• Daphna Vilozni, Adi Dagan, Ifat Sarouk, Bat-El Bar-Aluma, Moshe Ashkenazi, Yael Bezalel, and Ori Efrati.
• Department of Pediatric Pulmonology, the National Center for Cystic Fibrosis, Safra Children's Hospital, Sheba Medical Center, Tel Hashomer, Israel, associated with Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
• Isr Med Assoc J. 2020 Dec 1; 22 (12): 770-774.

BackgroundThe 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 (VASB) 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 VASB. 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.ObjectivesTo challenge the precision of normal KCOSB in CF.MethodsThe authors collected pulmonary function tests (PFT) data from 74 confirmed CF patients (mean age 26 ± 10 years) with various levels of pulmonary disease severity. Tests included spirometry, DLCOBP, and body plethysmography (BP). Anatomical dead space was calculated by deducting anatomical dead space from total lung capacity TLC(BP) to establish alveolar volume (VABP) and to determine KCOBP. We also included individual data of arterial pCO2 blood-gas level.ResultsKCOSB values were normal or higher in most patients, regardless of patient FEV1 value (R2 = 0.2204; P < 0.02). In contrast, the measurements of KCOBP were low corresponding 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).ConclusionsThe 10- second perfusion time of the inert gas during DLCOSB represent the communicative alveolar volume in CF patients with advanced pulmonary disease. The findings justify the use of DLCOSB with the deterioration of FEV1 and elevation of pCO2 levels.

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