Inspiratory drive is related to dynamic pulmonary hyperinflation in COPD patients

Diego Gatta,¹ Marco Fredi,² Giovanni Aliprandi,² Laura Pini,¹ Claudio Tantucci<sup>1

1</sup>Respiratory Medicine Unit, Department of Medical and Surgical Sciences, University of Brescia, Brescia, Italy; ²Respiratory Rehabilitation Unit, Hospital Domus Salutis, Brescia, Italy

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 on neuromuscular drive at rest.
Methods: We recruited 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 (P_0.1), maximal inspiratory pressure (MIP), and their ratio were measured at end-expiratory lung volume (EELV) before and after acute inhalation of 400 mcg of albuterol (metered-dose inhaler 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 P_0.1 showed a clinically significant decrease, despite the EELV diminution (P < 0.001). MIP was augmented following EELV reduction and therefore the P_0.1/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 P_0.1 decrease, MIP increase, and reduction of the P_0.1/MIP ratio were found only in COPD patients with a marked IC increase and these changes were closely related. These findings suggest that bronchodilators, by decreasing dynamic hyperinflation, may control exertional and/or chronic dyspnea partly through a reduction of central neuromuscular drive.

Keywords: chronic obstructive pulmonary disease, control of breathing, inspiratory muscles, dynamic hyperinflation, bronchodilators