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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 latter two factors can be combined as the partial pressure of inhaled oxygen in the alveoli. Partial pressures of inhaled oxygen exceeding 0.6 bar (FIO2 >0.6 at normal atmospheric pressure), administered for extended periods in the order of days, are toxic to the lungs. This is known as low-pressure oxygen poisoning, pulmonary toxicity, or ...
In conditions where the proportion of oxygen in the air is low, or when the partial pressure of oxygen has decreased, less oxygen is present in the alveoli of the lungs. The alveolar oxygen is transferred to hemoglobin, a carrier protein inside red blood cells, with an efficiency that decreases with the partial pressure of oxygen in the air ...
The ratio of partial pressure arterial oxygen and fraction of inspired oxygen, known as the Horowitz index or Carrico index, is a comparison between the oxygen level in the blood and the oxygen concentration that is breathed. This helps to determine the degree of any problems with how the lungs transfer oxygen to the blood. [5]
Arterial carbon dioxide tension, or partial pressure: P A CO 2: Alveolar carbon dioxide tension, or partial pressure: P v O 2: Oxygen tension of mixed venous blood: P (A-a) O 2: Alveolar-arterial oxygen tension difference. The term formerly used (A-a D O 2) is discouraged. P (a/A) O 2: Alveolar-arterial tension ratio; P a O 2:P A O 2 The term ...
The partial pressure of oxygen in the air or other breathing gas mixture in the lungs controls the oxygen loading of blood. A critical P O 2 of 30 millimetres of mercury (40 mbar) in the lungs will sustain consciousness when breathing is resumed after a breath-hold dive. This is about 4% oxygen in the lungs and 45% oxygen saturation of the ...
In the dependent region smaller alveolar volumes mean the alveoli are more compliant (more distensible) and so capable of more oxygen exchange. The apex, though showing a higher oxygen partial pressure, ventilates less efficiently since its compliance is lower and so smaller volumes are exchanged.
However even though the partial pressure of oxygen is about equilibrated between the pulmonary capillaries and the alveolar gas, this equilibrium is not maintained as blood travels further through pulmonary circulation. As a rule, PAO 2 is always higher than P a O 2 by at least 5–10 mmHg, even in a healthy person with normal ventilation and ...
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