Age-related changes of cardiac control function in man. With special reference to heart rate control at rest and during exercise.

Heart rate control function at rest and during exercise in regard to age were studied in 39 healthy male volunteers (age 15 to 75). The heart rate control function during exercise was evaluated by using system analysis of heart rate response to two-step exercises (66 and 84 steps/min). No age-related changes were found in the resting heart rate at supine position or in oxygen consumption at upright rest and during the exercises. However, the mean value and the magnitude of variation of the heart rate at upright rest and the difference of heart rate at upright and supine rest showed significant negative correlations with age. As age advanced, the transfer function of the system during exercise exhibited characteristic changes depending on the frequency ranges. These findings suggest that activity of both sympathetic and parasympathetic nervous systems were depressed at rest, and that contributions of sympathetic and vagal nervous systems during exercise are more enhanced and more depressed, respectively, in older subjects than in younger subjects.