Influence of body position and stool characteristics on defecation in humans.

2006Dec
Am. J. Gastroenterol.
Am J Gastroenterol 2006 Dec 6;101(12):2790-6. Epub 2006 Oct 6.
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Whether defecation is influenced by body position or stool characteristics is unclear.
We investigated effects of body position, presence of stool-like sensation, and stool form on defecation patterns and manometric profiles.
Rectal and anal pressures were assessed in 25 healthy volunteers during attempted defecation either in the lying or sitting positions and with balloon-filled or empty rectum. Subjects also expelled a water-filled (50 cc) balloon or silicone-stool (FECOM) either lying or sitting and rated their stooling sensation.
When attempting to defecate in the lying position, a dyssynergic pattern was seen in 36% of subjects with empty rectum and 24% with distended rectum. When sitting, 20% showed dyssynergia with empty rectum and 8% with distended rectum. More subjects (p < 0.05) showed dyssynergia in lying position. When lying, 60% could not expel balloon and 44% FECOM. When sitting, fewer (p < 0.05) failed to expel balloon (16%) or FECOM (4%). FECOM expulsion time was quicker (p < 0.02). Stool-like sensation was more commonly (p < 0.005) evoked by FECOM than balloon.
In the lying position, one-third showed dyssynergia and one-half could not expel artificial stool. Whereas when sitting with distended rectum, most showed normal defecation pattern and ability to expel stool. Thus, body position, sensation of stooling and stool characteristics may each influence defecation. Defecation is best evaluated in the sitting position with artificial stool.

Affiliation

Division of Gastroenterology/Hepatology, Department of Internal Medicine, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242-1009, USA.

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2006Dec
Am. J. Gastroenterol.
Am J Gastroenterol 2006 Dec 6;101(12):2790-6. Epub 2006 Oct 6.

Whether defecation is influenced by body position or stool characteristics is unclear.
We investigated effects of body position, presence of stool-like sensation, and stool form on defecation patterns and manometric profiles.
Rectal and anal pressures were assessed in 25 healthy volunteers during attempted defecation either in the lying or sitting positions and with balloon-filled or empty rectum. Subjects also expelled a water-filled (50 cc) balloon or silicone-stool (FECOM) either lying or sitting and rated their stooling sensation.
When attempting to defecate in the lying position, a dyssynergic pattern was seen in 36% of subjects with empty rectum and 24% with distended rectum. When sitting, 20% showed dyssynergia with empty rectum and 8% with distended rectum. More subjects (p < 0.05) showed dyssynergia in lying position. When lying, 60% could not expel balloon and 44% FECOM. When sitting, fewer (p < 0.05) failed to expel balloon (16%) or FECOM (4%). FECOM expulsion time was quicker (p < 0.02). Stool-like sensation was more commonly (p < 0.005) evoked by FECOM than balloon.
In the lying position, one-third showed dyssynergia and one-half could not expel artificial stool. Whereas when sitting with distended rectum, most showed normal defecation pattern and ability to expel stool. Thus, body position, sensation of stooling and stool characteristics may each influence defecation. Defecation is best evaluated in the sitting position with artificial stool.

1998Jul
Am. J. Gastroenterol.
Am J Gastroenterol 1998 Jul;93(7):1042-50

The pathophysiology of obstructive defecation is unclear. We investigated whether impaired rectoanal coordination causes obstructive defecation and if this dysfunction can be corrected by biofeedback therapy.
We prospectively studied 25 healthy subjects and 35 consecutive patients with constipation (>1 year) with anorectal manometry and balloon expulsion test. Symptoms were assessed from diary cards. Patients found to have obstructive defecation were offered biofeedback therapy. After treatment, their defecation dynamics and symptoms were reassessed.
Eighteen patients had obstructive defecation and 17 had normal defecation dynamics (nonobstructive). Five normals (20%) exhibited obstructive pattern but only one failed to expel balloon. In the obstructive group, during straining, the intrarectal pressure and defecation index were lower (p < 0.05), and anal residual pressure was higher (p < 0.01) when compared with the nonobstructive group or normals. After biofeedback therapy, the intrarectal pressure and defecation index increased (p < 0.02) and anal residual pressure decreased (p < 0.001); stool frequency, degree of straining, and bowel satisfaction scores improved (p < 0.05); 67% stopped laxatives and 11 patients discontinued stooling with digitation.
Patients with obstructive defecation showed impaired rectal contraction, paradoxical anal contraction, or inadequate anal relaxation. These features suggest that rectoanal coordination was impaired. Biofeedback therapy rectified these pathophysiological disturbances and improved constipation.

