Objective: The aim of this study was to investigate autonomic activity by means of heart rate variability analysis in a sample of irritable bowel syndrome (IBS) patients, allowing stratification into IBS symptom subgroups.
Methods: Thirty-three female IBS patients (mean age 37 yr) and 21 healthy female controls (mean age 38 yr) participated. Patients were stratified into 16 subjects with only lower bowel symptoms (IBS only) and 17 subjects with both lower bowel and dyspeptic symptoms (IBS+D). The protocol included standard polysomnography to assess stages of sleep with concomitant electrocardiographic measurement of beat-to-beat intervals of the cardiac cycle. Fifteen-min segments were selected from presleep waking, stage 2 of non-rapid eye movement (REM), and REM sleep and analyzed by spectral analysis of heart rate variability to calculate the high-frequency band, a measure of vagal tone, and the low-frequency/high-frequency ratio, an indicator of sympathovagal balance.
Results: The high-frequency band power during REM sleep was significantly lower, indicating substantial vagal withdrawal in IBS-only patients compared with IBS+D patients and controls. The low-frequency/high-frequency band ratio was significantly higher during REM sleep for IBS-only patients.
Conclusions: IBS-only patients had greater sympathetic dominance, indicated by elevated low-frequency/high-frequency band ratio, during REM sleep because of vagal withdrawal. Autonomic functioning, unique to REM sleep, differentiates IBS symptom subgroups, suggesting that autonomic functioning during REM sleep may be a useful biological marker to identify IBS patient subgroups.