Continuous measurement of conductivity of biological fluids.

Abstract

A circuit is described and evaluated for the continuous determination of the conductivity of biological fluids such as urine. A conductivity cell is placed in parallel with one arm of a balanced 4-arm bridge connected to a carrier amplifier. In the conductivity of the cell is at least 100 times less than that of the arm of the bridge, the response of the amplifier is linearly related to conductivity. The circuit has been used extensively for the biological assay of antidiuretic hormone (ADH) using ethanol-anesthetized rats. It was used with dogs to monitor water and electrolyte excretion and could be used to measure the hematocrit ratio or blood dilution.