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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.
Minute ventilation (or respiratory minute volume or minute volume) is the volume of gas inhaled (inhaled minute volume) or exhaled (exhaled minute volume) from a person's lungs per minute. It is an important parameter in respiratory medicine due to its relationship with blood carbon dioxide levels .
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.
Therefore it includes, firstly those units that are ventilated but not perfused, and secondly those units which have a ventilation-perfusion ratio greater than one. Alveolar dead space is negligible in healthy individuals, but it can increase dramatically in some lung diseases due to ventilation-perfusion mismatch.
In respiratory physiology, the ventilation/perfusion ratio (V/Q ratio) is a ratio used to assess the efficiency and adequacy of the ventilation-perfusion coupling and thus the matching of two variables: V – ventilation – the air that reaches the alveoli; Q – perfusion – the blood that reaches the alveoli via the capillaries
When observing a collection of alveoli in which PO 2 and PCO 2 are uniform, local alveolar ventilation and local blood flow define / : V A = Q × V A / Q {\displaystyle V_{A}=Q\times V_{A}/Q} From these equations it can be deduced that to have knowledge of either retention or excretion implies knowledge of the other.
The Bohr equation is used to quantify the ratio of physiological dead space to the total tidal volume, and gives an indication of the extent of wasted ventilation. The original formulation by Bohr, [1] required measurement of the alveolar partial pressure P A.
Equation Description Minute ventilation: tidal volume * respiratory rate: the total volume of air entering, or leaving, the nose or mouth per minute or normal respiration. Alveolar ventilation (tidal volume – dead space) * respiratory rate: the volume of air entering or leaving the alveoli per minute. Dead space ventilation: dead space ...