Prospective Evaluation of Autonomic Function and Intestinal Blood Flow in Health and Irritable Bowel Syndrome Shows Differences Limited to Patients With Constipation Predominance

Background: Autonomic dysfunction may contribute to symptom generation in irritable bowel syndrome (IBS), possibly driven by psychological morbidity and activation of the hypothalamic-pituitary-adrenal axis. Previous data are conflicting, perhaps due to lack of accounting for differential bowel patterns in IBS (constipation vs. diarrhea) or by diverse methodologies used to measure autonomic function. Our aim was to determine if autonomic response differed between IBS subtypes and healthy controls.

Methods: Forty female volunteers (20 IBS and 20 healthy) underwent comprehensive autonomic testing, fasting and postprandially, and in response to cold pressor and deep breathing challenges. Pulse transit time (PTT) and ultrasound measurements of intestinal blood flow were used as measures of systemic and local autonomic function, respectively. Outcomes were adjusted for baseline psychological comorbidities and gastric emptying (measured concurrently with scintigraphy).

Key results: Findings, confined to IBS patients with predominant constipation (IBS-C), included (1) lower fasting and a trend to larger postprandial increase in superior mesenteric artery end-diastolic velocity; (2) lower fasting PTT, suggesting higher sympathetic tone, but no difference in postprandial PTT change; and (3) attenuated increase in postprandial aortic peak systolic velocity. Response to systemic autonomic challenges did not differ between IBS and health. Some psychological factors mediated differences between groups in the fasting, but not postprandial, state.

Conclusions and inferences: IBS-C patients display systemic and local autonomic imbalance providing some support for recent therapies aimed at modulating autonomic state specifically in this patient group (e.g., acustimulation).