Ultra-short term Heart Rate Variability in Moderate and Severe Obstructive Sleep Apnea.

INTRODUCTION Obstructive sleep apnea (OSA) is characterized by intermittent hypoxia and recurrent arousals, leading to sympathetic overactivity and adverse cardiometabolic consequences. Heart rate variability (HRV), which reflects beat-to-beat fluctuations in heart rate, serves as a non-invasive marker of cardiac autonomic regulation. Although reduced long-term HRV has been described in OSA, literature on short- and ultra-short-term HRV (uST-HRV) is sparse.

METHODOLOGY In this cross-sectional study, adults with moderate and severe OSA were included. Stable, artifact-free 30-second electrocardiographic segments were extracted using a dedicated algorithm during rapid eye movement (REM) and non-REM (NREM) sleep, as well as during respiratory events (apneas and hypopneas). These segments were assessed for ultra-short term HRV comprising time domain and nonlinear indices.

RESULTS A total of 88 patients (44 moderate and 44 severe OSA) were studied. The mean (SD) age was 49.7 (14) years, with a male predominance (64.7%). Mean (SD) AHI was 16.8 (4.3) in moderate and 61.5 (23.1) in severe OSA respectively. HRV indices were significantly lower in female participants and among diabetics and hypertensives compared to their non-diabetic and non-hypertensive counterparts. Time-domain and non-linear HRV indices were also lower in severe OSA, NREM sleep and during hypopneic events compared to moderate OSA, REM sleep and apneic events respectively.

CONCLUSIONS 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. The exclusion of mild OSA and the focus on 30-second respiratory events limit the generalisability of these findings.