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23th August, 2011

PaO2 Normal Range

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Doctor DarwinWhile the air passes through alveoli a difference of partial pressures of oxygen between alveoli and a venous blood arriving to lungs is very big (PaO2-PvO2 = 60-65 mm hg)
While the air passes through alveoli a difference of partial pressures of oxygen between alveoli and a venous blood arriving to lungs is very big (PaO2-PvO2 = 60-65 mm hg)

An important component breathing process is a diffusion of the main gases (oxygen and carbon dioxide):

  • in lungs a gas exchange occurs between alveoli and pulmonary capillars through alveolocapillary membrane
  • in body tissues a gas exchange occurs between cells and peripheric capillars.

According to physic laws, a leading role in the diffusion belongs to the gradient of partial pressures of gas on either side of a diffusive membrane and as well as to the diffusion capacity of gas, which depends on its physical and chemical properties.

Partial pressure of oxygen and carbon dioxide varies through all chain of their moving between alveoli and tissues.




((partial pressure -[2,3,4,5,6])) ((O{{2}})) ((CO{{2}})) || (2:) >atmosphere ({{PiO2 = 150}}) ({{PiCO2 = 0.2-0.3}}) || (3:) >alveoli ({{PAO2 = 100-105}}) ({{PACO2 = 30-40}}) || (4:) >arteries ({{PaO2 = 70-100}}) ({{PaCO2 = 35-45}}) || (5:) >venuses ({{PvO2 = 35-45}}) ({{PvCO2 = 40-50}}) || (6:) >tissue ({{PtO2 = 10-20}}) ({{PtCO2 = 40-50}}) || 

While the air passes through alveoli a difference of partial pressures of oxygen between alveoli and a venous blood arriving to lungs is very big (PAO2-PvO2 = 60-65 mm hg). Such gradient is very important for adequate and fast oxygenation of a venous blood, as a diffusion capacity of oxygen is rather insignificant. Oxygen diffuses through alveolocapillary membrane mainly in first half of contact time between venous blood and alveolar gas. It occurs in less than 0,4 seconds (while total time of contact between erythrocyte and alveolar gas doesn't exceed 0,7-0,75 seconds). Then during oxygenation the gradient PAO2-PvO2 decreases and oxygen diffusion is retarded. In case of a alveolocapillary membrane thickening (due to inflammation of pulmonary tissue, lung hypostasis) oxygen diffusion also becomes damaged and retarded. In such situation in order to improve oxygenation we should increase PAO2 by additional inhalation of oxygen. Thus, increased gradient PAO2-PvO2 accelerates an oxygen diffusion. That's why O2-therapy (FiO2 = 30% and more) is so widely applied in the treatment of various forms of respiratory failures. We can estimate PAO2 (partial pressure of oxygen in arteries) with the simple formula: