Flow–Volume Loops Relative to Lung Volumes in a Normal Subject in a Patient with Chronic Obstructive Pulmonary Disease (COPD), a Patient with Fixed Obstruction (Tracheal Stenosis), and a Patient with Pulmonary Fibrosis (Restrictive Defect)

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Note the concave expiratory form in the patient with COPD and the flat inspiratory curve in the patient with a fixed obstruction.