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| 번호 | 제목 | 등록일 | 조회수 |
|---|---|---|---|
| 31 | Rectal Compliance in Females with Obstructed Defecation [2001년 7월 DCR] | 2011-11-17 | 3627 |
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M. J. Gosselink, M.D., W. C. J. Hop, Ph.D., W. R. Schouten, Ph.D.
From the Colorectal Research Group, Departments Surgery and Epidemiology and Biostatistics, Erasmus Medical Center, Rotterdam, The Netherlands
PURPOSE: This study was designed to investigate whether rectal compliance is altered in females with obstructed defecation.
METHODS: Eighty female patients with obstructed defecation and 60 control subjects were studied.
Rectal compliance was measured with an "infinitely compliant" polyethylene bag. This bag was inserted in the rectum and inflated with air to selected pressure plateaus (range, 0-60 mmHg; cumulative steps of 2 mmHg with a duration of ten seconds) using a computer-controlled electromechanical barostat system. Volume changes at the levels of distending pressures were recorded. The distending pressures, needed to evoke first sensation of content in the rectum, earliest urge to defecate, and the maximum tolerable volume were noted. RESULTS: In all cases, the compliance curve had a characteristic triphasic (S-shaped) form. The mean compliance curve obtained from the patients was identical to that of the controls. However, the course of the compliance curve fell above the normal range (mean + 2 SD) in 14 patients. In ten (71 percent) of these patients, a large rectocele was seen at evacuation proctography. Such a rectocele was observed in only five patients (7.6 percent) with a normal compliance curve (P < 0.001).Eighty percent of the controls experienced earliest urge to defecate during the second phase of the curve. In 75 percent of the patients, this occurred in the third phase. The mean. pressure threshold for first sensation, earliest urge to defecate, and maximum tolerable volume were significantly higher in patients compared with control subjects. Ten of the patients experienced no sensation at all in tile pressure range between 0 and 60 mmttg.
CONCLUSION: In females with obstructed defecation, the compliance of the rectal wall is normal.
For almost three decades, paradoxical contraction of the pelvic floor has been cited as the principal
cause of obstructed defecation. Recently, the clinical relevance of this abnormality has been questioned. We have shown that a call to stool, evoked by rectal distention with a balloon, is associated with an increase in rectal tone, proximal to the distending balloon. This expelling force, in addition to rectal sensory perception, appeared to be absent or greatly blunted in patients with obstructed defecation. These data suggest that rectal wall properties play an importent role in the pathogenesis of obstructed defecation. Therefore, we were interested if alterations in rectal compliance are also contributory.
Rectal compliance reflects the distensibility of the rectal wall. Compliance is defined as tile volumetric
response of the rectum to stretch when subjected to an increase in intraluminal pressure. Until now, it was not clear whether alterations in rectal compliance contribute to the problem of obstructed defecation. Some authors observed an increase in rectal compliance whereas others found no difference between patients and controls. These conflicting data are mainly due m the variety of methods and devices used to assess the compliance. According to Toma et el. and Whitehead et al., the optimal method to determine rectal compliance is to record the change in rectal volume per unit change in rectal pressure with the help of a polyethylene bag and a barostat system with minimal internal compliance. With the help of a computer system, the polyethylene bag is inflated to selected pressure plateaus, and volume changes at these various levels of distending pressures are recorded. After plotting a pressure-volume curve (i.e., pressure on the x-axis), the slope of this curve (△V/△p) can be determined. The aim of our study was to investigate whether rectal compliance is altered in females with obstructed defecation, with the help of the guidelines described above. DISCUSSION
Rectal compliance reflects the distensibility of the rectal wall, i.e., the volumetric response of the rectum
to stretch when subjected to an increase in intraluminal pressure. It has been suggested that determination of rectal compliance is useful because alterations in rectal distensibility adversely affect rectal function. Irradiation of the rectal wall, for example, may result in fibrosis due to obliterative endarteritis with subsequent local tissue ischemia. In patients with fibrosis of the rectal wall, the slope of the pressure-volume curve is declined, indicating a reduced distensibility. Decreased rectal compliance is associated with urgency and increased stool frequency. Based on these findings, it has been suggested that alterations in rectal compliance are contributo W to obstructed defecation. In previous studies, a variety of methods and devices have been used to assess rectal compliance and,
