High Frequency SARS for Neurogenic Bladder and Bowel Emptying

Background: Spinal cord injury (SCI) leads to neurogenic bladder dysfunctions, and often includes difficulty with emptying the bladder due to detrusor-sphincter dyssynergia (DSD). Current bladder management strategies include catheterization, pharmaceuticals, and/or surgery, but these interventions insufficiently meet individuals' needs. The neurogenic bladder can be emptied using sacral anterior root stimulation (SARS) with electrodes implanted on the sacral nerves to produce bladder contractions. However, this emptying can be impeded by reflex contractions of the urethral sphincter. The sacral sensory roots are typically transected (rhizotomy) to reduce these reflex contractions, but this rhizotomy also impairs desirable reflexes (e.g. sexual function) and sacral sensation if present. Experiments in animals have shown that sacral root stimulation at 600 Hz can inhibit urethral sphincter activity, which has the potential. This approach could be used in lieu of the rhizotomy to improve bladder emptying efficiency. Objective: The objective of this study is to test the feasibility and potential effectiveness of 600 Hz sacral root stimulation to limit urethral sphincter activity in individuals with neurogenic bladder dysfunction. The investigators hypothesize that sacral root stimulation at 600 Hz will result in lower urethral sphincter pressures compared to pressures in response to stimulation at the lower frequencies that are typically used for SARS. Study Design: In this feasibility study, the investigators will enroll 8 participants, male or female, who have SCI and who already use implanted sacral root anterior stimulation to manage their bladder. Participants will act as their own controls. Stimulus waveforms for urethral sphincter inhibition will be tested in the clinical laboratory in a single session. The investigators will not need to conduct new surgeries or implant procedures. The primary outcome measure is urethral sphincter pressure, and additional outcome measures include bladder pressure, rectal pressure, and bladder volume as measured in clinically standard urodynamics examination. Clinical Impact: This approach could help restore bladder function by reducing urethral sphincter activity that impedes bladder emptying for individuals with SCI. The investigators could improve approaches for promoting bladder emptying by eliminating the need for sacral posterior rhizotomy.