Electrical Stimulation of Somatic Afferent Nerves in the Foot Increases Bladder Capacity in Healthy Human Subjects

Purpose: We determined whether electrical stimulation of somatic afferent nerves in the foot could delay bladder filling sensations and increase bladder capacity in healthy humans without overactive bladder. Materials and Methods: Eight subjects underwent 90-minute foot stimulation using skin surface electrodes connected to a transcutaneous electrical nerve stimulator. The electrodes were attached to the bottom of the foot. Subjects completed a 3-day voiding diary, during which foot stimulation was applied on day 2. Stimulation parameters were pulse frequency 5 Hz, rectangular waveform pulse width 0.2 milliseconds and intensity 2 to 6 times the minimal stimulation current necessary to induce toe twitch. Stimulation intensity was set by each subject to a maximal level without causing discomfort. Subjects were provided with 500 to 1,000 ml of water to drink during stimulation. Results: Average +/- SE volume per void was 350 +/- 22 ml during the 24 hours before foot stimulation. This voided volume increased to a mean of 547 +/- 52 ml for up to 5 hours after stimulation (p <0.01). Average voided volume returned to 363 +/- 21 ml within 36 hours after stimulation. There were no adverse events. Conclusions: Foot stimulation can delay bladder filling sensations and significantly increase bladder capacity in healthy humans without overactive bladder. Although the study group was small, our results support moving forward with clinical trials of foot neuromodulation in patients with overactive bladder.