VD/VT

In medicine, the ratio of physiologic dead space over tidal volume (V_D/V_T) is a routine measurement, expressing the ratio of dead-space ventilation (V_D) to tidal ventilation (V_T), as in physiologic research or the care of patients with respiratory disease.^[1]

Equation

${\displaystyle {\frac {V_{D}}{V_{T}}}={\frac {P_{a}{\ce {CO2}}-P_{E}{\ce {CO2}}}{P_{a}{\ce {CO2}}}}}$

References