Human body surface electrocardiogram (ECG) is non-stationary and frequency-varying by nature that belongs to a typical nonlinear signal. Therefore, traditional linear and time–frequency​ analysis methods cannot fully disclose its nonlinear nature. Meanwhile, physiological complexity of heartbeat signal may vary with age, diseases, drug administrations, or even behavioral modifiers. To test the intrinsic relationships among them, we first put forward a theoretical model for nonlinear time series analysis and then took the generally accepted multifractal sets to verify it. Upon that, we then investigated the multifractal singularity spectrum areas of synchronous 12-lead ECG signals taken from crowds with different age stages, healthy conditions and drug medications. Our results suggested that aging and diseases can not only decrease multifractal complexity of the signals, but also increase inhomogeneity of it. With aging and deepening lesion, fractal-like structure of the heartbeat system is damaged or even structurally changed, which lead to the declination of physiological complexity and at the same time the increasement of irregularity and anisotropy of ECG signal’s propagation. In addition, the mean value of multifractal spectrum area of human 12-lead ECG signals also reflect the self-discipline regulation of human autonomic nervous system. The value descends with age growing or drug intervention to restrain sympathetic nerves. That suggest self-discipline control function weakens when people are getting old, or they are under repressed heartbeat activities with lower heart rate and lower blood pressure. Then, complexity of heartbeat signal declines and even tends to turn from multifractality to monofractality, which means drops off of human individual adaptability.

人体表面心电图（ECG）本质上是平稳的且随频率变化，属于典型的非线性信号。因此，传统的线性和时频分析方法无法完全揭示其非线性性质。同时，心跳信号的生理复杂性可能会随着年龄，疾病，药物管理甚至行为调节因素而变化。为了测试它们之间的内在联系，我们首先提出了一个用于非线性时间序列分析的理论模型，然后采用了公认的多重分形集对其进行了验证。在此基础上，我们随后研究了来自不同年龄阶段，健康状况和药物治疗人群的同步12导联心电图信号的多重分形奇异谱区域。我们的结果表明，衰老和疾病不仅可以降低信号的多重分形复杂度，而且可以增加信号的不均匀性。随着病变的老化和加深，心跳系统的分形结构被破坏，甚至在结构上发生变化，这导致生理复杂性的下降，同时也增加了ECG信号传播的不规则性和各向异性。此外，人12导联心电图信号的多重分形谱面积的平均值也反映了人自主神经系统的自律调节。该值随着年龄增长或药物抑制交感神经而下降。这表明，当人们变老，或者他们处于受抑制的心跳活动中时，自律控制功能会减弱，心率和血压会降低。