Figure 3. Selected panels to assess ventilatory responses to incremental exercise. In A, the traditional approach to assess ventilatory limitation in which peak minute ventilation (⩒E) almost “touches” the theoretical roof to ventilate-maximum voluntary ventilation (MVV) being calculated as FEV1 × 37.5-in a middle-aged man with COPD (53 years old; FEV1 = 56% of the predicted value; FEV1/FVC ratio = 0.5). In B, when the tidal volume (VT) reaches a critical proportion (≈70%) of the inspiratory capacity (IC) during cycling exercise close to TLC-inspiratory reserve volume (IRV) < 0.5-1.0 L-VT expansion is constrained, and any increment in ⩒E mainly occurs at the expense of a faster breathing frequency (f). ⩒CO2: carbon dioxide output.
