How to assess nocturnal hypoxaemic burden in Cardiology?

This commentary refers to ‘The hypoxic burden of sleep apnoea predicts cardiovascular disease-related mortality: the Osteoporotic Fractures in Men Study and the Sleep Heart Health Study’, by A. Azarbarzin et al., 2019;40:1149–1157. The apnoea–hypopnoea index (AHI), the most widely used clinical metric to assess sleep-disordered breathing (SDB) may not sufficiently reflect the complex pathophysiological mechanisms potentially contributing to cardiovascular outcome risk.1 Nocturnal hypoxaemic burden has been identified previously as a robust and independent predictor of all-cause mortality in heart failure patients.1 , 2 However, the predictive value of hypoxemic burden specifically due to SDB in the general population is unknown. In this context, Azarbarzin et al.3 evaluated whether hypoxic burden determined as the respiratory event-associated area under the oximetry curve from pre-event baseline during formal overnight sleep studies would predict all-cause and cardiovascular mortality among adults aged 40 and older in two large cohort studies. They showed that hypoxaemic burden quantified by their novel technique predicted cardiovascular mortality better than AHI. This study provides an important step towards a pathophysiology and outcome focused assessment of SDB. However, the challenge remains on how best to quantify hypoxaemic burden in the clinical setting, because comprehensive sleep studies are expensive and time-consuming. We developed an algorithm for detailed quantification and characterization of hypoxaemic burden using simple overnight oximetry without the necessity for comprehensive overnight sleep studies. In our recent study published in the European Heart Journal,4 we demonstrated that nocturnal hypoxaemic burden is not merely the consequence of frank desaturations associated with respiratory events, but also reflects non-specific drifts in oxygen saturation, both contributing towards the risk of cardiovascular death. When measured on simple pulse oximetry, assessment of overnight hypoxaemic burden becomes feasible not only for the standard clinical workup in cardiology but also for population screening. This may also facilitate monitoring night-to-night variability of hypoxaemic burden.1 , 5 Whether hypoxaemic burden derived from pulse oximetry alone or formal sleep studies are necessary to effectively quantify risk in the clinical setting, and whether its reduction constitutes a treatment target warrants further prospective and randomized studies. Conflict of interest: none declared.