Inspiratory and expiratory reactance at 5Hz in adult cystic fibrosis

Introduction: Progressive airways obstruction is a key feature of cystic fibrosis (CF) which has it origins in the small airways. Reactance at 5Hz (X 5 ), measured by impulse oscillometry (IOS), determines the capacitive properties of the peripheral lung. In COPD patients the respiratory phase difference in X 5 (inspiratory-minus-expiratory, ΔX 5 ) identifies individuals with expiratory flow limitation. Studies in CF, so far, have analysed whole breath impulse oscillometry. Aim: To determine the relationship between inspiratory and expiratory phase X 5 with spirometry and body plethysmography. Methods: Within-breath analysis of IOS (Jaeger) was performed on 25 patients with CF (FEV 1 range 26-119% of predicted). Results were correlated with spirometric and plethysmographic indices (Jaeger MasterLab). Results: Both inspiratory and expiratory X 5 correlated with FEV 1 (r= 0.842, p 1 values. They also demonstrated an inverse linear relationship with RV/TLC% ratio (r=-0.747, p 5 ) correlated with FEV 1 and RV/TLC% (r=0.662, p 5 in CF patients with lower FEV 1 values (greater disease severity). Conclusion: Measurement of inspiratory and expiratory X 5 are useful indices of airway obstruction and gas trapping in CF. IOS is quick, easy and portable to use at the patient bedside or outpatient clinic in contrast to body plethysmography. Calculating respiratory phase difference in X 5 (ΔX 5 ) may be a useful marker for identifying CF patients who have expiratory flow limitation.