Carbon dioxide, a byproduct of cell metabolism, plays a crucial role in the body’s oxygen exchange process. In diving, excess CO2 buildup can lead to hypercapnia, causing air starvation. Physiological quantities like VO2 max and RER help measure oxygen absorption and CO2 elimination during exertion, affecting metabolism. Stay tuned for parts two and three for more on the dangers of carbon dioxide in diving and ways to manage it.