Fig. 2.
Ventilatory response and hemoglobin saturation [arterial O2 saturation by pulse oximetry (SpO2)] during the final minute of leg cycling exercise at 4 different workloads with (fentanyl, gray bars) and without (placebo, black bars) partially blocked somatosensory neural feedback from the working locomotor muscles. A: respiratory frequency (fR). B: tidal volume (Vt). C: minute ventilation (V̇e). D: V̇e/V̇co2. E: end-tidal Pco2 (PetCO2). F: SpO2. The ANOVA P value indicates the overall main effect of fentanyl. *P < 0.05; 1P = 0.08.