Testing for V/Q MismatchTesting for V/Q Mismatch

• Nonuniform gas distribution

– Alveolar plateau of closing volume test

– Nitrogen washout

– Trapped gas

– Single breath of 133Xe

– 99mTc-labeled DTPA (diethylene triamine pentaacetic acid)

• Nonuniform gas distribution

– Alveolar plateau of closing volume test

– Nitrogen washout

– Trapped gas

– Single breath of 133Xe

– 99mTc-labeled DTPA (diethylene triamine pentaacetic acid)

Testing for V/Q MismatchTesting for V/Q Mismatch

• Nonuniform pulmonary blood flow

– Pulmonary angiogram

– Lung scans:

•131I-labeled MAA

•99mTc-labeled MAA

•133Xe

• Nonuniform pulmonary blood flow

– Pulmonary angiogram

– Lung scans:

•131I-labeled MAA

•99mTc-labeled MAA

•133Xe

• Mismatched V/Q– Physiologic shunts : shunt equation

•Anatomic

• Intrapulmonary– Absolute

– Shuntlike states (low V/Q)

– Physiologic dead space : Bohr equation•Anatomic

•Alveolar : (a-A)Dco2

– (A-a)Do2

– Lung scans after inhaled and infused markers

– Multiple inert gas technique

• Mismatched V/Q– Physiologic shunts : shunt equation

•Anatomic

• Intrapulmonary– Absolute

– Shuntlike states (low V/Q)

– Physiologic dead space : Bohr equation•Anatomic

•Alveolar : (a-A)Dco2

– (A-a)Do2

– Lung scans after inhaled and infused markers

– Multiple inert gas technique

Testing for V/Q MismatchTesting for V/Q Mismatch

....

Physiologic ShuntPhysiologic Shunt

Physiologic = Anatomic + IntrapulmonaryShunt Shunt Shunt

Absolute Shunt

Shuntlike States

Shunt EquationShunt Equation

QS

Qt

.

.QS

Qt

QS

Qt

QS

Qt

CC´ – CaO2 O2

CC´ – CvO2 O2

=

PHYSIOLOGIC DEAD SPACEPHYSIOLOGIC DEAD SPACE

PhysiologicDead space

Anatomic Dead space

Alveolar Dead space

= +

Bohr EquationBohr Equation

VD

VT

Pa - PECO2 CO2 CO2

Pa CO2

=

Causes of Increased Alveolar-Arterial Oxygen Partial Pressure Gradient

Causes of Increased Alveolar-Arterial Oxygen Partial Pressure Gradient

•Increased right - to left shunt–Anatomic

– Intrapulmonary

•Increased ventilation-perfusion mismatch

•Impaired diffusion

•Increased inspired partial pressure of oxygen

•Decreased mixed venous partial pressure of oxygen

•Shift of oxyhemoglobin dissociation curve

•Increased right - to left shunt–Anatomic

– Intrapulmonary

•Increased ventilation-perfusion mismatch

•Impaired diffusion

•Increased inspired partial pressure of oxygen

•Decreased mixed venous partial pressure of oxygen

•Shift of oxyhemoglobin dissociation curve

vol VA Q VA / Q Po2 Pco2 PN2 O2 CO2 pH O2 CO2

. . . .

(%) (liters/min) (mmHg) content (ml/100ml

)

in out (ml/min)

7 .24 .07 3.3 132 28 553 20.0 42 7.51

4 8

13 .82 1.29

0.63 89 42 582 19.2 49 7.39

60 39