Time matters in obstructive sleep apnoea: a neglected dimension of disease burden and treatment

Obstructive sleep apnoea (OSA) is traditionally characterised by its severity using the apnoea-hypopnoea index (AHI). However, the biological and clinical consequences of OSA are unlikely to depend on respiratory event frequency alone but also on the duration and cumulative burden of disease exposure over time and its interaction with comorbidities. This perspective proposes a conceptual framework for considering the temporal dimensions of OSA across the patient journey, including lifetime exposure before diagnosis, nightly exposure beyond the AHI, therapeutic exposure during treatment, and recurrent exposure resulting from treatment interruptions or suboptimal treatment efficacy. Evidence from epidemiological studies, physiological investigations, experimental models and clinical trials suggests that factors such as diagnostic delay, cumulative hypoxic burden, night-to-night variability, treatment adherence, residual disease on treatment and intermittent treatment interruption may all influence cardiovascular risk and clinical outcomes. These observations help explain why patients with similar AHI values may experience different symptom burden, cardiovascular consequences and treatment responses. Integrating these temporal dimensions provides a broader understanding of OSA as a chronic disease characterised by cumulative disease exposure rather than a condition defined by a single-night measure of severity. This framework offers a perspective for interpreting heterogeneous clinical outcomes and may improve phenotyping and risk stratification. However, cumulative OSA exposure cannot be reliably quantified currently and should be regarded as a conceptual framework. Future studies should incorporate both the intensity and duration of OSA exposure and treatment when evaluating disease burden and treatment effects.