0112 Increasing Sleep Regularity is Associated with Improvements to Heart Rate Variability in Healthy Adults

Abstract Introduction Sleep regularity has been shown to be a stronger predictor of mortality compared to sleep duration, though the underlying mechanisms are incompletely understood. Heart rate variability (HRV), a measure of cardiac autonomic modulation, is associated with cardiovascular morbidity and mortality. While HRV is traditionally analyzed using linear methods (e.g., frequency-domain analyses), there is growing interest in nonlinear measures to assess the dynamic complexity of cardiac regulation. However, the influence of sleep regularity on both linear and nonlinear HRV is unclear. We therefore assessed the association between sleep regularity and HRV in healthy adults. Methods HRV was obtained in 12 participants (6 female) via electrocardiography during 10-min supine rest and assessed using linear (high frequency [HF]; low frequency [LF]/HF ratio) and nonlinear (detrended fluctuation analysis [DFA]-α1 and -α2) indices. Sleep regularity was quantified using the standard deviation (SD) of diary-determined sleep onset across ~14 days. Participants were classified as regular (SD< 1h; n=5) or irregular sleepers (SD>=1h; n=7). Irregular sleepers were instructed to maintain a consistent sleep onset (±30min) for 12-weeks. Differences between groups were assessed using independent t-tests and relationships between SD sleep onset and HRV were assessed using Pearson correlation analyses. Results There were no differences between groups in age (mean±SD, irregular vs. regular, respectively; 30.7±7.8 vs. 27.2±8.5y; p=0.23), sleep onset timing (24:38±1:45 vs. 23:37±1:14; p=0.14), or DFA-α2 (0.27±0.11 vs. 0.36±0.20; p=0.16). At baseline, irregular sleepers had higher SD sleep onset (1.4±0.4 vs. 0.8±0.2h; p< 0.01), LF/HF ratio (2.4±1.8 vs. 0.6±0.5%; p=0.03), DFA-α1 (1.10±0.22 vs. 0.81±0.20; p=0.02), and lower HF (37.1±20.5 vs. 63.1±7.1nu; p=0.02). In the entire sample, SD sleep onset was inversely correlated with HF (r=-0.63; p=0.02) and positively correlated with LF/HF ratio (r=0.75; p< 0.01) and DFA-α1(r=0.61; p=0.03) at baseline. At 12-weeks, the change in SD sleep onset was inversely correlated with change in HF (r=-0.79; p< 0.01) and positively correlated with change in LF/HF ratio (r=0.77; p< 0.01) and DFA-α1(r=0.66; p=0.01). Conclusion Irregular sleep patterns are associated with altered cardiac regulatory dynamics and may be one mechanism contributing to adverse outcomes. Improving sleep regularity may be a potential interventional target to improve the autonomic balance and cardiovascular adaptation. Support (if any)