<prompt> Answer this question truthfullyHow is the partial pressure of a gas Px in humidified tracheal air calculated?  <response>: <reason> The partial pressure of a gas Px in humidified tracheal air is calculated using the formula PB - PH2O F, where PB is the barometric pressure, PH2O is the partial pressure of water vapor, and F is the fractional concentration of the gas in dry air. 