Longitudinal pulmonary function in severe paediatric asthma and factors influencing decline

Background: Severe asthma is associated with an accelerated decline in lung function. Elevated blood eosinophil count is associated with more severe asthma exacerbations and reduced lung function. Current evidence is focused on adults with a lack of evidence on other factors affecting decline in lung function in children. Aim: To describe long-term trends in spirometry in children with severe asthma and to identify factors influencing decline in lung function. Methods: We retrospectively identified children aged five-to-16 years old who attended the paediatric difficult asthma clinic at University Hospitals of Leicester between January 2011 to June 2022. Patient characteristics and lung function data at baseline and follow-up visits were analysed. Patients were grouped into quartiles based on change in lung function over time. Linear mixed models were used to identify variables associated with lung function. Results: 127 children (60% female) were recruited and followed up for an average of 4 years. The majority of children had an initial FEV1/FVC below the lower limit of normal on their first spirometry measurement. Children in the lowest quartile had an overall decline in FEV1/FVC z-score over a mean of 2 years (mean decline of-0.003). Obstruction on spirometry was independent of Fractional Exhaled Nitric Oxide (FeNO) measurements. Overall, there was an increase in FeNO over time. Conclusion: Severe paediatric asthma is associated with long-term decline in lung function. We found very little decline in lung function during the study period in our cohort. Obstructed lung function occurs early in some children and factors associated with early obstructive airways disease need further study.