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

OBJECTIVES: The spinal nerve stimulation (SNS) evoked motor threshold (Tmot ) 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). MATERIALS AND METHODS: In anesthetized female rats, wire electrodes were placed under each of the L6 spinal nerves to produce bilateral SNS. The relationship of Tmot 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. RESULTS: The chronaxie of the Tmot -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 (Tmot , 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. CONCLUSIONS: 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.

Comparison of Bladder Inhibitory Effects of Patterned Spinal Nerve Stimulation With Conventional Neuromodulation in the Rat.

OBJECTIVES: The present study compared the effectiveness of patterned frequency of spinal nerve stimulation (SNS) with continuous, fixed-frequency nerve stimulation in an animal model of the bladder reflex contraction (BRC). MATERIALS AND METHODS: In anesthetized female rats, wire electrodes were placed under each of the L6 spinal nerve to produce bilateral SNS. A cannula was placed into the bladder via the urethra, and the urethra was ligated to ensure an isovolumetric bladder. RESULTS: Using motor threshold intensity, continuous stimulation at fixed frequencies of 4 Hz (n = 5) and 10 Hz (n = 7) decreased the frequency of BRC of 71 ± 24% (mean, SEM) and 85 ± 18% of controls, respectively (vs. no stimulation, n = 10, p < 0.05, two-way analysis of variance [ANOVA]). Fixed-frequency stimulation at 0.01, 0.1, 1, 40, and 100 Hz, did not demonstrate a trend change on BRC. When stimulation frequency is delivered with a 4-6 pulse/burst pattern every 1-100 sec, neuromodulation has demonstrated a trend toward effectiveness, with a four-pulse 40 Hz burst stimulation per second showing the most difference, reducing the BRC frequency of 74 ± 8% of control (n = 8, p < 0.05, two-way ANOVA). However, it is not more effective than continuous neuromodulation at a fixed frequency of 4 Hz or 10 Hz at BRC inhibition. CONCLUSIONS: Burst stimulations may inhibit bladder contractions; however, they are not more effective than continuous neuromodulation. Without further knowledge regarding mechanisms and potential benefit of burst stimulation on bladder control in patients with neuropathological conditions, applications should utilize continuous fixed 10 Hz stimulation for maximal clinical outcomes.