It is known that heart activity changes during aging. In this paper, we evaluated alterations of heart activity from the complexity point of view. We analyzed the variations of heart rate of patients with congestive heart failure that are categorized into four different age groups, namely 30–39, 50–59, 60–69, and 70–79 years old. For this purpose, we employed three complexity measures that include fractal dimension, sample entropy, and approximate entropy. The results showed that the trend of increment of subjects’ age is reflected in the trend of increment of the complexity of heart rate variability (HRV) since the values of fractal dimension, approximate entropy, and sample entropy increase as subjects get older. The analysis of the complexity of other physiological signals can be further considered to investigate the variations of activity of other organs due to aging.

中文翻译：

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充血性心力衰竭患者基于年龄的心率变异性 (HRV) 分析

众所周知，随着年龄的增长，心脏活动会发生变化。在本文中，我们从复杂性的角度评估了心脏活动的变化。我们分析了充血性心力衰竭患者的心率变化，这些患者分为四个不同的年龄组，即 30-39、50-59、60-69 和 70-79 岁。为此，我们采用了三种复杂性度量，包括分形维数、样本熵和近似熵。结果表明，随着受试者年龄的增长，分形维数、近似熵和样本熵的值都在增加，因此受试者年龄增加的趋势体现在心率变异性复杂度（HRV）的增加趋势上。