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Original Research: Sleep Disorders |

Is Sleep Apnea a Winter Disease?Is Sleep Apnea a Winter Disease?: Meteorologic and Sleep Laboratory Evidence Collected Over 1 Decade

Cristiane Maria Cassol, PT, MSc; Denis Martinez, MD, PhD; Fernando Augusto Boeira Sabino da Silva, MSc; Marcia Kraide Fischer, PT, MSc; Maria do Carmo Sfreddo Lenz, MD, PhD; Ângelo José Gonçalves Bós, MD, PhD
Author and Funding Information

From the Graduate Program in Cardiology and Cardiovascular Sciences (Ms Cassol and Dr Martinez), Graduate Program in Medical Sciences (Dr Martinez and Ms Fischer), Universidade Federal do Rio Grande do Sul (UFRGS); Cardiology Division (Dr Martinez), Hospital de Clinicas de Porto Alegre; Sleep Clinic (Drs Martinez and Lenz); Institute of Mathematics, Department of Statistics (Mr Silva), UFRGS; and Institute of Geriatrics and Gerontology (Dr Bós), Pontifical Catholic University of Rio Grande do Sul, Porto Alegre, Brazil.

Correspondence to: Cristiane Maria Cassol, PT, MSc, Cardiology Division, Hospital de Clínicas de Porto Alegre, Universidade Federal do Rio Grande do Sul, Rua Ramiro Barcelos, 2350 Porto Alegre, RS, Brazil, 90035-903; e-mail: cristianecassol@gmail.com


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.


Chest. 2012;142(6):1499-1507. doi:10.1378/chest.11-0493
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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.

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