Influence of demographic, anthropometric and lifestyle characteristics on heart rate and its variability in the population.

OBJECTIVE: The purpose of this investigation was to assess the effects of age, gender, posture and their interactions, and of body mass index and lifestyle factors, on heart rate, its total variance and its variability in the frequency domain in a population-based sample of healthy subjects.
METHODS: RR interval and respiration were registered in the supine and in the standing position in 302 men and 312 women, aged 25-89 years; 424 subjects were healthy and had recordings suitable for analysis. Power spectral analysis was performed by use of autoregressive modelling and by fast Fourier transform, and the low-frequency (LF) and high-frequency (HF) components were expressed in both absolute (ms2) and normalized units
RESULTS: In the supine position, heart rate was higher in women than in men (P<0.001) and was not affected by age. Total variance and absolute LF and HF power markedly declined with age in each gender (P<0.001). Men had higher absolute LF power than women (P<0.001), whereas HF power was similar by gender; the age-related decline of HF power tended to be steeper in women (P = 0.06). The normalized LF and HF powers also decreased with age (P<0.01), except for the LF component in women; young men had higher LF power and lower HF power than young women, but the gender difference disappeared in the sixth decade of life. The LF: HF ratio was not influenced by age in supine men; the ratio was lower in women at young age, but increased to the level of men at greater age. Heart rate increased on standing, whereas its total variance was reduced; HF power declined, irrespective of the units, normalized LF power and the LF: HF ratio increased, whereas absolute LF power decreased (P<0.001). The postural changes of heart rate and of the frequency components did not differ by gender, but were attenuated with increasing age (P<0.05). Alcohol consumption did not influence heart rate and its variability, whereas independent effects of habitual physical activity, smoking habits and body mass index explained no more than 4% of the variance of some measures of heart rate variability.
CONCLUSIONS: Age, gender and/or some lifestyle factors significantly affect heart rate and various components of its variability in the supine position and in response to standing. The results are similar for autoregressive modelling and fast Fourier transform, but may differ according to the units in which the spectral components are expressed.