The acute effects of continuous and conditional neuromodulation on the bladder in spinal cord injury

Laboratory investigation using serial slow-fill cystometrograms.

To examine the acute effects of different modes of dorsal penile nerve stimulation on detrusor hyperreflexia, bladder capacity and bladder compliance in spinal cord injury (SCI).

Spinal Injuries Unit, Royal National Orthopaedic Hospital, Stanmore, Middlesex, UK.

Fourteen SCI patients were examined. Microtip transducer catheters enabled continuous measurement of anal sphincter, urethral sphincter and intravesical pressures. Control cystometrograms were followed by stimulation of the dorsal penile nerve at 15 Hz, 200 micros pulse width and amplitude equal to twice that which produced a pudendo-anal reflex. Stimulation was either continuous or in bursts of one minute triggered by a rise in detrusor pressure of 10 cm water (conditional). Further control cystometrograms were then performed to examine the residual effects of stimulation.

Bladder capacity increased significantly during three initial control fills. Continuous stimulation (n=6) significantly increased bladder capacity by a mean of 110% (+/-Standard Deviation 85%) or 173 ml (+/-146 ml), and bladder compliance by a mean of 53% (+/-31%). Conditional stimulation in a different group of patients (n=6) significantly increased bladder capacity, by 144% (+/-127%) or 230 ml (+/-143 ml). In the conditional neuromodulation experiments, the gap between suppressed contractions fell reliably as bladder volume increased, and the time from start of stimulation to peak of intravesical pressure and 50% decline in intravesical pressure rise was 2.8 s (+/-0.9 s) and 7.6 s (+/-1.0s) respectively. The two methods of stimulation were compared in six patients; in four out of six conditional neuromodulation resulted in a higher mean bladder capacity than continuous, but the difference was not significant.

Both conditional and continuous stimulation significantly increase bladder capacity. The conditional mode is probably at least as effective as the continuous, suggesting that it could be used in an implanted device for bladder suppression.