Pulmonary and Respiratory Terminology - Nomenclature

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.