Autonomic nervous system function in women with irritable bowel syndrome.

Autonomic nervous system (ANS) balance was assessed in women with and without irritable bowel syndrome (IBS) using laboratory tests of function (ie, expiratory/inspiratory ratio, Valsalva, posture changes, and cold pressor) and spectral and nonspectral measures of heart rate variability (HRV). Women with (N = 103) and without IBS (N = 49) were recruited, interviewed, then completed a laboratory assessment and wore a 24-hr Holter monitor Analysis using the entire sample showed little difference between IBS and control women and between subgroups with IBS on either laboratory measures or 24-hr HRV measures. However, analysis restricted to those women with severe IBS symptoms showed quite pronounced differences between two IBS subgroups on 24-hr HRV measures. Parasympathetic tone was significantly lower and ANS balance was significantly higher in the constipation-predominant compared to the diarrhea-predominant group. Subgroups of women with IBS do differ in ANS function as measured by 24-hr HRV; however, these differences are only apparent among women with severe symptoms. These findings point out the importance of considering symptom severity when interpreting studies of IBS.