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
As we know. Gravity works on blood in our bodies. When we stand, hydrostatic pressure in our legs increases compared to the level of the heart of brain. Does this occur in the lungs?
YES
What is the regional blood flow of the lungs?
Apex of the lung- decreased BP; decreased blood flow
Middle regions of the lung- BP is normal; blood flow is normal
Base region of the lung- BP high; Blood flow is high.
Is the intrapleural fluid acted on by gravity?
Yes. Thus, it affects the intrapleural pressure.
Due to gravity, there is more intrapleural fluid where?
Near the base, than the apex.
What is the intrapleural pressure and fluid concentration at the
- Apex
- Base
Apex- less intrapleural fluid= intrapleural pressure is more negative (up to -10cm H20)
Base- more intrapleural fluid=intrapleural pressure is less negative (-2–3 cmH20)
How does the intrapleural pressure differences of the lungs affect the sizes of the alveoli?
Apex=
- intrapleural fluid=
more negative pressure (-10)=
larger alveoli
Base=
+ intrapleural fluid=
Less negative pressure (-2-3 mmHg)
smaller alveoli
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 (because they are already pretty big).
For a given change in pressure, you will not produce a big change in volume.
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
For a given change in pressure, you will get a higher change in volume, compared to the alveoli in the apex.
Apex: ____ fluid, pressure is _______, size of alveoli= ____
Base: ____ fluid, pressure is ______, size of alveoli= _____
Apex= little fluid, pressure is more - than other regions, alveoli are larger than base
Base: more fluid, pressure is less negative than other regions, alveoli are smaller than apex, however, they will get a bigger change in volume
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 apex 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 a less negative intrapleural pressure. So the alveoli are small and do not increase in size much due to the intrapleural fluid
What is the ventilation perfusion ration?
V/Q
In a normal person, the ventilation/perfusion ratio is 4L min/ 5L/min= 0.8/
But this varies depending on the region.
High V/Q?
ratio is >0.8.
Ventillation is high compared to perfusion.
Low V/Q
<0.8
Ventilation is low compared to perfusion
What occurs when the V/Q ratio is 0.8?
PAO2=100mmHg
PACO2=40mmHg
PaO2= 40mmHg
PaCO2= 45mmgHg
The aveoli (lungs) and capillary will become to an equillbrium
What happens if we have a low V/Q (ventillation is low due to the airway being blocked by something).
- Blood will continue to travel to the alveolus, even though ventilation is low.
1. At first, our blood will come to an equillibrium with lungs (alveolus)
2. However, the O2 in the alveolus decreases (because the blood is removing the oxygen), while the CO2 increases (as the blood delivers CO2).
3. The same changes will occur in the blood.
4. Overtime, the alveolus will equillibriate with the venous blood and the blood that enters the alveolus will leave without exchanging O2 or CO2.
When blood enters and leaves the alveolus without exchanging O2 and CO2, what is this called?
A shunt.
- The blood gained nothing by going to the lungs; thus, it was as if it never went.
What is an example that would leave to a high V/Q?
If there is no blood coming to the alveolus; as a result, less blood is removing O2 and adding CO2.
What happens when there is a high V/Q?
-Perfusion is decreased. Thus, less blood will go to the area.
As a result, the alveolar O2 will increase, CO2 will decrease, bringing the alveolus closer to atmospheric conditions.
Eventually, the alveolar air will be similar to the air outside the body (atomospheric). because no the blood is not taking away the O2 or adding CO2.
BUT WAIT; a high V/Q ratio sounds great. We have a high O2 and less CO2. Is it a dream come true?
No. Because remember. Blood flow to the area is v low. Thus, not much benefits from it.
After time, with no blood picking up the O2, the alverolar air in the areas will be similar to the air outside the body.
What happens to the blood that couldnt get to the alveolus?
The blood will go to normal alveolus turn it from
normal alveolus–> alveolus wiith a low V/Q ratio, even though the airflow is normal.
This is due to the increase in blood flow (increase in perfusion) to the aveoli.
(decreases alveolar O2 and increases alveolar CO2)
In a High V/Q region
—-What is the—
PaO2
PaCO2
pHa
Volume of blood
PaO2= high
PaCO2= low
pHa= high
Volume of blood= low (the volume of blood that went to this area is low)
In a Low V/Q region,
what is the
PaO2
PaCO2
pH
volume of blood?
-PaO2–> low
PaCO2–> high
pH–> low
Volume of blood–> high relative to air.
BAD NEWS: tends to to get alot of blood that goes to this area.
Do we have V/Q inequalities in our bodies?
Yes, throughout our body we have minor V/Q inequalities.
What is the V/Q ratio in the apex (zone 1)?
- BP is decreased
- Blood flow is decreased (Perfusion is decreased)
== High V/Q ratio, results in a higher PaO2, lower PaCO2 and a higher pH
What is the V/Q ratio in the zone 2?
V/q ratio is 0.8.
Blood gases are PaO2= 100 mmHg,
PaCO2= 40 mmHg.
What is the V/Q ratio at the base zone 3?
High BP,
High blood flow (high perfusion)
= Low V/Q
Blood gases are not as good as we expect:
