Course Outline

When the reflex respiratory centers in the brain detect high carbon dioxide levels in the blood, they stimulate breathing. So, carbon dioxide is one of the main stimuli for breathing.

At rest, the average breathing rate is 10 to 20 breaths per minute. Due to a demand for oxygen by the body as a result of exercise and/or anxiety, the levels of carbon dioxide will increase 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.

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/or headache might occur. In extreme cases, there may be loss of consciousness. The simple solution to this problem is to take three or four deep, full breaths and flush before ascent.

Did you know? For every liter of oxygen metabolized, about 90% is converted into carbon dioxide.

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