Anorectal physiology is very complex. Comprehensive studies on this area have been performed only recently so that it can be understood better. The test methods are anorectal manometry, defecography, anal continence tests, electromyography for the anal sphincter muscles and the pelvic floor muscles, and nerve stimulation tests. Recently, together with such test methods, images of the pathophysiology of patients with not only normal anal continence and defecation but also disorders of continence and defecation could be obtained, so the importance of anorectal physiologic testing is increasing more and more [1, 2]. Therefore, in this report, together with factors having effects on anal continence, physiological test methods performed commonly in a department of colorectal surgery and their clinical applications, as well as biofeedback therapies performed frequently in outpatient clinics, were examined.

It is difficult to define anal continence clearly; nonetheless, it implies the ability to completely control defecation. Anal continence is a complex serial process achieved by conscious will and local reflex. For normal anal continence, the following complex factors are mutually and closely associated (Table 1).

Coloanal anastomosis performed to preserve the anal sphincter muscles after a protectomy mediates diverse effects on anal continence. This is thought to be associated with the reduction of the dilation of the intestine, ischemic changes at diverse levels, a decrease in anal pressure, etc. Anal incontinence is developed temporary in some patients. In the initial period after surgery, the anorectal inhibitory reflex is absent and appears again later, which is thought to be a phenomenon that appears as the neorectal compliance is improved with time.

Anorectal manometry is a test measuring the function of the anal sphincter muscles objectively. This test can help to determine the most appropriate treatment method for anal incontinence patients by evaluating the contribution levels of the nerves and the muscles involved in anal continence, detecting the site of the anal sphincter injury caused by trauma, and evaluating the level. In addition, the levels of the functions of the sphincter muscles can be evaluated objectively prior to surgery that might affect anal continence, and is the test can be performed to evaluate the causes of chronic constipation in children and young adults. Generally, it measures the luminal pressure at 6-8 cm above the anal verge with 1 cm inter valusing a radial catheter. It shows the high pressure zone (which refers to the lengths of the anal sphincter muscles), the resting pressure, the squeezing pressure, the anorectal inhibitory reflex, the rectal sensibility, etc.

An electromyogram is performed primarily to examine the presence or absence of relaxation failure of the puborectalis muscles. Generally, a surface electrode (plug electrode) is inserted into the anus, and the electric activities of the external sphincter muscles and the puborectalis muscles during the resting period, the squeezing period, and the pushing period are recorded. To assess the presence or absence of relaxation failure of the puborectalis muscles, whether or not the electric activities of these muscles are reduced during defecation (pushing period) is examined.

Among motor nerve conduction tests used for anorectal physiologic tests, the most frequently applied test is the PNTML test, and the test evaluates the nerve control of the external sphincter muscles. The method is to insert the rubber-glove-covered index finger to which an electrode is attached into the rectum, stimulate the pudendal nerve from the right and the left ischial spine areas, and measure the latency to the contraction of the external anal sphincter muscles. The normal value is 1.9 ± 0.2 ms, and a value elevated more than this implies injury of the pubic nerves [17]. A prolongation of this value can be observed in anal incontinence, solitary rectal ulcer syndrome, injury of the external anal sphincter muscles, and refractory constipation patients [2].

Defecography is a useful test method to find functional, as well as morphological, abnormalities in patients with defecation disorder. It is also a very useful test method to determine appropriate surgical treatment methods [18]. This test is of help to diagnose rectal intessusception, enteroceles, sigmoidoceles, paradoxic puborectalis contraction, descending perineum syndrome, and rectoceles. [19].

Endoanal ultrasonography is of help to diagnose structural abnormalities of the anal sphincter muscles and adjacent tissues. Indications are preoperative staging of anal cancer, anal incontinence, perianal abscess, and complex and recurrent anal fistulae.

Biofeedback therapy was first performed on anal incontinence patients in 1974 by Engel et al. [20] and now it is being performed at many institutions. The purpose of this therapy is to enhance the contraction capacity of the external sphincter muscles and to teach patients to perceive and react even if the rectum is dilated slightly. According to the Cochrane review reported in 2000, proofs of biofeedback therapy being effective for the reduction of anal incontinence were concluded not to be sufficient [21]. Nonetheless this therapy has advantages in that it is non-invasive and safe. Therefore, it is recommended as the first therapeutic method to be performed for anal incontinence patients, and it is thought to be effective as an adjuvant therapy after anal sphincter repair.

By the introduction of anorectal physiological tests, objective information on anorectal, as well as pelvic floor, functions that were difficult to understand in the past can be obtained. Thus, not only the diagnosis of functional, as well as morphological, diseases in this area but also a determination of treatment strategies and their results can be predicted. Nonetheless, such tests vary depending on the test laboratory and examiner, and the accuracy is limited; hence, treatments should be decided by considering clinical symptoms, not by completely depending on the tests.