Chest
Volume 142, Issue 6, December 2012, Pages 1499-1507
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Original Research
Sleep Disorders
Is Sleep Apnea a Winter Disease?: Meteorologic and Sleep Laboratory Evidence Collected Over 1 Decade

https://doi.org/10.1378/chest.11-0493Get rights and content

Background

The severity of obstructive sleep apnea increases by influence of conditions that are more frequent in winter. The hypothesis that the apnea-hypopnea index (AHI) of different patients undergoing polysomnography may be seasonally affected was tested.

Methods

The retrospectively analyzed database included 7,523 patients of both sexes who underwent in-laboratory baseline polysomnography to investigate any complaint of disordered sleep, during 1 decade, between January 2000 and December 2009. Data on climate and air pollution were obtained from official organizations. AHI was the main outcome variable. Cosinor analysis, a statistical method for the investigation of time series, was used to detect seasonality.

Results

The cosinor analysis confirmed the existence of a circannual pattern of AHI, with acrophase in winter and nadir during the summer. The seasonality is significant even after adjusting for sex, age, BMI, neck circumference, and relative air humidity. Median (25-75 interquartile range) AHI in the 6 months with colder weather was 17.8 (6.5-40.6/h), and in the warmer weather was 15.0 (5.7-33.2/h). The AHI correlated inversely with ambient temperature and directly with atmospheric pressure, relative air humidity, and carbon monoxide levels. Correlations with precipitation, particulate air matter < 10 μm, sulfur dioxide, and ozone were nonsignificant.

Conclusions

More sleep-disordered breathing events were recorded in winter than in other seasons. Cosinor analysis uncovered a significant seasonal pattern in the AHI of different patients undergoing polysomnography, independent of sex, age, BMI, neck circumference, and relative air humidity. This finding suggests that obstructive sleep apnea severity may be associated with other seasonal epidemiologic phenomena.

Section snippets

Research Subjects

The results of in-laboratory full-night polysomnography studies performed on 7,523 consecutive patients referred to a university-affiliated sleep clinic to investigate a suspected sleep disorder from January 2000 to December 2009 were analyzed retrospectively. We included studies carried out in individuals of both sexes aged 18 years and older. Only diagnostic, baseline, intervention-free polysomnographies were included. Studies lasting < 6 h or with < 3.5 h of time asleep were excluded.

A

Results

Polysomnographic results were obtained for 364 days, including February 29. Only for the purposes of tabulation and graphic representation were data reduced to four seasons or warm weather and cold weather. The means of anthropometric and clinical characteristics of the different populations undergoing polysomnography by season are shown in Table 1. The measurements were available for different numbers of patients. Male patients predominantly attended the sleep laboratory, with significant

Discussion

The present results demonstrate differences in the polysomnographic findings recorded in varying populations with the changing of seasons. The original finding of a circannual pattern of AHI in a large sample suggests that the seasonality of OSA severity is a viable hypothesis.

The population undergoing polysomnography to investigate sleep disorders in the winter displays more severe OSA than those examined in the summer. Regarding the main objective, to search for a seasonal pattern, the 364

Acknowledgments

Author contributions: Dr Martinez assumes responsibility for the data and is the guarantor of the manuscript.

Ms Cassol: contributed to study design, data collection, statistical analysis, and the writing of the manuscript.

Dr Martinez: contributed to study design, statistical analysis, and the writing of the manuscript, and also contributed to performing the sleep study and collecting data.

Mr Silva: contributed to cosinor analysis and the writing of the manuscript.

Ms Fischer: contributed to

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    Funding/Support: Financial support was granted by the Brazilian Government (CAPES and CNPq grants) and through the Research Incentive Fund [FIPE/09-478] of the Hospital de Clinicas de Porto Alegre.

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

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