What does the term 'diffusing capacity' refer to in the context of PFT?

The term 'diffusing capacity' refers to the efficiency of gas exchange in the lungs, particularly the ability of oxygen and carbon dioxide to transfer between the alveoli and the pulmonary capillaries. This concept is often measured using tests such as the DLCO (diffusing capacity of the lungs for carbon monoxide), which assesses how well gases pass from the air sacs in the lungs into the bloodstream.

A high diffusing capacity indicates effective gas exchange, meaning that the lungs are functioning well to oxygenate blood and remove carbon dioxide. Conversely, a low diffusing capacity may suggest issues such as emphysema, pulmonary fibrosis, or pulmonary hypertension, which can impair the ability of the lungs to exchange gases efficiently.

Understanding diffusing capacity is crucial in the evaluation of various pulmonary diseases and conditions, helping clinicians determine the severity of lung impairment and guiding treatment decisions. The other options describe different aspects of pulmonary function, such as lung expansion, airflow, and airway resistance, which do not specifically pertain to the efficiency of gas exchange.