Description

The air is made up of a mixture of gases (oxygen, nitrogen, water vapor and a small amount of carbon dioxide), each of which has a partial pressure. The sum of the partial pressures for these gases equals the barometric pressure.

partial pressure of oxygen in mm Hg in inspired air =

= (per cent concentration of oxygen in the inspired air) * ((barometric pressure) - (water vapor pressure)) / 100

= (fractional concentration of oxygen in the inspired air) * ((barometric pressure) - (water vapor pressure))

where:

• The barometric pressure is normally 760 mm Hg at sea level.

• Water vapor pressure is normally 47 mm Hg at 37 °C.

• The per cent concentration of oxygen in room air is about 21%.

Equations for Water Vapor Pressure and Temperature

water vapor pressure in mm Hg =

= 47.07 * (10 ^ ((6.36 * ((temperature in °C) - 37)) / (232 + (temperature in °C))))

where:

• temperature is in Centigrade from 0 to 40 °C

water vapor pressure in mm Hg =

= (10 ^ ((0.0244 * (temperature in °C)) + 0.7655)) + 0.4

Equations for Barometric Pressure and Altitude

barometric pressure in mm Hg =

= 760 * ((1 - (6.873 * (10 ^ (-6)) * (altitude in feet))) ^ 5.256)

where:

• altitude is in feet above sea level