Anorectal manometry is a method of examining the function and coordination of the internal and external sphincter, pelvic floor, and rectum by using a manometric device placed in the rectum to contract and relax the anus, and to help distinguish the type of outlet constipation. Introduction The internal and external anal sphincters are the anatomical basis of the pressure in the anal canal. In the resting state, approximately 80% of the anal canal pressure is generated by the contraction of the internal sphincter tone and the remaining 20% by the contraction of the external sphincter tone. In the case of active contraction of the anal sphincter, the anal canal pressure rises significantly and is generated mainly by contraction of the external sphincter. Therefore, measurement of anal canal pressure at rest and in the contracted state provides insight into the functional status of the internal and external anal sphincters. Along with the measurement of anorectal pressure, a number of indicators can be measured, including the rectal-anal inhibition reflex, the length of the anal canal high-pressure zone (also called the functional length of the anal canal), rectal sensory volume and maximum volume, and rectal compliance. Patient preparation No special preparation is usually required. Patients should defecate on their own one or two hours before the examination to avoid having feces in the rectum that may interfere with the examination. At the same time, do not perform enema, rectal finger examination or anoscopy to avoid interference with sphincter function and rectal mucosa, which may affect the examination results. The examiner should debug the instrument beforehand, and some necessary supplies, such as sterile gloves, syringes, paraffin oil, toilet paper, and cloth pads, should be placed at a convenient place for ready access during the examination. Operation method The patient lies on the left side, first place the balloon or probe in the anal canal, measure the anal canal resting pressure and maximum systolic pressure, then send the balloon into the rectal pot belly to measure the rectal resting pressure. The catheter is connected to a dragging device to measure the functional length of the sphincter. The catheter is replaced with a double-bladder catheter, with the large bursa placed in the abdominal jug and the small bursa (or probe) placed in the anal canal. A rapid inflation of 50-100 resistance into the large bursa and a decrease in anal canal pressure with a time duration greater than 30 seconds is considered a positive anal rectal inhibition reflex. Clinical significance Patients with anal incontinence have a significant decrease in anal canal resting pressure and systolic pressure, and the length of the anal canal hypertensive zone becomes shorter or disappears; irritating lesions around the rectum and anal canal, such as anal fissure and inter-sphincter abscess, can cause an increase in anal canal resting pressure; the recto-anal inhibition reflex disappears in patients with congenital megacolon, and the reflex can be lacking or retarded in patients with rectal prolapse; rectal sensory volume, maximum volume and compliance are significantly increased in patients with megarectum The inflammatory diseases of the rectum and tissue fibrosis after radiotherapy can cause a decrease in rectal compliance. The anorectal manometry can also provide objective indicators for preoperative condition and evaluation of the function of the anorectal sphincter before and after surgery. For example, if preoperative anorectal manometry is performed in patients with anal fissures, internal sphincterotomy can be performed for those with significantly elevated resting pressure, which can achieve better results, otherwise the results are not good; in patients with anal incontinence who undergo sphincter repair or formation, anorectal manometry can be performed before and after surgery to observe the postoperative rebound of anal canal pressure and the recovery of high pressure area, which can provide an objective basis for clinical efficacy.