AMA Manual of Style (10th edition ed.) : A Guide for Authors and Editors

AMA Manual of Style Committee

Publisher:: Oxford University Press

Print Publication Date:: Mar 2007

Print ISBN-13:: 9780195176339

Published to AMA Manual of Style:: Apr 2009

DOI:: 10.1093/jama/9780195176339.001.0001

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Symbols

Chapter:: Nomenclature
Author(s):: Harriet S. Meyer

15.16.1 Symbols

Symbols and their subgrouping into main symbols and modifiers are consistent with approved nomenclature formulated circa 1980 by the Commission of Respiratory Physiology (International Union of Physiological Sciences) and the Publications Committee of the American Physiological Society.²^,³ The following groupings of pulmonary-respiratory symbols are adapted from Fishman.²

Main symbols are typically capital letters set on the line and are the first elements of an expression. The same letter may stand for one entity in respiratory mechanics and another in gas exchange (eg, P stands for pressure in respiratory mechanics and partial pressure in gas exchange). The following are examples (note dots above some letters to indicate flow):

C	compliance, concentration
D	diffusing capacity
F	fractional concentration in a dry gas
P	pressure, partial pressure
Q	volume of blood
$\dot{Q}$	perfusion (volume of blood per unit time or blood flow)
R	resistance, gas (respiratory) exchange ratio
S	saturation
sG	specific conductance
V	volume of gas
$\dot{v}$	ventilation (volume per unit time)

Modifiers are set as small capitals (not subscript):

a	alveolar
b	barometric
ds	dead space
e	expired, expiratory
et	end-tidal
i	inspired, inspiratory
l	lung
t	tidal

Lowercase-letter modifiers (which are not subscript) follow small-capital modifiers, if both appear; note bar in last term:

a	arterial
aw	airway
b	blood
c	capillary
c′	pulmonary end-capillary
i	ideal
max	maximum
p	pulse oximetry
v	venous
$\bar{v}$	mixed venous

Gas abbreviations are usually the last element of the symbol, given as small capitals:

co	carbon monoxide
co₂	carbon dioxide
n₂	nitrogen
o₂	oxygen

(Note: At other times, when gas abbreviations are used on their own, large capitals are used, eg, carbon monoxide [CO].)

The main symbols and modifiers are combined in various ways to derive terms; common examples are the following:

Term	Expansion	Typical Units of Measure²^,^4-8
Pco₂	partial pressure of carbon dioxide	mm Hg or kPa
Paco₂	partial pressure of carbon dioxide, arterial	mm Hg or kPa
Po₂	partial pressure of oxygen	mm Hg or kPa
Pao₂	partial pressure of oxygen, arterial	mm Hg or kPa

(Note: The above 4 terms may be given without expansion at first mention; see also 14.11, Abbreviations, Clinical, Technical, and Other Common Terms, and 18.0, Units of Measure.)

Term	Expansion	Typical Units of Measure²^,^4-8
Pao₂	partial pressure of oxygen, alveolar	mm Hg or kPa
${P \bar{v} O}_{2}$	partial pressure of oxygen, mixed venous	mm Hg or kPa
Pb	barometric pressure	mm Hg or kPa
Pao₂ - Pao₂	alveolar-arterial difference (or gradient) in partial pressure of oxygen (preferred to AaDo₂)	mm Hg or kPa
Cao₂	oxygen concentration (or content), arterial	mL/dL or mmol/L
Cc′o₂	oxygen concentration (or content), pulmonary end-capillary	mL/dL
Cl	lung compliance	L/cm H₂O or L/mm Hg or L/kPa
Dlco	diffusing capacity of lung for carbon monoxide	mL·min⁻¹·mm Hg⁻¹
Fen₂	fractional concentration of nitrogen in expired gas	fraction
Fio₂	fraction of inspired oxygen	fraction
Pemax	maximum expiratory pressure	cm H₂O or mm Hg
Pimax	maximum inspiratory pressure	cm H₂O or mm Hg
Raw	airway resistance	cm H₂O·L⁻¹ ·s⁻¹ or kPa ·L⁻¹ ·s⁻¹
Sao₂	arterial oxygen saturation	%
sGaw	specific airway conductance	L · s⁻¹ · cm H₂O⁻¹ or L · s⁻¹ · kPa⁻¹
Spo₂	oxygen saturation as measured by pulse oximetry	%
Vds	volume of dead space	mL or L
$\dot{V} E$	expired volume per unit time	L/min
${\dot{V} O}_{2}$	oxygen consumption	mL/min or L/min or mmol/min
${\dot{V} o}_{2} max$	maximum oxygen consumption	mL/min or L/min or mmol/min
$\dot{V} / \dot{Q}$	ventilation perfusion ratio (also $\dot{V} A / \dot{Q}$ )	ratio
Vt	tidal volume	mL or L

*Note: Sometimes quantities are given per unit body weight, eg, Vt in liters per kilogram.

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AMA Manual of Style Committee

Symbols

Harriet S. Meyer

15.16.1 Symbols