Alveolar air equation
The alveolar air equation is the method for calculating partial pressure of alveolar gas (PAO2). The equation is used in assessing if the lungs are properly transferring oxygen into the blood. The alveolar air equation is not widely used in clinical medicine, probably because of the complicated appearance of its classic forms.
Abbreviated alveolar air equation
PAO2, PEO2, and PiO2 are the partial pressures of oxygen in alveolar, expired, and inspired gas, respectively, and VD/VT is the ratio of physiologic dead space over tidal volume.
Respiratory quotient (R)
Physiologic dead space over tidal volume (VD/VT)
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