Autonomic nervous system reactivity in irritable bowel syndrome

Autonomic dysfunction has been implicated as one of the factors involved in the pathogenesis of irritable bowel syndrome (IBS).

To evaluate autonomic function in patients with IBS.

Thirty-five patients with IBS and thirty healthy controls were evaluated by standard cardiovascular reflex tests. Parasympathetic function was assessed by measuring heart rate responses to deep and slow breathing (E:I ratio), Valsalva maneuver (Valsalva ratio) and head-up tilt tests (30:15 ratio). Sympathetic adrenergic function was assessed by measuring diastolic blood pressure responses to handgrip test at 4 min and cold pressor test at 1 min and also by change in systolic blood pressure in response to head-up tilt. Autonomic functions were tested twice, keeping at least a one-week interval, to find out stability over time. Anxiety status of the subjects was assessed by evaluating responses to a questionnaire.

Parasympathetic reactivity was significantly increased in IBS patients as compared to controls during visit 1 (E:I 1.7 [SD 0.2] vs 1.4 [0.1], p < 0.001; Valsalva ratio 2.0 [0.3] vs 1.5 [0.1], p < 0.001; 30:15 ratio 1.2 [0.1] vs 1.1 [0.01], p < 0.001). Similar results were obtained in visit 2. The diastolic blood pressure responses during handgrip and cold pressor tests were not different in comparison to controls during both the visits. However, tilting resulted in less marked rise in diastolic blood pressure (9.1 [4.1] vs 12.1 [6.8] mmHg, p < 0.01) at 0.5 min and less rise in heart rate (6.0 [2.5] vs 10.3 [6.3] per min, p < 0.01) at 1 min in IBS patients during visit 1. The anxiety score of IBS patients was significantly higher (46.2 [3.2] vs 21.6 [1.7], p < 0.001).

IBS patients have increased parasympathetic reactivity and a high level of anxiety trait.