Mechanisms of night-to-night variability in obstructive sleep apnoea.

Obstructive sleep apnoea (OSA) diagnosis and severity classification is typically determined from a single-night sleep study. However, high night-to-night variability (N2NV) in OSA severity is associated with adverse health outcomes and complicates diagnosis and treatment. While the contributions of the four main OSA endotypes (i.e., anatomical compromise, unstable ventilatory control, low arousal threshold, and poor upper-airway muscle function) on OSA severity are relatively well established, the extent to which specific mechanistic contributors to N2NV in OSA severity is poorly understood. This narrative review collates evidence-based and theoretically plausible contributors to high N2NV. We consider a plethora of physiological, behavioural, and environmental factors which are known to, or hypothetically contribute to variable OSA severity. How a single-night evaluation may fail to capture key mechanistic contributors to OSA and its variability is also highlighted. Understanding the complexity and interactive nature of these mechanisms may help inform diagnosis, risk stratification, and treatment selection for OSA via a more holistic, precision-medicine approach. Studies that include multi-night in-laboratory and at-home assessments combined with wearable/nearable sleep sensors are required to better understand the underlying mechanisms that contribute to high N2NV in OSA severity and its associated adverse consequences.