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Denis Martinez, MD, PhD; Cristiane Maria Cassol, PT, MSc; Fernando A. Boeira Sabino da Silva, MSc
Author and Funding Information

From the Graduate Program in Medical Sciences (Dr Martinez), Graduate Program in Cardiology and Cardiovascular Sciences (Dr Martinez and Ms Cassol), and Institute of Mathematics (Mr Silva), Department of Statistics, Universidade Federal do Rio Grande do Sul; and Cardiology Division (Dr Martinez), Hospital de Clínicas de Porto Alegre.

Correspondence to: Denis Martinez, MD, PhD, Graduate Program in Medical Sciences and Graduate Program in Cardiology and Cardiovascular Sciences, Universidade Federal do Rio Grande do Sul, Rua Ramiro Barcelos, 2350 Porto Alegre, RS, Brazil 90035-903; e-mail: dm@ufrgs.br


Financial/nonfinancial disclosures: The authors have reported to CHEST the following conflicts of interest: Dr Martinez owns a private sleep clinic. Ms Cassol and Mr Silva have reported that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2012;142(6):1689-1690. doi:10.1378/chest.12-1820
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Published online
To the Editor:

We thank Mr Ramos-Xavier and colleagues for their comments and knowledgeable appraisal of our work.1 Their disposition to engage in multicentric studies demonstrates their awareness of the relevance of the matter.

Our report on the seasonality of obstructive sleep apnea severity1 was performed in a humid subtropical climate, the Cfa group in the Köppen-Geiger climate classification (the Cfa group is an environment with significant precipitation in all seasons [f] and an average temperature of the warmest month above 22°C [a] belonging to the temperate [C] group of the Köppen-Geiger climate classification).2 Although only a small portion of the surface of the globe is subjected to this weather, many cities with productive sleep research centers share this climate (eg, Boston, Massachusetts; New York, New York; Philadelphia, Pennsylvania; Milan, Italy; São Paulo, Brazil; Hong Kong, China). It is possible to attempt to replicate the data in the same climate or to do a worldwide study.

It is feasible to undertake an initiative to analyze global polysomnographic data. Sleep laboratories from any part of the planet can send the polysomnography reports to us in databases containing full meteorologic data or at least daily relative air humidity. The mathematicians at our university are capable of extending the cosinor analyses to larger databases.

One opportunity to test immediately the seasonality of polysomnographic records may emerge from data Ramos-Xavier and colleagues already have. The epidemiologic study published in 2010 by Tufik and colleagues3 probably allows answering one doubt from our study. Patients with the most severe cases of sleep apnea may seek the sleep laboratory in the winter not exclusively because winter-related upper airway conditions such as colds or allergies might have worsened their apnea symptoms but simply because it is more convenient for them to take the time to seek treatment in the winter. The population-based sample from São Paulo was recruited using a probabilistic three-stage cluster sampling technique. Therefore, if the volunteers in the Tufik and colleagues3 study undergoing polysomnography randomly over the year have apnea-hypopnea indexes that fit a cosinor model, stronger evidence will be attained of the climatic influences on sleep apnea.

Besides seasonality of obstructive sleep apnea severity, we observed seasonal variation of some polysomnographic measurements that may be worth analyzing in larger samples. For instance, cardiac arrhythmias on polysomnography also have an acrophase in the winter months. We have focused on sleep apnea severity, but many other aspects related to the seasonality of sleep disorders deserve investigation.

References

Cassol CM, Martinez D, Silva FABS, Fischer MK, Lenz MD, Bós AJG. Is sleep apnea a winter disease? Meteorologic and sleep laboratory evidence collected over 1 decade. Chest. 2012;142(6):1499-1507.
 
Peel MC, Finlayson BL, McMahon TA. Updated world map of the Köppen–Geiger climate classification. Hydrol Earth Syst Sci. 2007;11:1633-1644. [CrossRef]
 
Tufik S, Santos-Silva R, Taddei JA, Bittencourt LR. Obstructive sleep apnea syndrome in the Sao Paulo Epidemiologic Sleep Study. Sleep Med. 2010;11(5):441-446. [CrossRef] [PubMed]
 

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References

Cassol CM, Martinez D, Silva FABS, Fischer MK, Lenz MD, Bós AJG. Is sleep apnea a winter disease? Meteorologic and sleep laboratory evidence collected over 1 decade. Chest. 2012;142(6):1499-1507.
 
Peel MC, Finlayson BL, McMahon TA. Updated world map of the Köppen–Geiger climate classification. Hydrol Earth Syst Sci. 2007;11:1633-1644. [CrossRef]
 
Tufik S, Santos-Silva R, Taddei JA, Bittencourt LR. Obstructive sleep apnea syndrome in the Sao Paulo Epidemiologic Sleep Study. Sleep Med. 2010;11(5):441-446. [CrossRef] [PubMed]
 
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