Disorder of autonomic nervous system and its vulnerability to external stimulation in functional dyspepsia.

To elucidate the role of autonomic nervous system in functional dyspepsia patients, we examined 24-h heart rate variability: the basal levels, responses after lunch, cold pressor and mental arithmetic tests, and the efficacy of an autonomic drug (tofisopam). The high-frequency component (HF: 0.15-0.40 Hz) and the ratio of HF to the low-frequency component (LF: 0.04-0.15 Hz; LF/HF ratio) were used as indicators of parasympathetic and sympathetic autonomic nervous system function. The HF component in the 24-h, daytime, and nighttime was low in 86.7%, 97.8%, and 66.7% of patients (n = 45) and the LF/HF ratio was high in 51.1%, 73.3%, and 26.6% of patients. Gastrointestinal symptom tended to be severe in patients with autonomic nervous system disorder (p = 0.085). The abnormal response in HF component after lunch occurred in 38.2% (13/34) of patients who revealed a greater tendency towards in indigestion score (p = 0.061). Delays in recovery to the basal autonomic nervous system level after stimulus of the cold pressor and the mental arithmetic tests occurred in parts of patients. Tofisopam partially improved autonomic nervous system dysfunction and abdominal pain/indigestion. Imbalanced autonomic nervous system function and vulnerability for recovery from external stimuli were observed in functional dyspepsia patients, which was associated with dyspeptic symptoms.