CO2 Production Ve (L/min) PeCO2 (mmHg) Conditions of measurement BTPSATPSATP PeCO2 : partial pressure of mixed expired CO2. ATPS : Ambient Temp Press Saturated, BTPS : Body Temp Press Saturated. VCO2 mL/min NB : VCO2 is expressed in standard conditions (STPD : Standard Temp Press Dry).