ATPD | Ambient temperature, ambient pressure, and dry |

ATPS | Ambient temperature and pressure saturated with water vapour |

BTPS | Body temperature (i.e. 37°C), ambient pressure, saturated with water vapour |

C | Centigrade |

CFC | Chlorofluorocarbons |

cm | Centimetres |

COHb | Carboxyhaemoglobin |

D_{L,CO} | Diffusing capacity for the lungs measured using carbon monoxide, also known as transfer factor |

D_{L,CO}/V_{A} | Diffusing capacity for carbon monoxide per unit of alveolar volume, also known as K_{CO} |

D_{M} | Membrane-diffusing capacity |

DT | Dwell time of flow >90% of PEF |

EFL | Expiratory flow limitation |

ERV | Expiratory reserve volume |

EV | Back extrapolated volume |

EVC | Expiratory vital capacity |

F_{A,X} | Fraction of gas X in the alveolar gas |

F_{A,X,t} | Alveolar fraction of gas X at time t |

FEF_{25-75%} | Mean forced expiratory flow between 25% and 75% of FVC |

FEF_{X%} | Instantaneous forced expiratory flow when X% of the FVC has been expired |

FEV_{1} | Forced expiratory volume in one second |

FEV_{t} | Forced expiratory volume in t seconds |

F_{E,X} | Fraction of expired gas X |

FIF_{X%} | Instantaneous forced inspiratory flow at the point where X% of the FVC has been inspired |

F_{I,X} | Fraction of inspired gas X |

FIVC | Forced inspiratory vital capacity |

FRC | Functional residual capacity |

FVC | Forced vital capacity |

H_{2}O | Water |

Hb | Haemoglobin |

Hg | Mercury |

Hz | Hertz; cycles per second |

IC | Inspiratory capacity |

IVC | Inspiratory vital capacity |

K_{CO} | Transfer coefficient of the lung (i.e.D_{L,CO}/V_{A}) |

kg | Kilograms |

kPa | Kilopascals |

L | Litres |

L·min^{−1} | Litres per minute |

L·s^{−1} | Litres per second |

lb | Pounds weight |

MEF_{X%} | Maximal instantaneous forced expiratory flow where X% of the FVC remains to be expired |

MFVL | Maximum flow–volume loop |

mg | Milligrams |

MIF | Maximal inspiratory flow |

mL | Millilitres |

mm | Millimetres |

MMEF | Maximum mid-expiratory flow |

ms | Milliseconds |

MVV | Maximum voluntary ventilation |

P_{A,O2} | Alveolar oxygen partial pressure |

PB | Barometric pressure |

PEF | Peak expiratory flow |

P_{H2O} | Water vapour partial pressure |

P_{I,O2} | Inspired oxygen partial pressure |

θ (theta) | Specific uptake of CO by the blood |

RT | Rise time from 10% to 90% of PEF |

RV | Residual volume |

s | Seconds |

STPD | Standard temperature (273 K, 0°C), pressure (101.3 kPa, 760 mmHg) and dry |

TB | Tuberculosis |

TGV (or V_{TG}) | Thoracic gas volume |

t_{I} | Time taken for inspiration |

TLC | Total lung capacity |

Tr | Tracer gas |

t_{tot} | Total time of respiratory cycle |

V_{A} | Alveolar volume |

V_{A,eff} | Effective alveolar volume |

VC | Vital capacity |

V_{c} | Pulmonary capillary blood volume |

V_{D} | Dead space volume |

V_{I} | Inspired volume |

V_{S} | Volume of the expired sample gas |

μg | Micrograms |