Longitudinal assessment of resting wakefulness heart rate variability and its association with sleep apnea severity.

This study investigates the relationship between heart rate variability (HRV) during wakefulness and sleep apnea severity, with a focus on long-term autonomic nervous system (ANS) dysregulation. Using longitudinal data from the Sleep Heart Health Study (SHHS), we analyzed 15-minute pre-sleep ECG segments from 112 carefully selected participants, applying strict exclusion criteria to minimize confounding from comorbidities and medications known to affect HRV. A comprehensive set of time-domain, frequency-domain, and nonlinear HRV features was extracted and compared across apnea severity groups defined by the Apnea-Hypopnea Index (AHI). Cross-sectional analysis revealed significant reductions in parasympathetic-linked HRV indices, including RMSSD, PNN50, and HF power, with increasing apnea severity, alongside elevated LF/HF ratios indicating sympathetic dominance. Longitudinal modeling via Linear Mixed-Effects Regression (LMER) demonstrated that declines in RMSSD and progressive alterations in SD1, SD2, and the SD1/SD2 ratio over time were significantly associated with worsening AHI, reinforcing the persistence of ANS imbalance even during wakefulness. These findings suggest that sleep apnea severity is associated with persistent alterations in autonomic regulation extending beyond nocturnal events, and highlight the potential research value of wakefulness HRV as a non-invasive correlate of apnea severity and associated cardiovascular risk.