HEART-RATE-VARIABILITY AND HEART-RATE IN HEALTHY-VOLUNTEERS - IS THE FEMALE AUTONOMIC NERVOUS-SYSTEM CARDIOPROTECTIVE

Aims Heart rate variability has been proposed as an indicator of cardi ovascular health. Since women have a lower cardiovascular risk, we hyp othesized that there are gender differences in autonomic modulation. M ethods and Results In 276 healthy subjects (135 women, 141 men) betwee n 18 and 71 years of age, 24 h heart rate and heart rate variability w ere determined. All heart rate variability parameters, except for pNN5 0 and high frequency power, were higher in men. After adjustment for h eart rate, we obtained gender differences for: the standard deviation (P=0.049), the standard deviation of the 5 min average (P=0.047), low frequency power (absolute values, P=0.002; normalized units, P<0.001) and ratio low frequency/high frequency (P<0.001). There were no signif icant gender differences in heart rate variability parameters denoting vagal modulation. Gender differences were confined to age categories of less than 40 years of age. The majority of heart rate variability p arameters decreased with age. Only in men, was a higher body mass inde x associated with a higher heart rate and with lower heart rate variab ility parameters (P<0.001). Conclusion Cardiac autonomic modulation as determined by heart rate variability, is significantly lower in healt hy women compared to healthy men. We hypothesize that this apparently paradoxical finding may be explained by lower sympathetic activity (lo w frequency power) in women. This may provide protection against arrhy thmias and against the development of coronary heart disease.