GENDER-RELATED AND AGE-RELATED DIFFERENCES IN HEART-RATE DYNAMICS - ARE WOMEN MORE COMPLEX THAN MEN

Objectives. This study aimed to quantify the complex dynamics of beat- to beat sinus rhythm heart rate fluctuations and to determine their di fferences as a function of gender and age. Background. Recently, measu res of heart rate variability and the nonlinear ''complexity'' of hear t rate dynamics have been used as indicators of cardiovascular health. Because women have lower cardiovascular risk and greater longevity th an men, we postulated that there are important gender related differen ces in beat-to beat heart rate dynamics. Methods. We analyzed heart ra te dynamics during 8-min segments of continuous electrocardiographic r ecording in healthy young (20 to 39 years old), middle aged (40 to 64 years old) and elderly (65 to 90 years old) men (n = 40) and women (n = 27) while they performed spontaneous and metronomic (15 breaths/min) breathing. Relatively high (0.15 to 0.40 Hz) and low (0.01 to 0.15 Hz ) frequency components of heart rate variability were computed using s pectral analysis. The overall ''complexity'' of each heart rate time s eries was quantified by its approximate entropy, a measure of regulari ty derived from nonlinear dynamics (''chaos'' theory). Results. Mean h eart rate did not differ between the age groups or genders. High frequ ency heart rate power and the high/low frequency power ratio decreased with age in both men and women (p < 0.05). The high/low frequency pow er ratio during spontaneous and metronomic breathing was greater in wo men than men (p < 0.05). Heart rate approximate entropy decreased with age and was higher in women than men (p < 0.05). Conclusions. High fr equency heart rate spectral power (associated with parasympathetic act ivity) and the overall complexity of heart rate dynamics are higher in women than men. These complementary findings indicate the need to acc ount for gender-as well as age-related differences in heart rate dynam ics. Whether these gender differences are related to lower cardiovascu lar disease risk and greater longevity in women requires further study .