Latency measurement of rectoanal reflexes

Latency values of rectoanal reflexes may be altered in disorders of the pelvic floor. Evaluation of this relatively uninvestigated aspect of rectoanal reflexes may have diagnostic implications in patients with disorders of defecation.

We studied the latency of rectoanal inhibitory and excitatory reflexes to sequential balloon distention of the rectum with 60 ml and 120 ml of air in 14 normal controls (mean age, 41.5 (range, 19-66) years), in 14 patients with fecal incontinence (FI) (mean age, 44.2 (range, 28-72) years), and in 14 patients with slow transit constipation (STC) (mean age, 40.6 (range 22-68) years).

The mean latency of inhibition (FI = 5.3 seconds; STC = 4.6 seconds; controls = 5.1 seconds) was remarkably similar for the three groups (P = 0.19). The mean latency of excitation in the proximal anal canal (FI = 2.8 seconds; STC = 2.5 seconds; controls = 2.8 seconds) was comparable in the three groups (P = 0.58). The mean latency of excitation in the distal anal canal (FI = 4.8 seconds; STC = 2.6 seconds; controls = 2.7 seconds) was prolonged in patients who were incontinent compared with the other two groups (P < 0.01).

Proximal rectoanal excitation and inhibitory reflexes, when present, have a constant latency, irrespective of the underlying condition. The different latency values for proximal and distal rectoanal excitatory reflexes in patients with FI may indicate disparate denervation damage to the external anal sphincter.