RESPIRATION PHYSIOLOGY: ALVEOLAR-ARTERIAL EQUILIBRATION -- Carbon Dioxide Non-Equilibration

CARBON DIOXIDE NON-EQUILIBRATION

A. Define: AaΔCO₂ = P_a-CO2 - P_A-CO2

B. Magnitude usually very small (almost complete equilibration), because

1. D_CO2 is very large ( >> D_O2)

2. P_a-CO2 and P_v-CO2 are not very different, due to high capacity of blood for CO₂

3. CO₂ dissociation is curve roughly linear

C. Thus, P_A-CO2 ≈ P_a-CO2

Note: can therefore use arterial blood gas sample and the alveolar air equation to estimate AaΔO2