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 ( D L CO SB), when adjusted for alveolar volume ( V A%), correlated with the severity of pulmonary dysfunction. The D L CO SB remained within the reference range except in those with severe lung impairment (61.88±15.48%). D L CO SB 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%, FEV 1%, FEV 1/FVC%, MVV%, and sGaw) and negative correlation (−0.36 and −0.21, respectively) with measures of air trapping (RV% and RV/TLC%). D L CO SB/ V A remained above 100% of predicted despite worsening lung disease and did not correlate with other measures of lung function. On the other hand, the D L CO SB and D L CO SB/ V A, when adjusted for V A%, decreased and were significantly correlated with worsening airflow limitation and, to a lesser extent, air trapping. The relatively preserved adjusted D L CO SB and D L CO SB/ V A 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.