25 Oct The Hypoxic Burden of OSA
The field of Sleep Medicine is a rapidly evolving landscape. Technological advancements in diagnostics and therapies are changing the way we diagnose and treat sleep disorders. The most common reported index used to diagnose Obstructive Sleep Apnoea (OSA) and other sleep related breathing disorders is the AHI or RDI. This index is simply the number of respiratory events divided by time (hours). This index as the sole metric of disease severity is limited, yet widely used.
The International Classification of Sleep Disorders sets an AHI classification for mild OSA at 5-14 events per hour, 15-29/hr for moderate OSA and no less than 30/hr for severe OSA. A respiratory event is defined as between 30% – 100% reduction from baseline airflow for at least 10 seconds and often have a cortical arousal from sleep or a 3% oxygen desaturation. Arousal index and oxygen desaturation index may also be reported; however, the primary index reported in a diagnostic sleep study report is the AHI or RDI. Yet we understand that repeated episodes of hypoxia directly relate to the most significant clinical features presented by the disease.
Researchers in Spain (Martinez-Garcia et al., 2023) believe that these two primary diagnostic indices (RDI / AHI) are qualitatively limited, as they fail to measure the downstream impact that the depth and duration of hypopnoeas and apnoeas have in sufficient detail. They offer an alternative metric: the hypoxic burden (HB).
Hypoxic Burden is defined as the sum of individual areas under the oxygen desaturation curve. This has shown some promise in identifying high risk individuals with OSA. In their most recent paper, the authors cite research from the last four years linking OSA related HB and several adverse health outcomes. However, this measurement (HB) is not yet readily available from most diagnostic sleep study systems that are currently used across the globe (Polysomnography).
Author: Khosro Zarif-Raftar (BRPT), Sleep Technician
Citation: Martinez-Garcia MA, Sánchez-de-la-Torre M, White DP, Azarbarzin A. Hypoxic Burden in Obstructive Sleep Apnea: Present and Future. Arch Bronconeumol. 2023 Jan;59(1):36-43. English, Spanish. doi: 10.1016/j.arbres.2022.08.005. Epub 2022 Sep 5. PMID: 36115739.