(22) Ventilation/Perfusion (Karius)

Question 1

What is the alveolar gas equation?

Answer 1

Question 2

What does the alveolar gas equation calculate?

Answer 2

What inspired O2 needs to be to produce a desired alveolar (and therefore arterial) O2 level

Question 3

Do this example:

Answer 3

Question 4

What can be deduced from estimating the PAO2 value?

Answer 4

Allows us to calculate the A-a O2 gradient

This is useful number for determining the ‘health’ of the alveoli

Question 5

What does an increase in the A-a O2 gradient indicate?

Answer 5

Diffusion impairment

(something is wrong with the alveoli)

Question 6

The alveolar gas equaltion allows us to predict…

Answer 6

The oxygen concentration in the alveoli

(helpful since non-invasive)

Question 7

What do you need to calculate the A-a O2 gradient?

Answer 7

Alveolar concentration of oxygen

Arterial concentration

Question 8

What is the normal A-a gradient?

Answer 8

20mmHg

Question 9

What is the regional blood flow in the lungs?

Answer 9

Question 10

Regional ventilation in the lungs:

Describe where the intrapleural pressure is highest and lowest

Answer 10

Intrapleural fluid is also acted on by gravity and affects the intrapleural pressure

Apex (less intrapleural fluid) = Intrapleural pressure is more negative (-10 cm H2O)

Base (more intrapleural fluid)= Intrapleural pressure is less negative than you expect (-2 -3 cm H2O)

Question 11

Describe the relative sizes of the alveoli at the base vs apex of the lung

Answer 11

At Apex: Alveoli are large at rest

At Base: Alveoli are small at rest

Question 12

Takeaways?

Answer 12

Note the changes in intrapleual pressures in the apex vs the base

Bigger volume change in base

Question 13

Answer 13

Question 14

What does (V/Q) ratio stand for?

Answer 14

Ventilation/Perfusion Ratio

Question 15

What is the average V/Q ratio?

Answer 15

V/Q

4L/min / 5 L/min

0.8

Question 16

What does a “high” VQ represent?

Answer 16

Ventilation is HIGH relative to perfusion

Question 17

What does a LOW V/Q represent?

Answer 17

Ventilation low compared to perfusion

Question 18

Normal V/Q ratio?

Answer 18

0.8

Question 19

Describe the enviornment you’d expect with a normal V/Q ratio of 0.8

Answer 19

Question 20

Describe what happens with a LOW V/Q ratio

Answer 20

The airway is blocked by something, but blood continues to arrive at the alveolus

In short time, O2 in that alveolus decreases while CO2 increases.

Question 21

What happens over time with a LOW V/Q ratio?

Answer 21

Question 22

What does this represent?

Answer 22

Physiologic shunt

Question 23

Answer 23

Question 24

Describe what V/Q inequalities exhist in the regions of the lung:

Zone 1:

Zone 2:

Zone 3:

Answer 24

Zone 1: V/Q is HIGH

Zone 2: V/Q is normal (0.8)

Zone 3: V/Q is LOW

Question 25

Answer 25

Question 26

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

Answer 26

Hypoxic Vasoconstriction