External Anal Sphincter Fatigability, an Electromyographic and Manometric Study

External anal sphincter is a Skeletal muscle under voluntary control. As described in previous studies, it is mainly composed of type 1 fibers. Fatigability is a concept which has been studied and described many times in skeletal limbs muscles. Two types of fatigue are described, peripheral of central fatigue. Fatigue can been physiologic but also pathologic (due to an affection of the muscle, the peripheral nervous system or the central nervous system). Many tools have been used to measure muscle fatigability (direct strength measure on isometric contraction, electromyography, echography, oxymetry...).

Besides many fatiguing methods have been developed for every each muscle depending on its histological structure.

Anal sphincter fatigability has already been described in few manometric studies with particularly 2 measures: Fatigue Rate and Fatigue Rate Index. Moreover, no fatiguing protocol has been standardized to study it.

The primary aim of this study is to define a fatiguing protocol for external anal sphincter in order to study it in further studies. Secondary aims are to assess Electromyography as a tool for measuring this fatigability and finally to assess the link between anal sphincter fatigability and symptoms reported by patients.

Patients over 18 years old, consulting for an Anorectal Manometry with a voluntary command on the external anal sphincter are included.

History and treatment, height, weight, sex, age, Fatigue impact scale, digestive symptoms with Neurologic Bowel Disorders score and Wexner scale, urinary tract symptoms with Urinary Symptom Profile (USP) score and electromyography (Root Mean Square (RMS) and Mean Power Frequency (MPF)) and manometric data (contraction peak, fatigue rate, fatigue rate index) were recorded.

The fatiguing protocol consists in 10 sustained external anal sphincter contractions with maximal voluntary contraction of 20 seconds followed by 10 seconds of resting. A training contraction is made before the fatiguing protocol. At the end of the protocol, patients undergo a classical anorectal manometry.

Primary outcome is the difference on root mean square in electromyography between the first and the last fatiguing contraction.

Secondary outcomes were mean power frequency and manometric data (i.e. Fatigue Rate index (FRI), Fatigue Rate (FR), contraction Peak)

Influence of age, sex, symptoms, pathologies, weight on fatigability will be studied in a second analysis