- The amount of available oxygen in the local atmosphere.
- Your lungs ability to assimilate the oxygen.
- The need for oxygen of your body.
When your body is stimulated by the sympathetic nervous system and your your pulse increases; hyperventilation may also occur.
The volume of each individual beat decreases, but the volume pumped by your heart increase. The volume of blood being oxygenated by your increases and your lungs have the job of acquiring more oxygen for this blood from your breath. Over time your lung's can improve there ability to render oxygen from your breath, but not having a source of air will break this entire cycle.