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We analyze heartbeat interval recordings from two independent databases: (a)19 healthy young (avg. age 25.7 years) and 16 healthy elderly subjects (avg.age 73.8 years) during 2h under resting conditions from the Fantasia database;and (b) 29 healthy elderly subjects (avg. age 75.9 years) during $\approx{}8$hof sleep from the SHHS database, and the same subjects recorded 5 years later.We quantify: (1) The average heart rate <RR>; (2) the SD $\sigma_{RR}$ and$\sigma_{\Delta{}RR}$ of the heartbeat intervals RR and their increments$\Delta{}RR$; (3) the long-range correlations in RR as measured by the scalingexponent $\alpha_{RR}$ using the Detrended Fluctuation Analysis; (4) fractallinear and nonlinear properties as represented by the scaling exponents$\alpha^{sign}$ and $\alpha^{mag}$ for the time series of the sign andmagnitude of $\Delta{}RR$; (5) the nonlinear fractal dimension $D(k)$ of $RR$using the Fractal Dimension Analysis. We find: (1) No significant difference in$\left<RR\right>$ (P>0.05); (2) a significant difference in $\sigma_{RR}$ and$\sigma_{\Delta{}RR}$ for the Fantasia groups (P<10^{-4}) but no significantchange with age between the elderly SHHS groups (P>0.5); (3) no significantchange in the fractal measures $\alpha_{RR}$ (P>0.15), $\alpha^{sign}$ (P>0.2),$\alpha^{mag}$ (P>0.3), and D(k) with age. Our findings do not support thehypothesis that fractal linear and nonlinear characteristics of heartbeatdynamics break down with advanced age in healthy subjects. While our resultsindeed show a reduced SD of heartbeat fluctuations with advanced age, theinherent temporal fractal and nonlinear organization of these fluctuationsremains stable.

american journal of physiology. regulatory, integrative and comparative physiology/american journal of physiology. regulatory, integrative, and comparative physiology

Fractal scale-invariant and nonlinear properties of cardiac dynamics  remain stable with advanced age: A new mechanistic picture of cardiac control  in healthy elderly