BACKGROUND: Rectoanal inhibitory reflex (RAIR) is routinely assessed in anorectal manometry and is of clinical value in the diagnosis of patients with constipation. However, no quantitative analysis is currently available for the assessment of RAIR. The aim of this study was to evaluate the diagnostic value of quantitative assessment of RAIR in patients with constipation. METHODS: Nine healthy subjects, 22 constipation patients (CO) and 26 fecal incontinence patients (FI) were enrolled in this study. RAIR was solicited by inflating the balloon with various volumes from 10 to 50mL. The percentage of relaxation was determined on the basis of the rectal resting sphincter pressure and residual pressure with the balloon distention. RESULTS: Percentage of internal sphincter relaxation induced by rectal distention in constipation patients was significantly lower with distention of 20, 30, 40, and 50mL in comparison with that in healthy subjects (Mixed model, P<0.05). The volume of distention required to achieve a relaxation of 50% was significantly higher in patients with CO (37.3±3.1mL) than that in healthy subjects (27.8±2.6mL, P<0.03) or FI (26.3±2.3mL, P<0.05). It was also found that the percentage of relaxation could be used to differentiate the patients with constipation with a specificity of 64% and a sensitivity of 67%. CONCLUSIONS: Patients with CO have impaired RAIR in comparison with healthy subjects and patients with FI. Quantitative assessment of RAIR is valuable in the diagnosis of patients with CO and may be incorporated in the clinical anorectal manometric test.
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