Phys 7 Ventilation-perfusion relationships Flashcards
PAO2
Alveolar gas equation calculates what?
PIO2
PAO2 does say anything by itself?
what does it help calculate?
A-a O2 gradient
<12 mm hg is normal (online and used in class)
what is normal A-a O2 gradient?
what if its out of this range?
<12 mm hg is normal (online and used in class)
normally <20 mm Hg given on slide use 12
Summary alveolar gas equation
what is A-a gradient higher than normal?
What if normal but abnormal PaO2 and PAO2 are both low?
Intrapleural fluid and gravity?
Intrapleural pressure and gravity?
middle is “normal”
Intrapleural pressure
what does the difference in intrapleural pressure and different levels of the lung cause?
- Apex intrapleural pressure is more neg so alveoli are large at rest
- with inspiration alveoli can only get a little larger (balloon that is already mostly full)
- Base intrapleural pressure is higher so alveoli are smaller
- with inspiration the alveoli can get much larger
V/Q
low V/Q ratio
(this example is complete block) V=0
With V=0 what will eventually happen?
When arterial and alveolar levels are the same
HIgh V/Q ratio
If Q is zero?
No blood coming to alveolus (it is alveolar dead space)
If we have no or low Q what will happen?
This sounds great but we dont have any substantial blood flow so not much blood, if any, benefits from this situation
What ultimately can happen when the Q gets very low in one alveolus?
Blood that couldnt get to obstructed alveoli will instead have to go to another alveolus
After blood goes to a different alveolus in a high V/Q situation what happens to the other alveoli?
the increased blood flow increases Q making the V/Q ratio lower this acts like other low V/Q ratio alveoli and the PAO2 and PaCO2 decrease
V/Q in the lungs standing up
Hypoxic Hypoxia
COPD
Fibrosis
Altitude
Anemic hypoxia
anemia
CO poisoning
Circulatory hypoxia
HIstotoxic hypoxia
