Effect on Bronchodilation Response and Ventilation Heterogeneity of Different Inhalation Volumes in COPD

During bronchodilator tests, it's common to ask patients with asthma or chronic obstructive pulmonary disease (COPD) to take bronchodilator therapy by inhaling after a maximal exhalation, when the respiratory system volume equals the residual volume. The same maneuver is required for the chronic therapy. Nevertheless, in patients with COPD the distribution of ventilation is more heterogeneous, especially when lung volumes are closer to residual volume . It is therefore predictable that the distribution of air volume containing bronchodilator that has been inhaled at residual volume is more heterogeneous than at higher volumes, such as at functional residual capacity. Accordingly, the bronchodilator can be preferentially distributed in more open airways than in less patent ones, with a heterogeneous distribution of the medication. Therefore, the overall bronchodilation should be greater when the drug inhalation is performed at functional residual capacity than at residual volume. It is common knowledge that the effectiveness of bronchodilator therapy with pMDI in subjects with COPD is greatly affected by the inhalation technique, which can be difficult to perform for many patients. Therefore, in addition to the possibility that inhalation of bronchilation therapy at residual volume could lower the drug effectiveness, this maneuver complicates the sequence of actions required to the patient, enhancing the risk of errors and decreasing the aderence to treatment. The aim of this study is to investigate whether the inhalation of a bronchodilator at different lung volumes can affect its effectiveness in terms of respiratory function, in patients with COPD. Assuming that the bronchodilator effectiveness is equal or greater when inhaled at functional residual capacity rather than at residual volume, the inhalation maneuver can be simplified for patients with COPD.