Kanters J K, Holstein-Rathlou N H, Agner E
Department of Internal Medicine, Elsinore Hospital, Helsingør, Denmark.
J Cardiovasc Electrophysiol. 1994 Jul;5(7):591-601. doi: 10.1111/j.1540-8167.1994.tb01300.x.
The term chaos is used to describe erratic or apparently random time-dependent behavior in deterministic systems. It has been suggested that the variability observed in the normal heart rate may be due to chaos, but this question has not been settled.
Heart rate variability was assessed by recordings of consecutive RR intervals in ten healthy subjects using ambulatory ECG. All recordings were performed with the subjects at rest in the supine position. To test for the presence of nonlinearities and/or chaotic dynamics, ten surrogate time series were constructed from each experimental dataset. The surrogate data were tailored to have the same linear dynamics and the same amplitude distribution as the original data. Experimental and surrogate data were then compared using various nonlinear measures. Power spectral analysis of the RR intervals showed a 1/f pattern. The correlation dimension differed only slightly between the experimental and the surrogate data, indicating that linear correlations, and not a "strange" attractor, are the major determinants of the calculated correlation dimension. A test for nonlinear predictability showed coherent nonlinear dynamic structure in the experimental data, but the prediction error as a function of the prediction length increased at a slower rate than characteristic of a low-dimensional chaotic system.
There is no evidence for low-dimensional chaos in the time series of RR intervals from healthy human subjects. However, nonlinear determinism is present in the data, and various mechanisms that could generate such determinism are discussed.
“混沌”一词用于描述确定性系统中不稳定或明显随机的时间依赖性行为。有人提出，正常心率中观察到的变异性可能归因于混沌，但这个问题尚未解决。
通过动态心电图记录10名健康受试者连续的RR间期来评估心率变异性。所有记录均在受试者仰卧休息时进行。为了测试非线性和/或混沌动力学的存在，从每个实验数据集中构建了10个替代时间序列。替代数据经过调整，使其具有与原始数据相同的线性动力学和相同的幅度分布。然后使用各种非线性测量方法对实验数据和替代数据进行比较。RR间期的功率谱分析显示出1/f模式。实验数据和替代数据之间的关联维数仅略有差异，这表明线性相关性而非“奇怪”吸引子是计算出的关联维数的主要决定因素。非线性可预测性测试表明实验数据中存在连贯的非线性动态结构，但预测误差作为预测长度的函数，其增加速度比低维混沌系统的特征速度要慢。
没有证据表明健康人类受试者的RR间期时间序列中存在低维混沌。然而，数据中存在非线性确定性，并讨论了可能产生这种确定性的各种机制。
