What is the FEV1/FVC ratio indicative of in COPD?

The FEV1/FVC ratio is a key measurement used to assess lung function, particularly in the context of obstructive and restrictive lung diseases. In Chronic Obstructive Pulmonary Disease (COPD), the FEV1 (forced expiratory volume in one second) is decreased more significantly than the FVC (forced vital capacity), leading to a reduction in the FEV1/FVC ratio.

In COPD, this ratio is indicative of airflow limitation due to the obstruction of airways. A ratio that is less than 70% is characteristic of COPD, confirming the diagnosis of an obstructive lung disease. The American Thoracic Society defines a reduced FEV1/FVC ratio as indicative of airway obstruction, which aids in distinguishing COPD from other respiratory conditions.

Thus, the correct answer of less than 70% reflects the pathological process occurring in COPD, where the airflow limitation is central to the disease's clinical presentation and diagnostic criteria. The other thresholds mentioned do not align with the typical characteristics observed in patients with COPD. For instance, a ratio equal to or greater than 70% might suggest normal lung function or restrictive lung disease, depending on other factors, but does not align with the obstructive nature of COPD.