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

Area of Science:

• Physiology
• Altitude Medicine
• Respiratory Control

Background:

• Ventilatory responses to hypoxia and hypercapnia are crucial for gas exchange homeostasis and high-altitude adaptation.
• Understanding the mechanisms of ventilatory sensitization during acclimatization is vital for managing altitude-related physiological challenges.

Purpose of the Study:

• To investigate the mechanisms behind the sensitization of hypoxic and hypercapnic ventilatory responses (HVR and HCVR) after acclimatization to moderate high altitude (3,800 m).
• To determine the contribution of ventilatory recruitment threshold (VRT) changes to the elevated HVR at high altitude.

Main Methods:

• Chemoreflex testing using the Duffin-modified rebreathing technique in 31 participants.
• Measurements of HVR, HCVR (under hyperoxic and hypoxic conditions), and VRT at sea level and after 2 days at high altitude.

Main Results:

• Acclimatization to high altitude significantly increased HVR and HCVR-Hyperoxia.
• A significant decrease in VRT under hypoxic conditions contributed to the elevated HVR at high altitude.
• Basal ventilation increased at high altitude, but this change was independent of oxygen conditions.

Conclusions:

• The increase in HVR at high altitude is partly driven by a greater decrease in VRT in hypoxia compared to hyperoxia.
• Respiratory adaptations at moderate high altitude involve complex interactions between VRT, baseline respiratory drive, and HCVR.
• This study provides novel insights into the mechanisms of respiratory acclimatization and ventilatory control at high altitude.