Do T90 and SaO₂ nadir identify a different phenotype in obstructive sleep apnea?

Introduction: Severity of obstructive sleep apnea (OSA) is commonly based upon the apnea-hypopnea index (AHI). However, patients with similar AHIs may demonstrate widely varying comorbidities and risk for cardiovascular disease. These varying manifestations of disease may be related to nocturnal hypoxia and not AHI. We hypothesize that parameters of oxygenation may identify a different phenotype in OSA. Purpose: To explore potential associations between lowest SaO₂ (SaO₂ nadir) and total sleep time spent with arterial oxygen saturation (SaO₂) < 90% (T90) with comorbidities and mortality in patients with moderate and severe OSA. Method: This was a retrospective study of patients between 2009 and 2014, with a new diagnosis of moderate-to-severe OSA without a concomitant respiratory disease. Data collection included demography, comorbidities, sleep study parameters, and mortality over a 5-year interval. Patients were categorized into two groups for analysis, group 1: SaO₂ nadir < 75%, and group 2: T90 > 20%. Results: Of the 365 patients, 163 (45%) recorded SaO₂ nadir < 75% and 127 (35%) recorded T90 > 20%. These oxygenation parameters were associated with more severe OSA by AHI (p < 0.001). T90 > 20% was associated with an increased risk of hypertension (HT) OR 2.95 (CI 1.87–4.76, p < 0.001) in patients with both moderate and severe OSA. T90 > 20% was also associated with an increased risk of type 2 diabetes mellitus (T2DM) OR 2.14 (CI 1.35–3.38, p = 0.001) and mortality 2.70 (CI 1.37–5.22, p = 0.0048). Conclusion: The findings demonstrate a correlation between SaO₂ nadir < 75% and T90 > 20% and increased severity of OSA. The findings also show a strong association between SaO₂ nadir < 75% and T90 > 20% and increased risk for comorbidities of HT and T2DM as well as mortality at 5 years. This analysis suggests that parameters of oxygenation should be used to describe a high-risk phenotype of OSA.