Clinical meaning
Pulmonary function tests (PFTs) provide quantitative measurements of lung volumes, capacities, and airflow dynamics essential for diagnosing and monitoring respiratory diseases. Spirometry measures forced vital capacity (FVC), forced expiratory volume in one second (FEV1), and the FEV1/FVC ratio — the cornerstone for distinguishing obstructive from restrictive lung disease. An FEV1/FVC ratio below 0.70 indicates obstructive disease (COPD, asthma), while proportionally reduced FEV1 and FVC with a preserved ratio suggests restrictive disease (pulmonary fibrosis, chest wall deformity). The diffusing capacity for carbon monoxide (DLCO) assesses gas transfer efficiency across the alveolar-capillary membrane and is reduced in emphysema, pulmonary fibrosis, and pulmonary vascular disease.
Diagnosis & workup
Diagnostics & workup: - Order and interpret complete PFTs including spirometry, lung volumes, and DLCO - Classify COPD using GOLD criteria (GOLD 1-4 based on post-bronchodilator FEV1) - Interpret high-resolution CT for interstitial lung disease patterns - Order and interpret CT pulmonary angiography for PE with Wells criteria scoring - Calculate Wells score for PE probability (low <2, moderate 2-6, high >6) - Order D-dimer for low-probability PE (PERC rule to exclude) - Interpret V/Q scan when CT angiography is contraindicated