Heart rate variability in normotensive healthy children with aging.

Although the heart rate variability (HRV) values in adults decrease with aging, those in children show a variety of changes. The present study was designed to investigate the relationship between HRV and aging, physique and blood pressure in 70 healthy male school children, between 6 and 12 years of age. The subjects were divided into 3 age groups (6-7, 8-9 and 10-12 years) and 3 other groups according to physique (thin, under -10%; normal, -10-20% and obese, over 20% of obesity index). After recording a 24-h ambulatory electrocardiograph, HRV was determined spectrally, using 3 components: the total-frequency (TF) component (0.01 to 0.5 Hz), the low-frequency (LF) component (0.04 to 0.15 Hz), the high-frequency (HF) component (0.15 to 0.5 Hz) and also a two component ratio (LF/HF). The HRV values between the 3 age groups had a significant effect on TF, LF and LF/HF during the 24-h period, with the values increasing with age. The HRV values between the 3 physique groups had no significant effect. Therefore, changes in HRV in school children are affected by age and not physique. It is possible that the increase in HRV values with age is caused by the development of the autonomic nervous system.

Seasonal variation in heart rate variability in asthmatic children.

Asthma is a "seasonal disease" with symptoms either aggravated by environmental changes during specific seasons or prevalent at certain times of the year for other reasons. We examined whether the heart rate variability (HRV) of asthmatic children changes by season. The HRV during a portion of one night (00:00-04:00) and day (12:00-16:00) and the entire 24h period (00:00-24:00) during each of the four seasons was analyzed. The data of 95 children with asthma and 106 healthy children, as controls, were assessed. In children with asthma during the 24h period, seasonal variation in the low-frequency (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 value in the summer was significantly higher than in autumn and spring (Scheffe 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 summer (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 of autonomic nervous system function, of asthmatic children is more susceptible to seasonal changes brought about by either endogenous annual rhythms or environmental weather phenomena.

[Circadian rhythm of parasympathetic nervous function in asthmatic children].

We examined the circadian rhythm of parasympathetic nervous function in asthmatic children. The subjects were 80 patients with asthma (mild 54 patients, moderate 15 patients and severe 11 patients) and 90 individuals in healthy children. All the patients underwent 24-electrocardiography in normal condition. We measured the %RR50 for hour and analyzed the rhythm using the single cosine fitting method, comparing the values of the Amplitude, the MESOR and the Acrophase in terms of the therapy and also the severity of asthma. Circadian rhythm disappeared in 9 of the 80 asthmatic children and was observed in all the individuals in the healthy children. The value of MESOR was lower in the asthmatic children than in the healthy children. There was no significant difference between the different severity or therapies in each group. In some asthmatic children, the circadian rhythm of parasympathetic nervous function disappeared, the parasympathetic nervous function was low in remission. It is suggested that the disorder of biologic rhythm is related to the pathogenesis of asthma.