Predicting cardiovascular events in sleep apnea
Obstructive sleep apnea generally is associated with increased risk for cardiovascular disease. Obstructive sleep apnea is usually measured using the apnea-hypopnea index, the number of times that breathing pauses or severely slows per hour of sleep. However, sleep studies using to diagnose obstructive sleep apnea produce a number of other measures. Whether those measures are associated with cardiovascular disease, and whether they predict cardiovascular disease as well or better than apnea-hypopnea index, is not known.
Obstructive sleep apnea (OSA) generally is associated with increased risk for cardiovascular (CV) disease. OSA is usually measured using the apnea-hypopnea index (AHI), the number of times that breathing pauses or severely slows per hour of sleep. However, sleep studies using to diagnose OSA produce a number of other measures.Whether those measures are associated with CV disease, and whether they predict CV disease as well or better than AHI, is not known. Tetyana Kendzerska (University of Toronto) and colleagues conducted a large cohort study of 10,149 participants referred for suspected OSA who underwent diagnostic polysomnography at the sleep laboratory at St Michael’s Hospital (Toronto, Canada) between 1994 and 2010. The patients were followed up through provincial health administrative data (Ontario, Canada) until May 2011 for CV disease (myocardial infarction, stroke, congestive heart failure, revascularization procedures) and death from any cause, analyzed as a composite outcome.A total of 1,172 (11.5%) of the 10,149 participants experienced the composite CV disease outcome. The researchers found that, after adjusting for potentially confounding factors, time spent with oxygen saturation < 90%, sleep time, number of awakenings, periodic leg movements, heart rate, and daytime sleepiness were all associated with the composite outcome, with the total sleep time spent with oxygen saturation below 90% being the strongest association (9 minutes vs. 0 minutes: hazard ratio=1.5, 95% confidence interval, 1.25-1.79). The size of increased relative risk ranged from 5% to 50%, after controlling for known CV risk factors. Furthermore, when the authors examined the outcomes individually, the OSA risk factors were associated with increased risk for all-cause mortality, hospitalization for congestive heart failure, and stroke, but not for acute myocardial infarction.AHI was associated with the composite outcome when analyzed by itself. However, after the other OSA-related factors were added to the model, AHI was no longer a significant predictor of the composite outcome.The authors also developed a nomogram to predict the CVD risk of individuals based on their sleep study scores. …
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