Inspiratory drive is related to dynamic pulmonary hyperinflation in COPD patients

Background: Baseline high neuromuscular drive is present in chronic obstructive pulmonary disease (COPD). In moderate-to-very severe COPD patients both static and/or dynamic pulmonary hyperinflation have been demonstrated at rest. Aim: To assess the influence of dynamic hyperinflation (DH) on neuromuscular drive at rest. Methods: We recruited prospectively 22 patients with severe-to-very severe COPD showing resting dynamic pulmonary hyperinflation, as assessed by the baseline reduction of inspiratory capacity (IC) (< 80% of predicted). IC, occlusion pressure (P01), maximal inspiratory pressure (MIP) and their ratio was measured at end-expiratory lung volume (EELV) before and after acute inhalation of 400 mcg of albuterol (MDI plus spacer). In these patients the bronchodilator response was assessed also as lung volume changes. Results: Only in COPD patients with a marked increase in IC (> 12% of baseline and at least 200 ml) after bronchodilator, resting P01 showed a clinically significant decrease, despite the EELV diminution (p<0.001). MIP was augmented following EELV reduction and therefore P01/MIP ratio was markedly decreased (p<0.001). In contrast, no changes in these indices were found after bronchodilator in COPD patients with insignificant variations of IC. Breathing pattern parameters did not vary in both sub-groups after albuterol. Conclusion: Following bronchodilator, significant P01 decrease, MIP increase and reduction of P01/MIP ratio were found only in COPD patients with marked IC increase and these changes were closely related. These findings suggest that bronchodilators by decreasing DH may control exertional and/or chronic dyspnea partly through a reduction of central neuromuscular drive.