Pulmonary function tests done by spirometry indicate A reduction in forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), forced expiratory flow between 25% and 75% expired volume (FEF 25 - 75), and FEV1/FVC ratio An increase in residual volume and the ratio of residual volume to total lung capacity Fifty percent of patients have evidence of reversible airway obstruction as shown by improvement in pulmonary function after administration of an inhaled bronchodilator.