Obesity is associated with a lower resting oxygen saturation in the ambulatory elderly: Results from the cardiovascular health study

BACKGROUND: The contribution of obesity to hypoxemia has not been reported in a communitybased study. Our hypothesis was that increasing obesity would be independently associated with lower A_pO2 in an ambulatory elderly population. METHODS: The Cardiovascular Health Study ascertained resting A_pO2 in 2,252 subjects over age 64. We used multiple linear regression to estimate the association of body mass index (BMI) with A_pO2 and to adjust for potentially confounding factors. Covariates including age, sex, race, smoking, airway obstruction (based on spirometry), self reported diagnosis of emphysema, asthma, heart failure, and left ventricular function (by echocardiography) were evaluated. RESULTS: Among 2,252 subjects the mean and median A_pO2 were 97.6% and 98.0% respectively; 5% of subjects had A_pO2 values below 95%. BMI was negatively correlated with A_pO2 (Spearman R = -0.27, P <.001). The mean difference in A_pO2 between the lowest and highest BMI categories (< 25 kg/m² and > 35 kg/m²) was 1.33% (95% CI 0.89 -1.78%). In multivariable linear regression analysis, A_pO2 was significantly inversely associated with BMI (1.4% per 10 units of BMI, 95% CI 1.2-1.6, for whites/others, and 0.87% per 10 units of BMI, 95% CI 0.47-1.27, for African Americans). CONCLUSIONS: We found a narrow distribution of A_pO2 values in a community-based sample of ambulatory elderly. Obesity was a strong independent contributor to a low A_pO2, with effects comparable to or greater than other factors clinically associated with lower A_pO2.