| Summary: | Sample Entropy (SampEn) is a popular method for assessing the regularity of physiological signals. Prior to the entropy calculation, certain common parameters need to be initialized: Embedding dimension <i>m</i>, tolerance threshold <i>r</i> and time series length <i>N</i>. Nevertheless, the determination of these parameters is usually based on expert experience. Improper assignments of these parameters tend to bring invalid values, inconsistency and low statistical significance in entropy calculation. In this study, we proposed a new tolerance threshold with physical meaning (<inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>r</mi> <mi>p</mi> </msub> </mrow> </semantics> </math> </inline-formula>), which was based on the sampling resolution of physiological signals. Statistical significance, percentage of invalid entropy values and ROC curve were used to evaluate the proposed <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>r</mi> <mi>p</mi> </msub> </mrow> </semantics> </math> </inline-formula> against the traditional threshold (<inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>r</mi> <mi>t</mi> </msub> </mrow> </semantics> </math> </inline-formula>). Normal sinus rhythm (NSR), congestive heart failure (CHF) as well as atrial fibrillation (AF) RR interval recordings from Physionet were used as the test data. The results demonstrated that the proposed <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>r</mi> <mi>p</mi> </msub> </mrow> </semantics> </math> </inline-formula> had better stability than <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>r</mi> <mi>t</mi> </msub> </mrow> </semantics> </math> </inline-formula>, hence more adaptive to detect cardiovascular diseases of CHF and AF.
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