What is the primary compensatory response to hypoxia in healthy aircrew at altitude?

• A. Decreased respiratory rate
• B. Increased ventilation and heart rate to improve oxygen delivery
• C. Increased hemoglobin synthesis
• D. Effects of hypercapnia

Answer: (B)

When healthy aircrew ascend to altitude, the body’s first job is to offset the drop in oxygen availability. The quickest and most effective response is to increase ventilation, driven by chemoreceptors that sense lower arterial oxygen. This hyperventilation raises the amount of oxygen that can enter the blood. At the same time, heart rate climbs to boost cardiac output, helping deliver the available oxygen to tissues more rapidly. Together, these changes improve oxygen delivery in the short term.

Increased hemoglobin production can occur, but that’s a longer-term adaptation to sustained hypoxia, not the immediate fix. Hypercapnia isn’t the primary compensatory mechanism; the ventilatory drive typically increases to avoid CO2 buildup rather than rely on it.