A Spinal Cord Injured Animal Model of Lower Urinary Tract Function: Observations Using Direct Bladder and Pelvic Plexus Stimulation With Model Microstimulators

Abstract

Background: Microstimulators are new devices that should be considered for managementof lower urinary tract problems following spinal cord injury (SCI) such as urinary retention. These devices are small(less than 25 mm by 5 mm) with the electrodes located on the ends of the stimulator. However, it is notknown whether the small electrodeson these devices would be effective in stimulating the plexus of nervesthat innervate thebladder. The aim of the present study was to provide preliminary observations with modelmicrostimulators (M-Micro) for inducing bladder contractions in an SCI animal model. Bladder wall andpelvic plexus stimulation sites were compared. Additional investigations evaluated parameters such asstimulation polarity, frequency, and period as well as bladder filling volume.Methods: In an initial survival surgery, bilateral M-Micros were implanted on the bladderwall and the pelvic plexus along the urethra in 3 female cats. A second survival surgerywas conducted 3 to 5 weeks laterto produce a Tl 0 SCI. Studies are reportedfollowing the second survival surgery. These studies included the effects of stimulation and bladder filling.Results: The postmortem location of the implanted pelvic plexus M-Micro was previouslydescribed asnear the bladder neck. Therefore, the pelvic plexus location is described in this reportas “pelvic plexus(bladder neck)”stimulation. The observations showed effective stimulation with pelvic plexus (bladder neck)stimulation andvoiding in some cases. Stimulation was limited byside effects of increased abdominalpressure and leg movement. Other factors also affected the response to stimulation, includingthe initial bladder volume and stimulating parameters. Fluoroscopy showed that when stimulation did not inducevoiding the striated urethral sphincter was closed.Conclusions: This case series of 3 SCI animals showed that the small electrodes on the M-Micro could beused to stimulate the bladder with contractions and voidingin some cases. The pelvic plexus (bladder neck)location for the M-Micro may be a better location than higher on the bladder wall. Limiting side effects ofstimulation included legmovement and increased abdominal pressure. Additional important factors included the stimulation parameters, initial bladder volume, and the function of the skeletal urethral sphincter.