Influence of age on the immediate heart rate response to the active orthostatic test

Dynamics of the heart rate changes following standing up from the supine position was investigated in 41 healthy men aged 20 to 59 years, classified according to the age into three groups: (22 to 26 yrs, n=14), (33 to 49,yrs, n=13) and (51 to 59 yrs, n=14). The protocol consisted of twice repeated sequence: lying down - standing up - lying down. The subjects remained in each position for 8 minutes. The average and beat-to-beat heart rate (HR) were continuously calculated using the specialized computer program analysing ECG. The initial response was analysed using both the indices known from literature and newly introduced by the authors. The high reproducibility of the response was observed and the correlations between the indices were analysed. The relationship between the indices characterising the pattern of the response and age were analysed using the linear regression model. Most of these indices showed a tendency towards attenuation of the HR response with age. The closest correlation with age was found for the index characterising the initial increase of HR after standing up (r=-0.610, p<0.001). There were no correlations between the indices of HR response to standing up and the height or body mass of the healthy subjects.