In the context of lung function, what does the FEV1/FVC ratio help to differentiate?

The FEV1/FVC (Forced Expiratory Volume in one second/Forced Vital Capacity) ratio is a critical measurement in pulmonary function tests that helps differentiate between obstructive and restrictive lung diseases.

In obstructive lung diseases, such as asthma or chronic obstructive pulmonary disease (COPD), there is an increase in resistance to airflow due to narrowing of the airways. This leads to a relatively low FEV1 value while the FVC may remain normal or only slightly reduced, resulting in a decreased FEV1/FVC ratio. Typically, in these cases, the ratio is less than 70%, indicating that the patient has an obstruction to airflow.

Conversely, in restrictive lung diseases, such as pulmonary fibrosis or obesity hypoventilation syndrome, both FEV1 and FVC are reduced, but the FEV1/FVC ratio can remain normal or even increase because the reduction in FEV1 and FVC is proportional. In such cases, the ratio might be at or above 70%.

By analyzing the FEV1/FVC ratio, healthcare professionals can identify whether a lung condition is primarily obstructive or restrictive, guiding further management and treatment approaches. This distinction is essential for proper diagnosis and therapeutic strategy formulation.