Appendix D Symbols and abbreviations

Symbols used in this book are in accord with recommendations for editors of medical and scientific publications in the United Kingdom.¹ There continues to be variation between journals, particularly between Europe and the USA. The use of these symbols is very helpful for an understanding of the quantitative relationships that are so important in respiratory physiology.

Primary symbols (large italic capitals) denoting physical quantities.

F	fractional concentration of gas
P	pressure, tension or partial pressure of a gas
V	volume of a gas
Q	volume of blood
C	content of a gas in blood
S	saturation of haemoglobin with oxygen
R	respiratory exchange ratio (RQ)
D	diffusing capacity
B	binding capacity

^• denotes a time derivative; e.g. ventilation, blood flow

Secondary symbols denoting location of quantity.

in gas phase	in blood
(small capitals)	(lower case)
i inspired gas	a arterial blood
e expired gas	v venous blood
a alveolar gas	c capillary
d dead space	t total
t tidal	s shunt
b barometric (usually pressure)

⁻ denotes mixed or mean; e.g. mixed venous blood, mixed expired gas

′ denotes end; e.g. e′ end-expiratory gas, c′ end-capillary blood

Tertiary symbols indicating particular gases.

O₂ oxygen

CO₂ carbon dioxide

N₂O nitrous oxide

etc

f denotes the respiratory frequency

BTPS, ATPS and STPD – see Appendix C.

Examples of respiratory symbols

	alveolar oxygen tension
	oxygen content of mixed venous blood
	oxygen consumption