Inspiratory and expiratory sinus arrhythmia in healthy human.
Level 4 - case-series / case-control
Single-group observational physiological study in healthy volunteers at rest
PubMed 40173080 · doi:10.14814/phy2.70245
What was done
Breathing and ECG were recorded in 33 healthy human subjects at rest. RR intervals were categorized based on their timing within respiratory phases: II (both R waves in inspiration), IE (inspiration to expiration), EE (both R waves in expiration), and EI (expiration to inspiration). For each subject, II and EE intervals were plotted against normalized mean inspiratory and expiratory durations, respectively, to calculate linear regression slopes and correlation coefficients for within- and between-individual comparisons.
What was found
The relationships between RR intervals and normalized phase durations appeared linear in most cases, with heart rate changes occurring at different rates across subjects. Overall, the slope associated with II intervals was not higher in absolute terms than the slope associated with EE intervals within the same subject. The abstract reports no numerical values, correlation coefficients, or p-values.
Why it matters
The findings highlight distinct dynamics between inspiratory and expiratory sinus arrhythmia, suggesting that research assessing vagal cardiac modulation should target the expiratory phase.
Limits
Small sample size (n = 33) limited to healthy individuals at rest. The abstract provides no exact quantitative metrics, p-values, or confidence intervals. No interventions, clinical populations, or external physiological stressors were evaluated.