22. Ventilation and Perfusion Flashcards
What is equala to [oxygen]alveolar= [oxygen in lungs] - [oxygen used by tissue] (calculation)
ALVEOLAR GAS EQUATION
PAo2 = Pio2 - PaCo2 / R
PAo2= alveolar partial pressure of oxygen PiO2= inspired partial pressure of oxygen, including water vapor (760-47 x oxygen%) AT SEA LEVEL PaCO2= arterial CO2 R= respiratory quotient (co2 produce/O2 used tissues)
What does alveolar has equation tell us?
What inspired O2 needs to be to produce a desired alveolar/arterial O2 level
The alveolar gas equation is not very useful. However it allows you to calculate what, which is useful for determind the health of the alveoli?
The A-a O2 gradient!
What is the calculation for A-aO2 gradient?
PAO2 - PaO2 = number! gradient
What is the normal A-aO2 gradient?
Less than 20mmHg
An increase in the A-aO2 gradient could suggest what?
That something is wrong with alveolar diffusion
Quick review of regional blood flow in the lungs. Which regions will have high, medium and low blood flow/pressures?
Zone 1 at apex is low flow/pressure
Zone 2 is average
Zone 3 is high at base d/t gravity
Due to gravity, intrapleural fluid is more near the base than the apex. So where there is less intrapleural fluid, there is ?
More intrapleural intrapleural pressure (-10 at apex) and less intrapleural pressure at base (-2–3cmH20)
Since intrapleural pressure is more negative at the apex, the alveoli are large at rest. What happens at the base?
pressure is less so alveoli are small because they are not as expanded by the pressure
What occurs in the large alveoli at the apex of the lung due to the high intrapleural pressure during inspiration?
The alveoli get a little larger
What occurs in the small alveoli at the base of the lung due to the low intrapleural pressure during inspiration?
The alveoli get much larger
Overall, the aleveolar volume between apex and base alveoli are much difference. With base alveoli have 20-40% volume and apex having 90-95% volume. Why?
Alveoli are larger in the base due to the lack of intrapleural fluid, which allows for volume in the apex to be increased, decreasing the intrapleural pressure, and increasing the size of alveoli.
In the base, there is more intrapleural fluid d/t gravity, so there is less room for the lungs to expand, so less volume, leading to less intrapleural pressure. So the alveoli are small and do not increase in size much due to the intrapleural fluid
Ventilation (V) / Perfusion (Q) ratio over the entire lung (average) is what?
4L/min / 5L/min = 0.8 which is the average but varies in different regions
High V/Q is when ventilation is high relative to perfusion (>0.8) . What occurs during Low V/Q (<0.8)?
Ventilation is low compared to perfusion
During an extreme condition, such as the airway being blocked by something, the ventilation would be 0. What will occur in the alveoli and blood?
O2 in that alveolus decreases (blood removes it) and CO2 increases (as blood delivers it). So the normal values of PAO2 and PACO2 (100 and 40) in the alveoli will drop to 80 and 42 leading to the same drop in the blood
If the alveolus is blocked over a long period of time, it will not equilibriate with the blood, and blood will?
leave without exchanging oxygen or CO2
THIS represents a shunt; as if blood never went to the lungs
An example of high V/Q ratio is no blood coming to the alveolus. With less blood removing oxygen and adding CO2, what would happen?
O2 would continue to increase and CO2 decrease, which brings the alveolus closer to atmospheric conditions (ex: PAO2 = 120 PACO2=20
After time, with no blood picking up the O2, the alverolar air in the arease will be similar to the air outside the body. What happens to the blood that couldnt get to the alveolus goes where and causes what?
goes to normal alveolus and turning it into low V/Q! This occurs because even though the air flow is normal, there is an increased amount of blood to deplete O2 before it can be replaced
At the apex (ZONE 1) the V/Q ratio is HIGH leading to?
higher PaO2, lower PaCO2 (ex 130, 28)
In the middle of the lung (ZONE2), the V/Q ratio is about 0.8- normal, leading to?
Normal PaO2 and PaCO2 (100, 40)
In the base of the lung (ZONE3) the V/Q ration is low/not as good, leading to?
Lower PaO2 and higher PaCO2 (89, 42)
What can we do to minimize the difference in V/Q ratios in the different zones of the lungs?
Hypoxic Vasoconstriction: constriction of pulmonary vessels to redirect blood away from hypoxic regions
