Technological Institute of Informatics, Polytechnic University of Valencia, Alcoi Campus, Plaza Ferrandiz y Carbonell, Spain.
Artif Intell Med. 2011 Oct;53(2):97-106. doi: 10.1016/j.artmed.2011.06.007. Epub 2011 Aug 10.
There is an ongoing research effort devoted to characterize the signal regularity metrics approximate entropy (ApEn) and sample entropy (SampEn) in order to better interpret their results in the context of biomedical signal analysis. Along with this line, this paper addresses the influence of abnormal spikes (impulses) on ApEn and SampEn measurements.
A set of test signals consisting of generic synthetic signals, simulated biomedical signals, and real RR records was created. These test signals were corrupted by randomly generated spikes. ApEn and SampEn were computed for all the signals under different spike probabilities and for 100 realizations.
The effect of the presence of spikes on ApEn and SampEn is different for test signals with narrowband line spectra and test signals that are better modeled as broadband random processes. In the first case, the presence of extrinsic spikes in the signal results in an ApEn and SampEn increase. In the second case, it results in an entropy decrease. For real RR records, the presence of spikes, often due to QRS detection errors, also results in an entropy decrease.
Our findings demonstrate that both ApEn and SampEn are very sensitive to the presence of spikes. Abnormal spikes should be removed, if possible, from signals before computing ApEn or SampEn. Otherwise, the results can lead to misunderstandings or misclassification of the signal regularity.
目前有一项研究工作致力于描述信号规则度量近似熵（ApEn）和样本熵（SampEn），以便在生物医学信号分析的背景下更好地解释它们的结果。本文探讨了异常尖峰（脉冲）对 ApEn 和 SampEn 测量的影响。
创建了一组测试信号，包括通用合成信号、模拟生物医学信号和真实 RR 记录。这些测试信号被随机生成的尖峰污染。在不同的尖峰概率和 100 次实现下，计算了所有信号的 ApEn 和 SampEn。
对于具有窄带线谱的测试信号和更好地建模为宽带随机过程的测试信号，尖峰的存在对 ApEn 和 SampEn 的影响是不同的。在前一种情况下，信号中存在外部尖峰会导致 ApEn 和 SampEn 增加。在后一种情况下，它会导致熵减少。对于真实的 RR 记录，由于 QRS 检测错误等原因，尖峰的存在也会导致熵减少。
我们的研究结果表明，ApEn 和 SampEn 都对尖峰的存在非常敏感。如果可能的话，应该从信号中去除异常尖峰，然后再计算 ApEn 或 SampEn。否则，结果可能会导致对信号规则的误解或错误分类。
