Advanced Lung Disease In Patients With Cystic Fibrosis Is Associated With Low Diffusion Capacity

Background: The single-breath diffusing capacity of the lungs (DLCOSB) test measures the extent to which carbon monoxide (CO) passes from the lung air sacs into the blood. The accessible alveolar volume (VA(SB)) is measured by inert gas during a 10-second period. The single-breath transfer coefficient of the lung for carbon monoxide (KCOSB) is the DLCOSB divided by VA(SB) Cystic fibrosis (CF) disease comprises progressive airway obstruction with bronchiectasis and parenchyma fibrosis. Yet, the KCOSB appears insignificant in the assessment of pulmonary function in CF.Objectives: To challenge the precision of normal KCOSB in CF.Methods: The authors collected pulmonary function tests (PFT) data from 74 confirmed CF patients (mean age 26 +/- 10 years) with various levels of pulmonary disease severity. PFTs included spirometry, DLCOSB and lung volumes calculated via body plethysmography (BP). Alveolar volume (VA(BP)) was calculated by deducting "anatomical dead space" from total lung capacity (TLCBP) and KCOBP was then determined. We also included individual data of arterial pCO(2) blood-gas level.Results: KCOSB values were normal or higher than normal in most patients, regardless of patient FEV1 value (R-2 = 0.2204; P < 0.02) or their trapped-air levels. In contrast, the measurements of KCOBP were low parallel with low FEV1 values, and negatively correlated with the elevation of trapped air and pCO(2) levels (R-2 = 0.1383; P = 0.0133, P > 0.05, respectively).Conclusions: The measurement of VA(SB) using the short, 10-second perfusion time of the inert gas, represent only the communicative alveolar volume in CF patients with moderate to severe airway obstruction. The findings justify the use of VA(BP), measured with DLCOSB which correlate with the deterioration of FEV1 and elevation of pCO(2) level.