Question

The amount of oxygen present in the blood depends in part on the partial pressure of inspired oxygen in the trachea, P_IO2. This can be calculated from the barometric pressure, the fraction of O₂ molecules in dry air, and the vapor pressure of water at body temperature (because inhaled air is humidified in the trachea).

20.9% of the molecules in dry air are O₂ molecules and the vapor pressure of water at body temperature (37 °C) is 47 mm Hg. Taking the total pressure of the humidified inhaled air to be equal to the barometric pressure, calculate the P_IO2 for a person in Leadville, CO (elevation 3025 meters), if the prevailing barometric pressure is 515 mm Hg.