Pulmonary function tests, part 1: Applying the basics

Spirometry is the gold standard for identifying airway obstruction. The principal parameters used are forced vital capacity (FVC), forced expiratory volume in 1 second (FEV₁), and the FEV₁:FVC ratio. When the FEV₁:FVC ratio is reduced, the percent of predicted FEV ₁ is used to grade the severity of airway obstruction. The appearance of the inspiratory and expiratory flow-volume loops can suggest disease patterns. For example, the inspiratory flow-volume loop is flattened in variable extrathoracic obstruction of the airway. In variable intrathoracic obstruction, the expiratory flow-volume loop is blunted. Vital capacity and FEV₁ are used to gauge bronchodilator response; the postbronchodilator FEV ₁ is a more stable parameter for serial comparison of obstruction.