Recent research has shown that patients with obstructive sleep apnea (OSA) are at higher risk of developing cardiovascular (CV) disease. The AHI, or apnea-hypopnea index, is used to measure OSA. The AHI is technically the number of times the person’s breathing pauses or slows down significantly per hour during sleep. However, there are other measures taken during a sleep study when looking for OSA as well. It is unknown whether these other measures are associated with or can predict heart disease as good as AHI can, or better.
At the University of Toronto, a group of researchers led by Tetyana Kendzerska did a cohort study of over 10,000 people who were referred for suspected obstructive sleep apnea and underwent sleep study (polysomnography) at St. Michael’s Hospital sleep lab between the years 1994 and 2010. The provincial health administrative data in Ontario was used to follow up the patients up to 05/2011. They were evaluated for any form of cardiovascular disease including myocardial infarction, congestive heart failure, revascularization procedures, and stroke. Death from any other causes was analyzed as a composite outcome.
Of the 10,149 patients followed, about 11.5% (1172 people) had the composite outcome. Researchers did adjust for some factors including sleep time, awakenings, leg movements, time spent with low oxygen saturation (under 90%), daytime sleepiness, and heart rate, and it was found that the strongest association to the composite outcome was the total sleep time spent with oxygen saturations below 90%.
Increased relative risk ranged between 5% and 50% after adjusting and controlling for the other well-known heart disease risk factors. Additionally, it was noted that OSA risk factors were linked to more hospitalizations for heart failure, stroke, and an increased risk for mortality when outcomes were examined individually. It is notable that there was no increased risk for acute myocardial infarction (heart attack).
When looked at by itself, AHI was linked to the composite outcome noted above. After OSA risk factors were added to the whole model, the apnea-hypopnea index was no longer a predictor.
A nomogram was used to help predict the risk of cardiovascular disease in people based on their sleep study; however, this nomogram needs to be further validated by using it in a separate sample of patients before they can use it clinically in this study.
The one limitation to the study was that there was no way to tell how compliant patients were with OSA treatments using a CPAP machine. When patients with an insurance claim for a CPAP device were excluded, all except one of the associations were found.
The researchers reported that there might need to be a revision of the definition of OSA, which would reflect not only the frequency of hypopneas or apneas, but the other health consequences as well that result from OSA such as sleep deprivation, fragmented sleep, sympathetic activation, and decreased oxygen saturation levels. The most predictive measure of cardiovascular risk is the “downstream” phenomena, authors note. The predictors of OSA identified in this study could be identified using much simpler studies, like home sleep studies, rather than polysomnography.
Rachael Herman is a professional writer with an extensive background in medical writing, research, and language development. Her hobbies include hiking in the Rockies, cooking, and reading.