Preliminary observations of a synergistic bladder-sphincter relationship following spinal cord injury in a quadruped animal

BACKGROUND/OBJECTIVES: High urethral resistance or detrusor-sphincter dyssynergia (DSD) is characterized by obstructed voiding during bladder contractions. DSD is caused by an exaggerated pelvic floor reflex resulting from sensory input from elevated pressure in the bladder that produces reflex constriction of the urethral sphincter. The objective of this study was to determine whether sensory input from the bladder produced synergistic or dyssynergic pelvic floor reflexes following SCI in an animal model. METHODS: A pelvic floor reflex that shares the same motor pathway with DSD is the bulbocavernosus (BC) reflex. The BC reflex was elicited with electrical stimulation in 4 male cats with T1 spinal injury, and recorded as an anal sphincter contraction. Recordings were obtained during control and elevated bladder pressures. Increased bladder pressure was induced with either manual pressure (Crede procedure) or spontaneous contractions resulting from bladder filling. RESULTS: During the control period, the BC reflex indicated by the peak anal pressure response was 23 +/- 6 cmH2O. During elevated bladder pressure of 34 +/- 18 cmH2O, the BC response decreased to 10 +/- 3 cmH2O (not significant), showing a synergistic relationship. Anal sphincter tone between BC reflex tests showed a dyssynergic response. All 4 animals showed increased tone during elevated bladder pressures that averaged 9 +/- 5 cmH2O. Because abdominal pressure was not recorded, the significance is not clear. However, there was further support of a dyssynergic relationship based on increases in the anal and urethral electromyography recordings and some pelvic floor spasms during the elevated bladder pressure. CONCLUSIONS: Because 2 different pelvic floor activities were observed during increased bladder pressures, this animal model may be described best as a mixed model. This model shows both synergistic and dyssynergic relationships between the bladder and the BC contractions. Although observed changes were not significant, the unique observations of synergistic bladder-sphincter activity shown by the inhibited BC reflex is in marked contrast to the strictly dyssynergic bladder-sphincter relationship seen in SCI patients.