| Summary: | Summary: Background: The bronchodilation test is used to detect reversible airways obstruction, which is important for diagnosing asthma. Since asthma activity is influenced by seasons, with higher activity in the spring and fall, this study aimed to determine if the FEV1 response to bronchodilation is season-dependent. Methods: All enrolled asthmatic patients underwent pulmonary function testing. Bronchodilation was assessed by measuring FEV1 change (ΔFEV1) before and after inhalation of fenoterol 0.4 mg delivered by metered-dose inhaler with a spacer. Results: There were 348 adult patients with positive bronchodilator test (ΔFEV1 > 12% and 200 mL). In the younger population (n = 223 aged < 65 years), the ΔFEV1 in winter (January–March) was +331.5 ± 119.0 mL (mean ± SD) and +337.6 ± 110.2 mL in summer (July–September). These were significantly less than the results in the other two seasons (April–June, + 398.9 ± 149.1 mL and October–December, + 397.4 ± 183.3 mL; p = 0.015). In the elderly (n = 125 aged ≥ 65 years), the ΔFEV1 throughout the four seasons was similar (p = 0.410). Conclusions: In younger adults, the bronchodilator variabilities are low in winter and summer, suggesting lower sensitivity of the test due to decreased asthma activity during these seasons. Bronchodilation in the elderly is not season dependent. Keywords: season, asthma, bronchodilation, FEV1, lung function
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