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| 번호 | 제목 | 등록일 | 조회수 |
|---|---|---|---|
| 123 | Effect of Perineal Compression on the Rectal Tone [2003년 10월 DCR] | 2011-11-17 | 3624 |
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A Study of the Mechanism of Action
Ahmed Shafik, M.D., Ph.D.,* Ismail Ahmed, M.D., M.Ch.,* Olfat El-Sibai, M.D., Ph.D.†
From the *Department of Surgery and Experimental Research, Faculty of Medicine, Cairo University, Cairo,Egypt, and the †Department of Surgery, Faculty of Medicine, Menoufia University, Shebin El-Kom, Egypt
PURPOSE: Digital pressure on the perineum was reported o result in an increase of the rectal tone.This effect has been related to a reflex action named perineorectal reflex but was not verified. The mechanism of action of perineal pressure on the rectal tone was studied.
METHODS: Eighteen healthy volunteers (mean age +/- standard deviation, 39.7 +/- 11.8 years; 10 males) were studied. The barostat system used consisted of a polyethylene balloon connected to a strain gauge and a computer-controlled, air-injection system. The balloon was introduced into the rectum, and the rectal tone was assessed by recording the balloon volume variations in response to digital pressure on the perineum. The test was repeated after individual anesthetization of perineum and rectum. It was performed again using normal saline instead of Xylocaine®.
RESULTS: During perineal pressure, all the volunteers exhibited rectal tone increase with a mean decrease in the balloon volume of 72.3 +/- 14.7 percent. There was no significant difference (P > 0.05) in the rectal tone response between females and males nor between young and elderly patients. The mean latency was 17.3 +/- 1.8 ms. Perineal pressure 20 minutes after individual anesthetization of perineum and rectum effected no significant rectal tone changes. The response returned after the anesthetic effect had waned. The rectal tone response after saline administration was similar to that
before administration. CONCLUSION: The study has shown that rectal tone increase during digital perineal pressure represents most probably a reflex action. This was evidenced by absence of rectal tone response on individual anesthetization of the assumed two arms of the reflex arc: perineum and rectum. The perineorectal reflex may be of diagnostic significance in rectal motor disorders and has the potential to be used as an investigative tool, provided further studies are performed to prove these points.
The intricate mechanism of defecation is under the control of reflex and voluntary actions, which facilitate or inhibit its actions. Most of the time the rectum is empty of stools. When stools enter the rectum, the rectoanal inhibitory reflex is evoked and results in rectal contraction, internal anal
sphincter relaxation, and defecation. If defecation is inopportune or not desired, voluntary external anal sphincter contraction initiates the voluntary anorectal inhibition reflex, which effects reflex rectal relaxation and waning of the desire to defecate. The rectum has an intrinsic and an extrinsic nervous mechanism. The intrinsic is represented by the enteric nervous plexus, whereas the extrinsic mechanism is mediated by the parasympathetic nerves, which involve the sacral segments of the spinal cord. Rectal distention evokes not only the rectoanal inhibitory reflex but also the parasympathetic extrinsic reflex; the former is mediated through the enteric nervous plexus, whereas the latter through the parasympathetic nerve fibers in the pelvic nerves. It had been reported that exertion of digital pressure on the perineum produces rectal tone increase. Preston and Lennard-Jones advocated that the puborectalis muscle is pushed upward by this maneuver, thus straightening the anorectal angle. However, this effect has not been confirmed by evacuation proctography.Other investigators related this effect to a reflex action called perineorectal reflex but did not prove it. We studied the mechanism of action of perineal pressure on the rectal tone.
DISCUSSION
The current study may shed some light on the mechanism of rectal tone increase on perineal pressure.
The increase in the rectal tone apparently denotes an increase in rectal motor activity, which presumably initiates the defecation reflex. Rectal contraction evokes the rectoanal inhibitory reflex with a resulting internal anal sphincter relaxation and defecation. This effect might explain why some females with obstructed defecation apply digital pressure on their perineum to ease defecation. It may be argued that perineal pressure exerted in patients with obstructed defecation, compresses an existing rectocele, an effect that assists defecation. However, it is the vaginal and not the perineal route that effects rectocele compression. Frequently, females with rectocele resort to vaginal assistance to facilitate defecation. Furthermore, the current study revealed that the rectal tone increase on perineal pressure occurred in normal patients who had no rectocele; however, it also was reported to occur in patients with obstructed defecation. The mechanism of rectal tone response to perineal pressure is unknown; is it reflex in nature or the result of a direct action? This point needs to be discussed. Perineorectal Reflex : The rectal tone response to perineal pressure has been related by some investigators to the upward push the puborectalis muscle receives by this maneuver. This might straighten the anorectal angle and thus serve in aligning the rectum with the anal canal; however, this
effect has not been confirmed by evacuation proctography. Besides, the rectoanal alignment does not explain the cause of increase of the rectal tone. We postulate that the rectal tone increase on digital perineal pressure represents a reflex relationship between the two actions. This relation is evidenced by reproducibility and by its absence on individual anesthetization of the perineum or rectum, the assumed two arms of the reflex arc. Xylocaine blocks the sensory fibers (C and A-fibers), which are responsible for pain and reflex activity. The afferent limb of
the reflex arc seems to comprise the sensory nerve endings in the perineum, which are stimulated by digital pressure on the perineum. Afferent impulses seem to be transmitted to the sacral segments by the pudendal nerve (S2, 3, 4). The efferent impulses pass via the autonomic supply to the rectum. Some investigators assume that the extrinsic parasympathetic sacral nerves play a role in the mediation of the perineorectal reflex. Rectal sensory perception and rectal motor function are thought to be mediated through these sacral nerves. The rectal tone response showed no difference between the mild and strong perineal pressure. This
finding most likely denotes that perineal stimulation occurs through the perineal sensory fibers and not through the deep perineal structures. Previous studies have demonstrated the presence of the perineorectal reflex in the majority of females with obstructive defecation, although the rectal tone response was significantly lower than in the normal patients. We do not know the cause of the decreased rectal tone response in these patients. The current results have shown that the rectal response is most probably reflex, and the latency of the reflex was determined. We hypothesize that a significant prolongation of the latency as well as a diminished rectal tone response to perineal pressure may denote a defect in the reflex pathway, such as rectal muscle or nerve damage from a disease of the peripheral nerves, spinal nerve roots or the spinal cord, or
from a central lesion. We believe that the perineorectal reflex, after being studied in the various pathologic rectal conditions, may prove to be of diagnostic significance in the investigation of patients with rectal disorders. The reflex assesses the integrity of the rectal musculature and innervation and may have other clinical applications than facilitating defecation in patients with obstructed defecation. |
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