Inhaled air is relatively constant in its composition. It contains 20,96% O2, 0,04% CO2 and 79,0% N.
Exhaled air contains 16,4% O2, 4,1% CO2, and 79,5% N.
These figures relate to dry air at a temperature of 0 ° C and a pressure of 101080 Pa.
Under normal circumstances, the inhaled air still contains a small amount of water vapor and exhaled at 37 degrees saturated steam. The water vapor pressure at this temperature is equal to 6650 Pa. Therefore, when inhaled dry air at a pressure of 101080 Pa, the gas pressure in the alveoli is equal to 94 430 Pa.
Alveolar air contains 14-15% O2, 5-6% CO2 and 80-80,5% N. The composition of alveolar air is critical to blood oxygen saturation, or arterialization (oxygenation).
For gas exchange between alveolar air and venous role matters not the content of the gases, and the difference in the partial pressures of O2 and CO2 them.
Voltage of CO2 in alveolar air varies slightly depending on the sex of age, muscular work and changes in barometric pressure.
Despite the fluctuations in the frequency of breathing, the CO2 content in the alveolar air is relatively constant, since the acceleration or slowing of breathing compensated decrease or increase the depth of breathing.
Gas exchange in children is associated with the differences in the regulation of alkali-oxygen equilibrium. For example, a child 5 years Breath 3 times less CO2 than in adults.