Assessment of acute bronchodilator effects from specific airway resistance changes in stable COPD patients

• In COPD patients, acute bronchodilator response is currently assessed in terms of FEV1 and FVC changes, according to ATS/ERS criteria.
• These changes are poorly associated to beneficial effects of bronchodilation, such as reduction of hyperinflation, gas trapping, and dyspnea.
• In COPD patients, bronchodilator induced changes of total airway resistance were closely related to improvements of lung mechanics and dyspnea.
• In contrast, concomitant changes of FEV1 correlated with those of FVC only.
• Changes of total specific airway resistance better identify the beneficial impact of bronchodilators.

BackgroundIn COPD patients, reversibility is currently evaluated from the changes of forced expiratory volume at 1 s (ΔFEV1) and forced vital capacity (ΔFVC). By lowering peripheral airway smooth muscle tone, bronchodilators should decrease dynamic hyperinflation, gas trapping, and possibly dyspnea at rest. Hence, we hypothesize that specific airway resistance changes (ΔsRAW) should better characterize the acute response to bronchodilators.MethodsOn two days, 60 COPD patients underwent dyspnea evaluation (VAS score) and pulmonary function testing at baseline and one hour after placebo or 300 μg indacaterol administration.ResultsSpirographic and ΔsRAW-based criteria identified as responders 24 and 45 patients, respectively. ΔsRAW correlated with changes of intrathoracic gas volume (ΔITGV) (r = 0.61; p < 0.001), residual volume (ΔRV) (r = 0.60; p < 0.001), ΔFVC (r = 0.44; p = 0.001), and ΔVAS (r = 0.73; p < 0.001), while ΔFEV1 correlated only with ΔFVC (r = 0.34; p = 0.008). Significant differences in terms of ΔITGV (p = 0.002), ΔRV (p = 0.023), and ΔVAS (p < 0.001) occurred only if patients were stratified according to ΔsRAW.ConclusionsIn assessing the acute functional effect of bronchodilators, ΔsRAW-based criterion is preferable to FEV1-FVC-based criteria, being more closely related to bronchodilator-induced improvements of lung mechanics and dyspnea at rest.