Key Point

Researchers have recently found an independent relationship between change in apnea-hypopnea index and change in HDL cholesterol or triglyceride levels in patients with moderate to severe obstructive sleep apnea.

BOCHUM, GERMANY—Change in apnea-hypopnea index is associated with change in HDL cholesterol or triglyceride levels, according to a study by Jan Börgel, MD, and colleagues.¹

The researchers identified 470 consecutive sleep laboratory patients who had a diagnosis of moderate to severe obstructive sleep apnea. Cardiovascular risk profile—including medical history and results of physical examination, polysomnography, ECG, echocardiography, and blood analysis —was determined at the time of the initial polysomnography. Of 153 patients who were treated with bilevel positive airway pressure (BiPAP) or continuous positive airway pressure (CPAP) therapy, 127 did not have changes in their lipid-lowering therapy and were reevaluated by polysomnography after six months. LDL and HDL cholesterol levels were available for 86 of the 127 patients.

CORRELATION BETWEEN APNEA AND HDL LEVELS

According to Dr. Börgel, multivariate regression analysis showed a significant association between apnea-hypopnea index and serum HDL cholesterol levels. This association was independent of age, sex, BMI, diabetes, and use of lipid-lowering medication. No independent associations were found between apnea-hypopnea index and any of the following: total cholesterol, triglyceride, or serum LDL cholesterol levels.

In the subgroup of patients who received BiPAP or CPAP therapy without a change in their lipid-lowering therapy, mean serum HDL cholesterol levels increased significantly, by 5.8%, from 46.9 to 49.6 mg/dL^-1. According to the researchers, this change in serum HDL cholesterol level demonstrates the reversibility of, and also confirms the association between, lipid serum levels and apnea-hypopnea index in untreated obstructive sleep apnea.

All patients with abnormal serum lipid/lipoprotein levels showed significant improvement under BiPAP or CPAP. The mechanism for lipid metabolism modification by BiPAP or CPAP therapy is unknown, said the researchers. "On the one hand, the reduction of sympathetic nerve activity may account for an improved lipid profile. On the other hand, effective treatment of obstructive sleep apnea may result in increased physical activity and a reduction of hypersomnolence during the day. It is well known that physical activity can also improve lipid serum levels," they said. The researchers noted that information regarding physical activity and waist-hip ratio should be considered in future studies.

"These observations may help to explain the increased rate of cardiovascular disease in obstructive sleep apnea patients and underline the importance of BiPAP/CPAP treatment," concluded the researchers.

—Karen L. Spittler

Reference
1. Börgel J, Sanner BM, Bittlinsky A, et al. Obstructive sleep apnoea and its therapy influence high-density lipoprotein cholesterol serum levels. Eur Respir J. 2006; 27:121-127.

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