Effect of Altitude on Alveolar Oxygen Pressure
Effect of Altitude on Alveolar Oxygen Pressure
This Demonstration shows the effects of changes in altitude on alveolar oxygen pressure using the alveolar gas equation: =×(-O)-1.2, where is the alveolar partial pressure in mmHg, is the fraction of inspired oxygen, and O is the vapor pressure of water at 37 °C, 47 mmHg.
PaO
2
FiO
2
P
ATM
pH
2
PaCO
2
Pa
FiO
2
pH
2
As altitude increases, the atmospheric pressure decreases. This causes a decrease in partial pressure of oxygen in the arteries. The slider for changes the percentage of oxygen in the air from 21% (the normal fraction) to 50% (the maximum amount that avoids lung toxicity). For simplicity, , the partial pressure of carbon dioxide, is set to 35 mmHg as a reasonable average value.
FiO
2
PaCO
2
The changes in partial pressure of oxygen are shown numerically and graphically. The lines on the graph represent the altitudes at four different locations and the corresponding changes in as is increased. The visual model shows an increase in oxygen molecules as is increased, as well as a color gradient in the blood cells to represent the level of oxygenation in the blood.
PaO
2
FiO
2
PaO
2