What is a key indicator of a restrictive lung disease in PFT results?

In the context of pulmonary function testing (PFT) results, a key indicator of restrictive lung disease is reduced total lung capacity (TLC). Restrictive lung diseases are characterized by the inability of the lungs to fully expand, which leads to a decrease in the total volume of air the lungs can hold. This reduction in TLC is a hallmark of restrictive pathology, regardless of whether the underlying cause is intrinsic (such as interstitial lung disease) or extrinsic (such as a neuromuscular disorder or pleural disease).

When TLC is measured during PFTs, values typically lower than the predicted normal range suggest that the lungs cannot expand properly, emphasizing the restrictive nature of the disease. This contrasts with obstructive lung diseases, where patients often present with normal or increased lung volumes but reduced airflow rates.

While other parameters, such as the FEV1/FVC ratio and FEF25-75%, provide useful information in assessing lung function, they do not specifically indicate restriction. A normal FEV1/FVC ratio usually suggests that obstruction is not the primary issue, and elevated FEF25-75% would generally indicate better small airway function, which is less characteristic of restriction. Thus, reduced TLC stands out as the defining measurement in