The Volumetric Response to Bronchodilators in Stable Chronic Obstructive Pulmonary Disease

Abstract

A significant proportion of patients with COPD show post-bronchodilator improvement in lung volume even though this response is rarely considered when classifying subjects as having reversible or irreversible airway disease. We studied 266 patients with a clinical and physiological diagnosis of COPD who underwent pulmonary function testing and had their spirometric response to 5 mg salbutamol assessed. After the bronchodilator 125 (47%) patients increased their forced vital capacity by more than the known variability of the test while 60 (23%) showed only a volume response without improvement in expiratory flow. These ‘volume responders’ had greater degrees of airflow obstruction–lower FEV₁ (p < 0.001) and FEV₁/FVC (p < 0.05)—and a higher residual volume at rest (p = 0.005) with similar degrees of emphysema measured by K_CO. Subjects with evidence of greater dynamic airway collapse, assessed by the ratio of early to mid expiratory flow, were less likely to have a flow response but more likely to have a volume response after salbutamol (p < 0.005). This would be compatible with volume response being commoner in patients who exhibit tidal expiratory flow limitation. We suggest that post-bronchodilator absolute change in FVC provides important additional physiological information when interpreting bronchodilator reversibility testing.

Key words: :

• Bronchodilator response
• chronic obstructive pulmonary disease
• volume response