Relation between anal electrosensitivity and rectal filling sensation and the influence of age

The aim of this study was to assess the effect of age and sex on the rectal filling sensation and anal electrosensitivity and to explore the relation between anal electrosensitivity and the parameters of the rectal filling sensation.

Anal mucosal electrosensitivity and anorectal manometry, including the rectal filling sensation test were performed in 19 control subjects; 10 were younger than 60 years and 9 were older than that. Altogether, there were 11 men and 8 women.

Anal electrosensitivity did not differ between the two age groups. Women had a significantly lower electrosensitivity 4 and 5 cm from the anal verge than men, as well as a significantly shorter anal high-pressure zone. The rectal filling sensation did not differ between sexes. In the older age group, the rectal volumes required to induce filling sensations were smaller than those observed in the younger age group, but rectal pressures were comparable; as a consequence, rectal compliance was lower in older subjects. Anal electrosensitivity at different anal levels did not correlate with the rectal volume or pressure parameters of successive rectal filling sensations. The pressure recorded in the proximal anal canal at the consecutive rectal filling sensations strongly correlated with the rectal balloon pressure needed to elicit them.

The zones of high anal electrosensitivity and high pressure seem to coincide. The fact that both are shorter in females did not influence the parameters of the rectal filling sensation. Lower rectal volumes but comparable rectal pressures were needed to induce the rectal filling sensation in the older age group. Rectal sensation did not correlate with anal electrosensitivity, probably because the receptors are not stimulated by the type of anal stimulation used or because different receptors are involved. Hence, the rectal filling sensation test cannot be replaced by the simpler anal electrosensitivity test.