Rationale — The inter-relationships between obstructive sleep apnea (OSA) and obesity are complex and bidirectional; however, the current evidence regarding their combined effect o cardiovascular risk is limited and conflicting. Animal studies suggest that obesity may exacerbate the cardiovascular consequences of intermittent hypoxemia.
Objectives — In this historical observational study, we investigated whether obesity increases the effect of nocturnal hypoxemia on the incidence of cardiovascular events in adults with suspected OSA.
Methods — All adults with suspected OSA who underwent diagnostic polysomnography at a large academic hospital between 1994 and 2010 were linked to provincial health administrative data to determine a composite cardiovascular outcome (hospitalization due to heart failure, myocardial infarction, stroke or revascularization procedures). Using a competing-risk model and controlling for confounders, hazards were compared between four groups: (1) obese (BMI>30 kg/m2) with oxygen desaturation (> 9 minutes of sleep spent with SaO2<90%), (2) obese without desaturation, (3) non-obese with desaturation and (4) non-obese without desaturation. Interaction was measured using the relative excess risk due to interaction (RERI).
Measurements and Main Results — 10,149 participants were followed, with 17%, 25%, 8%, and 50% in groups 1 through 4 respectively. Over a median of 7.8 years, 896 (8.8%) first cardiovascular events occurred. Group 1 was associated with the highest hazard as compared to other groups using group 4 as a reference (HR [group 1], 95% CI = 1.84, 1.46-2.32, HR [group 2] =1.59, 1.29-1.95; HR [group 3] =1.51, 1.15-1.98). The RERI was -0.25 (95%CI: -0.78-0.27) indicating no interaction.
Conclusions — In adults with suspected OSA, the highest cardiovascular risk was found in obese patients with nocturnal oxygen desaturation; however, the effect of these two factors together does not exceed the effect of each factor considered individually.