Exertional dyspnoea in patients with mild-to-severe chronic obstructive pulmonary disease: neuromechanical mechanisms

In patients with chronic obstructive pulmonary disease (COPD), exertional dyspnoea generally arises when there is imbalance between ventilatory demand and capacity, but the neurophysiological mechanisms are unclear. We therefore determined if disparity between elevated inspiratory neural drive (IND) and tidal volume (V-T) responses (neuromechanical dissociation) impacted dyspnoca intensity and quality during exercise, across the COPD severity spectrum. In this two-centre, cross-sectional observational study, 89 participants with COPD divided into tertiles of FEV1 %predicted (Tcrtile 1 = FEN/ i = 87 +/- 9%, Tertile 2 = 60 +/- 9%, Tertile 3 = 32 +/- 8%) and 18 non-smoking controls, completed a symptom-limited cardiopulmonary exercise test (CPET) with measurement of IND by diaphragm electromyography (EMGdi (%max)). The association between increasing dyspnoea intensity and EMGdi (%max) during CPET was strong (r = 0.730, P < 0.001) and not different between the four groups who showed marked heterogeneity in pulmonary gas exchange and mechanical abnormalities. Significant inspiratory constraints (tidal volume/inspiratory capacity (V-T/IC) >= 70%) and onset of neuromechanical dissociation (EMGdi (%max):V-T/IC > 0.75) occurred at progressively lower minute ventilation ((V) over dot(E)) from Control to fertile 3. Lower resting IC meant earlier onset of neuromechanical dissociation, heightened dyspnoea intensity and greater propensity (93% in Tertile 3) to select qualitative descriptors of unsatisfied inspiration: We concluded that, regardless of marked variation in mechanical and pulmonary gas exchange abnormalities in our study sample, exertional dyspnoea intensity was linked to the magnitude of EMGdi (%max). Moreover, onset of critical inspiratory constraints and attendant neuromechanical dissociation amplified dyspnoea intensity at higher exercise intensities. Simple measurements of IC and breathing pattern during CPET provide useful insights into mechanisms of dyspnoea and exercise intolerance in individuals with COPD.

Automated summary

This study aimed to determine the relationship between dyspnea and COPD severity. The study found that dyspnea intensity was associated with inspiratory neural drive and increased at higher exercise intensities. Measurements of inspiratory capacity and breathing pattern during exercise can provide insights into mechanisms of dyspnea and exercise intolerance in individuals with COPD.