Fig. 5.

Schematic presentation of the relationship between minute ventilation (V_E) and end-tidal carbon dioxide ($\text{P}\text{E}{\text{T}}_{\text{C}{\text{O}}_2}$) along a representative isometabolic curve. Note a decrease in the slope of V_E/$\text{P}\text{E}{\text{T}}_{\text{C}{\text{O}}_2}$ with supplemental O₂ (solid line) compared with room air (dashed line), confirming a decline in the hypocapnic ventilatory responsiveness or controller gain upon exposure to supplemental O₂. The two-sided arrows indicate the CO₂ reserve during the two exposure conditions: a greater magnitude of CO₂ reserve with supplemental O₂ (solid arrow) compared with room air exposure (dashed arrow) was observed. Points A and B represent the apneic threshold (AT) with supplemental O₂ and room air exposure, respectively.