Abbreviation | Physiological parameter | Significance |

P_{aCO2} | Arterial carbon dioxide tension (kPa) | Reflective of the concentration of CO_{2} in the arterial blood |

d | Dead space volume (L) | Volume of air that is inhaled that does not take part in gas exchange |

V_{T} | Tidal volume (L) | Volume of air moved into and out of the lungs during each ventilation cycle |

V′_{E} | Minute ventilation (L·min^{−1}) | Volume of gas exhaled/inhaled in 1 min, equal to the V_{T} multiplied by the RR |

V′_{CO2} | Carbon dioxide production (L·min^{−1}) | |

d/V_{T} | Ratio of dead space volume to tidal volume | A higher value indicates a larger proportion of air not engaging in gas exchange within the lungs |

V′_{E}/V′_{CO2} | Gradient of the V′_{E}/V′_{CO2} slope | The minute ventilation required to exhale 1 L of CO_{2} |

Equation A: | ||

RR | Respiratory rate (min^{−1}) | Number of breaths taken per minute |

d_{syst} | Dead space volume of the apparatus used (L) | Volume of air that remains within the CPET apparatus e.g. breathing valve, connectors and mouth piece exterior to the mouth |

V_{eqCO2} | Ventilatory equivalent for carbon dioxide | Measures the efficiency of ventilation |

Equation B: |

Equation A describes the relationship of the *V*′_{E}/*V*′_{CO2} slope to the physiological variables of *P*_{aCO2}, d and *V*_{T}. Equation B describes the relationship of *V*_{eqCO2} to the *V*′_{E}, d_{syst}, RR and *V*′_{CO2}. Definitions and significance of the relevant parameters are also described for the understanding of the presented equations CPET: cardiopulmonary exercise testing.