How are our body effected by different barometer pressure during diving?

CO2 retention with its attendant dangers of death from convulsions and hypoxia (low oxygen level) is primarily of concern to the scuba diver due to "skip breathing". Other mechanisms of CO2 retention are breath-hold diving, breathing in a sealed environment, faulty regulator, exercise at extreme depth and using contaminated air.

Symptoms include rapid respiration in 4-6%, rapid pulse rate, shortness of breath in 7-10% and convulsions and unconsciousness in 11-20%.

The CO2 level in the blood is unchanged by the ambient pressure (i.e., the depth) per se, since the partial pressure of carbon dioxide in a scuba diver's blood is a function only of metabolism and the rate and depth of breathing—the same factors that determine blood CO2 concentration on land.

All of the CO2 developed during breathing from open circuit equipment underwater is normally expelled from the apparatus in the exhaled breath as bubbles. The partial pressure of CO2 produced by the body does not increase with depth as do other gases in breathing mixes, such as nitrogen, oxygen, carbon monoxide and hydrocarbons.

Abnormal carbon dioxide accumulation in the blood can occur from too high a level of metabolism, such as from exercise at depth, or from inadequate breathing. If the diver takes shallow breaths or skip breathes, a larger proportion of the CO2 is not completely expelled and is re-inhaled on the next breath. The medical term for high carbon dioxide in the blood is hypercapnia; when the level is high enough it can cause "CO2 toxicity," which can lead to shortness of breath, headache, confusion and drowning (depending on how severe).

Elevated CO2 levels play a significant role in oxygen toxicity and in nitrogen narcosis. The acceptable CO2 level for diving operations is 1.5% surface equivalent (10.5 mmHg); the acceptable level for hyperbaric oxygen therapy operations is one that allows a vent schedule of 4 scfm per person displacement.