Urethral pressure profiles in the female canine implanted with sacral anterior nerve root electrodes

The purpose of this work was to study the pressure distribution along the urethra in female canines with and without electrical stimulation of the sacral anterior roots innervating the bladder and urethra. Urethral pressure profiles were recorded in two orientations, dorsal and ventral, with microtransducer catheters. Two pulse types were applied at 1 Hz, 500 micros quasitrapezoidal pulses to selectively activate the small axons and 100 micros rectangular pulses. Four parameters were measured from each profile; maximum urethral pressure (MUP), bladder pressure (Pv), functional urethral length (FUL), and the position of the maximum peak from the bladder neck (PMP). Two derived measures, the estimated maximum urethral closing pressure (UCP) and the position of the maximum as a percentage of the FUL (PM%) were calculated. There were highly significant differences (P<0.01) in the value and position of the estimated UCP in the two orientations of the transducers. The highest pressures were recorded in the ventral orientation near the terminal portions of the urethra. Principal sphincter activity during electrical stimulation of the ventral sacral roots was also confined to this part. Selective small fiber activation did not result in any significant increase in this peak pressure from passive values.