To the Editor:
We read with interest the article by Trzepizur et al1 in CHEST (June 2013). They investigated the hypothesis of an independent association between nocturnal intermittent hypoxemia and dyslipidemia in obstructive sleep apnea (OSA). Total cholesterol and low-density lipoprotein cholesterol were not associated with oxygen desaturation index (ODI). In contrast, nocturnal intermittent hypoxemia and OSA severity were associated with higher triglyceride (TG) levels and lower high-density lipoprotein cholesterol (HDL-c) levels after adjustment for confounding factors. The association among ODI, TG, and HDL-c was independent of the metabolic syndrome.
Metabolic dyslipidemia is one of the most important cardiac risk factors. Regular physical activity may improve metabolic dyslipidemia.2 Factors such as reduced activity levels and increased appetite may be associated with metabolic dyslipidemia in patients with OSA.3 The authors did not mention the relationship between physical activity and higher TG levels and lower HDL-c levels. We think that the results of the study would be stronger if the authors talked about physical activity in patients.
OSA is one of the more critical clinical manifestations of sleep-disordered breathing.4 It is a prevalent sleep disorder leading to cardiovascular and metabolic complications.5 OSA has been related most notably to hypertension, but also to several other cardiovascular diseases, including peripheral arterial disease, ischemic heart disease, heart failure, stroke, cardiac arrhythmias, and pulmonary hypertension.4 These factors not only affect OSA but also influence metabolic syndrome. It would be useful if the authors provided data about these risk factors, especially heart failure, peripheral arterial disease, and pulmonary hypertension.
Finally, renal or hepatic dysfunction; any abnormality in thyroid function tests; inflammatory diseases; confounding effects of sex; confounding effects of some medications, such as antihypertensive treatment including angiotensin-converting enzyme inhibitors, angiotensin receptor blocker, beta blockers, aspirin, and medications for weight loss; and a medical history of drug addiction may influence metabolic dyslipidemia.6 The results of the study might be stronger if the authors had given information about these factors. We believe that these findings will provide advantageous information about the measurements of the association among ODI, TG, and HDL-c independent of the metabolic syndrome.
Footnotes
Editor’s Note: Authors are invited to respond to Correspondence that cites their previously published work. Those responses appear after the related letter. In cases where there is no response, the author of the original article declined to respond or did not reply to our invitation.
Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.
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References
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