Feasibility of Implant Driven Micturition in Paraplegic Dogs

Abstract

This study evaluates the feasibility of using existing technology for implant driven micturition in paralyzed dogs (part I) and also examines a less invasive technique for implant driven micturition (part II). Part I. Sacral nerve root dimensions and bladder and urethral pressure responses to intradural and extradural sacral nerve root stimulation were measured to determine the optimal location and size for sacral nerve root electrodes. Part II. Sacral nerve roots were stimulated via wire electrodes introduced into the S2 foramina. Ten dogs (five dogs in part I and five dogs in part II). Part I. Microtip pressure transducers were used to monitor bladder and urethral pressure responses to sacral nerve root stimulation with tripolar hook electrodes. After euthanasia, sacral nerve root, and spinal canal dimensions were measured. Part II. Bipolar electrical stimulation of the sacral nerve roots was performed by introducing wire electrodes into the S2 foramina. Bladder and urethral pressures were recorded as in part I. Part I. Stimulation of SI produced an increase in urethral, but not bladder, pressure. Stimulation of S2 or S3 produced increases in bladder pressure and decreases in urethral pressure. Intradural and extradural nerve roots were not significantly different with respect to nerve dimensions or effects on nerve stimulation. Part II. High bladder pressures were achieved, but effective voiding could not be produced, primarily because of urethral resistance. Part I. Extradural implantation was determined to be the most appropriate site based on ease of dissection, nerve root dimensions, and decreased risk of iatrogenic trauma. Enough space is available to implant two to four tripolar spiral nerve cuffs. Part II. Transforaminal sacral nerve root stimulation did not effectively empty the bladder. Clinical trials in paraplegic dogs are necessary to evaluate the number of sacral nerve cuff electrodes necessary to produce effective bladder emptying.