therefore, a wide range of normal values has been reported. The methods and the devices used in previous studies have been criticized. In most studies rectal compliance is assessed by volumetric distention of a latex balloon with air or fluid. The intrarectal pressure, responding to this volumetric distention, is recorded with a pressure transducer within or outside the balloon. The data obtained are plotted in a pressure-volume curve (i.e., pressure on the x-axis), and the slope of this curve (△V/△p) is considered to represent rectal compliance. It has been stated, however, that the pressure response to a given volume stimulus reflects elastance rather than compliance. Fmthermore, it is mathematically incorrect to plot the dependent value (i.e., volume) on the y-axis. A major drawback of a latex balloon is that it supplies a compliance term of its own. Toma et al. compared latex balloons with polyethylene bags. In contrast with polyethylene
bags, latex balloons continue to increase when high pressures are applied, i.e., they still expand within a rigid tube, thereby not reflecting its low compliance. The authors also confirmed that polyethylene bags have an infinitely high compliance. Using a pressure transducer in or outside the distending latex balloon, the recorded pressure is partially
generated by the tension of the balloon itself. In 1988, Ackervatl et al. introduced manovolumetry for rectal compliance measurements. They recorded
rectal volume in response to rectal distention with a preset pressure. This technique was originally designed for investigation of bladder and stomach compliance and is now considered the correct way to measure compliance. At present, the optimum device to measure compliance correctly is a computer-controlled electronic barostat system, introduced by Azpiroz and Malegalada. This device is able to provide a constant cumulative pressure stimulus and record the corresponding volume at each pressure step. Although we have not corrected our data for the internal compliance of our barostat device, we think that we are allowed to compare the individual data of our patients and controls, because this small error is systematic. Nevertheless, to be able to compare our data with data from other studies, correction for the distensibility of the internal system of the barostat will be necessary. Some authors advocate the determination of the incremental elastic modulus of the rectal wall to investigate the viscoelasticity of the rectal wall during stress and strain. Stress is evaluated by inflating a
balloon with air and simultaneously measuring the pressure within the balloon. Stress is calculated by relating the area under the pressure-radius curve. Strain is measured by inflation of a balloon in the rectum and simultaneously measuring the intrarectal radius by endosonography. Strain is taken as the ratio of change in radius to the original radius. Thereafter, a stress-strain graph is plotted, and the slope of this curve reflects rectal wall stiffness or incremental elastic modulus. Simultaneous measurement of pressure within the balloon and the radius of the rectum can be performed by impedance planimetry. It is unclear whether this method provides more information than the compliance measurement used in this study. In most studies, compliance has been given as one single value, calculated from the slope of the curve
(△V/△p). None of the reports has made clear which slope was taken. In our opinion, it is difficult to determine which slope of the S-shaped curve should be used. It might be worthwhile to investigate entire pressure-volume curves. To our knowledge, only De Medici et al. have compared entire compliance curves of control subjects with those of patients with obstructed defecation. In their study, the mean compliance curve of the patients was found to fall within the normal range. In our study, the mean compliance curve obtained from the patients with obstructed defecation was identical to the mean compliance curve of the control subjects. Despite this finding, the course of the compliance curve fell above the normal range (mean + 2 SD) in 14 patients. In 10 (71 percent) of these 14 patients, a large rectocele (>3 cm) was seen at evacuation proctography. Such a large rectocele was observed in only 5 (7.6 percent) of the 66 patients with a normal compliance curve. It has been suggested that rectoceles are due to laxity of the rectovaginal septum. In our opinion, this laxity might be represented by the steeper compliance curve. Another explanation for increased compliance in females with a large rectocele might be the fact that the barostat bag assumed the shape of the rectum including the rectocele at the anterior side, thereby measuring rectal plus rectocete capacity and compliance. The measurement of rectal volume in response to cumulative pressure steps with a polyethylene bag
