Impact of Hypoxemia Severity on Cardiac Autonomic Regulation in Children With Sleep‐Disordered Breathing: A <scp>McGill</scp> Oximetry‐Based Analysis

ABSTRACT Sleep‐related breathing disorders (SRBD) represent a significant paediatric health concern. Traditional polysomnographic indices, such as the apnoea–hypopnoea index, may not fully capture the physiological burden of paediatric SRBD, highlighting the need to better characterise the impact of nocturnal hypoxemia on cardiac autonomic regulation. This study evaluated the impact of intermittent nocturnal hypoxia on cardiac autonomic function in children with suspected SRBD by examining associations between hypoxemia severity, assessed using the McGill Oximetry Score (MOS) and heart rate variability (HRV) indices. A total of 127 children aged 2–17 years who underwent attended overnight polysomnography with a total sleep time of at least 4 h were included. Study participants were categorised into four groups according to MOS (MOS 1–4). Whole‐night HRV analysis revealed significantly lower parasympathetic‐related indices in the MOS 3 and MOS 4 groups compared with the other groups ( p = 0.012). High‐frequency power decreased progressively with increasing MOS ( p = 0.043), whereas the LF/HF ratio increased significantly ( p &lt; 0.001). Other indices reflecting short‐term variability and autonomic balance showed similar trends with increasing MOS ( p = 0.032 and p = 0.038, respectively). Similar patterns were observed in 20‐min ECG segments during both NREM and REM sleep. These findings demonstrate that intermittent nocturnal hypoxia, as quantified by MOS, is closely associated with cardiac autonomic imbalance in children with SRBD. Higher MOS values were associated with reduced parasympathetic modulation and altered autonomic balance, supporting the clinical relevance of hypoxemia‐based metrics for assessing autonomic dysfunction risk.