Figure 3.

Dyspnea intensity (Borg units) (A), diaphragm electromyography (EMGdi) (B) and selected ventilatory and indirect gas exchange responses (C–I) to incremental cycle exercise test in patients with moderate COPD and age-matched healthy controls. Values are mean ± SEM. Square symbols represent tidal volume-ventilation inflection points. ^*p < 0.05 for COPD vs. control subjects at rest, at standardized work rates, at peak exercise, or at the tidal volume-ventilation inflection points. EMGdi/EMGdi,max, an index of inspiratory neural drive to the crural diaphragm; $\dot{\text{V}}$E, minute ventilation; V_E/VCO₂, ventilatory equivalent for carbon dioxide; PETCO₂, partial pressure of end-tidal carbon dioxide; SpO₂, oxygen saturation by pulse oximetry; VT, tidal volume; Fb, breathing frequency; IRV, inspiratory reserve volume; TLC, total lung capacity. Reproduced with permission from the publisher (Faisal et al., 2016).