AMA Manual of Style - Stacy L. Christiansen, Cheryl Iverson 2020
Pulmonary and Respiratory Terminology
Nomenclature
Standardization of symbols in respiratory physiology dates from at least 1950.1
Despite the familiarity of abbreviations in pulmonary and respiratory medicine, authors and editors are encouraged to expand all terms at first mention, except as noted.
Both symbols and abbreviations are used. Symbols consist of separate elements in various combinations whose letters may differ from the initial letters of the expansion, eg, Q̇ (perfusion). Abbreviations are usually initialisms.
14.16.1 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 and respiratory symbols are adapted from Fishman,2 Primiano and Chatburn,4 West,5,6 and Longo et al.7
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 of gas in blood |
D |
diffusing capacity |
F |
fractional concentration in a dry gas |
P |
pressure or partial pressure |
Q |
volume of blood |
Q̇ |
perfusion (volume of blood per unit time) |
R |
respiratory exchange ratio |
S |
saturation of hemoglobin with oxygen |
sG |
specific conductance |
T |
temperature |
V |
volume of gas |
V̇ |
volume of gas per unit time |
Modifiers are set as small capitals (not subscript):
A |
alveolar |
B |
barometric |
D |
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′ |
end-capillary |
i |
ideal |
max |
maximum |
p |
pulse oximetry |
v |
venous |
v̄ |
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 listed in Table 14.6-1.
Table 14.16-1. Examples of Gas Symbols
Term |
Expansion |
Typical units of measure2,5,6,7 |
PCO2a |
partial pressure of carbon dioxide |
mm Hg or kPa |
PACO2a |
partial pressure of carbon dioxide, arterial |
mm Hg or kPa |
PO2a |
partial pressure of oxygen |
mm Hg or kPa |
PAO2a |
partial pressure of oxygen, arterial |
mm Hg or kPa |
PAO2 |
partial pressure of oxygen, alveolar |
mm Hg or kPa |
PV̅O2 |
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−1or kPa∙L−1∙s−1 |
SaO2 |
arterial oxygen saturation |
% |
sGaw |
specific airway conductance |
L∙s−1∙cm H2O−1or L∙s−1∙kPa−1 |
Spo2 |
oxygen saturation as measured by pulse oximetry |
% |
VDS |
volume of dead space |
mL or L |
V̇E |
expired volume per unit time |
L/min |
V̇O2 |
oxygen consumption |
mL/min or L/min or mmol/min |
V̇O2max |
maximum oxygen consumption |
mL/min or L/min or mmol/min |
V̇/Q̇ |
ventilation perfusion ratio (also V̇/Q̇) |
ratio |
VT |
tidal volume |
mL or L |
a This term may be given without expansion at first mention (see also 14.11, Clinical, Technical, and Other Common Terms, and 18.0, Units of Measure).
Note: Sometimes quantities are given per unit body weight, eg, VT in liters per kilogram.
14.16.2 Abbreviations.
Table 14.6-2 lists some common abbreviations from pulmonary function testing; they should always be expanded at first mention.
Table 14.16-2. Common Pulmonary Function Test Abbreviations
Term |
Expansion |
Typical unit of measure |
CC |
closing capacity |
L |
CV |
closing volume |
L |
ERV |
expiratory reserve volume |
L |
FEF |
forced expiratory flow |
L/min |
FEF25%-75% |
FEF, midexpiratory phase |
L/min or L/s |
FEF200-1200 |
FEF between 200 and 1200 mL of forced vital capacity |
L/min or L/s |
FEV |
forced expiratory volume |
L |
FEV1a |
FEV in first second of expiration |
L |
FEV1 (percent predicted)a |
FEV in first second of expiration, taking into account age, height, sex, and race |
% |
FEV1/FVCa |
percent of FVC exhaled in first second |
expressed as a ratio or a percent |
FIVC |
forced inspiratory vital capacity |
L |
FRC |
functional residual capacity |
L |
FVC |
forced vital capacity |
L |
IRV |
inspiratory reserve volume |
L |
IVC |
inspiratory vital capacity |
L |
MVV |
maximum voluntary ventilation |
L/min |
PEF, PEFR |
peak expiratory flow rate |
L/min |
RV |
residual volume |
L |
TLC |
total lung capacity |
L |
VC |
vital capacity |
L |
a Note that all 3 of these should be reported.
14.16.3 Mechanical Ventilation.
The following should be expanded at first mention:
APRV |
airway pressure release ventilation |
BiPAP |
bilevel positive airway pressure (cm H2O) |
CPAP |
continuous positive airway pressure (cm H2O) |
ECMO |
extracorporeal membrane oxygenation |
ET |
tube endotracheal tube |
HFV |
high-frequency ventilation |
NIPPV |
noninvasive positive pressure ventilation |
NIV |
noninvasive ventilation |
PAV |
proportional assist ventilation |
PEEP |
positive end-expiratory pressure (cm H2O) |
VPAP |
variable positive airway pressure (cm H2O) |
Principal Author: Cheryl Iverson, MA
Acknowledgment
Thanks to George T. O’Connor, MD, MS, JAMA, and Boston University School of Medicine, Boston, Massachusetts, for reviewing and providing comments.
References
1.Standardization of definitions and symbols in respiratory physiology. Fed Proc. 1950;9(3):602-605.
2.Fishman AP, ed. Handbook of Physiology: A Critical, Comprehensive Presentation of Physiological Knowledge and Concepts. Vol 2, section 3, pt 1. American Physiological Society; 1986:endpapers.
3.Macklem PT. Symbols and abbreviations. In: Fishman AP, ed. Handbook of Physiology: A Critical Comprehensive Presentation of Physiological Knowledge and Concepts. Vol 2, section 3, pt 1. American Physiological Society; 1986:ix.
4.Primiano FP Jr, Chatburn RL. Zen and the art of nomenclature maintenance: a revised approach to respiratory symbols and terminology. Respir Care. 2006;51(12):1450-1457.
5.West JB. Pulmonary Pathophysiology: The Essentials. 8th ed. Lippincott Williams & Wilkins; 2013.
6.West JB. Respiratory Physiology: The Essentials. 9th ed. Lippincott Williams & Wilkins; 2012.
7.Longo D, Fauci A, Kasper D, Hauser S, Jameson J, Loscalzo J, eds. Harrison’s Principles of Internal Medicine. 18th ed. McGraw-Hill; 2011:3605, 3607.