The Guarding Reflex Anal, Study of the Modulation Function of Rectal Distension

The term Guarding Reflex refers to a progressive, involuntary increase in the external urethral sphincter (EUS) activity during bladder filling. Situations increasing intra-abdominal pressure, as cough, or Valsalva effort, increases this EUS activity. This is a mechanism of continence, preventing from unwanted urine leakage in situation of stress.

Anal continence is essential, and any impairment of this function can have a severe impact on quality of life. The anal canal is composed of the internal anal sphincter (IAS) at the top, with smooth musculature and the external anal sphincter (EAS) at the bottom, with striated musculature. The activity of the external anal sphincter is controlled by sympathetic and somatic innervation. Anal continence at rest is mainly insured by the tone of the internal anal sphincter. The external anal sphincter activity during gradually rectal filling is continuous and varies according to the volume of rectal distension.

During an effort, or a cough, the increasing intra-abdominal pressure is transmitted to the rectum. Increased intra-abdominal pressure during an expiratory against resistance effort proportionally increases the response of the external anal sphincter. The reflex contraction of the EAS is an active mechanism under spinal control, and result in a stronger contraction than a voluntary one. This reflex contraction is the equivalent of "Guarding Reflex" and provides part of the continence in situation of stress.

Previous studies focused on the search of segmental or supra segmental control of this reflex. Few studies have examined factors affecting the modulation of the EAS response during stress.

The main purpose of this study is to research a correlation between the ano rectal distension volume and the external anal sphincter response to a stress.

Patient over eighteen years old, consulting for anorectal manometry examination in order to explore anorectal disorders are included.

Age, sex, ano rectal symptoms, treatments, past history, manometrics data, area under the curve for electromyography activity of the EAS and intercostal muscles during cough with a Valsalva effort are recorded. Slope curve representing the EAS response to stress according to the intercostal activity reflecting cough (intensity response curve) effort are calculated.

The protocol consists in distending the rectum at four different volumes : empty rectum, volume for first sensation of filling, volume for desire to defecate and maximal tolerable volume. For each volume, the patient is asked to cough three times gradually, and perform a Valsalva effort three times gradually.

Primary outcome is the difference in curve slope (intensity response curves) between empty rectum and maximal tolerable volume at cough

Secondary outcomes are the differences in curve slope between each volume of distension at cough, and the differences in curve slope between each volume of distension at Valsalva type effort.

Inclusion criteria

• Over 18 years old
• Ano rectal disorders

Exclusion criteria

• Inability to understand simple orders
• Anal hypotonia
• Peripheral neurological disorder
• Anal incontinence