Seasonal variation in heart rate variability in asthmatic children

Asthma is a "seasonal disease" with symptoms either aggravated by environme ntal changes during specific seasons or prevalent at certain times of the y ear for other reasons. We examined whether the heart rate variability (HRV) of asthmatic children changes by season. The HRV during a portion of one n ight (00:00-04:00) and day (12:00-16:00) and the entire 24h period (00:00-2 4:00) during each of the four seasons was analyzed. The data of 95 children with asthma and 106 healthy children, as controls, were assessed. In child ren with asthma during the 24h period, seasonal variation in the low-freque ncy (LF) band (0.04-0.15 Hz) and the high-frequency (HF) band (0.15-0.4 Hz) were detected (HF: F= 6.81, p = .0003, LF: F = 4.18, p = .008). The HF val ue in the summer was significantly higher than in autumn and spring (Scheff e test: autumn vs. summer, s = 4.46, p < .001; spring vs. summer, s = 2.86, p < .05), while the LF value in autumn was significantly lower than in sum mer (s = 3.42, p < .01). In the control group, no seasonal variation in HF, LF or LF/HF was detected. The findings infer the HRV,a surrogate measure o f autonomic nervous system function, of asthmatic children is more suscepti ble to seasonal changes brought about by either endogenous annual rhythms o r environmental weather phenomena.