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Alveolar pressure (P alv) is the pressure of air inside the lung alveoli. When the glottis is opened and no air is flowing into or out of the lungs, alveolar pressure is equal to the atmospheric pressure, that is, zero cmH 2 O .
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.
In normal health pulmonary arterial (Pa) pressure exceeds alveolar pressure (PA) in all parts of the lung. It is generally only observed when a person is ventilated with positive pressure or hemorrhage. In these circumstances, blood vessels can become completely collapsed by alveolar pressure (PA) and blood does not flow through these regions.
The alveolar pressure is estimated by measuring the pressure in the airways while holding one's breath. [2] The intrapleural pressure is estimated by measuring the pressure inside a balloon placed in the esophagus. [2] Measurement of transpulmonary pressure assists in spirometry in availing for calculation of static lung compliance.
Positive end-expiratory pressure (PEEP) is the pressure in the lungs (alveolar pressure) above atmospheric pressure (the pressure outside of the body) that exists at the end of expiration. [1] The two types of PEEP are extrinsic PEEP (PEEP applied by a ventilator) and intrinsic PEEP (PEEP caused by an incomplete exhalation).
The alveolar gas equation is the method for calculating partial pressure of alveolar oxygen (p A O 2). The equation is used in assessing if the lungs are properly transferring oxygen into the blood. The alveolar air equation is not widely used in clinical medicine, probably because of the complicated appearance of its classic forms.
Where PAO2 represents alveolar oxygen pressure, Patm represents atmospheric pressure (at sea level 760 mm Hg), PH2O represents partial pressure of water (approximately 45 mm Hg), FiO2 represents the fraction of inspired oxygen (for room air, 0.21), PaCO2 represents the partial pressure of carbon dioxide in the alveoli (in normal physiological ...
For F I O 2 values equal to or greater than 0.5, the alveolar–arterial gradient value should be used in the APACHE II score calculation. Otherwise, the PaO 2 will suffice. [4] The ratio between partial pressure of oxygen in arterial blood and F I O 2 is used as an indicator of hypoxemia per the American-European Consensus Conference on lung ...