On choosing heart-rate-variability (HRV) metrics to reflect vagus-nerve functioning: The construct counts, not the...

Area of Science:

• Psychophysiology
• Cardiorespiratory Interactions
• Heart Rate Variability Analysis

Background:

• Numerous methods quantify respiratory heart-rate variability (RespHRV), leading to confusion about the "superior" metric.
• Divergent evidence and claims about specific indices (e.g., vagal blockade, respiration-free measures) have fueled debate.

Purpose of the Study:

• To argue that the primary challenge in RespHRV research is construct validity, not algorithmic differences between metrics.
• To emphasize the necessity of anchoring RespHRV interpretation in its physiological basis as cardiorespiratory coupling.

Main Methods:

• Review of existing literature on RespHRV quantification methods and their interpretation.
• Analysis of claims regarding vagal blockade, respiration-free metrics, and nonstationarity in RespHRV.
• Emphasis on the importance of comparable preprocessing pipelines and statistical methods.

Main Results:

• Commonly used RespHRV metrics are highly correlated when processed uniformly.
• Apparent metric divergences often stem from non-uniform processing, design flaws, or over-interpretation.
• Vagal blockade studies may not isolate vagal tone due to partial blockade and unconstrained sympathetic activity.
• RespHRV is inherently respiratory; respiration-free claims are often based on weak evidence.
• Nonstationarity requires evaluation of estimation bias, and filtering can introduce bias.

Conclusions:

• The field should prioritize uniform preprocessing, accurate respiration measurement, and appropriate statistical comparisons over metric debates.
• Construct validity and cautious interpretation grounded in cardiorespiratory coupling are crucial for advancing RespHRV research.