Changes in hypoxic and hypercapnic ventilatory responses at high altitude measured using rebreathing methods

We report the first measurements of the hypoxic ventilatory response (HVR) after 2 days at high altitude using a CO 2 rebreathing technique. We evaluated mechanisms by which the HVR becomes elevated with acclimatization (increased hypercapnic ventilatory response sensitivity in hypoxia, increased baseline respiratory drive in hypoxia, or lower ventilatory recruitment thresholds in hypoxia). For the first time, we report that decreases in the ventilatory recruitment threshold in hypoxia contribute to elevated HVR at high altitude.