Anorectal Manometry (ARM) is a specialized diagnostic procedure used to evaluate the function of the muscles and nerves that control bowel movements. This test precisely measures the pressures within the rectum and the anal sphincter muscles. By assessing the strength and coordination of these structures, doctors gain a clearer understanding of how the lower digestive tract works.
Why the Test is Necessary
A doctor typically recommends Anorectal Manometry for patients experiencing chronic issues with bowel control or evacuation. The primary reasons for ordering this test include investigating the cause of long-term constipation that has not responded to initial treatments. It is useful for identifying a condition called defecatory dysfunction, where the muscles fail to coordinate properly during a bowel movement.
The procedure also evaluates fecal incontinence, which is the inability to control the passage of stool. Manometry can pinpoint whether the anal sphincter muscles are too weak or if there is a problem with the reflexes that govern continence. It may also be used to assess the function of the anorectal muscles before and after certain surgical procedures.
Preparing for the Procedure
Proper preparation is necessary to ensure the test yields accurate results. Patients are usually asked to stop eating solid foods approximately six hours before the scheduled appointment. Limiting the intake of all liquids is also required for a few hours immediately preceding the test.
Adjustments to current medications are often required, especially for drugs that affect muscle motility or nerve function. Patients are typically instructed to temporarily stop taking narcotic pain relievers and certain promotility agents, sometimes for up to 48 hours before the procedure. The most important preparatory step is cleansing the lower bowel, which usually involves administering two over-the-counter enemas at home a couple of hours before arrival. This ensures the rectum is clear, as the presence of stool can interfere with the sensor readings.
The Testing Process
The Anorectal Manometry procedure is performed without general anesthesia and typically takes about 30 to 45 minutes to complete. The patient changes into a gown and is positioned lying on their left side with the knees bent toward the chest. A healthcare provider may first perform a brief digital rectal examination to check the general muscle tone and anatomy.
A small, flexible catheter, about the size of a thermometer, is then gently lubricated and inserted a few inches into the rectum. This catheter is equipped with multiple pressure-sensitive transducers that record muscle activity along the anal canal. The first readings measure the resting pressure, which is primarily maintained by the internal anal sphincter muscle.
The patient is then instructed to perform different maneuvers. They are asked to squeeze the anus as if trying to hold back a bowel movement; this measures the strength of the voluntary external anal sphincter. Next, the patient is asked to push or bear down as if having a bowel movement, and the pressure changes during this simulated evacuation are recorded.
During the test, a small balloon attached to the catheter is inflated incrementally with air or water to assess rectal sensation. The patient reports when they first feel the sensation of fullness, the urge to defecate, and the maximum volume they can comfortably tolerate. Following the manometry, a separate balloon expulsion test may be performed. The patient attempts to push out a water-filled balloon while sitting on a commode, and the time it takes provides information about the ability to coordinate the muscles necessary for defecation.
Understanding the Results
The pressure readings and reflex responses gathered during the test offer specific insight into the underlying cause of the patient’s symptoms. Low resting pressure in the anal canal suggests weakness in the internal anal sphincter, a common finding in fecal incontinence. Conversely, an abnormally high resting pressure may contribute to chronic constipation or anal pain.
When the patient attempts to push, the anal sphincter muscles should relax to allow evacuation while the rectal pressure increases. If the anal muscles tighten instead of relaxing, this inappropriate contraction is known as dyssynergia and is a frequent cause of outlet obstruction constipation.
The test also checks for the rectoanal inhibitory reflex (RAIR), a natural reflex where the internal anal sphincter temporarily relaxes when the rectum is stretched. An absent RAIR can indicate a specific nerve or muscle disorder in the rectum. Abnormalities in the rectal sensation test, such as feeling the urge to defecate at a very low volume (hypersensitivity) or a very high volume (reduced sensation), can point toward conditions like irritable bowel syndrome or a nerve issue. These findings guide the doctor toward a targeted treatment plan, which may include dietary changes, medications, or biofeedback.