A new study funded by the National Institutes of Health (NIH) has revealed the mechanism that connects obstructive sleep apnea (OSA) to an increased cardiovascular risk.
Sleep Apnea. Image Courtesy of Drcamachoent
OSA is a disorder that causes breathing to stop and start while sleeping. This occurs when the airway gets blocked as a result of the relaxation of the throat muscles. Around 54 million adults in the U.S., and roughly 425 million globally, are believed to have this potentially deadly sleep disorder.
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Studies have shown a link between obstructive sleep apnea and cardiovascular disease, which is the world’s leading cause of death. Findings in this new research highlight what drives the observed link.
“These findings will help better characterize high-risk versions of obstructive sleep apnea,” said Ali Azarbarzin, Ph.D., the director of the Sleep Apnea Health Outcomes Research Group at Brigham and Women’s Hospital and Harvard Medical School and a study author. “We think that including a higher-risk version of obstructive sleep apnea in a randomized clinical trial would hopefully show that treating sleep apnea could help prevent future cardiovascular outcomes.”
The findings were reported in the American Journal of Respiratory and Critical Care Medicine.
Higher cardiovascular risks
OSA has been linked to heart attack and other cardiovascular issues in research. To establish the link between the sleep disorder and increased cardiovascular risk, researchers examined the data of over 4,500 adults that were middle-aged or older in this study. The data were obtained from the Osteoporotic Fractures in Men Study (MrOS) and the Multi-Ethnic Study of Atherosclerosis (MESA).
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The team wanted to better understand the mechanisms triggering OSA and pinpoint the ones that could better predict cardiovascular risks, including death. It assessed several physiological features, including hypoxic burden, ventilatory burden, and nighttime arousals.
Hypoxic burden refers to a reduction in the levels of oxygen in the blood during sleep, while ventilatory burden are blockage-induced breathing disruptions. Nighttime arousal describes waking up abruptly from sleep following a breathing interruption.
The MrOS data included more than 2,600 men who were followed for roughly nine to 12 years. Men and women totaling 1,973 from the MESA were followed for around seven years. The participants had medical check-ins and completed sleep assessments while also sharing their health information during these periods.
Around 382 subjects in MrOS had a primary cardiovascular event while about 110 in MESA experienced the same. MESA participants showed a 45 percent higher associated primary cardiovascular event risk for every observed hypoxic burden measure. The increased risk was 13 percent in MrOS.
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Full or partial airway closures were responsible for 38 percent of risks in MESA and 12 percent in MrOS.
Other findings
Researchers found that nighttime arousals (sudden awakenings) did not show an association with cardiovascular outcomes in MESA. However, they showed an association with cardiovascular-related mortality in MrOS.
Of note, the team found that large drops in blood oxygen levels during sleep resulted mainly from severe airway obstruction. Other factors, including central obesity and reduced lung function, were less to blame.
“That’s something that makes this metric specific to sleep apnea,” said Gonzalo Labarca, M.D., a study co-author.
The researchers expressed hope that their findings may improve how OSA is assessed. They could advance the design of clinical trials on this disorder and its measurement in clinical practice.
Findings in the current research still have to be confirmed in future research, the study authors noted.
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References
Labarca, G., Vena, D., Hu, W.-H., Esmaeili, N., Gell, L., Yang, H. C., Wang, T.-Y., Messineo, L., Taranto-Montemurro, L., Sofer, T., Barr, R. G., & others. (2023). Sleep Apnea Physiological Burdens and Cardiovascular Morbidity and Mortality. American Journal of Respiratory and Critical Care Medicine. https://doi.org/10.1164/rccm.202209-1808OC
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