Gas Exchange V-Q Flashcards
What happens in ventilation perfusion mismatch?
No gas exchange
Is perfusion and ventilation even throughout the lung?
No - gravitational effects
Why does gravity have an effect on the lungs?
Apical regions more distended than basal when upright
Where does most perfusion and ventilation occur?
Bottom of alveoli - gradient
When does PAO2 depend on?
Balance between rate of addition of O2 via VE and rate of removal in blood
What also affects regional distribution of ventilation and perfusion?
Structural differences throughout lung
What happens with less compliant alveoli?
Receive lower volume of gas - point of elastic recoil that balances distending pressure occurs earlier
What happens with increased resistance in alveoli?
Slower air flow - fills less quickly - less ventilated
What happens when V/Q falls?
Reduced rate of oxygen addition
PO2 falls - rate of oxygen leaving declines
new balance at a low level
What is the shunt effect of low VA/Q regions?
Reduction of PaO2
Normal or reduced PaCO2
Widening of A-aO2 gap
What is a physiological shunt?
Anatomical shunt + intrapulmonary shunt (V/Q=0) + shunt effect of low V/Q regions (V/Q<1)
What are regions of low V/Q equivlant to?
Blood flow through: portion of ‘perfectly’ ventilated and perfused alveoli
portion passing through an anatomical shunt
What can correct reduced PaO2 caused by low V/Q?
Inspiration of high FIO2
What happens if alveoli is completely blocked Q=0?
PO2 = bit below air PO2
PCO2 = 0
No gas exchange
What happens in high VA/Q?
Blood flow restricted - high PO2 and low PCO2
