Evaluation of Pulse-Width of Spinal Nerve Stimulation in a Rat Model of Bladder Micturition Reflex

The spinal nerve stimulation (SNS) evoked motor threshold (T_mot ) response across different pulse-widths (PWs) was first explored and a subset of selected stimulation PWs were further assessed with respect to bladder reflex contraction (BRC).

In anesthetized female rats, wire electrodes were placed under each of the L6 spinal nerves to produce bilateral SNS. The relationship of T_mot response with PW was analyzed using a monoexponential nonlinear regression. A cannula was placed into the bladder via the urethra to ensure an isovolumetric bladder. Saline infusion induced BRC.

The chronaxie of the T_mot -PW curve was 0.04 ms. The stimulation charges/energies (current × PW) associated with shorter PWs of 0.02, 0.03, and 0.06 ms were significantly lower than those with longer PW (e.g., >0.15 ms). SNS (T_mot , 10 Hz) at selected PWs from 0.03 to 0.21 ms inhibited the frequency of BRCs. There were no significantly different attenuations among tested PWs. SNS of PWs of 0.03, 0.06, and 0.09 ms decreased bladder contraction frequency from 103 ± 3%, 100 ± 4%, and 103 ± 4% of controls, to 52 ± 16% (n = 8, p = 0.02, paired t-test), 56 ± 15% (n = 11, p = 0.02) and 40 ± 19% (n = 10, p = 0.01), respectively.

Effective PWs to produce bladder inhibitory effects in the rat appear much shorter than 0.21 ms typically used with sacral neuromodulation in practice. Potential battery savings manifested by shorter PW while maintaining equivalent efficacy would provide more efficient therapy delivery and increased longevity of the stimulator.