By Caroline Wilbert
WebMD Health News
Reviewed By Louise Chang, MD
Oct. 24, 2008 -- Sleep apnea -- even if it is so mild that people have no daytime drowsiness -- may increase the risk of cardiovascular disease, a study shows.
The study, published in the American Journal of Respiratory and Critical Care Medicine, compared patients with mild sleep apnea to a comparison group that didn't have sleep apnea. There were 64 participants with mild sleep apnea and 15 participants without sleep apnea.
To compare the risk for heart disease, researchers tested endothelial function, which is how well the cells in the lining of the blood vessels work, and artery stiffness. Endothelial dysfunction and arterial stiffness are involved in developing atherosclerosis, or hardening of the arteries. Moderate to severe sleep apnea has already been linked to increased artery stiffness, endothelial dysfunction, and high blood pressure.
Malcolm Kohler, MD, from the Oxford Centre for Respiratory Medicine in England, and colleagues found that patients with mild sleep apnea had worse endothelial function and greater arterial stiffness than the comparison group without sleep apnea.
Researchers also tested blood pressure, another way to gauge cardiovascular disease risk. The groups tested similarly on blood pressure.
The researchers write that "although this was not associated with significantly increased blood pressure, the findings of this study suggest that patients with minimally symptomatic OSA [obstructive sleep apnea] are at increased cardiovascular risk, as has been demonstrated in more severe disease."
"It was previously known that people with OSA (obstructive sleep apnea) severe enough to affect their daytime alertness and manifest in other ways are at increased risk of cardiovascular disease, but this finding suggests that many more people -- some of whom may be completely unaware that they even have OSA -- are at risk than previously thought," Kohler says in a news release.
In an accompanying editorial, Geraldo Lorenzi-Filho MD, PhD, points out that just one in five patients with sleep apnea complains of drowsiness during the day. "It is now recognized that OSA triggers a cascade of biological reactions, including increased sympathetic activity, systemic inflammation, oxidative stress, and metabolic alterations that are potentially harmful to the cardiovascular system," he writes in the editorial.
Kohler and colleagues are now investigating the effects of continuous positive airway pressure (CPAP) therapy on arterial stiffness and endothelial function in patients with sleep apnea.
SOURCES: Kohler, M. American Journal of Respiratory and Critical Care Medicine, November 2008; vol 178: pp 984-988. Lorenzi-Filho, G. American Journal of Respiratory and Critical Care Medicine, November 2008; vol 178: pp 892-893. News release, American Thoracic Society.
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