Search

Evidence for differences between the periurethral striated muscle and external anal sphincter of the cat is provided by measurement of the contractile properties in situ and in vitro and the electrophysiologic properties in vitro. In the periurethral striated muscle, the contractile pressure response was faster, d-tubocurarine sensitivity was greater, d-tubocurarine blockade had a shorter duration, and fatigue was faster but not uniquely fast as compared with results for the external anal sphincter. These results suggest that the periurethral striated muscle has similar characteristics to certain fast twitch muscles. Effect of succinylcholine on the periurethral striated muscle and external anal sphincter was similar. Miniature end-plate potentials had large amplitudes which appeared to be correlated to the small diameter of the periurethral striated muscle fibers. Since only focally distributed miniature end-plate potentials could be found, true physiologically slow muscle fibers were absent.

Three models of an artificial sphincter for treatment of urinary incontinence are described. Each of the models shares the two basic features of a cuff that encircles the urethra and a totally implantable hydraulic system for volitionally inflating the cuff to control the flow of urine. The models differ in the means by which pressure in the cuff is maintained below safe operating limits. In one model, pressure is regulated by a pressure-relief valve. This model has a clinical success rate of 66 percent over 5 years. The success rate has been increased by improvements in mechanical design, surgical technique, and patient selection. In another model, cuff pressure is regulated by means of a balloon which inflates at constant pressure as fluid is pumped into the balloon and cuff simultaneously to occlude the urethra. In the third model, pressure is also controlled by a balloon. To void, fluid is pumped from the cuff into the balloon. It then automatically flows back to the cuff through a fluid resistance to reestablish continence. Clinical trials of the balloon-regulated models are currently in progress.

In 29 rats, responses evoked by pelvic and hypogastric nerve stimulation were recorded from postganglionic nerves to bladder and penis (clitoris). Responses to pelvic nerve stimulation had nonsynapsing and synapsing components. The nonsynapsing component was relatively large in main nerve to penis and small in lateral nerve to penis and nerves to bladder. Pelvic nerve fiber synapsing on pelvic ganglion neurons to bladder had a large subliminal fringe, while fibers synapsing on neurons supplying penis (clitoris) had a small subliminal fringe. Recruitment was greater in nerves to bladder and lateral nerve to penis (clitoris) compared to main nerve to penis (clitoris), indicating more synapsing fibers in the former nerves. Almost all hypogastric fibers to bladder were direct. A small subliminal fringe was demonstrated for hypogastric fibers synapsing on neurons supplying penis. No subliminal fringe was evident for the bladder. Pelvic and hypogastric nerve interaction on pelvic ganglion neurons could not be demonstrated with either single shock or tetanic trains of conditioning stimuli. With antidromic stimulation, conduction velocities of afferent fibers in pelvic nerve ranged from 0.15 m per sec to 2.9 m per sec. In hypogastric nerve they ranged from 0.35 m per sec to 2.8 m per sec.