Characterizing the recto-anal inhibitory reflex parameters in spinal cord injured subjects compared to published healthy control values

Abstract Study Design: Cohort study design Objectives: (i) Compare Rectoanal Inhibitory Reflex (RAIR) parameters in spinal cord injury (SCI) patients vs. published healthy control (HC) values (ii) Explore correlations and associations between RAIR parameters and SCI duration, location, and AIS levels. Setting: University of Michigan Methods: Prospective analysis of SCI participants who underwent High Resolution-Anorectal Manometry (HR-ARM). RAIR was tested by inflating 50 ml into the rectal balloon and immediately deflating. RAIR presence = ≥25% of internal anal sphincter pressure [IAS] (mmHg) amplitude reduction. RAIR parameters included: IAS (mmHg), reflex duration [RD] (seconds), and amplitude reduction [AR] (%). Subjects were categorized by AIS level and completeness of injury. Results: 30 SCI (cervical= 20; thoracic= 10) subjects underwent HR-ARM. Demographics included: 80.0% male, 90.0% Caucasian, mean age of 48.3 (14.2) (Range:24-75), and mean BMI of 26.6 (7.0) (Range:16.9–41.2). SCI subjects have significant mean differences, RD ( p =<0.001), and AR ( p =<0.001), compared to HC (N = 21), but no significant mean differences in IAS pressure. There were no significant correlations between SCI injury duration and IAS ( r =-.17; p =NS), RD ( r= 0.31; p =NS) and AR ( r= -0.09; p =NS). No significant mean differences between SCI level and the AIS completeness within RAIR parameters. Conclusion: Cervical and Thoracic SCI subjects have abnormal RAIR parameters compared to healthy controls. As there is minimal scientific evidence demonstrating digital rectal stimulation [DRS] as an effective method of promoting IAS relaxation for stool evacuation, an altered RAIR response on HR-ARM for SCI subjects provides a scientific basis to determine the use of DRS for bowel evacuation.