Introduction:
Pulmonary function testing (PFT) and specifically forced expiratory volume in one second (FEV1) is commonly used to monitor lung disease progression and pulmonary exacerbations (PEx) in patients with cystic fibrosis (CF)1. While CF patients tend to have non-reversible obstructive patterns on PFTs2, reversible obstruction is not uncommon3. Improvement in FEV1 after inhalation of bronchodilator (BD) in individuals with CF can be attributed to bronchodilation, improved mucociliary clearance4–6 and potentially due to directly modulating function of the cystic fibrosis transmembrane conductance regulator (CFTR) protein7–9. It can be speculated that for some individuals with CF, bronchial hyperresponsiveness or asthma can also contribute to a reversible pattern of airways obstruction10,11.
A recent American Thoracic Society (ATS)/ European Respiratory Society (ERS) statement proposed that initial spirometry testing in obstructive airway diseases should include post BD assessment, and for follow-up tests, the need for BD testing should be assessed clinically12. BD responsiveness is a major characteristic of asthma, and positive acute response to BD defined as a 12% or greater increase in FEV1 helps to confirm this diagnosis13. Although common in CF as well, the role of assessing BD responsiveness in different disease settings remains unclear. Levine et. al. showed that BD response measured in clinically stable CF patients did not correlate with markers of atopy or clinical severity, and overall was of limited value3. We previously demonstrated in pediatric patients with CF that BD testing does not assist in differentiating allergic bronchopulmonary aspergillosis (ABPA) from other causes of worsening of lung function14. Lung function is often monitored during PEx to evaluate objectively whether patients respond to treatment. In this study we aimed to assess the clinical value of BD testing performed during hospital admission for treatment of PEx. Specifically, we aimed to assess the correlation of BD response with severity of lung disease prior to PEx and the recovery from PEx. We also aimed to assess whether CF patients with significant BD response have distinguishable characteristics from those without BD response.