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Anorectal Manometry
High-definition anorectal manometry is a state-of-the-art technique used to measure anorectal muscle function in real-time and in three-dimensions. The anal sphincters are composed to two types of muscles; the involuntary internal sphincters and the voluntary external sphincters. The coordinated function of these muscles are essential to normal defecation.
1. Content moving into the rectum increasing rectal pressure.
2. This triggers the involuntary relaxation of the internal anal sphincter, this reflex action is also called rectoanal inhibitory reflux (RAIR).
3. If not ready for defecation, the external anal sphincter contracts to hold content in rectum.
4. For defecation, rectal pressure is increased via abdominal contraction while anal sphincters relax to push content to anus
Preparing for high-definition anorectal manometry (ARM)
You will be asked to use an enema (e.g. Fleet enema) at home to clear your bowels and refrain from eating 12 hours before the test.
During the procedure, you will be asked to lie on your side. A small catheter is passed through your anal canal into the rectum.
| Manoeuvres | What are you asked to do? | What are we measuring? |
|---|---|---|
| Resting | Asked to remain still for 30 seconds | Baseline pressure measurements are taken |
| Squeeze | Asked to squeeze your anal sphincter | The squeeze strength of the internal and external anal sphincters |
| Push | Simulate defecation | An increase in rectal pressure and relaxation of the anal sphincter muscles |
| Balloon fill | A small balloon is inflated in the rectum and you are asked to respond at first sensation, urge, and discomfort | Simulated content triggering the rectoanal inhibitory reflex (RAIR): an involuntary relaxation of the internal anal sphincter. Rectal compliance and sensation are also measured |
Anorectal motility disorders
Dyssynergic defecation
Dyssynergic defecation is caused by the dis-coordination of muscles during the push manoeuvre, the external anal sphincter may not relax appropriately or even paradoxically contract. This causes difficulties defecating and excessive straining.
The causes of dyssynergic defecation can range from mental stress, inappropriate diet, to improper defecation technique. Biofeedback therapy is generally very effective at treating dyssynergic defecation and has an improvement rate in 80% of patients.
Faecal incontinence
Faecal incontinence generally have low resting anal sphincter pressures along with weak squeeze pressures. Women and the elderly tend to have weaker sphincter pressures and are more prone to faecal incontinence. Biofeedback and Kegel (pelvic floor) exercises are effective treatment in a majority of cases. Dietary changes to bulk up the stool such as increased fibre and reduced coffee and alcohol intake can further improve the condition.
In some rare cases, the presence of a large rectocele or rectal prolapse can cause faecal incontinence. Surgical interventions, such as Altemeier's procedure (perineal rectosigmoidectomy) have shown excellent results.
Constipation
Patients with constipation often have high resting and squeeze anal sphincter pressures. Minimally invasive sphincterotomy surgery or botox injections in puborectalis muscle can help relax the anal sphincter and improve symptoms in the majority of cases.
Megarectum and slow intestinal transit can also cause constipation. In these cases, a strict regiment of laxatives, dietary management, and keeping a faecal diary have been proven to be successful.
Neuropathic cases, such as multiple sclerosis and Hirschsprung's, can cause constipation by the loss of nerves in the colon. Treatment involves a bowel regiment and laxative usage.
