Guzmán-Vargas L, Reyes-Ramírez I, Hernández-Pérez R, Angulo-Brown F
Unidad Profesional Interdisciplinaria en Ingeniería y Tecnologías Avanzadas, Instituto Politécnico Nacional, México D.F., México.
Methods Enzymol. 2011;487:409-29. doi: 10.1016/B978-0-12-381270-4.00014-7.
We study the statistical properties of excursions in heart interbeat time series. An excursion is defined as the time employed by a walker to return to its mean value. We consider the homeostatic property of the heartbeat dynamics as a departing point to characterize the dynamics of excursions in beat-to-beat fluctuations. Scaling properties of excursions during wake and sleep periods from two groups are compared: 16 healthy subjects and 11 patients with congestive heart failure (CHF). We find that the cumulative distributions of excursions for both groups follow stretched exponential functions given by g(τ)~e(-aτ(b)) with different fitting parameters a and b, leading to different decaying rates. Our results show that the average characteristic scale associated with the excursion distributions is greater for healthy data compared to CHF patients whereas sleep-wake transitions are more significant for healthy data. Next, we explore changes in the distributions of excursions when considering (i) a shifted mean value to define an excursion and (ii) the sum of the kth excursion successor. Besides, the presence of temporal correlations in the excursions sequences is evaluated by means of the detrended fluctuation analysis. We observe the presence of long-range correlations for healthy subjects, whereas for the CHF group, correlations are described by two regimes; over short scales the fluctuations are close to uncorrelated noise, and for large scales the fluctuations reveal long-range correlations. Finally, we apply a stability analysis of excursions based on the Allan variance which reveals that healthy dynamics is more stable than heart failure excursions.
我们研究了心脏搏动间期时间序列中偏移的统计特性。偏移被定义为行走者回到其平均值所花费的时间。我们将心跳动力学的稳态特性作为一个出发点，来刻画逐搏波动中偏移的动力学。比较了两组在清醒和睡眠期间偏移的标度特性：16名健康受试者和11名充血性心力衰竭（CHF）患者。我们发现，两组偏移的累积分布都遵循拉伸指数函数g(τ)~e^(-aτ^b)，其中拟合参数a和b不同，导致衰减率不同。我们的结果表明，与CHF患者相比，健康数据中与偏移分布相关的平均特征尺度更大，而睡眠-清醒转换对健康数据更为显著。接下来，我们探讨了在考虑（i）用于定义偏移的均值偏移和（ii）第k个偏移后继的总和时偏移分布的变化。此外，通过去趋势波动分析评估了偏移序列中的时间相关性。我们观察到健康受试者存在长程相关性，而对于CHF组，相关性由两种状态描述；在短尺度上，波动接近不相关噪声，而在大尺度上，波动显示出长程相关性。最后，我们基于阿伦方差对偏移进行了稳定性分析，结果表明健康动力学比心力衰竭偏移更稳定。
