What does a decrease in FEF25-75% suggest?

A decrease in FEF25-75%, which stands for Forced Expiratory Flow at 25% to 75% of the lung volume, suggests obstruction primarily in small airways. This specific measure focuses on the flow of air in the mid to end portion of the forced expiration, reflecting the condition of the smaller airways rather than the larger bronchial passages.

In individuals with small airway obstruction, such as seen in conditions like asthma or chronic obstructive pulmonary disease (COPD), the airflow becomes restricted, leading to a reduced FEF25-75%. This decrease indicates that there is difficulty in expelling air from the small airways, which can be critical in diagnosing and assessing the severity of certain lung diseases.

In contrast, conditions affecting the large airways would typically show a different pattern in PFT results, predominantly influencing measures such as FEV1 or FEV1/FVC ratio rather than FEF25-75%. Therefore, the interpretation of a decreased FEF25-75% is specifically indicative of small airway involvement and dysfunction.