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GENERAL SYMBOLS

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P

Partial pressure in blood or gas

PO2 = partial pressure of O2

A bar over the symbol indicates a mean value.

P̄= mean pressure, as distinct from instantaneous pressure

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

  V̇O2 = oxygen consumption per minute, mL

  V̇CO2 = 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

  FEV1/FVC, % = 100 × FEV1/FVC

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

  XA = XA, Xa = Xa

Additional qualifiers of the primary symbol may be identified as shown

  PEO2 = Pressure of CO2 in the expired air, mm Hg

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 0̊C, 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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