Fluid Volume Conductance for Determination of Bladder Volume

Abstract

Clinical urodynamics is the present standard for diagnosing voiding dysfunction. The nonphysiological nature of this exam often hinders symptom reproduction in the laboratory. Currently, a small intrabladder device is being developed to conduct ambulatory urodynamics. This study investigates the feasibility of using fluid volume conductance for the realtime intravesical volume measurement needed in urodynamics. Prototype devices are polymer bodies having 4 electrodes. Electrode configurations and probe geometries were tested in bladder-like latex vessels using saline having conductivity similar to urine. Sensitivity to temperature and fluid concentration were determined using fresh pig bladders in vitro. The voltage across the fluid volume was found to be inversely related to volume. The ideal probe configuration was found to be an ellipsoid having strip electrodes spaced at 25deg. Increasing fluid temperature and concentration increased solution conductivity, significantly decreasing the measured voltage. Urine's dynamic chemical properties therefore necessitate real-time compensation of conductivity in clinical application; which could be accomplished with another smaller electrode array.