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| 번호 | 제목 | 등록일 | 조회수 |
|---|---|---|---|
| 21 | Effect of Continuous Rectal Distention on Anal Resting Pressure [2001년 5월 DCR] | 2011-11-17 | 3431 |
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Anna Mularczyk, M.D., Paolo A. Bianchi, M.D., Guido Basilisco, M.D.
From Cattedra di Gastroenterologia, Istitttlo di Scienze Mediche dell'Universita degli Studi di Milano, IRCCS Ospedale Maggiore di Milano, Milan, Italy
PURPOSE: Intermittent distention of the rectum induces internal anal sphincter relaxation, but whether continuous rectal distention might affect the resting pressure of the anal canal and the frequency of internal anal sphincter relaxations has not yet been investigated. The aim of this study was to record anal pressure under resting conditions and at two levels of continuous rectal distention.
METHODS: Anal pressure was recorded by means of water-perfused catheters under resting conditions and at two levels of rectal distention controlled by an electronic barostat in eight healthy subjects.
RESULTS: Continuous rectal distention did not significantly change mean anal resting pressure, but it
did significantly decrease the amplitude of ttltraslow waves (from 29 + 9 mmHg under resting conditions to 23 + 6 and 21 + 3 mmHg during lesser and greater rectal distention; P = 0.017 and P = 0.012, respectively) and increase the frequency of internal anal sphincter relaxations (from 1.3 -+ 1.3/hour under resting conditions to 8.8 _+ 4.3/hour and 11.0 --- 4.8/hour during lesser and greater distention; P = 0.012 in both comparisons). CONCLUSIONS: The resting pressure of the anal canal is maintained during continuous rectal distention. The decreased amplitude of ultraslow waves and increased frequency of the internal anal sphincter relaxations induced by rectal distention reveal a complex functional relationship between the rectum and the anal canal.
Intermittent distention of the rectum induces internal anal sphincter relaxation (IASR), but progressive
distention at low infusion rates does not. This suggests that the resting pressure of the internal anal sphincter may be maintained if the rectum is continuously distended, but whether continuous rectal distention affects the resting pressure of the anal canal and the frequency of IASRs has not yet been investigated. The aim of our study was to record the effects of two levels of continuous rectal distention on anal resting pressure in healthy subjects. DISCUSSION
Although continuous rectal distention did not modify the mean resting pressure of the anal canal in
healthy subjects, it significantly reduced the amplitude of the ultraslow waves and increased the frequency of IASRs. The resting pressure of the anal canal is one of the most important factors in maintaining fecal continence and is mainly generated by the smooth muscle tone of the internal anal sphincter, with the external anal sphincter playing a contributory role. Regulated by the intrinsic and extrinsic nervous system, resting pressure is not stable but is characterized by fluctuations that are classified according to their frequency and amplitude as slow waves, ultraslow waves, or IASRs. In the present study, the reduced amplitude of the ultraslow waves during distention may reflect a nonspecific effect of the distending rectal balloon on the sensitivity of the recording catheters in the anal canal. However, given the nonsignificant differences in mean anal resting pressure during the distentions, this possibility appears unlikely. More interestingly, the reduced amplitude of the uttraslow waves during rectal distention suggests a possible functional relationship between the rectum and the anal canal other than the rectoanal inhibitory reflex. IASRs interrupt the fluctuations of slow and ultraslow waves and have been observed in approximately
17 percent of healthy subjects at an average frequency of 4.6/hour during a continuous stationary manometric recording and in all subjects at an average frequency of 2 to 20/hour (with minimum frequency at night and maximum frequency in the postprandial period) during ambulatory recordings. In accordance with these results, the frequency of IASRs in the present study varied from 1.3 to 11.0/hour, with a significant increase during continuous rectal distentions. IASRs have been found to be associated with intermittent rectal distentions or contractions, colonic distentions, and propagated waves in the colon. The continuous rectal distentions used in the present study were controlled by an electronic barostat, which is a sensitive means of detecting pressure variations in large-capacity organs. This technique allowed us to show that at least under our experimental conditions, IASRs can occur even in the absence of rectal contraction or relaxation. We did not record colonic motility, and the possibility that the increased frequency of IASRs may have been due to an increase in the frequency of propagated colonic contractions was not assessed. On the other hand, our data suggest that the increased frequency of IASRs may be related to greater susceptibility of the internal anal sphincter to relaxation, and this may be reflected by the reduced-amplitude ultraslow waves induced by rectal distention. This hypothesis is in line with clinical observations of patients with proctalgia fugax, in whom the amplitude of the ultraslow waves was abnoi~nally pronounced and the sphincter was refractory to the relaxation induced by rectal distention. It is believed that IASRs allow rectal contents to be sampled by the specialized sensory epithelium of the
anal mucosa, thus updating the central nervous system. Under our experimental conditions, the rectum was previously cleaned by enemas, and at least during the distention periods, the presence of the distended balloon greatly reduced the possibility that any rectal content could enter the anal canal and be sampled. Our study shows that IASRs were not perceived per se; moreover, sensations of distention and desire to defecate were reported more frequently during rectal distentions but were unrelated to IASRs. Particular caution should therefore be adopted before concluding that there is anything other than a chance association between these sensations and anal relaxation in a distended rectum. |
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