Age trends in circadian characteristic of heart rate and heart rate variability in health

In different age groups, heart rate was measured around the clock at 7.5-minute intervals with an ambulatory monitor. Heart rate variability was gauged by the standard deviation over 1-hour intervals. Changes in heart rate and in heart rate variability with age were assessed by linear regression overall, and at each separate clock hour. By the single cosinor method, single- and multiple-component models reveal the circadian stage-dependence of heart rate and heart rate variability and of their changes with age. The results suggest the desirability of focusing not only on single samples or time-unspecified mean values, but also on the dynamics of a broad time structure (chronome) in studies of aging.