Nanomachines developped by Freitas that improve a person's endurance and physical performance by maximizing their lungs' intake of oxygen, or assisting with breathing for a short time when no oxygen is available. They are injected into the blood stream.
Soldiers are infused with respirocytes during Basic training. Some say this turns them into supersoldiers.
Even with the technical assist, however, it is still possible to expel too much carbon dioxide, raise the alkalinity of the blood, and start shutting down blood flow to the brain. This is because hyperventilation is not caused by too much oxygen in the blood; it is brought on by too little CO2.