of a representative animal. Partial pressure of CO2 in expired gas (solid line) and inspired gas (dotted line) plotted against volume so as to create a loop. The area within the loop corresponds to tidal elimination of CO2 (VTCO2). The area below the inspiratory limb (grey) corresponds to re-inspired volume of CO2 proximal of the CO2 sensor (VICO2). Airway dead space distal to the CO2 sensor (VDaw) is indicated (vertical interrupted line).