Anal Sphincter Tone

Resting and squeeze pressures represent different control states of the anal sphincter complex. Resting pressure reflects baseline activity, particularly from the involuntary internal sphincter, whereas squeeze pressure reflects voluntary contraction of the external sphincter. Measuring both values helps clinicians evaluate whether continence mechanisms and conscious deferral of defecation are functioning appropriately.

Rectal distension initiates reflex relaxation of the internal sphincter, producing a change from its baseline contractile state. The external sphincter can then be consciously contracted to postpone defecation when bowel emptying is not appropriate. This interaction shows why continence depends on coordinated reflex and voluntary responses rather than on constant contraction alone.

Abnormal tone may contribute to either fecal incontinence or obstructed defecation. Because these conditions involve different continence and evacuation problems, the clinical significance of an abnormal finding depends on the patient’s symptoms and the broader examination. Tone assessment therefore contributes to diagnostic reasoning rather than providing a complete interpretation by itself.

Clinicians commonly begin with a digital rectal examination to assess tone directly. When additional measurement is needed, anorectal manometry provides pressure data, including resting and squeeze pressures. The examination offers a clinical assessment, while manometry adds quantified information that can support evaluation of suspected sphincter or pelvic floor dysfunction.

Anorectal manometry may be used when clinicians need more detailed information than the digital examination provides. By measuring resting and squeeze pressures, it characterizes baseline and voluntary sphincter function in quantitative terms. Those results can assist with diagnosis, guide treatment planning, and support evaluation of pelvic floor disorders when tone abnormalities are clinically relevant.

Assessment findings can inform several stages of clinical care, including diagnosis, treatment planning, and follow-up evaluation of pelvic floor disorders. They may help relate sphincter function to symptoms such as fecal incontinence or obstructed defecation. Using clinical examination and, when needed, pressure measurements gives clinicians information for interpreting functional abnormalities in context.