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Fig. 6 | COPD Research and Practice

Fig. 6

From: Lung hyperinflation in COPD: applying physiology to clinical practice

Fig. 6

Relationships between exertional dyspnea intensity and ventilation and the ratio of tidal volume to inspiratory capacity (VT/IC) are shown during symptom-limited cycle exercise in COPD. There is a progressive increase in the dyspnea/ventilation curve with worsening disease. After the VT/IC ratio plateaus (corresponding to the VT inflection point), dyspnea rises steeply to intolerable levels. Quartiles (Q) of COPD severity are based on forced expiratory volume in 1 s (FEV1) expressed as percent predicted (ranges: Q1 = 54.5–85.1; Q2 = 43.8–54.1; Q3 = 34.9–43.6; Q4 = 16.5–34.9). Data plotted are mean values at steady-state rest, isotime (i.e., 2 min, 4 min), the VT/\( \dot{\mathrm{V}} \) E inflection point and peak exercise. (From: [29])

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