Gender differences of heart rate variability in healthy volunteers.

OBJECTIVE To identify the basic values of heart rate variability in Pakistani population and to verify our hypothesis that there are gender differences in cardiovascular autonomic modulation. METHODS The descriptive cross sectional study based on convenience probability sampling was conducted at Armed Forces Institute of Cardiology/National Institute of Heart Diseases (AFIC/NIHD) Pakistan. The duration of the study was from December 2009 to July 2010. It involved 24-hour holter monitoring of 45 healthy individuals using holter electrocardiography (ECG) recorder. Heart rate variability was analysed in time (SDNN, SDANN, SDNNi, rMSSD, pNN50) and frequency domains (power, VLF, LF, and HF). RESULTS The time domain indices; SDNN (male = 140 +/- 36ms vs. females = 122 +/- 33ms; p = 0.09), SDANN (male = 123 +/- 34ms vs. females = 111 +/- 34ms; P = 0.23), SDNNi (male = 64 +/- 19ms vs. females = 52 +/- 14ms; P = 0.03), and pNN50 (male = 14 +/- l0ms vs. females = 12 +/- 7ms; P = 0.43) were decreased in female volunteers when compared with males. Comparison of frequency domain indices; Total power (male = 4041 +/- 3150ms(2) vs. females = 2750 +/- 1439ms(2); P = 0.07), VLF (male = 2912 +/- 2675ms(2) vs. females = 1843 +/- 928ms(2); P = 0.06), LF (male = 788 +/- 397ms(2) vs. females = 556 +/- 346ms(2); P = 0.04) and HF (male = 318 +/- 251ms(2) vs. females = 312 +/- 277ms(2): P = 0.94) amongst males and females showed attenuated heart rate variability in females. Of all the observed values, SDNNi and LF were found significantly (p < 0.05) decreased in women. CONCLUSION In healthy population, heart rate variability is low in women than men. It reflects sympathetic dominance in women in our population.