H_{2}O removed from sampled gas; CO_{2} does not interfere with analysers |

V_{A,BTPS} = (V_{I,ATPD}–V_{D,INST}–V_{D,ANAT})×(F_{I,Tr}/F_{S,Tr})×(P_{B}/(P_{B}–47))×(310/(273+T)) |

V_{A,STPD} = (V_{I,ATPD}–V_{D,INST}–V_{D,ANAT})×(F_{I,Tr}/F_{S,Tr})×(P_{B}/760)×(273/(273+T)) |

H_{2}O and CO_{2} removed from sampled gas |

V_{A,BTPS} = (V_{I,ATPD}–V_{D,INST}–V_{D,ANAT})×(F_{I,Tr}(1+F_{A,CO2})/F_{S,Tr})×(P_{B}/(P_{B}–47))×(310/(273+T)) |

V_{A,STPD} = (V_{I,ATPD}–V_{D,INST}–V_{D,ANAT})×(F_{I,Tr}(1+F_{A,CO2})/F_{S,Tr})×(P_{B}/760)×(273/(273+T)) |

If no measurement of F_{A,CO2} is available, then it may be assumed to be 0.05 |

H _{2}O in sampled gas equilibrated to room air; CO_{2} does not interfere with analysers. IfF_{I,Tr} is read by the analysers, the equations are the same as for when H_{2}O is removed from sampled gas. If tank values (i.e. dry gas concentrations) are used for F_{I,Tr}, then the following equations are used |

V_{A,BTPS} = (V_{I,ATPD}–V_{D,INST}–V_{D,ANAT})×(F_{I,Tr}/F_{S,Tr})×((P_{B}–P_{H2O})/(P_{B}–47))×(310/(273+T)) |

V_{A,STPD} = (V_{I,ATPD}–V_{D,INST}–V_{D,ANAT})×(F_{I,Tr}/F_{S,Tr})×((P_{B}–P_{H2O})/760)×(273/(273+T)) |

Neither H_{2}O nor CO_{2} removed from sampled gas, no interference with analysers, heated sample tubing to prevent condensation |

V_{A,BTPS} = (V_{I,ATPD}–V_{D,INST}–V_{D,ANAT})×(F_{I,Tr}/F_{S,Tr})×(310/(273+T)) |

V_{A,STPD} = (V_{I,ATPD}–V_{D,INST}–V_{D,ANAT})×(F_{I,Tr}/F_{S,Tr})×((P_{B}–47)/760)×(273/(273+T)) |

In these calculations, room temperature (T) is measured in Celsius and gas pressures are measured in mmHg. In all four cases, the inspired volume (

*V*_{I}) is the measured volume of inhaled dry gas and, thus, is considered under ambient temperature, ambient pressure, and dry (ATPD) conditions. The conversion to body temperature, ambient pressure, saturated with water vapour (BTPS) and standard temperature, pressure and dry (STPD) may require factors to compensate for the diluting or concentrating effects of adding or deleting H_{2}O or CO_{2}at the gas sampling site. Therefore, standard gas condition conversion formulae must be adjusted as described previously.*V*_{A}: alveolar volume;*V*_{D,INST}: instrument dead space;*V*_{D,ANAT}: anatomic dead space;*F*_{I,Tr}: fraction of tracer (Tr) gas in the inspired test gas;*F*_{S,Tr}: fraction of the Tr gas in the alveolar sample, which may differ from the fraction of alveolar Tr gas, depending on the effects of CO_{2}and H_{2}O as noted;*F*_{A,CO2}: fraction of CO_{2}in the alveolar sample.