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

8. Helium Dilution F V = F (V + V ) HEi SPi HEf SPf Lf
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
F V = F (V + V )
HEi SPi
HEf SPf Lf

10. BODY PLETHYSMOGRAPH PBOX x VBOX = PBOX x (VBOX - V)i i f i
where (VBOX - V) = VBOX i f
PM x VL = PM x (VL + V) i i f i
where (VL + V) = VL i f

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

13. PHYSIOLOGIC DEAD SPACE
Anatomic Dead space
Alveolar
Dead space = +

14. 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
FA = fractional concentration of CO2 in alveoli that are
both ventilated and perfused
CO2
VD = dead space for CO2 ( physiological dead space)

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

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

18. Bohr Equation
Pa PE VD
CO2
CO2
CO2 = VT Pa
CO2

19. 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

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

27. Nitrogen Concentration %
Expired volume, L