Constipation is a common disorder, and current treatments are generally unsatisfactory. Biofeedback might help patients with constipation and dyssynergic defecation, but its efficacy is unproven, and whether improvements are due to operant conditioning or personal attention is unknown.
In a prospective randomized trial, we investigated the efficacy of biofeedback (manometric-assisted anal relaxation, muscle coordination, and simulated defecation training; biofeedback) with either sham feedback therapy (sham) or standard therapy (diet, exercise, laxatives; standard) in 77 subjects (69 women) with chronic constipation and dyssynergic defecation. At baseline and after treatment (3 months), physiologic changes were assessed by anorectal manometry, balloon expulsion, and colonic transit study and symptomatic changes and stool characteristics by visual analog scale and prospective stool diary. Primary outcome measures (intention-to-treat analysis) included presence of dyssynergia, balloon expulsion time, number of complete spontaneous bowel movements, and global bowel satisfaction.
Subjects in the biofeedback group were more likely to correct dyssynergia (P < .0001), improve defecation index (P < .0001), and decrease balloon expulsion time (P = .02) than other groups. Colonic transit improved after biofeedback or standard (P = .01) but not after sham. In the biofeedback group, the number of complete spontaneous bowel movements increased (P < .02) and was higher (P < .05) than in other groups, and use of digital maneuvers decreased (P = .03). Global bowel satisfaction was higher (P = .04) in the biofeedback than sham group.
Biofeedback improves constipation and physiologic characteristics of bowel function in patients with dyssynergia. This effect is mediated by modifying physiologic behavior and colorectal function. Biofeedback is the preferred treatment for constipated patients with dyssynergia.

To elucidate the role of the rectosigmoid junction (RSJ) in the mechanism of defecation.
Fourteen healthy volunteers were enrolled in the study (10 men, 4 women; mean age 38.2 +/- 10.6 years). The pressures in the rectum, anal canal, and RSJ as well as rectal balloon expulsion were recorded in response to balloon distension of the RSJ in increments of 10 ml of carbon dioxide (CO2) to 50 ml. The experiments were repeated after individual anesthetization of the RSJ, rectum, and anal canal. The expulsion of a 50-ml distended balloon located in the anesthetized rectum was tested.
RSJ distension with 10 ml of CO2 produced no significant pressure changes in the RSJ, rectum, or anal canal. A 20-ml distension effected a significant pressure rise in the RSJ (P < 0.05) and the rectum (P < 0.01) and a decline in the anal canal (P < 0.05); the rectal balloon was expelled to the exterior. Similar pressure changes (P > 0.05) were recorded with a 30-, 40-, and 50-ml balloon distension. The mean latency for the RSJ response was 12.6 +/- 2.2 ms and for the rectum 15.8 +/- 2.6 ms. The balloon, distended with 50 ml of CO2 and located in the rectum, was not expelled to the exterior. Balloon expulsion occurred only with distension with volumes of above 80 ml. Individual anesthetization of the RSJ, rectum, and anal canal followed by RSJ distension produced no significant pressure changes in RSJ, rectum, and anal canal as well as no rectal balloon expulsion.
The rectal contraction upon RSJ distension affirms the hypothesis of the possible involvement of a reflex, which we term "rectosigmoid-rectal reflex." This reflex relationship is evidenced by reproducibility and its absence on anesthetization of either the RSJ or the rectum, both presumably representing the two arms of the reflex arc. It is postulated that stools passing from the sigmoid colon to the rectum distend the RSJ and evoke the rectosigmoid-rectal reflex, which produces rectal contraction. The role of the reflex in defecation disorders needs to be studied.

The anorectum and lower urinary tract (LUT) are closely related organs: anorectal and LUT dysfunction often occur concomitant, and therapeutic actions in one organ may influence function of the other. The aim of this study was to explore the physiologic relationship between anorectal and LUT function in healthy volunteers.
Two groups of healthy volunteers were studied. Anorectal and LUT sensory function was evaluated in ten volunteers during rectal balloon and bladder filling. The second group of 100 volunteers reported on defecation and micturition during five toilet visits. They graded perception on rectal and bladder fullness on a visual analogue scale and marked which organ evacuation started first.
The volumes at which the different sensations of rectal filling during balloon distension were perceived was significantly higher with full bladder than with empty bladder (P<0.04). Five hundred toilet visits were described. Although mean perception grade of rectal fullness was significantly higher than for bladder fullness (P<0.0001), defecation started only in 36% of the reported visits before micturition. Only when the rectum was considered completely full, or the bladder completely empty, defecation occurred more frequently before micturition. In all other cases, micturition more frequently occurred before defecation.
When the bladder is full, sensation of rectal filling is decreased. When healthy people visit the toilet to defecate, the initiation of micturition often precedes that of defecation, even if both organs are considered equally full.

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Affiliation Details

  • Division of Gastroenterology/Hepatology, Department of Internal Medicine, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242-1009, USA.
  • Division of Gastroenterology/Hepatology
Affiliation Division of Gastroenterology/Hepatology, Department of Internal Medicine, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242-1009, USA.