Characterization of autonomic dysfunction in patients with irritable bowel syndrome by means of heart rate variability studies

Abstract

OBJECTIVE: Our aim was to characterize autonomic dysfunction in patients with irritable bowel syndrome (IBS) using heart rate variability (HRV) studies. METHODS: EKG signals were obtained from 35 patients (mean age, 39.1 ± 9.5 yr, M:F ratio = 2.9:1) and 18 healthy controls (mean age, 38.2 ± 6.5 yr, M:F ratio = 2:1) in supine, standing, and deep-breathing modes. Fast Fourier transformation and autoregressive techniques were used to analyze the HRV power spectra in very low (VLF, 0.0078–0.04 Hz), low (LF, 0.04–0.14 Hz), and high (HF, 0.14–0.4 Hz) frequency bands. RESULTS: In the supine position, the VLF power spectral density (PSD) in IBS was significantly higher than normal (3 vs 1.3 beats per minute [bpm] 2/Hz, p < 0.01). On changing from the supine to standing position, the normals (NC) had raised median PSDs in the VLF (1.3 vs 12.8 bpm 2/Hz, p < 0.01) and LF (1.6 vs 6.1 bpm 2/Hz, p < 0.01) bands, as a sign of increased sympathetic tone, whereas the median HF PSDs (parasympathetic tone) remained unchanged (1.8 bpm 2/Hz each, p = 0.8). Similarly, the IBS patients had increased VLF (3.04 vs 14.93 bpm 2/Hz, p < 0.01) and LF (2.8 vs 8.7 bpm 2/Hz, p < 0.01) PSDs on standing up, but the HF PSD was also raised (from 2.4 to 5.7 bpm 2/Hz, p = 0.04). On changing from standing to the deep-breathing mode, the normals had a significant increase in the HF (from 1.8 to 10.3 bpm 2/Hz, p < 0.001) and a significant reduction of the VLF (from 12.8 to 2.2 bpm 2/Hz, p < 0.01) PSDs. The reduction of the LF PSD was not significant (from 6.1 to 5.6 bpm 2/Hz, p = 0.6). In IBS, HF PSD remained constant (5.7 bpm 2/Hz each, p = 0.6), whereas the LF PSD increased from 8.7 to 24.2 bpm 2/Hz ( p < 0.0001). The VLF PSD was reduced (from 14.9 to 4.1 bpm 2/Hz, p < 0.0001). In IBS, the median sympathovagal outflow ratio was significantly lower in the standing position (1.4 vs 2.8, p < 0.02) and higher in the deep-breathing mode (7.33 vs 0.42, p < 0.0001) than normal. CONCLUSIONS: IBS patients have reduced sympathetic influence on the heart period in response to orthostatic stress and diminished parasympathetic modulation during deep breathing.