Transcript Pulmonary Gas Exchange I

Lectures on respiratory physiology
Pulmonary Gas Exchange I
PO2 cascade in a hypothetical perfect lung
Perfect Lung
Effect of hypoventilation
All the expired CO2 comes from the alveolar
gas
Alveolar Ventilation Equation using PCO2
Alveolar Gas Equation
PACO2
PAO2  PIO2 F
R
Using the Alveolar Gas Equation
PACO2
PAO2  PIO2 F
R
40
PAO2  150 0.8
PAO2  100
Alveolar gas equation for hypoventilation
PACO2
PAO2  PIO2 F
R
80
PAO2  150 0.8
PAO2  50
What inspired O2 concentration is required to
return the alveolar PO2 to normal?
PACO2
PAO2  PIO2 F
R
80
100  PIO2 F
0.8
PIO2  200
PIO2  FIO2  713
200
FIO2 
 0.28
713
Inspired O2 concentration  28%
Causes of hypoventilation
PO2 cascade showing a diffusion step
Time courses for PO2 in the capillary
Thickened blood-gas barrier
PO2 cascade showing addition of shunt
O2 concentrations with a shunt
Deriving the shunt equation
The shunt equation
Shunt causes a low arterial PO2 with 100% O2