Inspiratory drive is related to dynamic pulmonary hyperinflation in COPD patients
Diego Gatta,1 Marco Fredi,2 Giovanni Aliprandi,2 Laura Pini,1 Claudio Tantucci1
1Respiratory 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 (P0.1), 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 P0.1 showed a clinically significant decrease, despite the EELV diminution (P < 0.001). MIP was augmented following EELV reduction and therefore the P0.1/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 P0.1 decrease, MIP increase, and reduction of the P0.1/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
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