Seasonal fluctuation of lung function in cystic fibrosis: A national register-based study in two northern European populations

Abstract

Background: Many risk factors for lung disease in cystic fibrosis (CF) display a seasonal pattern yet it is unclear whether this is reflected in seasonal fluctuations in lung function.

Methods: We conducted a longitudinal study using CF registries in Denmark and the UK. 471 individuals with a median of 104 FEV₁ measurements per person and 7586 individuals with a median of nine FEV₁ measures per person were included from Denmark and the UK respectively. We estimated the effect of seasonality on percent predicted FEV₁ trajectories using mixed effects models whilst adjusting for clinically important covariates.

Results: We found no significant cyclical seasonal variation in lung function in either country. The maximum variation in percent predicted FEV₁ around the yearly average was estimated to be 0.1 percentage points (95%CI 0 to 0.21) and 0.14 percentage points (95%CI 0 to 0.29) in Denmark and the UK, respectively. When considering possible step-like changes between the four seasons, we found that lung function was higher in spring compared to winter in the UK (0.34 percentage points, 95%CI 0.1 to 0.59) though the difference was not of clinical significance.

Conclusion: In both the UK and Denmark there may be small seasonal changes in lung function but this effect is not of clinical importance.

Keywords: Fluctuation; Percent predicted FEV1; Season; Seasonality.