Lung diffusing capacity for nitric oxide and carbon monoxide in relation to morphological changes as assessed by computed tomography in patients with cystic fibrosis

BACKGROUND: Due to large-scale destruction, changes in membrane diffusion (Dm) may occur in cystic fibrosis (CF), in correspondence to alterations observed by computed tomography (CT). Dm can be easily quantified via the diffusing capacity for nitric oxide (DL(NO)), as opposed to the conventional diffusing capacity for carbon monoxide (DL(CO)). We thus studied the relationship between DL(NO )as well as DL(CO )and a CF-specific CT score in patients with stable CF. METHODS: Simultaneous single-breath determinations of DL(NO )and DL(CO )were performed in 21 CF patients (mean ± SD age 35 ± 9 y, FEV(1 )66 ± 28%pred). Patients also underwent spirometry and bodyplethysmography. CT scans were evaluated via the Brody score and rank correlations (r(S)) with z-scores of functional measures were computed. RESULTS: CT scores correlated best with DL(NO )(r(S )= -0.83; p < 0.001). Scores were also related to the volume-specific NO transfer coefficient (KNO; r(S )= -0.63; p < 0.01) and to DL(CO )(r(S )= -0.79; p < 0.001) but not KCO. Z-scores for DL(NO )were significantly lower than for DL(CO )(p < 0.001). Correlations with spirometric (e.g., FEV(1), IVC) or bodyplethysmographic (e.g., SR(aw), RV/TLC) indices were weaker than for DL(NO )or DL(CO )but most of them were also significant (p < 0.05 each). CONCLUSION: In this cross sectional study in patients with CF, DL(NO )and DL(CO )reflected CT-morphological alterations of the lung better than other measures. Thus the combined diffusing capacity for NO and CO may play a future role for the non-invasive, functional assessment of structural alterations of the lung in CF.