PULMONARY 06: VENTILATION/PERFUSION

Question 1

In an ideal ventilation/perfusion ratio, we transport what?

Answer 1

What we use in the tissues

Question 2

How do we measure V/Q? What units?

Answer 2

mL O2/mL blood

Question 3

If the V/Q ratio is greater than 1, this means____

Answer 3

Ventilation has exceeded perfusion

Question 4

If V/Q ratio is less than 1 this means ____

Answer 4

Perfusion has exceeded ventilation

Question 5

A normal V/Q ratio is __

Answer 5

near 1 (0.8)
This indicates slightly more perfusion than ventilation

Question 6

What are the two extremes of O2/CO2 that we experience?

Answer 6

1. Inspired air, where there is a VERY high pO2 and very low PCO2
2. Mixed-venous blood, where there is a lower PO2 and pCO2 that exceeds the pO2 (40 for O, 46 for CO2)

Question 7

What happens to the v/q ratio in high ventilation?

Answer 7

We shift the VQ ratio toward a higher number, alveolar O2 and CO2 approach atmospheric

Question 8

If we increase V/Q ratio too much, this is an indication of what, clinically speaking?

Answer 8

Dead space alveolus; this means there are places with ventilation but no perfusion. Perfusion may be blocked due to something like a pulmonary embolism.

Question 9

If we see that there is a very very low V/Q ratio, what is this an indication of, clinically speaking?

Answer 9

A shunt alveolus; this is a bypass and would indicate there are areas where we have no ventilation in the system. We do have perfusion through the system, however. Therefore, alveolar content is approaching that of mixed venous blood

Slide 9

Question 10

Ventilation and perfusion are both elevated in the (base/apex) of lung and why

Answer 10

Base of lung due to gravity

Question 11

Which is more skewed toward the base of the lung, ventilation or perfusion?

Answer 11

Perfusion, although not by much

Question 12

About where on the lung do ventilation and perfusion match each other

Answer 12

2/3 of the way up

Question 13

Average V/Q over the entire system is what

Answer 13

0.8

Slide 13

Question 14

The V/Q ratio determines WHAT for any single lung unit

Answer 14

Gas exchange

Question 15

V/Q is high in what part of the lung

Answer 15

apex

Question 16

V/Q is low in what part of the lung

Answer 16

Base

Question 17

V/Q mismatch and venous drainage (shunting) results in PaO2 slightly above or below the PAO2

Answer 17

Slightly below

Question 18

Is some level of V/Q mismatch normal in a normal physiological state

Answer 18

Yes

Question 19

Hypoxia

Answer 19

Decreased O2 delivery to tissue

Question 20

Hypoxemia

Answer 20

Decreased O2 in arterial blood (<60mmHg clinically, technically <80mmHg)

Question 21

Ischemia

Answer 21

Loss of blood flow

Question 22

What is AaDO2

Answer 22

Alveolar-arterial difference of O2

Question 23

What is hypoxemia with normal AaDO2 an indication of?

Answer 23

High altitude (decreased PiO2)
Hypoventilation

Basically, not enough oxygen is getting into the airways, so therefore blood oxygen is also low

Question 24

What is hypoxemia with INCREASED AaDO2 an indication of?

Answer 24

Diffusion limitations, V/Q mismatch, right-to-left shunts.

Basically, there is oxygen in the airways, but it’s not getting to the blood

Question 25

How do you determine alveolar-arterial difference of PO2

Answer 25

Patient breathes in 150mmHg oxygen, you get what thei rblood gas is, and you solve for the difference

Question 26

What does alveolar PO2 depend on

Answer 26

Rate of removal from blood (metabolic demand) | Rate of replenishment of O2 by alveolar ventilation

Question 27

If you stop breathing, what is the effect on alveolar O2 and CO2

Answer 27

Po2 decreases | PCO2 increases

Question 28

In hypoventilation, will supplemental oxygen be sufficient to help raise PaO2?

Answer 28

Yes

Question 29

Between high altitude, hypoventilation, diffusion limitations, right-left shunts, and V/Q mismatches, which is the one situation that supplemental oxygen will NOT result in an improved blood-oxygen level

Answer 29

R-to-L shunt

Question 30

Why does supplemental oxygen help if you have a diffusion limitation?

Answer 30

You're increasing the driving force by increasing P1 You might use this in the case of lung edema, fibrosis, etc

Question 31

Why will supplemental oxygen NOT help blood oxygen level in the case of a shunt?

Answer 31

A shunt is a bypass/alley / connection. This means that the blood is going from R heart to L heart without being oxygenated. In these examples, blood does not see alveolar capillary beds. Therefore, you can increase oxygen but that blood is never going to see it.

Question 32

What are normal anatomical shunts?

Answer 32

``` Thebesian vessels (myocardium drainage into heart chamber) Bronchial circulation drainage ```

Question 33

What are pathologic anatomic shunts

Answer 33

Vascular lung tumors | pulmonary arteriovenous malformations

Question 34

What is a capillary/Physiological shunt

Answer 34

Blood does go through pulmonary capillaries, but does not fully equilibrate This can be caused by tumors that block airflow, pneumothorax, severe pneumonia and edema, foregin bodies

Question 35

What is the most common reason for hypoxemia in patients with respiratory disorders

Answer 35

V/Q mismatch

Question 36

What are some reasons for a V/Q mismatch

Answer 36

Broadly speaking, anything that perterubs ventilation Asthma COPD fibrosis Cystic fibrosis

Question 37

Why does adding oxygen help in the case of a V/Q mismatch

Answer 37

If you take a single inhale of oxygen it won't necessarily go into the space very well particularly if there's an issue of poor ventilation. But we consider supplemental oxygen to not be transient, but over hours/days. Over time, because we have more access to this spce, it will eventually get to raising the PiO2 and rely on diffusion of oxygen from that increased driving pressure. It'll get into the blood plasma space eventually nd into RBC's, and O2 can get to a normal level. Increasing O2 to the entire system isn't great either, but it can at the very least rescue the V/Q ratio

Question 38

Two main mechanisms of compensation with regard to V/Q mismatch and hypoxemic conditions

Answer 38

Hypoxic vasoconstriction | Bronchiolar constriction

Question 39

What is hypoxic vasoconstriction? What instigates it? During what is this very important?

Answer 39

It is instigated by a low PAO2 (indicating high perfusion) It redirects perfusion to ventilated parts of the lung Arterial O2 level does not affect this at all Baby's first breath! tere is a dramatic decrease in PVR and increase in pulmonary blood flow (15% CO before birth to 100%)

Question 40

What is bronchiolar constriction? What instigates it?

Answer 40

Instigated by high PAO2, low CO2, and a high pH - indicative of the airways sensing CO2 changes and shuttling itself , rather than circulatory side like in hypoxic vasoconstriction It is when the bronchioles themselves constrict to redirect ventilation to perfused parts of the lung.