Sex and age differences in the association between heart rate variability and cardiac chronotropy: A replication-extension study.

Using heart rate variability (vmHRV) as a proxy of cardiac vagal modulation, previous studies have hinted at sex differences in the vagal control of cardiac chronotropy in young adults, but little is known in older individuals. The current study aimed at investigating for the first time the moderating role of both sex and age in the relationship between vmHRV and cardiac chronotropy in younger (n = 106, mean age: 19.9 (3.5) years) and older (n = 109, mean age: 72.8 (2.6) years) individuals. Further, we explored the effects of hormone replacement therapy on such association in a sub-sample of post-menopausal women (n = 17). Resting measures of the average inter-beat interval (IBI, as index of cardiac chronotropy) and vmHRV were collected. The results indicate (i) stronger associations between vmHRV and IBI in young adults and post-menopausal women compared to age-matched men, (ii) a weaker or no association in older women and men, respectively, and (iii) no effects of hormone replacement therapy in post-menopausal women. This study provides evidence of sex and age differences in the association between vmHRV and cardiac chronotropy, offering novel insight into vagal mechanisms of cardiac chronotropic control that may inform our understanding of sex- and age-related vulnerability to negative health outcomes.