Seasonal Changes in Heart Rate Variability in 11- to 13-Year-Old Girls

Heart rate variability (HRV) was assessed each quarter during a year in 11- to 13-year-old girls with a Valenta medical diagnostic system. The HRV was highest in winter and lowest in summer (in 12-year-old girls) and autumn (in 11- and 13-year-old girls), indicating seasonal changes in the degree of b-adrenergic effects on the heart (lowest in winter and highest in summer and/or autumn). The changes were most pronounced in 11-year-old girls, i.e., at the onset of puberty. Seasonal changes in the HRV can be explained by changes in the blood levels of direct and indirect endogenous modulators of chemoresponsiveness and are considered to be a mechanism of human adaptation to external conditions.