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Pressure as a function of the height above the sea level. The human body can perform best at sea level, [7] where the atmospheric pressure is 101,325 Pa or 1013.25 millibars (or 1 atm, by definition). The concentration of oxygen (O 2) in sea-level air is 20.9%, so the partial pressure of O 2 (pO 2) is 21.136 kilopascals (158.
Arterial blood oxygen tension (normal) P a O 2 – Partial pressure of oxygen at sea level (160 mmHg in the atmosphere, 21% of standard atmospheric pressure of 760 mmHg) in arterial blood is between 75 mmHg and 100 mmHg. [4] [5] [6] Venous blood oxygen tension (normal) P v O 2 – Oxygen tension in venous blood at sea level is between 30 mmHg ...
The alveolar oxygen partial pressure is lower than the atmospheric O 2 partial pressure for two reasons. Firstly, as the air enters the lungs, it is humidified by the upper airway and thus the partial pressure of water vapour (47 mmHg) reduces the oxygen partial pressure to about 150 mmHg.
The concentration of oxygen (O 2) in air is 20.9% so the partial pressure of O 2 (PO 2) at sea level is about 21.2 kPa (6.3 inHg; 3.07 psi). In healthy individuals, this saturates hemoglobin, the oxygen-binding red pigment in red blood cells. [7]
Hyperventilation of atmospheric air at atmospheric pressures does not cause oxygen toxicity, because sea-level air has a partial pressure of oxygen of 0.21 bar (21 kPa) whereas toxicity does not occur below 0.3 bar (30 kPa).
This pressure is always below 20% of the total barometric pressure. At sea level, alveolar partial pressure of oxygen is 104 mmHg, reaching 6000 meters above the sea level. This pressure will decrease up to 40 mmHg in a non-acclimated person, but in an acclimated person, it will decrease as much as 52 mmHg.
This is because a person who is used to living at sea level needs about 0.20 bar (20 kPa; 2.9 psi) partial oxygen pressure to function normally and that pressure can be maintained up to about 40,000 ft (12,192 m) by increasing the mole fraction of oxygen in the air that is being breathed.
An oxygen partial pressure equivalent to sea level can be maintained at an altitude of 10,000 metres (34,000 ft) with 100% oxygen. Above 12,000 metres (40,000 ft), positive pressure breathing with 100% oxygen is essential, as without positive pressure even very short exposures to altitudes above 13,000 metres (43,000 ft) lead to loss of ...