Idiopathic pulmonary fibrosis (IPF) is a devastating progressive lung disease affecting the parenchyma. Nitrogen multiple-breath washout (N -MBW) is a lung function test that measures ventilation inhomogeneity, a biomarker of small airway disease. We assessed clinical properties of N -MBW in IPF.
METHODS
In this prospective cohort pilot study, 25 IPF patients and 25 healthy controls were assessed at baseline and 10 patients at median 6.2 months later. Outcomes included the lung clearance index (LCI) from N -MBW, forced vital capacity (FVC) from spirometry, diffusion capacity of the lungs for carbon monoxide (DL ), bronchiectasis score from computed tomography scans, the Gender-Age-Physiology (GAP score for IPF) stage and death or lung transplantation (LTx). Study end points were feasibility, repeatability, discriminative capacity and correlation with disease severity and structural lung damage.
RESULTS
All patients were able to perform N -MBW. LCI was repeatable and reproducible. Median (interquartile range (IQR)) LCI in IPF was 11.6 (10.1-13.8) in IPF versus 7.3 (6.9-8.4) in controls (P < 0.0001). LCI correlated with DL corrected for haemoglobin (corrDL ; r = -0.49, P = 0.016), bronchiectasis score (r = 0.45, P = 0.024) and the GAP stage (r = 0.59, P = 0.002), but not with FVC. FVC was not related to bronchiectasis. During follow-up, six patients died and one received LTx. LCI correlated with the latter compound outcome: hazard ratio (95% CI) was 2.43 (1.26; 4.69) per one LCI SD from the patient population.
CONCLUSION
N -MBW is a feasible, reliable and valid lung function test in IPF. LCI correlates with diffusion impairment, structural airway damage and clinical disease severity. LCI is a promising surveillance tool in IPF that may predict mortality.
