Effect of urethral stretch on urethral pressure profile.

Urethral pressure profiles were recorded in anesthetized dogs with the urethra in both the relaxed and stretched positions. Similar studies were done with fresh specimens of intact dog bladder and urethra removed en bloc. Clinical studies were performed on women during surgical correction of stress incontinence. The pressure profiles reflected the intrinsic smooth muscular activity of the urethra, inasmuch as they were all obtained under full relaxation by anesthesia and with the abdomen open. In all cases, functional as well as anatomical lengths of the urethra were increased with stretch. The rise in urethral closure pressure was most marked in the proximal third of the urethra. Changes were more notable in women with stress incontinence than in the normal dog. Similar results were noted in the in vitro studies. Length-tension properties of smooth and striated muscles offer a clear explanation for the rationale and effectiveness of surgical procedures done for the correction of stress incontinence.