22. Ventilation and Perfusion

Question 1

What is equala to [oxygen]alveolar= [oxygen in lungs] - [oxygen used by tissue] (calculation)

ALVEOLAR GAS EQUATION

Answer 1

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)

Question 2

What does alveolar has equation tell us?

Answer 2

What inspired O2 needs to be to produce a desired alveolar/arterial O2 level

Question 3

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?

Answer 3

The A-a O2 gradient!

Question 4

What is the calculation for A-aO2 gradient?

Answer 4

PAO2 - PaO2 = number! gradient

Question 5

What is the normal A-aO2 gradient?

Answer 5

Less than 20mmHg

Question 6

An increase in the A-aO2 gradient could suggest what?

Answer 6

That something is wrong with alveolar diffusion

Question 7

Quick review of regional blood flow in the lungs. Which regions will have high, medium and low blood flow/pressures?

Answer 7

Zone 1 at apex is low flow/pressure
Zone 2 is average
Zone 3 is high at base d/t gravity

Question 8

Due to gravity, intrapleural fluid is more near the base than the apex. So where there is less intrapleural fluid, there is ?

Answer 8

More intrapleural intrapleural pressure (-10 at apex) and less intrapleural pressure at base (-2–3cmH20)

Question 9

Since intrapleural pressure is more negative at the apex, the alveoli are large at rest. What happens at the base?

Answer 9

pressure is less so alveoli are small because they are not as expanded by the pressure

Question 10

What occurs in the large alveoli at the apex of the lung due to the high intrapleural pressure during inspiration?

Answer 10

The alveoli get a little larger

Question 11

What occurs in the small alveoli at the base of the lung due to the low intrapleural pressure during inspiration?

Answer 11

The alveoli get much larger

Question 12

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?

Answer 12

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

Question 13

Ventilation (V) / Perfusion (Q) ratio over the entire lung (average) is what?

Answer 13

4L/min / 5L/min = 0.8 which is the average but varies in different regions

Question 14

High V/Q is when ventilation is high relative to perfusion (>0.8) . What occurs during Low V/Q (<0.8)?

Answer 14

Ventilation is low compared to perfusion

Question 15

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?

Answer 15

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

Question 16

If the alveolus is blocked over a long period of time, it will not equilibriate with the blood, and blood will?

Answer 16

leave without exchanging oxygen or CO2

THIS represents a shunt; as if blood never went to the lungs

Question 17

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?

Answer 17

O2 would continue to increase and CO2 decrease, which brings the alveolus closer to atmospheric conditions (ex: PAO2 = 120 PACO2=20

Question 18

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?

Answer 18

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

Question 19

At the apex (ZONE 1) the V/Q ratio is HIGH leading to?

Answer 19

higher PaO2, lower PaCO2 (ex 130, 28)

Question 20

In the middle of the lung (ZONE2), the V/Q ratio is about 0.8- normal, leading to?

Answer 20

Normal PaO2 and PaCO2 (100, 40)

Question 21

In the base of the lung (ZONE3) the V/Q ration is low/not as good, leading to?

Answer 21

Lower PaO2 and higher PaCO2 (89, 42)

Question 22

What can we do to minimize the difference in V/Q ratios in the different zones of the lungs?

Answer 22

Hypoxic Vasoconstriction: constriction of pulmonary vessels to redirect blood away from hypoxic regions