Fig. 4.

Hypercapnic and combined hypoxic/hypercapnic responses for ventilation (A) and CBF (B). After acclimatization, $\mathrm{P}\mathrm{E}{\mathrm{T}}_{\mathrm{C}{\mathrm{O}}_{\mathrm{2}}}$ in normoxia decreases from ~40 Torr (dashed, vertical lines) to ~34 Torr, with a small increase in absolute value of ventilation and CBF. A: hypoxia significantly increased the ventilatory response to hypercapnia at baseline (HH_cvR > H_cvR, P < 0.0005) but not after acclimatization. The absolute value of ventilation in normoxia increased significantly with hypoxia at baseline and after acclimatization conditions (P < 0.05). B: the same pattern of changes and significant differences are seen for the CBF response to CO₂ also. Data are mean values; error bars indicate 1 SE.