Bladder volume measurement with electrical impedance analysis in spinal cord-injured patients

The purpose of the study contained herein was to determine the usefulness of electrical impedance for measurement of bladder volume in spinal cord-injured patients, with an assessment of the relationship between electrical impedance and bladder volume exclusively. The study was performed during urodynamic studies to match the exact bladder volume. Thirteen patients with complete spinal cord injuries were recruited. We used silver-silver chloride compound electrodes composed of one pair of current and amplitude electrodes to minimize the influence of superficial skin impedance. Each compound electrode was attached on the lower abdomen bilaterally after skin cleansing. Constant current (60 kHz-1.0 mA), converted from 9 V of direct current, was applied, and corresponding electrical impedance (Ohm) was measured at "pre" (before urodynamic empty bladder), "full" (with a urodynamic filled bladder), and "post" (after urodynamic empty bladder) status. Electrical impedance at the full status was definitely lower than that at the pre and post statuses in all subjects, with a statistically significant difference (P < 0.001). The correlation between electrical impedance and bladder volume was negative (r = -0.7988), and the fact of how much the variation in electrical impedance could be explained by variation in bladder volume was estimated (r(2) = 0.6381). From these findings, we have determined that the electrical impedance analysis technique can be an alternative measure of bladder volume indirectly.