Inhalation from different pulmonary volumes does not impact bronchodilator efficacy in COPD patients

Patients with Chronic Obstructive Pulmonary Disease (COPD) are typically instructed to inhale bronchodilators (BD) after a full deflation to residual volume (RV), a manoeuvre requiring coordination and effort. However, so far, no study has demonstrated superior BD efficacy when inhalation starts from RV compared to functional residual capacity (FRC). Since ventilation distribution heterogeneity rises with decreasing volume in COPD patients, we hypothesise that BD inhalation from different volumes may impact its efficacy. This study was aimed at comparing the effects of salbutamol via pressurized metered dose inhaler (pMDI) on lung function when inhaled from residual volume (RV) or functional residual capacity (FRC). Sixteen stable COPD patients were randomized to inhale salbutamol 400 µg from RV or from FRC during two different sessions. Dyspnea, spirometric and plethysmographic lung volumes, and phase III slope during the single-breath nitrogen test (SBN2) were assessed pre and post-BD. In both sessions, BD administration decreased dyspnea (P=0.025), increased FVC (P=0.013) and FEV1 (P=0.037) and reduced RV (P=0.003), FRC (P=0.016), sRaw (P=0.001) and phase III slope (P=0.039). The effect of BD on these parameters was not influenced by the starting inhalation volume (P>0.05). Our results suggest that inhaling a bronchodilator via pMDI from FRC rather than from RV does not affect its efficacy in terms of dyspnoea sensation and lung function. If confirmed, this finding may allow to simplify BD inhalation manoeuvres without negatively affecting BD benefits, potentially improving patients’ adherence.