In the context of obstructive lung disease, what is a significant finding on pulmonary function testing?

In the context of obstructive lung disease, a significant finding on pulmonary function testing is a FEV1/FVC ratio less than 70%. This ratio measures the proportion of a person's vital capacity that they can forcibly exhale in one second (FEV1) compared to the total volume of air they can exhale (FVC). In obstructive lung diseases, such as asthma or chronic obstructive pulmonary disease (COPD), there is a significant decrease in the FEV1 due to obstruction in the airways, leading to an increased total or residual volume. As a result, the FEV1/FVC ratio falls below the normal threshold of 70%, indicating the presence of obstruction.

Finding a FEV1/FVC ratio greater than 80% would typically indicate that the patient does not have an obstructive process affecting their lung function. A normal FEV1 value alone may not provide sufficient information about the presence of obstructive disease without considering the ratio. Increased total lung capacity can occur but is not as definitive in identifying obstructive disease as the FEV1/FVC ratio being less than 70%. Thus, the ratio is a key indicator used in diagnosing and assessing the severity of obstructive lung disease.