Fig. 2.

Oxyhemoglobin saturation and gas exchange during exercise. Exercise was performed with intact (control) and blocked (fentanyl) leg muscle afferent feedback in nomoxia, normocapnic hypoxia, and normoxic hypercapnia conditions. $\text{S}{\text{p}}_{{\text{O}}_2}$, estimated oxyhemoglobin saturation; $\text{P}\mathrm{E}{\mathrm{T}}_{{\text{O}}_2}$, end-tidal partial pressure of O₂; $\text{P}\mathrm{E}{\mathrm{T}}_{\text{C}{\text{O}}_2}$, end-tidal partial pressure of CO₂.