Which condition is characterized by an FEV1/FVC ratio of less than 70%?

The condition characterized by an FEV1/FVC (Forced Expiratory Volume in 1 second to Forced Vital Capacity) ratio of less than 70% is obstructive lung disease. This measurement is critical in distinguishing between obstructive and restrictive patterns in pulmonary function tests. In obstructive lung disease, such as asthma or chronic obstructive pulmonary disease (COPD), there is an increase in airway resistance, leading to a greater difficulty in exhaling air. This means that the FEV1 is significantly reduced compared to FVC, resulting in a decreased FEV1/FVC ratio.

In contrast, restrictive lung disease involves a reduction in lung volumes, particularly FVC, but the FEV1/FVC ratio can be normal or even increased because both FEV1 and FVC decrease proportionally. Conditions such as interstitial lung disease typically lead to this pattern. Combined lung disease refers to features of both obstructive and restrictive patterns but would not have a consistently low FEV1/FVC ratio in isolation. Therefore, the defining feature of obstructive lung disease is the decreased FEV1/FVC ratio below 70%, which confirms that airflow limitation is present.