In a patient with obstructive lung disease, which value is typically decreased?

In patients with obstructive lung disease, the FEV1 (forced expiratory volume in one second) is significantly diminished, leading to a reduced FEV1/FVC (forced vital capacity) ratio. This decreased ratio is a hallmark of obstructive conditions such as asthma or chronic obstructive pulmonary disease (COPD).

In obstructive lung disease, although the FVC may be normal or even increased due to air trapping, the FEV1 declines markedly. This imbalance results in the FEV1/FVC ratio being less than 70%, indicating an obstructive pattern. Therefore, the correct identification of the decreased FEV1/FVC ratio is crucial for diagnosing and understanding the severity of obstructive lung diseases.

Other values, such as FVC, may not show the same decrease in obstructive lung disease, and in some cases, TLC (total lung capacity) may be normal or even increased due to hyperinflation. PEF (peak expiratory flow) can also vary but is generally not as definitive as the FEV1/FVC ratio in terms of diagnosing obstructive patterns.