Influence of ageing on body state and trait determinants-related changes in cardiac autonomic nervous function

Abstract

Objective To explore the influence of ageing on body state and trait determinants-related changes in cardiac autonomic regulation. Methods A total of 1703 subjects from outpatients were recruited. The heart rate variability (HRV) and circadian blood pressure rhythm were measured with 24-hour electrocardiograph monitoring and ambulatory blood pressure monitoring respectively. HRV data were analyzed in time domains including Standard deviation of all normal to normal (NN) intervals(SDNN), Standard deviation of the average of NN intervals in all 5 min segments of the entire recording(SDANN), Mean absolute differences of successive NN intervals.(MSD), Square root of the mean squared differences of successive NN intervals.(rMSSD), Number of pairs of adjacent NN intervals differing by more than 50 ms divided by the total number of NN intervals in the entire recording(pNN50) using customized program.Data was collected including the age, gender, 24-hour average heart rate, 24-hour average blood pressure and 24-hour blood pressure rhythm (dipper or non-dipper type). The influence of these state determinants on HRV and the difference of these influence in senile (>65 years old) and presenile group (≤65 years old) groups were studied. Results (1)SDNN、SDANN decreased gradually with the age stratification ( 65y)(P 65y subjects. Bivariate correlation analysis showed significant negatively correlations of age with all time domain indexes in presenile group (P 0.05). (2)T-test analysis showed males have lower MSD, rMSSD, pNN50 than females(P 0.05). (3) Bivariate correlation analysis showed 24-hour average heart rate was strongly negatively correlated with all time-domain indexes(P 0.05). (4) T-test analysis showed the high 24-hour average blood pressure subjects were lower in all HRV indexes than normal 24-h average blood pressure subjects whereas only MSD, Square root of the mean squared differences of rMSSD, pNN50 were significant(P 0.05). (5) T-test analysis showed no-dipper type blood pressure subjects have lower SDANN than dipper type blood pressure subjects(P<0.01). Bivariate correlation analysis showed no-dipper type blood pressure was mainly negatively correlated with SDNN, SDANN both in presenile and senile group(P<0.05). Conclusions Body state and trait determinants can inhomogenously or selectively affect HRV time-domain indexes, but these effects tend to disappear in old people suggesting a physiologic disconnection with ageing between cardiovascular autonomic nervous action and body pathophysiologic determinants. Key words: Heart rate; Autonomic nervous system; Age factors