance change was shown to be independent of pressure change under no-flow conditions. Some possible mechanisms are discussed, as well as factors involved in applying the method to tissue studies.