Testing for VQ Mismatch Nonuniform gas distribution Alveolar

Testing for V/Q Mismatch • Nonuniform gas distribution – Alveolar plateau of closing volume test – Nitrogen washout – Trapped gas – Single breath of 133 Xe – 99 m. Tc-labeled DTPA (diethylene triamine pentaacetic acid)

Testing for V/Q Mismatch • Nonuniform pulmonary blood flow – Pulmonary angiogram – Lung scans: • • • 131 I-labeled MAA 99 m. Tc-labeled 133 Xe MAA

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 • • Anatomic Alveolar : (a-A)Dco 2 – (A-a)Do 2 – Lung scans after inhaled and infused markers – Multiple inert gas technique

Physiologic Shunt = Anatomic + Intrapulmonary Shunt Absolute Shuntlike States

Shunt Equation. QS. Qt = CC´O 2 – Ca O 2 2 – Cv O 2

PHYSIOLOGIC DEAD SPACE Anatomic Physiologic = + Dead space Alveolar Dead space

Bohr Equation VD CO 2 VT Pa = - PE CO 2 Pa CO 2

Causes of Increased Alveolar-Arterial Oxygen Partial Pressure Gradient • Increased right - to left – Anatomic – Intrapulmonary shunt • 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 . Po 2 Pco 2 (liters/min) P N 2 (mm. Hg) O 2 CO 2 p. H content (ml/100 ml) O 2 CO 2 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