Influence of age and gender on autonomic regulation of heart

Heart rate variability (HRV) is a non-invasive method to measure cardiac autonomic function. Impairments in HRV have been proposed as independent risk factor for increased cardiac mortality and morbidity. Cardio protective phenomenon in females has been hypothesized to be due to differential autonomic tone. Age related loss of vagal control has been reported as predisposing factor for the development of cardiovascular disease. In this study we assessed effect of age and gender on autonomic regulation of heart in healthy volunteers. HRV data of 189 subjects (114 males and 75 females) were analyzed in time and frequency domains using customized program. Artifact free 5 min electrocardiogram segment was used for analysis. It was ensured that none of the subject had medical illness such as diabetes, hypertension, thyroid disorders, cardiac disorders, diseases potentially related with autonomic neuropathy and major psychiatric illness by careful history and clinical examination. HRV recordings were done under standard laboratory condition. On correlation analysis SDNN, RMSSD, total power negatively correlated with age suggesting reduced autonomic regulation of heart with increase in age (SDNN: r = -0.444, p < 0.01; RMSSD: r = -0.552, p < 0.01; total power: r = -0.474, p < 0.01); similarly High frequency power (HF.nu) negatively correlated with age (r = -0.167, p = 0.02), denoting loss of vagal tone with aging. LF/HF ratio correlated positively with age (r = 0.19, p < 0.01) suggesting a relative increase of sympathetic activity with increase in age. On multiple regression analysis to control for effect of age and heart rate while comparing males and females, LF.nu showed significant reduction suggesting lower sympathetic tone in females (β = -6.64; p < 0.01) and HF.nu showed increase at trend level (β = 4.47; p = 0.053). In conclusion, there is overall reduction in autonomic control of heart with increase in the age. Sympathetic tone predominates and vagal tone diminishes with aging process. Females showed greater vagal tone than male. This differential autonomic tone indicate age, gender related predisposition to cardiovascular disease.