Sleep

Ultra-short term Heart Rate Variability in moderate and severe Obstructive Sleep Apnea.

Nagaraju K, Venkatnarayan K, et al. • Respiratory medicine • 2026

PubMed 41580095 DOI 10.1016/j.rmed.2026.108654

TL;DR

Ultra-short-term HRV varies with OSA severity, sleep stage, and type of respiratory event, with reduced HRV observed in severe OSA, NREM sleep, and during hypopneic events.

Key Findings

Results

Time-domain and nonlinear HRV indices were lower in severe OSA compared to moderate OSA.

88 patients total were studied: 44 with moderate OSA and 44 with severe OSA
Mean (SD) AHI was 16.8 (4.3) in moderate OSA and 61.5 (23.1) in severe OSA
Ultra-short-term HRV was assessed using 30-second artifact-free ECG segments extracted by a dedicated algorithm
Both time-domain and nonlinear HRV indices were significantly lower in the severe OSA group

Results

HRV indices were lower during NREM sleep compared to REM sleep.

Stable, artifact-free 30-second ECG segments were extracted during both REM and non-REM (NREM) sleep stages
Time-domain and nonlinear HRV indices were lower during NREM sleep than during REM sleep
This finding suggests that autonomic modulation of heart rate differs meaningfully between sleep stages in OSA patients

Results

HRV indices were lower during hypopneic events compared to apneic events.

ECG segments were extracted specifically during respiratory events including both apneas and hypopneas
Time-domain and nonlinear HRV indices were lower during hypopneic events than during apneic events
This counterintuitive finding suggests that the autonomic response differs between complete and partial airway obstruction events

Results

HRV indices were significantly lower in female participants compared to male participants.

The study sample had a male predominance, with 64.7% male participants
Mean (SD) age of the cohort was 49.7 (14) years
Female sex was associated with significantly lower HRV indices independent of other variables

Results

HRV indices were significantly lower in participants with diabetes and hypertension compared to those without these comorbidities.

Diabetic participants had lower HRV compared to non-diabetic counterparts
Hypertensive participants had lower HRV compared to non-hypertensive counterparts
These findings are consistent with known effects of these comorbidities on cardiac autonomic regulation

Methods

Ultra-short-term HRV using 30-second ECG segments was feasible and informative for assessing cardiac autonomic regulation in OSA patients.

This was a cross-sectional study design
A dedicated algorithm was used to identify stable, artifact-free 30-second ECG segments from polysomnography recordings
Both time-domain and nonlinear HRV indices were computed from these ultra-short-term segments
The authors note that literature on short- and ultra-short-term HRV in OSA is sparse, positioning this as a gap-filling study
Exclusion of mild OSA and focus on 30-second respiratory events were noted as limitations to generalizability

What This Means

This research suggests that heart rate variability (HRV) — a measure of how the nervous system controls heart rhythm — differs meaningfully depending on the severity of obstructive sleep apnea (OSA), the stage of sleep, and the type of breathing event occurring. The study examined 88 adults with either moderate or severe OSA, analyzing very short (30-second) windows of heart rhythm data captured during sleep studies. People with severe OSA showed lower HRV than those with moderate OSA, and HRV was also lower during non-REM sleep compared to REM sleep. Surprisingly, HRV was lower during partial breathing pauses (hypopneas) than during complete breathing pauses (apneas). The study also found that certain patient characteristics were associated with lower HRV: being female, having diabetes, or having high blood pressure were all linked to reduced HRV, suggesting these groups may have greater disruption to their heart's autonomic regulation. These findings matter because lower HRV is generally associated with worse cardiovascular health outcomes, and this study suggests that even very brief ECG recordings during sleep can capture meaningful differences in autonomic nervous system function across different OSA severities and sleep conditions. This research suggests that ultra-short-term HRV analysis could be a useful, non-invasive tool for better understanding autonomic dysfunction in OSA patients. However, the study only included moderate and severe OSA (excluding mild OSA), and the findings may not apply to all OSA patients. Future research including milder disease and larger, more diverse populations would help confirm and extend these findings.

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Citation

Nagaraju K, Venkatnarayan K, Venugopal R, Nagendra R, Veluthat C, Ramachandran P, et al.. (2026). Ultra-short term Heart Rate Variability in moderate and severe Obstructive Sleep Apnea.. Respiratory medicine. https://doi.org/10.1016/j.rmed.2026.108654

Key Findings

What This Means

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