Influence of age on linear and nonlinear measures of autonomic cardiovascular modulation

Abstract

Background: Age has been identified as an independent risk factor for cardiovascular diseases. In addition, autonomic imbalance toward sympathetic preponderance has been shown to facilitate the occurrence of heart disease. Here, we aimed to assess autonomic modulation of cardiovascular parameters during normal ageing applying well-established linear and novel nonlinear parameters.

Methods: Linear and nonlinear measures of heart rate variability and complexity as well as measures of QT interval variability and baroreflex sensitivity were obtained from a total of 131 healthy, medication-free participants from a continuous age range between 20 and 90 years, who were allocated to three different age groups.

Results: Heart rate variability and complexity significantly decreased with age, while regularity of heart rate time series increased. In addition, QT interval variability linearly increased with age, while baroreflex sensitivity showed a pronounced decrease. Overall, concerning effects of ageing, linear and nonlinear parameters showed equal differentiation between groups.

Conclusion: These data indicate a shift of autonomic balance toward sympathetic predominance in higher age groups, limiting the reactiveness of the cardiovascular system to adjust to different demands and increasing the risk for developing tachyarrhythmias.

Figure 1

Comparison of cardiovascular autonomic parameters between different age groups. (A) Heart rate. (B) Root mean squared differences of successive normal‐to‐normal intervals (RMSSD). (C) Compression Entropy Hc. (D) Probability of high variability sequences with a time limit of 10 ms (phvar10). (E) Fractal dimension of QT interval time series (FD_QT). (F) QT variability index (QTvi). (G) Bradycardic slope of baroreflex (bslope). (H) Joint symbolic dynamics of symmetric baroreflex‐like words (JSDsym). Data presented as box plots. Boxes indicate 25^th and 75^th percentile with the horizontal line indicating the median. ▪ mean. ○ 1^st and 99^th percentile. – minimum and maximum of data. *P < 0.05; **P < 0.01; ***P < 0.001.

Figure 2

Correlations between cardiovascular autonomic parameters and age. (A) Root mean squared differences of successive normal‐to‐normal intervals (RMSSD). (B) Compression entropy, a complexity measure of heart rate time series, decreases similarly to RMSSD, but with higher correlation coefficients. (C) Decrease of baroreflex sensitivity with age as represented by bradycardic slopes (bslope). (A)–(C) are measures of vagal modulation of heart rate time series, which thus decrease in older age. (D) QT variability index, a measure of sympathetic influence at the level of the heart, increases with age, with an even enhanced steepness in the >60 years group. Correlation data are presented as r‐values and as linear fit regression lines for each age group separately (bold black lines) and for all age groups taken together (thin intermittent line). *P < 0.05; **P < 0.01; ***P < 0.001; n.s. – not significant.