Carbon dioxide (CO2) is one of the main stimuli triggering your urge to breathe. It’s not required for you to understand what the exact mechanism within your body that controls partial pressures of carbon dioxide and oxygen (O2) is or how the changes in the blood's acidity affects the urge to breathe. However, as a diver, you should understand the basics of breathing. You can also improve your diving enjoyment by using some of the breathing exercises taught in yoga, martial arts, and meditation.
At rest, the average breathing rate is between 10 to 20 breaths per minute. Under normal conditions, this breathing rate and the depth of your breathing is automatically and unconsciously controlled by respiratory centers deep in the brain.
An increased demand for oxygen by the body as a result of exercise or anxiety proportionally increases the levels of carbon dioxide in the blood, and the breathing rate will increase in relation.
As the carbon dioxide levels reduce (at rest), the breathing rate will return to normal. If oxygen levels are too low but the respiratory centers do not detect overabundance of carbon dioxide, it is possible that breathing is not stimulated. This is what happens in the case of shallow water blackout, mostly breath-hold diving. The important lesson for you in this instance is that lack of oxygen alone will not make a diver breathe.
When diving, the high-oxygen partial-pressure level is more than enough for the body to function. However, as the partial pressure of oxygen drops on ascent, possible symptoms of light-headedness, dizziness, nausea, and headache might occur. In extreme cases, there may be loss of consciousness. The simple solution to this problem is to take three or four normal full breaths before ascent.
Did you know? It's worth noting that every unit of oxygen metabolized in a diver's body is converted to almost the same volume of carbon dioxide.