Using Modified Sample Entropy to Characterize Aging-Associated Microvascular Dysfunction.
Using Modified Sample Entropy to Characterize Aging-Associated Microvascular Dysfunction.
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DOI：
10.3389/fphys.2016.00126
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发表时间：
2016
影响因子：
4
通讯作者：
Jan YK
中科院分区：
文献类型：
--
作者：
Liao F;Jan YK
皮肤微血管功能可以通过皮肤血流（SBF）对热刺激的反应来评估。通常，调节机制的活动通过响应的光谱分析来量化。然而，频谱测量无法表征SBF信号的非线性动力学。样本熵（SampEn）是一种常用的时间序列规律性程度的非线性度量。然而，SampEn值取决于所研究的动态的频率与采样率之间的关系。因此，当时间序列数据被过采样时，SampEn可能会给出误导性的结果。我们修改了SampEn的定义，通过在要比较的向量的连续数据点之间包括滞后来解决过采样问题。可以选择滞后作为时间序列的自互信息函数的第一个最小值。我们使用模拟信号和年轻组和老年组的SBF数据测试了修改后的SampEn的性能。结果表明，修改后的SampEn产生一致的结果，不同的采样率的模拟数据，但SampEn不能。与基线相比，两组中最大血管舒张期的血流数据显示出更高程度的规律性，与年轻组相比，老年组的规律性更高。此外，我们的研究结果表明，在第二个高峰期间，血流振荡（BFO）的更有规律的行为主要归因于增强的心脏振荡。这项研究表明，改良的SampEn方法可能有助于评估微血管功能。
Cutaneous microvascular function can be assessed by skin blood flow (SBF) response to thermal stimuli. Usually, the activities of the regulatory mechanisms are quantified by means of spectral analysis of the response. However, spectral measures are unable to characterize the nonlinear dynamics of SBF signal. Sample entropy (SampEn) is a commonly used nonlinear measure of the degree of regularity of time series. However, SampEn value depends on the relationship between the frequency of the studied dynamics and sampling rate. Hence, when time series data are oversampled, SampEn may give misleading results. We modified the definition of SampEn by including a lag between successive data points of the vectors to be compared to address the oversampled issue. The lag could be chosen as the first minimum of the auto mutual information function of the time series. We tested the performance of modified SampEn using simulated signals and SBF data in the young and old groups. The results indicated that modified SampEn yields consistent results for different sampling rates in simulated data, but SampEn cannot. Blood flow data showed a higher degree of regularity during the maximal vasodilation period as compared to the baseline in both groups and a higher degree of regularity in the older group as compared to the young group. Furthermore, our results showed that during the second peak the more regular behavior of blood flow oscillations (BFO) is mainly attributed to enhanced cardiac oscillations. This study suggests that the modified SampEn approach may be useful for assessing microvascular function.