Lung Hyperinflation Is Associated with Pulmonary Exacerbations in Adults with Cystic Fibrosis

Background: Forced expiratory volume 1 second (FEV1) has traditionally been used as a readily available marker of health in adult cystic fibrosis (CF). However, due to the obstructive nature of this disease, it is possible that lung hyperinflation could be more closely related to disease severity than is FEV1. The purpose of this study was to determine if hyperinflation is more closely associated with quality of life, functional status, and pulmonary exacerbations than FEV1 in patients with CF. Methods: Sixty-eight adult patients with CF were evaluated in this retrospective study. We used IC and functional residual capacity (FRC) and their ratios to total lung capacity (TLC) as measures of lung hyperinflation. We used bivariate correlations and backwards regression analysis to assess possible associations between FEV1, lung hyperinflation, and measures of disease severity including questionnaire based quality of life, pulmonary exacerbation frequency, and mortality. The respiratory component of the Cystic Fibrosis Questionnaire–Revised (CRQ-R-Respiratory) was used as a measure of quality of life. Results: Both FEV1 and IC were negatively correlated with pulmonary exacerbations over a 3 year period (p = 0.004, r2 = 0.127; p < 0.001, r2 = 0.307, respectively), while FRC/TLC correlated positively with exacerbations (p = 0.007). Backwards regression analysis showed that among pulmonary function variables, IC had the strongest relationship with exacerbations over 3 years. A lower CFQ-R-Respiratory score was associated with greater mortality (p = 0.005). However, no statistically significant relationships were found between lung function and mortality. Conclusions: FEV1 and lung hyperinflation-as measured by IC and FRC/TLC-are both associated with pulmonary exacerbation frequency. This suggests that chronic dynamic hyperinflation contributes significantly to disease severity in adult cystic fibrosis.