Advanced lung disease in patients with cystic fibrosis is associated with low diffusion capacity

Background: The single-breath diffusing capacity of the lungs (DLCO_SB) 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 (KCO_SB) is the DLCO_SB divided by VAg_B Cystic fibrosis (CF) disease comprises progressive airway obstruction with bronchiectasis and parenchyma fibrosis. Yet, the KCO_SB appears insignificant in the assessment of pulmonary function in CF. Objectives: To challenge the precision of normal KCO_SB 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, DLCO_SB and lung volumes calculated via body plethysmography (BP). Alveolar volume (VA_BP) was calculated by deducting "anatomical dead space" from total lung capacity (TLC_BP) and KCO_BP was then determined. We also included individual data of arterial pC0₂ blood-gas level. Results: KCO_SB values were normal or higher than normal in most patients, regardless of patient FEV1 value (R² = 0.2204; P < 0.02) or their trapped-air levels. In contrast, the measurements of KCO_BP were low parallel with low FEV1 values, and negatively correlated with the elevation of trapped air and pCO₂ levels (R² = 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 DLCO_SB which correlate with the deterioration of FEV, and elevation of pCO₂ level.