Seated Evaluation of Anorectal funcTion by High Resolution Anorectal Manometry: a Randomized Comparison of Measurements in the Seated and Left Lateral Positions

High Resolution Anorectal Manometry (HR-ARM) with data presented as pressure topography is a recent addition to the tests available for diagnosis of defecatory disorders including fecal incontinence and constipation.HR-ARM represents an advance on conventional manometry because closely spaced sensors across the anal sphincter remove the need for a pull-through procedure and facilitate data acquisition and interpretation. In particular measurements are not confounded by changes in position of the catheter relative to anal sphincter that occur during voluntary contraction and, especially, simulated defecation.

Notwithstanding these technological improvements, important concerns remain about the validity of manometry measurements during simulated defecation. These concerns are based on the observation in both conventional and HR-ARM that a large proportion of healthy individuals appear to have abnormal anorectal function ("dyssynergia") during simulated defecation.This limitation led to the recommendation that the finding of dyssynergia on manometry should be confirmed by defecography. This is unsatisfactory as diagnostic tests should not have a high rate of "false positives" and also because this increases the time and costs needed to complete diagnostic investigation in patients with defecatory disorders.

The high rate of abnormal findings in healthy individuals may be because current manometry procedures and other anorectal tests (e.g. rectal balloon expulsion) are usually performed, not in the upright, seated position (USP) usually adopted for defecation, but in the un-physiological left lateral position (LLP). Several factors may contribute. First, defecation in the LLP is not aided by gravity as it is in the sitting position. Second, anorectal anatomy may be altered and less conducive to the passage of stool in the LLP. Third, simulating defecation in the LLP does not reflect normal behavior and, despite optimal interaction and explanation by the investigator, changes in patient behavior may result in apparent "dyssynergia" Finally, social stress, related to proximity of the investigator observing defecation, makes individuals feel unable to strain at stool or attempt defecation.

A simple probe holder device that, by adhering to the skin is positioned at the natal cleft to support the ManoScan HR ARM catheter can be used to assess anorectal pressures in the sitting position (both produced by Given Imaging, Yoqeam, Israel). This simple device stabilizes the catheter position when the patient is in USP on a commode and allows the investigator to withdraw behind the curtains of the examination cubicle.