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The Effect of Continuous Positive Airway Pressure on C-Reactive Protein Levels in Patients With Obstructive Sleep Apnea Syndrome FREE TO VIEW

Silke Ryan, MD, PhD; Walter McNicholas, MD, FCCP
Author and Funding Information

From the Sleep Research Laboratory, St. Vincent's University Hospital.

Correspondence to: Silke Ryan, MD, PhD, Department of Respiratory Medicine, St. Vincent ’s University Hospital, Elm Park, Dublin 4, Ireland; e-mail: silke.ryan@ucd.ie


Financial/nonfinancial disclosures:The authors have reported to CHEST the following conflicts of interest: Dr Ryan has no potential conflicts with any companies/organizations whose products or services may be discussed in this article. Dr McNicholas is a shareholder in BiancaMed, a medical device company. Dr McNicholas has also participated in industry advisory committees for Respironics and Novartis during 2008

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/site/misc/reprints.xhtml).


© 2010 American College of Chest Physicians


Chest. 2010;137(2):496-497. doi:10.1378/chest.09-1778
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To the Editor:

We read with great interest the recent report in CHEST (July 2009) by Ishida and colleagues1 and note their finding of significant reductions in C-reactive protein (CRP) levels in a group of patients with obstructive sleep apnea syndrome (OSAS) following treatment with nasal continuous positive airway pressure (CPAP). The question of CRP levels being elevated in patients with OSAS remains controversial, particularly because of the confounding impact of obesity and other cardiovascular diseases and medication on CRP levels. There are many published reports on this topic, some demonstrating independent relationships between CRP and OSAS, whereas others do not show significant relationships after adjustment for relevant confounding variables, as discussed in a recent review.2 In particular, the Wisconsin Sleep Cohort Study of 907 adults failed to detect an independent association between CRP and OSAS after adjustment for BMI.3 Furthermore, the impact of CPAP therapy on CRP levels is controversial, with some reports showing reductions, whereas others do not.2,4,5 In particular, a recent randomized control trial found no difference in CRP levels between therapeutic and sham CPAP after 4 weeks’ therapy.4 Unfortunately, the present report fails to include most of the previous published reports on this topic and thus could be criticized for providing an unbalanced discussion.

We also believe that the present report suffers from several potential limitations. The authors do not provide important additional baseline and follow-up information on potential confounding variables that may have influenced CRP levels, such as medications and changes in lipid and glucose profiles at follow-up. Furthermore, the statistical analysis may have been influenced by factors such as three outliers with especially high CRP values indicating a proinflammatory state in the good compliance group predisposing to a false-positive response to therapy, and small patient numbers (N = 5) in the poor compliance group predisposing to a false-negative result. Better insight into the true relationship of CRP with OSAS and the impact of CPAP therapy might have been provided by additional statistical analysis, particularly using nonparametric statistical testing and after exclusion of outliers. The field is in clear need of large, well-designed, and well-controlled studies to answer the question of possible independent relationships between CRP and OSAS since the majority of published reports, including the present, are limited by small patient numbers and many suffer from potential limitations in study design.

Ishida K, Kato M, Kato Y, et al. Appropriate use of nasal continuous positive airway pressure decreases elevated C-reactive protein in patients with obstructive sleep apnea. Chest. 2009;1361:125-129. [CrossRef] [PubMed]
 
Ryan S, Taylor CT, McNicholas WT. Systemic inflammation: a key factor in the pathogenesis of cardiovascular complications in obstructive sleep apnoea syndrome? Thorax. 2009;647:631-636. [PubMed]
 
Taheri S, Austin D, Lin L, Nieto FJ, Young T, Mignot E. Correlates of serum C-reactive protein (CRP)—no association with sleep duration or sleep disordered breathing. Sleep. 2007;308:991-996. [PubMed]
 
Kohler MM, Ayers L, Pepperell JCT, et al. Effects of continuous positive airway pressure on systemic inflammation in patients with moderate to severe obstructive sleep apnoea: a randomised controlled trial. Thorax. 2008;641:67-73. [CrossRef] [PubMed]
 
Steiropoulos P, Tsara V, Nena E, et al. Effect of continuous positive airway pressure treatment on serum cardiovascular risk factors in patients with obstructive sleep apnea-hypopnea syndrome. Chest. 2007;1323:843-851. [CrossRef] [PubMed]
 

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References

Ishida K, Kato M, Kato Y, et al. Appropriate use of nasal continuous positive airway pressure decreases elevated C-reactive protein in patients with obstructive sleep apnea. Chest. 2009;1361:125-129. [CrossRef] [PubMed]
 
Ryan S, Taylor CT, McNicholas WT. Systemic inflammation: a key factor in the pathogenesis of cardiovascular complications in obstructive sleep apnoea syndrome? Thorax. 2009;647:631-636. [PubMed]
 
Taheri S, Austin D, Lin L, Nieto FJ, Young T, Mignot E. Correlates of serum C-reactive protein (CRP)—no association with sleep duration or sleep disordered breathing. Sleep. 2007;308:991-996. [PubMed]
 
Kohler MM, Ayers L, Pepperell JCT, et al. Effects of continuous positive airway pressure on systemic inflammation in patients with moderate to severe obstructive sleep apnoea: a randomised controlled trial. Thorax. 2008;641:67-73. [CrossRef] [PubMed]
 
Steiropoulos P, Tsara V, Nena E, et al. Effect of continuous positive airway pressure treatment on serum cardiovascular risk factors in patients with obstructive sleep apnea-hypopnea syndrome. Chest. 2007;1323:843-851. [CrossRef] [PubMed]
 
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