Autonomic regulation after exercise evidenced by spectral analysis of heart rate variability in asthmatic children

Background: Bronchial asthma is associated with abnormal autonomic nervous function in childhood. Exercise is one of the most common precipitating fac tors of acute asthmatic crises although the exact mechanism of autonomic re gulation in asthmatic children after exercise is unclear. Objective: The aim of this study was to investigate the features of autonom ic regulation after exercise in asthmatic and control children. Methods: Pulmonary function tests and heart rate variability spectral analy sis were performed in 15 asthmatic children and 7 control children (age 6 t o 15 years) during and after an exercise challenge. Results: The maximum % fall of forced expiratory volume in 1 second (FEV1) was significantly greater (P < .01) in asthmatic subjects (9.1 +/- 5.1%) th an in normal control subjects (1.0 +/- 2.5%). The high frequency band (HF) amplitude, an index of cardiac vagal tone, 5 minutes after exercise was sig nificantly higher (P < .05) in the asthmatic subjects (14.4 +/- 7.9 msec) t han in control subjects (5.9 +/- 2.6 msec). Furthermore, the difference in the HF amplitude between the control group and the exercise-induced asthma group was significant both 5 minutes (P < .01) and 10 minutes (P < .05) aft er challenge. There was a significant correlation (P = .565, P = .0165) bet ween HF amplitude 5 minutes after exercise and the magnitude of the decreas e in FEV1. On the other hand, no significant difference was observed in the low frequency band amplitude between the controls and the asthmatic subjec ts. The ratio of low frequency to high frequency power, which is suggested to correlate with cardiac sympathetic activity, did not differ between the two groups. Conclusion: These findings suggest that autonomic nervous activities, parti cularly vagal response after exercise, in asthmatic children is different f rom that in control children.