Low AHI with elevated T90 as a clinical clue to underlying respiratory impairment in the sleep heart health study

Extract The apnoea–hypopnoea index (AHI) remains the dominant metric for classifying sleep-disordered breathing severity, but it captures event frequency, not the depth, duration, or cumulative burden of nocturnal oxygen desaturation. Oxygenation-based metrics, including T90 (percentage of sleep time with SpO2 <90%) and sleep apnoea-specific hypoxic burden, provide cardiopulmonary prognostic information beyond AHI [1–3], suggesting that nocturnal hypoxaemia captures dimensions not reflected by AHI.