Influence of Body Position on Defecation in Humans.

OBJECTIVES To compare three positions for defecation by measuring abdominal pressure and the anorectal angle simultaneously. METHODS We recruited six healthy volunteers. The videomanometric measures included simultaneous fluoroscopic images, abdominal pressures, subtracted rectal pressures and anal sphincter pressures. Three positions were used: sitting, sitting with the hip flexing at 60 ° with respect to the rest of the body, and squatting with the hip flexing at 22.5 ° with respect to the rest of the body. RESULTS Basal abdominal pressure before defecation on hip-flex sitting was lower than that with normal sitting, although the difference did not reach statistical significance. Basal abdominal pressure before defecation on squatting (26 cmH2 O) was lower than that with normal sitting (P < 0.01). Abdominal pressure increase (strain) on hip-flex sitting was lower than that with normal sitting, although this difference did not reach statistical significance. Similarly, the abdominal pressure increase on squatting was smaller than that with normal sitting, and yet the difference did not reach statistical significance. The rectoanal angle on defecation on hip-flex sitting did not differ from that with normal sitting. The rectoanal angle on defecation on squatting (126 °) was larger than that with normal sitting (100 °) (P < 0.05), and was also larger than that with hip-flex sitting (99 °) (P < 0.01). CONCLUSION The results of the present study suggest that the greater the hip flexion achieved by squatting, the straighter the rectoanal canal will be, and accordingly, less strain will be required for defecation.