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Nitrogen Washout

Nitrogen Washout. Total volume expired x %N 2 = Original volume of N 2 in lungs. Original volume of N 2 in lungs x 1.25 = Original lung volume. F V = F (V + V ). HE i SP i. HE f SP f. L f. Helium Dilution. Amount of solute (mg) =

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Nitrogen Washout

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  1. Nitrogen Washout Total volume expired x %N2 = Original volume of N2 in lungs Original volume of N2 in lungs x 1.25 = Original lung volume

  2. F V = F (V + V ) HEi SPi HEf SPf Lf Helium Dilution Amount of solute (mg) = concentration of solute (mg/ml) x volume of solvent (ml) Total amount of He before test = total amount of He at end of test

  3. BODY PLETHYSMOGRAPH • PBOXx VBOX = PBOX x (VBOX - V) i i f i where (VBOX - V) = VBOX i f • PMx VL = PM x (VL + V) i i f i where (VL + V) = VL i f

  4. VT = VD + VA VA = VT - VD n(VA) = n (VT) – n(VD) . . . VA = VE - VD ANATOMIC DEAD SPACE

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

  6. VD = dead space for CO2 ( physiological dead space) CO2 FA = fractional concentration of CO2 in alveoli that are both ventilated and perfused CO2 BOHR EQUATION DERIVATION FE x VT = Fi x VD + FA x VA CO2 CO2 CO2 CO2 The volume of CO2 in mixed expired air The volume of CO2 coming from dead space The volume of CO2 coming from alveoli Where F = fractional concentration E = mixed expired I = inspired A = alveolar

  7. FE x VT = FA (VT – VD ) CO2 CO2 CO2 FE x VT = (FA x VT ) – (FA x VD ) CO2 CO2 CO2 CO2 VD x FA = VT (FA -FE ) CO2 CO2 CO2 CO2 Substituting (VT – VD ) for VA : CO2

  8. FA - FE P CO2 Since F = CO2 PTotal Pa CO2 VD CO2 CO2 CO2 = FA VT CO2 Pa - PE VD CO2 CO2 CO2 = VT

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

  10. Alveolar Ventilation and PA CO2 . . VE = VA x FA . CO2 CO2 V VA CO2 FA  . CO2 Since FA x (760 – 47) = PA CO2 CO2 . V VA CO2 Then PA . CO2

  11. ALVEOLAR AIR EQUATION PACO2 PAO2 = PIO2 - + F R PACO2 PAO2 = FIO2 2 R ( PB - PH O) -

  12. Nitrogen Concentration % Expired volume, L

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