|488||The Perineorectal Reflex [2002년 3월 DCR]||2011-11-17||1865|
The Perineorectal Reflex in Health and Obstructed Defecation
M. J. Gosselink, M.D., Ph.D., W. R. Schouten, M.D., Ph.D.
From the Colorectal Research Group, Department of Surgery, Erasmus Medical Center, Rotterdam,
PURPOSE: Many females with obstructed defecation apply digital pressure on their perineum to facilitate defecation. This study investigated the impact of this maneuver on rectal tone.
METHODS: Forty-five female patients with obstructed defecation were studied. Thirty-four patients (76
percent) regularly applied digital pressure on their perineum to facilitate defecation. Total colonic transit time was normal in 32 patients and prolonged in 13 patients. For comparison, 17 female controls were studied. With the subject in the left lateral position, a thin, “infinitely” compliant polyethylene bag was inserted into the rectum at 10 cm from the anal canal. Rectal tone was assessed by measuring
variations in bag volume with a computer-controlled electromechanical air injection system. After an adaptation period of 15 minutes, digital pressure was applied to the anterior perineum by one of the authors (WRS). In a second recording session, the tonic response of the rectum to an evoked urge to defecate was examined.
RESULTS: During the application of perineal pressure, all controls showed an increase in rectal tone (mean value, 52.8 + - 19 percent). In the whole patient group, this response was significantly
lower (mean value, 24.2 + - 19 percent; P < 0.001). Eight of these patients (18 percent) showed no response at all. None of them applied perineal pressure. In the remaining 37 patients (72 percent), the perineorectal reflex was present but was significantly lower (mean value, 29.8 + - 17 percent; P < 0.001). Thirty-four of these females (92 percent) stated that they applied perineal pressure on a regular basis to
facilitate their defecation. All controls showed an increase in rectal tone during an evoked urge to defecate (mean value, 37.8 + - 8 percent). In the patients, this response was significantly lower (16.7 + - 6 percent). Eight of these patients showed no increase in rectal tone at all. These patients were the same patients in whom the perineorectal reflex was absent. Regarding the tonic response of the rectum to perineal pressure, no difference was found between patients with a normal colonic transit time and those with a prolonged colonic transit time.
CONCLUSION: Digital pressure applied on the perineum results in an increase in rectal tone. This perineorectal reflex is present, although significantly lower, in the majority of females with obstructed
defecation. This observation might explain why females with obstructed defecation frequently apply perineal pressure to facilitate defecation.
Many females with obstructed defecation report the need of manual assistance to facilitate their
defecation. Some females can only expel feces if they open their anal canal with a finger. Others insert
a finger into the vagina to support the rectovaginal septum during evacuation. Vaginal assistance is frequently reported by females with a large rectocele. Another maneuver is the application of digital pressure on the perineum. Preston and Lennard-Jones have suggested that the puborectalis muscle is
pushed upward by this maneuver. This might straighten the anorectal angle, enhancing the alignment
between the rectum and anal canal. This effect of digital pressure on the perineum has not been
confirmed by evacuation proctography. The present study was conducted to investigate the impact of
digital pressure on the perineum on rectal tone.
The present study clearly demonstrates that digital pressure on the perineum induces an increase in
rectal tone. The utility of this perineorectal reflex in healthy subjects is unknown. In mammals, maternal
anogenital licking is known to stimulate defecation of the pup. It had been reported earlier that the bladder responds to perineal stimulation.
Pressure on the perineum inhibits bladder contractions. It has been suggested that this inhibition of
bladder contractions contributes to the suppression of the micturition reflex during sexual intercourse. It is well known that children frequently press their heels on their perineum to avoid micturition when they feel an urge to urinate while they are playing or watching television.
The perineorectal reflex was present in 37 of 45 females (82 percent) with obstructed defecation. However, this tonic response of the rectum was significantly lower than in controls. Thirty-four of these
females (92 percent) reported that they frequently applied pressure on the perineum to facilitate defecation. The perineorectal reflex was absent in 8 of the 45 patients (18 percent). None of them applied digital pressure on the perineum. None of these patients showed a tonic response of the rectum during an evoked urge to defecate. The mechanism underlying the perineorectal reflex is unknown. Rectal sensory perception, as well as rectal motor function, is thought to be mediated by the extrinsic parasympathetic sacral nerves. Furthermore, the pons cerebri might have a coordinating function. There is growing evidence that the impaired sensorimotor function in females with obstructed defecation might
be caused by a deficit of these extrinsic parasympathetic sacral nerves. It is well known that, in some
females, obstructed defecation starts after pelvic surgery. Patients who have undergone rectopexy frequently experience diminished rectal sensory perception. This has been attributed to the division of the “lateral ligaments,” which contain branches of the parasympathetic sacral nerves. After hysterectomy, changes in bowel function have in retrospect been reported by 43 percent of the females. The parasympathetic sacral nerves run from and to the rectum through branches that are situated on each side of the rectum, around the cervix uteri, and on both lateral vaginal surfaces. This extensive network of nerve fibers is difficult to spare during hysterectomy and dissection of the rectovaginal septum. Gurnari et al. showed that constipation occurs more frequently the more radical the hysterectomy is performed. Smith and colleagues studied rectal function in 14 females with intractable constipation after hysterectomy. In retrospect, these patients had significantly decreased rectal sensory perception. Also, patients with the cauda equina syndrome suffer from obstructed defecation. Furthermore, direct injury to the extrinsic parasympathetic sacral nerves has been reported to result in obstructed defecation. Finally, low spinal anesthesia, blocking all parasympathetic sacral nerves, abolishes rectal sensory perception. These observations confirm that the extrinsic parasympathetic sacral nerves play an important role in rectal sensorimotor function.
The finding that the tonic response of the rectum to an evoked urge to defecate, as well as the perineorectal reflex, is absent or blunted in patients with obstructed defecation does suggest that the extrinsic parasympathetic sacral nerves also play a role in the mediation of the perineorectal reflex. This assumption is supported by the observation that digital pressure on the perineum does not facilitate defecation in patients with a spinal cord injury at the sacral level, in whom the extrinsic parasympathetic sacral nerves are blocked.
It is well known that normal micturition is coordinated by a “center of micturition,” located in the anterior side of the pons cerebri. This center receives neural projections from the bladder as well as from
the perineum. During stimulation of the perineum, the neurons of this pontine micturition center are
inhibited. This observation illustrates the coordinating role of this pontine micturition center in the inhibiting perineovesical reflex. There is growing evidence that defecation, like micturition, is coordinated
by a comparable center in the pons cerebri. It has been shown that pontine neurons receive neural projections from the rectum. These neurons start to exhibit a stimulating firing pattern during perineal stimulation. Therefore, in our opinion, it might be possible that the pons cerebri is also involved in the
perineorectal reflex. The perineorectal reflex is characterized by an increase in rectal tone, whereas the perineovesical reflex is characterized by inhibition of bladder contraction. It has been reported that micturition and defecation are alternating actions. Distention of the bladder or stimulation of nerves running from the bladder inhibits the defecation reflex. Conversely, distention of the rectum or stimulation of nerves running from the rectum inhibits the micturition reflex.
Digital pressure applied on the perineum results in an increase in rectal tone. This perineorectal reflex is present, although significantly lower, in the majority of females with obstructed defecation. This observation might explain why females with obstructed defecation frequently apply perineal pressure to facilitate defecation.