ABSTRACT
By definition, spirometry demonstrates the presence of airflow obstruction. The forced expiratory volume at 1 s (FEVļ) is decreased out of proportion to any reduction in the forced vital capacity (FVC), producing a decrease in the ratio of these two volumes (FEVx/ FVC). Although complete reversibility excludes the diagnosis, up to 20% of patients with COPD have at least a 15% improvement in FEVļ or FVC following bronchodilator admin istration. Lung volume measurements are usually normal in patients with mild COPD. As the disease worsens, hyperinflation is demonstrated by an increase in the functional resid ual capacity (FRC), residual volume (RV), and total lung capacity (TLC). In patients with emphysema, destruction of the alveolar capillary bed reduces the diffusing capacity for carbon monoxide (DLæ ) in proportion to disease severity.
