This equation is represented by the following expression: `P_aO_2 = F_"In"O_2 (P_"ATM" – P_"WV") – (("PaO_2)/R)` and computes the partial pressure of alveolar oxygen.
The alveolar gas equation calculates the partial pressure of oxygen in the pulmonary alveoli. The pulmonary alveolar partial pressure is then typically used to calculate the alveolar-arterial gradient of oxygen.
The following are the inputs to the Alveolar Gas Equation:
The alveolar partial pressure is typically given in kPa.
With a little more information on the input variables, the user can figure out how to either obtain these from data or search for a further explanation of how to ddefine the input values.
EQUATION INPUTS
Respiratory Quotient (RQ): The term in this equation for the respiratory quotient (R) is calculated from the ratio of `"CO"_2` removed from the body to the `O_2` inspired:
`R = "CO"_2` eliminated / `O_2` consumed
In this ratio, the `"CO"_2` and `O_2` are in the same units and expressed in quantities proportional to the number of molecules, such as gas volumes at STP or moles. See the vCalc equations for Respiratory Quotient [STP] and the Respiratory Quotient [moles].
Inspired Oxygen (`F_"In"O_2`): This term represents the fractional percentage of oxygen in the air breathed in.
Partial Pressure of C`O_2` (`P_a"CO"_2`) : The arterial partial pressure of carbon dioxide
Atmospheric Pressure (`P_"ATM"`): This term is the local air pressure typically recorded in mmHg.
Water Vapor Pressure (`P_"WV"`): This term is the saturated vapour pressure of water at body temperature and the prevailing atmospheric pressure