CO₂ elimination (VCO₂)

During exercise, CO2 production by the muscles increases dramatically. The CO2 is transported from the muscles to the lungs via the bloodstream. Two mechanisms permit the efficient transport of the increased quantities of CO2: (1) cardiac output may increase more than fivefold during exercise; and (2) venous CO2 content rises during exercise. Unlike oxygen, CO2 is very soluble in blood. In the physiologic range, the CO2 content is approximately proportional to the partial pressure of CO2 (pCO2). Mixed venous pCO2 levels may increase from 42–45 mm Hg at rest to as much as 60 mm Hg (or more) at peak exercise.

where 𝑉CO2 is the CO2 elimination (ml/min),

RR is the respiratory rate (bpm), 

𝑉(𝑡) is the airway flow (ml/min),

[CO₂(t)] is the measured percent of carbon dioxide concentration (%), 

T _in is the inspiratory time (s) and 

T _ex is the expiratory time (s).

https://link.springer.com/chapter/10.1007/978-3-030-16818-6_4

https://link.springer.com/article/10.1007/s00421-013-2754-0