CPFT Practice Exam 2025 – Complete Test Prep Guide

The correct condition associated with a decrease in DLCO, or diffusing capacity of the lungs for carbon monoxide, is pulmonary fibrosis. This condition involves the scarring and thickening of the lung tissue, which affects the ability of the alveoli (the tiny air sacs in the lungs) to exchange gases effectively. In pulmonary fibrosis, the increased stiffening of lung tissue impedes the diffusion of oxygen and carbon dioxide, leading to a reduced DLCO measurement.

In contrast, conditions such as asthma and chronic bronchitis can either maintain or increase DLCO, depending on the severity and nature of the disease. Asthma typically involves bronchospasm and increased airway resistance without significant alterations to the lung parenchyma, which is why DLCO may not be decreased. Chronic bronchitis primarily affects the airways and can lead somewhat to air trapping, but the alveolar structure is usually less compromised than in pulmonary fibrosis. Pulmonary embolism can sometimes produce mixed findings on DLCO, primarily due to ventilation-perfusion mismatch, but it does not consistently result in a decreased DLCO. Thus, pulmonary fibrosis is the condition most directly linked to a decreased DLCO measurement.