Puborectalis muscle (PRM) is a ?U? or ?sling? shaped muscle that is thought to be a major player in the anal continence
function. Current thinking is that it is important for maintaining the anorectal angle (ARA). Studies conducted in our
laboratory during last 12 years show new aspects of the PRM function. 1) PRM contraction causes closure of the proximal half
of the anal canal. For these studies, we utilized novel techniques of 3D transperineal ultrasound imaging of the pelvis and high
definition manometry. 2) PRM forms the inferior margin of the pelvic floor hiatus through which anal canal, vagina and urethra
emmerge from the abdominal cavity to the exterior (atmosphere). We hypothesized that contraction of the PRM lifts the anal
canal, vagina and uretha ventrally and reduce the size of pelvic floor hiatus, thus compressing all structures contained in it again
each other and in turn against the pubic symphsis. Accordingly, we found a high pressure zone in the vagina. Characteristics of
the vaginal high pressure zone show tonic or sustained/continuous pressure that increases significantly with voluntary squeeze.
Furthermore, we measured directionality of pressures in the vaginal high pressure zone using high definition manometry, 3D-US
and magnetic resonance imaging. These studies show that vaginal pressures are distributed in the dorso-ventral direction, which
is consistent with the direction of forces related to the shortening of PRM. All of the above studies were conducted in healthy
nullipara women. 3) To determine if PRM contraction has a role in the urethral closure function, we conducted studies in rabbits.
PRM was stimulated electrically and pressures were recorded using a sleeve sensor. These studies show that PRM contraction
increases pressure in the anal canal, vagina and urethra. In fact urethral closure pressure with PRM stimulation was 2-3 times
more than with the urethral rhabdosphincter stimulation. In summary, puborectalis muscle, which forms the pelvic floor hiatus
causes closure of the anal, vaginal and urethral orifices. Since PRM gets frequently damaged during vaginal delivery, we propose
that its dysfunction must play critical role in various pelvic floor disorders.
Ravinder Mittal is a Professor of Medicine and Director of GI function laboratory at the University of California, San Diego. A graduate of University
of Delhi in India, he completed clinical and research training in gastroenterology at the Yale University. He was a tenured professor of medicine at
the University of Virgina in Charlottesville, Virginia prior to coming to UCSD in 1997. He is the author of more than 100 original papers and 25 book
chapters. His research has been funded continuously by NIH since 1988.
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