Is sleep apnea a winter disease?: meteorologic and sleep laboratory evidence collected over 1 decade.
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.
Graduate Program in Cardiology and Cardiovascular Sciences, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, Brazil. Electronic address: cristianecassol@gmail.com.
Cristiane Maria
CM
Cassol
Graduate Program in Cardiology and Cardiovascular Sciences, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, Brazil; Graduate Program in Medical Sciences, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, Brazil; Cardiology Division, Hospital de Clinicas de Porto Alegre, Porto Alegre, Brazil; Sleep Clinic, Porto Alegre, Brazil.
Denis
D
Martinez
Institute of Mathematics, Department of Statistics, UFRGS, Porto Alegre, Brazil.
Fernando Augusto Boeira Sabino
FABS
da Silva
Graduate Program in Medical Sciences, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, Brazil.
Marcia Kraide
MK
Fischer
Sleep Clinic, Porto Alegre, Brazil.
Maria do Carmo Sfreddo
MDCS
Lenz
Institute of Geriatrics and Gerontology, Pontifical Catholic University of Rio Grande do Sul, Porto Alegre, Brazil.
Ângelo José Gonçalves
ÂJG
Bós
D000328:Adult; D000367:Age Factors; D015992:Body Mass Index; D005260:Female; D006801:Humans; D006813:Humidity; D008297:Male; D008875:Middle Aged; D009333:Neck / Q000033:anatomy & histology; D017286:Polysomnography; D015995:Prevalence; D012189:Retrospective Studies; D012621:Seasons; D012720:Severity of Illness Index; D012737:Sex Factors; D020181:Sleep Apnea, Obstructive / Q000175:diagnosis* / Q000453:epidemiology*