Electromyography (sEMG) is one of the principal techniques used to evaluate the internal and external sphincters and pelvic floor muscles. Paradoxical sEMG is used to assess the role of the paradoxical puborectalis contraction during defecation. The patient is generally placed in the left lateral position. This study is performed noninvasively by using electromyography (sEMG) surface electrodes. The active electrodes are placed perianally and a ground electrode is placed on the patient to evaluate the sphincter muscle activity during normal resting and then with sphincter muscle activity during push (strain) and squeeze maneuvers can be studied.
Anorectal Manometry is performed to evaluate patients with constipation and/or fecal incontinence and is a basic study of anorectal function. It can provide useful information regarding the pathophysiology of these disorders or those that can cause anorectal pain. It provides information about anorectal pressures, muscle tone at rest and during squeezing, and the coordination between the rectum and the anal sphincters.
The most important parameters to evaluate during tests are Maximal voluntary squeeze pressure, rest/relax pressures and internal anal sphincter inhibitory reflex to rectal distension (RAIR), the rectal volume sensory thresholds, sphincter length to include the high-pressure zone (HPZ) and defecation dynamics (balloon expulsion study).
The study is performed with the patient in the left lateral position. Bowel preparation is recommended. A 4-channel catheter with a compliant balloon at the end is inserted to 6cm for pressure monitoring and measurements at every 1cm interval.
Maximal voluntary squeeze pressure is obtained by having the patient squeeze as hard as possible for 10-20 seconds and then repeat the squeeze once or twice with rest or relaxation of the muscles at 10-20 second intervals. The RAIR is the relaxation of the proximal internal anal sphincter in response to rectal distention. This is performed by inflating a balloon in the rectal lumen and observing for a decrease in the resting anal pressure. A drop of at least 50% of the resting pressure after distention in at least one channel is considered a positive reflex.
Rectal sensation measurements or volume sensory thresholds consist of intermittent balloon distension of the rectum and provide information on the rectal capacity that elicits urges to defecate. Distension of the rectum is registered in the brain. Fecal continence is maintained by the resting tone and reflex of the internal and external anal sphincters together with the muscle of the pelvic floor. Rectal compliance is measured from the data obtained during the rectal balloon sensations. Rectal compliance reflects the capacity and ability to distend the rectum.
Balloon expulsion may be performed to simulate defecation. The inability to expel the balloon or the time it takes to expel it is recorded.