Modeling effects of age and sex on cardiovascular variability responses to aerobic ergometer exercise.

After collecting data on the cardiovascular responses to ramp-type exercise tests on a cycle ergometer from 194 healthy male and female subjects aged from 20 to 69 years, we constructed a mathematical model that simulates typical patterns of the cardiovascular variability responses to ramp-type exercise loads below the anaerobic threshold. This was done by reflecting the following physiological mechanisms: (1) suppression of parasympathetic nerve activity, (2) reduction of total peripheral resistance, (3) resetting of the operating point in the baroreflex curve, (4) increase in stroke volume, and (5) increase in the coupling of stroke volume to pulse pressure. We estimated the values of model parameter that best fit the measured experimental data. The estimated steepness of the slope with which parasympathetic nerve activity decreased was lower in subjects with a higher anaerobic threshold, tended to increase with age, and in every age decade was higher for females than for males.