How to calculate VO2 (and VCO2) in a channel calculation?

The oxygen consumption is the amount of oxygen that is used up by the organism's body over time.


Therefore the calculation would be:


VO2 = Chminute volume * (ChO2 – O2inspired) / 100


whereas Chminute volume is the channel that calculates the Minute Volume (Spirometry extension), ChO2 is the channel that records the O2 concentration in % and O2inspired is the O2 concentration of the inspired air (usually 20,9 %).


To be more precise, the VO2 is calculated as the difference of inspired and expired Minute volumes:


VO2 = ViFiO2 – VeFeO2


where Fi is an inspired fraction, Fe is an expired fraction, and Vi and Ve are the minute volumes of inspired and expired air.


As a standard practice only expiration (or inspiration) is measured and the other values need to be calculated using the Haldane transformation (the sum of O2, CO2 and N fraction equals 1).


Also, a volume correction is applied: VO2 is expressed at STPD (Standard Temperature and Pressure in Dry conditions: 0 °C (273.15 K) and 760 mmHg, zero humidity) but measurements are at BTPS (Body Temperature (36.6 °C), Ambient Pressure, saturated with water vapour). All these have to be taken into account. For a detailed description see LabChart Help | Metabolic | Metabolic Calculations.


The final formula is:

servlet.ImageServer?id=015w0000001Jmaw&oid=00D20000000HncM


with

servlet.ImageServer?id=015w0000001Jmb6&oid=00D20000000HncM


and

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This translates in LabChart's Channel Calculation | Arithmetics to (see also attached file):


Ch6*

(760-(13,955-(0,658425*36.6)+(0,0419*(36.6^2))))/(273+36.6)*(273/760)*

(0,2093*((1-(0,01*Ch1)-(0,01*Ch2))/0,7904)-(0,01*Ch1)))


where Ch6 is the Minute Ventilation, Ch1 is %O2 and Ch2 is %CO2.


The whole calculation can be smoothed using the smoothsec() function:


smoothsec(

(Ch6*

(760-(13,955-(0,658425*36.6)+(0,0419*(36.6^2))))/(273+36.6)*(273/760)*

(0,2093*((1-(0,01*Ch1)-(0,01*Ch2))/0,7904)-(0,01*Ch1)));15)


VCO2 is calculated using the equation that correspond to that given above for VO2, but with the obvious substitutions:


smoothsec(

(Ch6*

(760-(13,955-(0,658425*36.6)+(0,0419*(36.6^2))))/(273+36.6)*(273/760)*

(0,0003*((1-(0,01*Ch1)-(0,01*Ch2))/0,7904)+(0,01*Ch2)));15)