Certified Pulmonary Function Technologist (CPFT) Practice Exam

The correct answer refers to pulmonary vascular diseases, such as pulmonary hypertension, where a decreased diffusion capacity for carbon monoxide (DLCO) can be observed while maintaining normal spirometry values. This phenomenon occurs because DLCO specifically measures how well oxygen passes from the air sacs of the lungs into the blood, providing insights into the alveolar–capillary membrane function and lung vascularity. In conditions like pulmonary hypertension, the small blood vessels in the lungs may be impaired due to increased pressure, which hinders the transfer of gases despite no obstruction or restriction in airflow, as depicted by normal spirometry metrics.

Normal spirometry values indicate that the airways are not obstructed and that the airflow during breathing is functioning properly. However, pulmonary vascular diseases primarily affect the vessels and not the mechanics of breathing itself. Therefore, the diffusion capacity is affected due to changes in the pulmonary vasculature instead of structural changes in the lungs that would demonstrate a reduction in spirometric measures.

Other conditions, such as chronic obstructive pulmonary disease (COPD) or interstitial lung disease, tend to show changes in both spirometry and DLCO values as they involve airway obstruction or lung parenchyma involvement, respectively. Asthma can also present with normal spirometry results