Ventilatory acclimatization to high altitude is prevented by CO2 breathing

Area of Science:

• Physiology
• Altitude Medicine
• Respiratory Regulation

Background:

• High altitude exposure triggers hypoxia, stimulating ventilation.
• Respiratory alkalosis, a consequence of this increased ventilation, may paradoxically inhibit further ventilatory drive.
• Understanding ventilatory acclimatization mechanisms is crucial for managing altitude-related physiological challenges.

Purpose of the Study:

• To investigate the role of respiratory alkalosis in inhibiting ventilation during high-altitude exposure.
• To determine if preventing alkalosis with supplemental CO2 alters the acclimatization response.
• To examine the effect of CO2 supplementation on ventilatory stability and hypoxic responsiveness.

Main Methods:

• Four subjects inspired 3.77% CO2 in ambient air for 100 hours in a hypobaric chamber simulating high altitude.
• Ventilation was measured at rest and during exercise, normalized for oxygen uptake.
• Control subjects (n=4) were exposed to high altitude without CO2 supplementation.
• Hyperoxic and isocapnic hypoxic ventilatory responses were assessed.

Main Results:

• Subjects receiving supplemental CO2 exhibited immediate and stable increases in ventilation.
• Control subjects showed the expected progressive increase in ventilation over time (ventilatory acclimatization).
• CO2 supplementation prevented the leftward shift of the hyperoxic CO2 ventilatory response curve seen in controls.
• The CO2-supplemented group did not show an increased ventilatory response to isocapnic hypoxia.

Conclusions:

• Supplemental CO2 at high altitude effectively prevents ventilatory acclimatization.
• Prevention of respiratory alkalosis appears to be the mechanism by which CO2 maintains ventilation.
• This suggests that maintaining central nervous system [H+] is critical for sustained hypoxic ventilatory stimulation.