Which of the following conditions might lead to a reduced DLCO?

A reduced DLCO (diffusing capacity of the lungs for carbon monoxide) is indicative of impaired gas exchange in the lungs. Emphysema, a type of chronic obstructive pulmonary disease (COPD), typically leads to a loss of alveolar surface area due to the destruction of alveolar walls. This reduction in available surface area negatively impacts the diffusion of gases, including carbon monoxide, which is used in the DLCO test. Therefore, individuals with emphysema often present with a significantly decreased DLCO, reflecting the loss of functional lung tissue.

In contrast, while conditions like obstructive sleep apnea and asthma can influence pulmonary function, they do not primarily affect the alveolar architecture or surface area in the same way emphysema does. Chronic bronchitis can lead to airflow obstruction but does not typically cause a reduction in DLCO unless significant emphysematous changes have developed.