The diffusing capacity in adult cystic fibrosis

Abstract

The value of adjusting the diffusing capacity for the lung volume has been demonstrated in a large number of patients with other lung diseases but has not been validated in patients with cystic fibrosis (CF). Pulmonary function test results on a cohort of 52 adult CF patients were analyzed to determine whether the diffusing capacity of carbon monoxide by single breath method (DLCOSB), when adjusted for alveolar volume (VA%), correlated with the severity of pulmonary dysfunction. The DLCOSB remained within the reference range except in those with severe lung impairment (61.88±15.48%). DLCOSB has a significant (P<0.05) positive correlation (0.70,0.67,0.48,0.69, and 0.31, respectively) with measures of airflow limitation (FVC%, FEV1%, FEV1/FVC%, MVV%, and sGaw) and negative correlation (-0.36 and -0.21, respectively) with measures of air trapping (RV% and RV/TLC%. DLCOSB/VA remained above 100% of predicted despite worsening lung disease and did not correlate with other measures of lung function. On the other hand, the DLCOSB and DLCOSB/VA, when adjusted for VA%, decreased and were significantly correlated with worsening airflow limitation and, to a lesser extent, air trapping. The relatively preserved adjusted DLCOSB and DLCOSB/VA values in CF patients up until late in its course may be explained the predominant airway involvement, minimal loss of alveolar-capillary units, and enhanced V/Q relationship due to claustration in CF. © 2003 Elsevier Science Ltd. All rights reserved.