Statistical strategies to quantify respiratory sinus arrhythmia: Are commonly used metrics equivalent?

Three frequently used RSA metrics are investigated to document violations of assumptions for parametric analyses, moderation by respiration, influences of nonstationarity, and sensitivity to vagal blockade. Although all metrics are highly correlated, new findings illustrate that the metrics are noticeably different on the above dimensions. Only one method conforms to the assumptions for parametric analyses, is not moderated by respiration, is not influenced by nonstationarity, and reliably generates stronger effect sizes. Moreover, this method is also the most sensitive to vagal blockade. Specific features of this method may provide insights into improving the statistical characteristics of other commonly used RSA metrics. These data provide the evidence to question, based on statistical grounds, published reports using particular metrics of RSA.

► Commonly used metrics for quantifying RSA are highly correlated.
► Several RSA metrics violate distributional requirements for parametric analysis.
► The Porges–Bohrer metric (RSAP–B) is appropriate for parametric analyses.
► The relationship between commonly used metrics and RSAP–B is moderated by respiration and nonstationarity in heart period.
► RSAP–B is significantly more sensitive to vagal blockade than other common metrics.