connected to a computer-controlled electromechanical barostat system, reveals a characteristic triphasic compliance curve (Fig. 2). Others have observed the same curve. During the first phase, the increase of pressure only gives rise to a small increase of volume, probably reflecting an initial resistance of the rectal wall. The second phase of the compliance curve is situated around the mathematical point of inflection and is characterized by a larger increase of volume, presumably reflecting an adaptive relaxation of the rectal wall. The last phase of the compliance curve is more flattened and probably represents increasing resistance of the rectal wall against further distention. At this point, the distensibility of the rectal wall is reaching its limits. There are very little data concerning the triphasic shape of the curve and the morphology of the rectal
wall. It is interesting to consider what may contribute to the shape of the curve. Passive mechanical properties in addition to active muscular components may be involved. Passive mechanical properties are represented by connective tissue and noncontractile muscle fibers. Collagen fibers are coiled at low" pressures. This aspect probably accounts for the plateau of the first phase. When the load is increased, collagen fibers gradually uncrimp. This might explain the steep increase of the second phase, the point of inflection. Finally, the third phase is reached, in which the collagen fibers are actually being overstretched. This hypothesis may be confirmed by comparing compliance of the human rectum, in vitro and in vivo, with the administration of appropriate smooth muscle relaxants, combined with histological research. We have found some reports regarding rectal wall properties in vitro but, to our knowledge, no reports correlating in vitro and in vivo data have yet been published. The tone of the smooth muscle fibers in the rectal wall might possibly contribute to the shape of the
compliance curve. Active muscular resistance may account for the first and third phase and adaptive relaxation of the smooth muscle fibers for the second phase. This is supported by the observation that the rectal compliance curve has been tound to be almost linear in patients with complete spinal cord lesions. After implantation of sacral spinal stimulators in these patients, the pressure-volume curve regains its characteristic triphasic shape. In patients with active ulcerative colitis, rectal wall compliance has been found to be decreased, in contrast with patients with quiescent ulcerative colitis and healthy controls. Since ulcerative colitis is known to be a disease that mainly affects colonic mucosa, it is likely that a decrease in rectal compliance is caused by an increase in smooth muscular tone. We suppose that a combination of passive elements, combined with active contractile properties of smooth muscles in the rectal wall, can account for the distensibility of the rectum, but further research on this subject is warranted.
Defecation requires adequate intrarectal pressure, which can be raised by increasing intrapelvic pressure, achieved by voluntary contraction of the diaphragm and abdominal wall muscles. Furthermore, increase of rectal wall tone proximal to the fecal mass, in addition to normal feelings of an urge to defecate, are essential for normal rectal evacuation. Our patients with obstructed defecation required larger pressures and higher volumes to evoke an urge to defecate when compared with control subjects. Diminished rectal perception of balloon distention has been reported previously in patients with constipation.
Eighty percent of the control subjects experienced a call to stool during the second phase of the compliance curve. In 75 percent of the patients, this occurred significantly later, at the end of the third phase. These data do suggest that rectal sensory perception is interwoven with rectal compliance. However, in our patients with obstructed defecation, the mean pressure-volume curve was similar to that found in control subjects. Following this finding, it is unlikely that alterations in rectal wall components, such as collagen and smooth muscle fibers, contribute to the problem of obstructed defecation. In a previous study, we were able to demonstrate that rectal sensorimotor function is significantly impaired in patients with obstructed defecation. 4 Based on these data and the results of the present study, it might be possible that patients with obstructed defecation have a derangement that mainly affects the afferent or efferent nervous pathways.
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