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



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.


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.


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%.


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).


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.

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Author information

Dr. Labarca: principal investigator, data extraction, data analysis, manuscript redaction, and final approval. Dr. Campos, Thibaut: data extraction, data analysis, and final approval. Dr. Jorquera, Dreyse: data acquisition, data synthesis, critical analysis, and final approval.

Correspondence to Gonzalo Labarca.

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The authors declare that they have no conflict of interest.

Ethical approval

All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee from Clinica Las Condes, Santiago, Chile, and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

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For the retrospective cohort included in this study, formal consent from patients was not required.

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Labarca, G., Campos, J., Thibaut, K. et al. Do T90 and SaO2 nadir identify a different phenotype in obstructive sleep apnea?. Sleep Breath 23, 1007–1010 (2019). https://doi.org/10.1007/s11325-019-01860-0

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  • Comorbidities
  • Sleep apnea
  • Obstructive
  • Hypertension
  • Cardiovascular