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General Symbols

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P

Partial pressure in blood or gas PO2 = partial pressure of O2

image

A bar over the symbol indicates a mean value. image = mean pressure, as distinct from instantaneous pressure

image

A time derivative (rate) is indicated by a dot above the symbol

  • O2 = oxygen consumption per minute, mL

  • CO2 = CO2 production per minute, mL

% X

Percent sign preceding a symbol indicates percentage of the predicted normal value

X/Y%

Percent sign following a symbol indicates a ratio function with the ratio expressed as a percentage. Both components of the ratio must be designated

image

XA, Xa

A small capital letter or a lower-case letter on the same line following a primary symbol is a qualifier to further define the primary symbol. Alternatively, subscript letters may be used

image

Additional qualifiers of the primary symbol may be identified as shown

image

Gas Phase Symbols

Primary Symbols

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V

Volume of gas

Flow of gas

F

Fractional concentration of a gas

Qualifying Symbols

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I

Inspired

Vi = inspired volume

E

Expired

Ve = expired volume

e = expired volume per minute

A

Alveolar

Va = alveolar volume

V̇ = alveolar ventilation per minute

T

Tidal

Vt = tidal volume

D

Dead space

Vd = volume of dead space

d = dead-space ventilation per minute

B

Barometric

Pb = barometric pressure

STPD

Standard conditions: temperature 0°C, pressure 760 mm Hg, and dry (0 mm Hg water vapor)

BTPS

Body conditions: body temperature and ambient pressure, saturated with water vapor at these conditions

ATPD

Ambient temperature and pressure, dry

ATPS

Ambient temperature and pressure, saturated with water vapor at these conditions

an

Anatomic

p

Physiological

f

Respiratory frequency, per minute

max

Maximum

t

Time

Blood Phase Symbols

Primary Symbols

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Q

Volume of blood

Blood flow

Q̇  = cardiac output, L/min

C

Concentration in the blood phase

CO2 = concentration of oxygen in blood, mL of O2 per 100 mL of blood

S

Saturation in the blood phase

SO2 = Saturation of hemoglobin with O2, percent

Qualifying Symbols

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a

Arterial

CaO2 = concentration of O2 in arterial blood, mL of O2 per 100 mL of blood

c

Capillary

CcO2 = concentration of O2 in capillary blood, mL of O2 per 100 mL of blood

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