Respiratory quotient:
RQ = (CO2 evolved)/(O2 consumed)
In simple terms:- Foodstuffs are metabolized in the presence of oxygen, to liberate CO2.
Hence, it will depend on which nutrient is being metabolized.
RQ for mixed diet = 0.8
RQ for - CHO rich diet = 1
RQ for a fat-rich diet = 0.7 (since fats will consume more oxygen; the value of RQ is less).
Alveolar air equation: (It gives PO2 in the alveolar air; alveolar air has inspired air (N2 & O2), water vapor (which gets added to the inspired air in the dead space), and CO2 (coming from the pulmonary capillary)
PaO2 = [FIO2 X (Pb - PH2O)] - [PaCO2/R]
FIO2 is fraction of oxygen in the inspired air
Pb is barometric pressure (760 mm Hg at sea level)
PH2O is partial pressure of water vapor
PaCO2 is partial pressure of CO2 in alveolus
R = RQ = Respiratory quotient
{RQ is used in this equation because CO2 replaces O2 in the alveolar air).