Characterizing Rectoanal Inhibitory Reflex in Constipated Patients using Anorectal Manometry

Posted by Clark Love on Jul 7, 2022 1:25:51 PM



Anorectal manometry (ARM) is a diagnostic test used to evaluate abnormalities

of the anal sphincter muscles and the rectum. If you have a patient who presents an abnormal rectoanal inhibitory reflex (

RAIR) that impacts their ability to defecate normally, it may be worth considering anorectal manometry to assess their need for further treatment. Here's what to know about this diagnostic tool.

Anorectal Manometry Fundamentals

Anorectal manometry is a test that works by measuring the pressure of the anal sphincter and the rectum. It entails the insertion of a flexible, lubricated catheter into the rectum via the anus, passing the exterior anal sphincter (EAS) and interior anal sphincter (IAS). This catheter contains a series of high-resolution transducers that feeds data into a machine that measures pressure transients.


The test typically begins by having the patient assume a semi-recumbent position and inserting the catheter about 4 cm into the rectum. As it is slowly withdrawn, the doctor or nurse technician may instruct the patient to attempt maneuvers such as trying to defecate or cough as readings are continuously gathered, revealing resting and squeezing pressures.


This data paints a vivid picture of pressures in posterior, left, anterior, and right quadrants to help practitioners evaluate symptoms such as:

  • Reduced anorectal sensation,
  • Abnormal sphincter function or deficiencies,
  • Anorectal pressure asymmetry and dysfunction[1], and
  • Paradoxical contractions or dyssynergia of the pelvic floor.[2]


Pressure-measuring ARM tests are commonly used in conjunction with other diagnostics. For instance, it's commonly paired with procedures where patients attempt to describe their sensation of or expel a water-inflatable balloon.


Anorectal Manometry and Characterization of RAIR

How might ARM play a role in helping caregivers understand RAIR and the factors that contribute to it? The anorectal manometry test is used to help determine the cause of problems with bowel movements, including incontinence, constipation, and difficulties with evacuation. It may also be used to assess the need for surgery to correct these problems.

The key to remember is that the rectoanal inhibitory reflex ought to happen in a particular order – Ideally, the anal sphincter muscles should relax after the rectum is distended as people attempt to pass stools by pushing. In constipated patients, however, these muscles might inappropriately tighten at the wrong time.

ARM tests can aid caregivers by building a topographic map of what happens during an individual's rectoanal inhibitory reflex. One 2012 study demonstrated how different patients' relaxation pressures varied along the anterior-posterior and circumferential axes both at rest and during RAIR. This study also showed that appropriately administered ARM tests could be used to create detailed three-dimensional maps of muscle activity in different areas[3].

The ability to map out IAS and EAS function visually and over time may also improve the usefulness of associated diagnostic procedures, such as anal sphincter electromyography (EMG). For instance, high fidelity ARM could conceivably make it easier to associate EMG activity with transients that occur during RAIR cycles.

It's also worth noting that ARM plays a role in the confirmation or ruling out of other conditions that may contribute to constipation. For instance, Hirschsprung's disease (HD), which commonly presents chronic constipation, is also associated with an absent rectoanal inhibitory reflex related to the absence of distal GI tract ganglion cells causing IAS achalasia. A 2020 analysis of 1,072 ARM results, however, revealed that a significant minority of young patients presented IAS achalasia for other reasons than HD, indicating that ARM could be a powerful tool for understanding the specific mechanisms of chronic constipation and improving care.[4]

Other researchers have taken an even stronger stance. One team went as far as to claim in 2018 that ARM tests can help exclude Hirschsprung's disease with total certainty after discovering that its 97 percent sensitivity rate was comparable to that of invasive rectal suction biopsy, the most common confirmation method for HD, although it's important to understand that anorectal manometry still isn't suitable for confirming HD.[5] Since this condition commonly occurs in very young patients, the minimally invasive ARM test could be a more viable option than biopsies for the early assessment of many GI cases even though it's by no means an all-out replacement.

Anorectal manometry may also help caregivers understand variations between different patient groups to ensure more accurate diagnoses at the individual level. For instance, high-resolution variants of the ARM test coupled with balloon expulsion tests revealed distinct patterns of dyssynergia between constipated men and women independent of what researchers would expect from sex-specific baseline differences.[6]

Finally, ARM is an accessible diagnostic procedure for a wide range of caregivers. Clinics, hospitals, endoscopy centers, and other practices can perform comprehensive, methodical testing – including anal sphincter EMG, balloon expulsion, and other procedures – without having to train staff or purchase equipment. They can also choose to have the results interpreted by board-certified gastroenterologists and integrated into secure, web-based health records software, making it easier to draw accurate conclusions.


Putting Anorectal Manometry to Good Use at Your Practice

Brighter Health Network makes it easy to expand your services to include ARM testing instead of having to send patients to specialists. We provide comprehensive services that let you conduct tests on-site with the help of skilled nurses so that your existing staff can concentrate on other jobs. We also offer temporary staffing designed to fill in gaps caused by people leaving or taking time off.

Our goal is to make ARM and urodynamic testing administration as straightforward as possible so that your patients benefit. Our team members are fully trained in modern ARM equipment and techniques, so they can readily adapt to the way you work and conduct testing according to your precise requirements.

If want to integrate comprehensive anorectal manometry into your operations – or continue providing the service during staffing fluctuations? Get in touch with an expert at Brighter Health Network today for a quote.

Get Anorectal Manometry Brochure and Pricing


[1] Scott, S.M., Carrington, E.V. The London Classification: Improving Characterization and Classification of Anorectal Function with Anorectal Manometry. Curr Gastroenterol Rep 22, 55 (2020).

[2] Craft TM, Parr MJ, Nolan JP (2004-11-10). Key Topics in Critical Care, Second Edition. CRC Press. p. 1011. ISBN 9781841843582.

[3] Cheeney, G et al. "Topographic and manometric characterization of the recto-anal inhibitory reflex." Neurogastroenterology and motility: the official journal of the European Gastrointestinal Motility Society vol. 24,3 (2012): e147-54. doi:10.1111/j.1365-2982.2011.01857.x

[4] Baaleman, D.F., Malamisura, M., Benninga, M.A., Bali, N., Vaz, K.H., Yacob, D., Di Lorenzo, C. and Lu, P.L. (2021), The not-so-rare absent RAIR: Internal anal sphincter achalasia in a review of 1072 children with constipation undergoing high-resolution anorectal manometry. Neurogastroenterology & Motility, 33: e14028.

[5] Meinds, Rob J.∗; Trzpis, Monika†; Broens, Paul M.A.∗,† Anorectal Manometry May Reduce the Number of Rectal Suction Biopsy Procedures Needed to Diagnose Hirschsprung Disease, Journal of Pediatric Gastroenterology and Nutrition: September 2018 - Volume 67 - Issue 3 - p 322-327

DOI: 10.1097/MPG.0000000000002000

[6] Prichard, D.O., Fetzer, J. Recto-anal Pressures in Constipated Men and Women Undergoing High-Resolution Anorectal Manometry. Dig Dis Sci (2022).

Topics: Anorectal Manometry, Rectoanal Inhibitory Reflexes

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