Why Does the Urge to Breathe Not Reflect Oxygen Levels?
The Question
Why can a freediver feel comfortable even when oxygen levels are dangerously low?
Short Answer
Because the urge to breathe is driven primarily by carbon dioxide, not oxygen.
Deeper Explanation
Carbon dioxide rises during a breath-hold and stimulates breathing. Oxygen, however, can fall to critical levels without producing strong sensations. This mismatch explains why hypoxic blackout can occur without severe discomfort.
What This Means for Freedivers
- Comfort does not equal safety
- CO₂ tolerance training does not increase oxygen reserves
- External safety systems are essential