Effect of levator ani muscle contraction on urethrovesical and anorectal pressures and role of the muscle in urination and defecation

Objectives. To investigate the effect of levator ani muscle (LAM) (the main muscle in the pelvic floor) contraction on the anorectal and urethrovesica l pressures and elucidate its role in the mechanisms of defecation and urin ation. Methods. In 18 healthy volunteers (10 men and 8 women; mean age 38.6 +/- 10 .2 years), the LAM was stimulated to contract by a concentric needle electr ode, and the anal, rectal, urethral, and vesical pressure responses were re corded. The test was repeated once after LAM anesthetization with Xylocaine injection and again after saline instead of Xylocaine injection into the L AM. Results. On LAM stimulation, the anal and urethral pressures had a signific ant decline (both P <0.05), and the rectal and vesical pressures exhibited no significant changes (both P >0.05). The anal, rectal, urethral, and vesi cal pressures did not show significant changes on stimulation of the anesth etized LAM; after saline injection, the pressure response was similar to th at before injection (P >0.05). These results were reproducible. Conclusions. LAM contraction lowers the anal and urethral pressures and app ears to assist in the evacuation process. We therefore propose that the LAM is a muscle of evacuation and that LAM dysfunction could lead to defecatio n and urination disorders. UROLOGY 58: 193-197, 2001. (C) 2001, Elsevier Sc ience Inc.