Electromyographic evaluation of the external urethral sphincter during cystometry in male cats.

Electromyographic (EMG) evaluation of the external urethral sphincter (EUS) was conducted during cystometry in 11 adult male cats sedated with xylazine and ketamine. A percutaneously placed antepubic catheter was used for bladder infusion and recording intravesicular pressures during cystometrography (CMG). A fine-wire electrode was placed percutaneously into or near the EUS for recording EMG during CMG. The bladder was infused with sterile 0.9% NaCl solution at a rate of 2 to 3 ml/min until a detrusor reflex was initiated. Intravesicular pressures at the onset of infusion, immediately prior to micturition, at the onset of urine flow, and at the maximal voiding pressure were recorded. The time from infusion to micturition, from opening pressure to return to baseline, and from the beginning to the end of the CMG were also recorded. The total volume of 0.9% NaCl solution infused and the residual bladder volume after micturition were also measured. Recordings were replicated once during each trial in all cats, and trials were replicated once approximately 1 week later in 4 cats. Micturition patterns were characterized by slight to moderate EUS EMG activity during vesicular filling, with reduction in activity during emptying. Maximal EMG activity was recorded at the completion of the reflex and was associated with pulsatile expulsion of small amounts of urine. The simultaneous recording of CMG and EUS EMG with fine-wire electrodes was simple and reliable for assessing the neuromuscular integrity and synchrony of detrusor and EUS muscles. There were no significant differences in variables between recordings within trial 1, but there were differences (P less than or equal to 0.05) between trials for pressure at the onset of urine flow and maximal voiding pressure.