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The partial pressure of oxygen (pO 2) in the pulmonary alveoli is required to calculate both the alveolar-arterial gradient of oxygen and the amount of right-to-left cardiac shunt, which are both clinically useful quantities. However, it is not practical to take a sample of gas from the alveoli in order to directly measure the partial pressure ...
For example, at 50 metres (164 ft) underwater, the total absolute pressure is 6 bar (600 kPa) (i.e., 1 bar of atmospheric pressure + 5 bar of water pressure) and the partial pressures of the main components of air, oxygen 21% by volume and nitrogen approximately 79% by volume are: pN 2 = 6 bar × 0.79 = 4.7 bar absolute
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.
The concentration of oxygen in the air (mmols O 2 per liter of air) therefore decreases at the same rate as the atmospheric pressure. [26] At sea level, where the ambient pressure is about 100 kPa, oxygen constitutes 21% of the atmosphere and the partial pressure of oxygen (P O 2) is 21 kPa (i.e. 21% of 100 kPa).
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]
In which pO 2 is the chosen maximum partial pressure of oxygen in atmospheres absolute and the FO 2 is the fraction of oxygen in the mixture. For example, if a gas contains 36% oxygen (FO 2 = 0.36) and the limiting maximum pO 2 is chosen at 1.4 atmospheres absolute, the MOD in feet of seawater (fsw) [ Notes 1 ] is 33 fsw/atm x [(1.4 ata / 0.36 ...
partial pressure = total absolute pressure × volume fraction of gas component. For the oxygen component, P O 2 = P × F O 2. where: P O 2 = partial pressure of oxygen P = total pressure F O 2 = volume fraction of oxygen content. The minimum safe partial pressure of oxygen in a breathing gas is commonly held to be 16 kPa (0.16 bar).