Testing 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)

Testing for V/Q Mismatch Nonuniform pulmonary blood flow Pulmonary angiogram Lung scans: 131I-labeled MAA 99mTc-labeled MAA 133Xe

Testing for V/Q Mismatch Mismatched V/Q Physiologic shunts : shunt equation Anatomic Intrapulmonary Absolute Shuntlike states (low V/Q) Physiologic dead space : Bohr equation Alveolar : (a-A)Dco2 (A-a)Do2 Lung scans after inhaled and infused markers Multiple inert gas technique . .

Physiologic Shunt Physiologic = Anatomic + Intrapulmonary Shunt Shunt Absolute Shunt Shuntlike States

Shunt Equation QS Qt . CC´ – Ca O2 CC´ – Cv =

PHYSIOLOGIC DEAD SPACE Anatomic Dead space Alveolar Dead space = +

Bohr Equation Pa - PE VD CO2 CO2 CO2 = VT Pa CO2

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

. . . . 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