By Stephanie Leveene
Study findings based on observations from a sleep clinic in Brazil indicate that obstructive sleep apnea (OSA) may worsen during the winter months.
Environmental factors have been shown to influence OSA. While seasonal variation may be one of these factors, to date there have been few studies that have looked at a possible link between sleep and climate, and the data from these studies appear to be inconclusive.
Cristiane Maria Cassol (Hospital de Clínicas de Porto Alegre, Universidade Federal do Rio
Grande do Sul, Brazil) and colleagues conducted a retrospective analysis of in-laboratory full-night polysomnography studies performed in their clinic in 7523 adults over a 10-year period. Apnea, airflow, snoring, and presence of cardiac arrhythmias were recorded.
Polysomnographic data were grouped into four seasonal periods; OSA severity data were grouped into warm-weather and cold-weather periods. Seasonality was analyzed with a cosinor analysis (sinusoidal function).
Cassol and colleagues found a circannual pattern of OSA, with the crest of the apnea-hypopnea index (AHI) occurring in cold weather and the nadir occurring in warm weather, according to results published in Chest. This significant increase in AHI was independent of gender, BMI, or age. The highest percentage of patients with severe OSA was noted during cold weather.
There was a direct correlation between AHI and atmospheric pressure, air humidity, and carbon monoxide levels. More cases of arrhythmia occurred in winter than during any other season. Differences in snoring intensity, sleep time, and awakenings between the time periods were not significant.
Cassol and colleagues note that several circumstances could explain the fact that most patients with severe OSA attended the clinic during cold weather, including the greater prevalence of upper-airway difficulties during that season. They also found a larger neck circumference in patients in wintertime, but are unsure of its effects on AHI.
The investigators conclude that "patients that undergo polysomnography in the wintertime exhibit more sleep disordered breathing events than patients attending the sleep laboratory in other seasons. The original finding of a significant seasonal pattern in the AHI of different patients, uncovered by cosinor analysis, confirms the hypothesis of seasonality of OSA severity."
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