Study Reveals Mechanisms Linking Sleep Apnea to Heart Health

A recent study published by the National Institute of Health sheds light on the link between obstructive sleep apnea (OSA) and cardiovascular risk. OSA has long been associated with an increased likelihood of cardiovascular issues such as heart attacks, strokes, and even death. However, this research, supported in part by the National Institutes of Health (NIH), provides valuable insights into the underlying mechanisms responsible for this association. 

The study, led by Dr. Ali Azarbarzin from Brigham and Women’s Hospital and Harvard Medical School, aimed to identify specific features of OSA that might explain why some individuals with the condition face a higher risk of developing cardiovascular diseases or experiencing related adverse events. To achieve this, the researchers analyzed data from two significant studies: the Osteoporotic Fractures in Men Study (MrOS) and the Multi-Ethnic Study of Atherosclerosis (MESA).

The combined data included information from over 4,500 middle-aged and older adults. By examining physiological features of OSA, such as hypoxic burden (reduction in blood oxygen levels during sleep), ventilatory burden (interruptions in breathing due to airway obstruction), and nighttime arousals (sudden awakenings due to interrupted breathing), the team sought to better understand the factors contributing to increased cardiovascular risks in OSA patients. 

Traditionally, the severity of sleep apnea has been measured by the number of airway blockages that occur during an hour of sleep. However, this study aimed to delve deeper into the underlying mechanisms and identify specific predictors of cardiovascular risks associated with OSA. Over the course of nine to twelve years, 2,627 men with an average age of 76 were followed in the MrOS study.

Additionally, data from 1,973 men and women with an average age of 67, followed for about seven years, were analyzed from the MESA study. During the study period, participants underwent medical check-ins, and sleep assessments, and provided health-related information. Among the participants, approximately 110 individuals in MESA and 382 in MrOS experienced primary cardiovascular events. 

The findings of the study revealed that for each measure of the observed reduction in blood oxygen levels (hypoxic burden), individuals in the MESA study had a 45% increased associated risk of experiencing a primary cardiovascular event. In the MrOS study, the observed increased risk was 13%. The partial or complete closure of the airways (airway obstruction) accounted for 38% of the observed cardiovascular risks in MESA and 12% in MrOS. Additionally, the study found that high hypoxic burden was primarily due to severe airway obstruction and not factors such as abdominal obesity or reduced lung function. 

Dr. Gonzalo Labarca, an instructor in medicine at Brigham and Women’s Hospital and Harvard Medical School, emphasized the specificity of this metric to sleep apnea. “The connections are less explained by obesity or another factor,” he stated. While sudden awakenings from sleep (arousals) were not significantly associated with cardiovascular outcomes in the MESA study, they were linked to cardiovascular-related deaths in the MrOS study. 

The research outcomes have the potential to transform how sleep apnea is assessed and treated, but further validation through future studies is necessary. Understanding the mechanisms underlying the relationship between sleep apnea and cardiovascular risk could lead to more effective clinical trial designs and improve patient care. 

Dr. Marishka K. Brown, director of the National Center for Sleep Disorders Research at the National Heart, Lung, and Blood Institute (NHLBI), part of the NIH, highlighted the significance of the study in potentially shaping the future of sleep apnea research and clinical practices. According to previous estimates, nearly 425 million adults worldwide, and approximately 54 million in the United States, suffer from obstructive sleep apnea, placing them at a higher risk of cardiovascular disease, which remains the leading cause of death globally. 

The study received partial support from NHLBI, the National Center for Advancing Translational Sciences, the National Institute on Aging, and the National Institute of Arthritis and Musculoskeletal and Skin Diseases. This groundbreaking study provides essential insights into the connection between obstructive sleep apnea and cardiovascular risk.

By identifying the underlying mechanisms responsible for the link, it opens the door to more targeted and effective approaches for managing and preventing cardiovascular complications in individuals with OSA. As the prevalence of OSA continues to rise globally, understanding and addressing this relationship becomes ever more crucial in mitigating the impact of cardiovascular diseases on public health.