Ventilation- perfusion relationship

Question 1

What can ventilation and perfusion be measured in?

Answer 1

Litres/min

Question 2

Define ventilation.

Answer 2

The amount of air getting into the lungs

Question 3

What does alveolar ventilation tell us?

Answer 3

How much fresh air can reach the alveoli and therefore participate in gas exchange.

Question 4

Define perfusion.

Answer 4

Blood flow through the pulmonary circulation

Question 5

What do we ideally want ventilation in litres/min to match?

Answer 5

Perfusion in litres/ min

E.G. amount of air getting into the lungs per minute to be equal to the amount of blood flowing past the lungs per minute

Question 6

Blood flow and ventilation decrease with what?

Answer 6

Height across the lung

Question 7

Where is there more ventilation and perfusion?

Answer 7

At the base of the lung.

Question 8

At the bottom of the lungs, which is higher, blood flow or ventilation?

Answer 8

Blood flow

Question 9

Why is blood flow higher at the bottom of the lungs compared to ventilation?

Answer 9

Arterial pressure exceeds alveolar pressure and therefore the blood vessels push on the alveoli and compress them.

Question 10

Why is blood flow less at the apex of the lungs?

Answer 10

Arterial pressure is less than alveolar pressure so compresses the arterioles.

Question 11

At the apex of the lung, is there more ventilation or perfusion?

Answer 11

Ventilation

Question 12

If both ventilation and blood flow decrease, which decreases at a faster rate?

Answer 12

Blood flow

Question 13

If the perfusion and ventilation are matched, what is the ratio?

Answer 13

1

Question 14

Describe the ratio at the base of the lungs.

Answer 14

Ventilation<perfusion
Therefore, ration <1

Question 15

Describe the ratio at the apex of the lungs.

Answer 15

Ventilation>perfusion
Therefore, ratio >1

Question 16

Describe what happens when perfusion=ventilation.

Answer 16

Deoxygenation blood flows into lungs via pulmonary artery
Gas exchange between blood and alveoli can take place meaning blood becomes rich in oxygen.

Question 17

Describe what happens when perfusion>ventilation.

Answer 17

Deoxygenation blood flows into lungs via pulmonary artery.
Blood passes well ventilated area of the lungs so gas exchange can take place but then some blood passes through poorly ventilated areas and cannot pick up oxygen/drop of CO2.
Therefore, decrease in the partial pressure of oxygen as well oxygenated blood mixes w poorly oxygenated blood.

Please just read through, looks overwhelming but makes sense!

Question 18

Define shunt.

Answer 18

Passage of blood through areas of the lungs which are poorly ventilated.

Question 19

If shunting occurs, what happens to the blood vessels around the poorly ventilated area of the lung.

Answer 19

Blood vessels constrict in response to the decrease in the partial pressure of oxygen.
This means they reduce the amount of blood that flows to the poorly ventilated area.

Question 20

What do blood vessels in the systemic circulation do in response to tissue hypoxia?

Answer 20

They dilate.

This is because it is their job to deliver oxygen so it’s important that more blood can get to this area.

Question 21

What happens to perfusion when we constrict blood vessels?

Answer 21

Reduce perfusion

Question 22

What happens to ventilation when we dilate blood vessels?

Answer 22

Increase ventilation

Question 23

What is it known as when ventilation>blood flow?

Answer 23

We get alveolar dead space.

Question 24

Where does alveolar dead space occur?

Answer 24

At the dead space of the lungs.

Question 25

What is the opposite of alveolar dead space?

Answer 25

Shunt

Question 26

In shunt, compare levels of perfusion vs ventilation.

Answer 26

Perfusion>ventilation.

Question 27

In shunt, compare levels of PO2 and PCO2

Answer 27

Alveolar partial pressure of oxygen falls.
Alveolar partial pressure of carbon dioxide rises.

Question 28

What happens in response to the increase in the partial pressure of CO2?

Answer 28

Bronchial dilation

Question 29

What happens in response to the decrease in the partial pressure of O2?

Answer 29

Pulmonary vasoconstriction.

Question 30

In alveolar dead space, compare levels of perfusion vs ventilation.

Answer 30

Ventilation>perfusion.

Question 31

In alveolar dead space, compare levels of PO2 and PCO2

Answer 31

Alveolar partial pressure of oxygen rises.
Alveolar partial pressure of carbon dioxide falls.

Question 32

What happens in response to the decrease in the partial pressure of CO2?

Answer 32

Bronchial constriction

Question 33

What happens in response to the increase in the partial pressure of O2?

Answer 33

Pulmonary vasodilation

Question 34

Define alveolar dead space.

Answer 34

Alveoli which are ventilated but not perfused.

Question 35

Define anatomical dead space.

Answer 35

Air in the conducting zone of the respiratory tract which cannot participate in gas exchange because walls in this region are too thick.

Question 36

Which walls in the respiratory tract are too thick for gas exchange to take place?

Answer 36

Nasal cavities, trachea, bronchi and upper bronchioles.

Question 37

What is physiological dead space?

Answer 37

Alveolar dead space + anatomical dead space.

Question 38

Define respiratory sinus arrhythmia.

Answer 38

Normal change in heart rate during the breathing cycle.

Question 39

What happens to heart rate when you breathe in?

Answer 39

HR increases.

Question 40

What happens to heart rate when you breathe out?

Answer 40

HR deacreases.

Question 41

Why do we have respiratory sinus arrhythmia?

Answer 41

To minimise ventilation:perfusion mismatch