5. Blood Supply, Gas Exchange, Ventilation and Perfusion

Question 1

What is the bronchial circulation (nutritive) supplied by?

Answer 1

The bronchial arteries arising from the systemic circulation

Question 2

What is the role of the bronchial circulation?

Answer 2

To supply oxygenated blood to airway smooth muscle, nerves and lung tissue

Question 3

What does the pulmonary circulation (gas exchange) consist of?

Answer 3

Left and right pulmonary arteries originating from the right ventricle

Question 4

What does the pulmonary circulation do?

Answer 4

• Carries entire cardiac output from RV. -Unique system
• Supplies the dense capillary network surrounding the alveoli and returns oxygenated blood to the left atrium via the pulmonary vein

Question 5

Describe the flow and pressure of the pulmonary circulation.

Answer 5

-High flow, low pressure

Question 6

How does air diffuse across membranes?

Answer 6

Down partial pressure gradients

Question 7

What does A stand for?

Answer 7

alveolar

Question 8

What does a stand for?

Answer 8

arterial blood

Question 9

What does ṽ stand for?

Answer 9

mixed venous blood (e.g. in pulmonary artery)

Question 10

What does PaO2 mean?

Answer 10

partial pressure of oxygen in arterial blood

Question 11

What does PACO2 mean?

Answer 11

partial pressure of carbon dioxide in alveolar air

Question 12

The rate of diffusion across the membrane is:

Answer 12

• Directly proportional to the partial pressure gradient
• Directly proportional to gas solubility
• Directly proportional to the available surface area
• Inversely proportional to the thickness of the membrane
• Most rapid over short distances

Question 13

What can affect gas exchange?

Answer 13

Various pathologies

Question 14

Describe the membrane of the alveoli?

Answer 14

• Large surface area
• Thin membrane
• Creates short diffusion distance

Question 15

Diffusion: emphysema

Answer 15

Destruction of alveoli reduces surface area for gas exchange

Question 16

Diffusion: fibrotic lung disease

Answer 16

Thickened alveolar membrane slows gas exchange. Loss of lung compliance may decrease alveolar ventilation

Question 17

Diffusion: pulmonary oedema

Answer 17

Fluid in interstitial space increases diffusion distance. Arterial PCO2 may be normal due to higher CO2 solubility in water.

Question 18

Diffusion: asthma

Answer 18

Increased airway resistance decreases airway ventilation

Question 19

What is the ventilation-perfusion relationship?

Answer 19

They ideally match each other

Question 20

What is ventilation in alveoli matched to through?

Answer 20

pulmonary capillaries

Question 21

What is the distribution of blood flow in the lungs influenced by?

Answer 21

Hydrostatic (blood) pressure (Pa) and alveolar pressure.

Question 22

What is blood flow inversely proportional to?

Answer 22

Vascular resistance and declines with height across the lung

Question 23

Why is blood flow high at the base of the lungs?

Answer 23

Arterial pressure exceeds alveolar pressure and vascular resistance is therefore low.

Question 24

Why s blood flow low at the apex of the heart?

Answer 24

Arterial pressure is less than alveolar pressure. This compresses the arterioles and vascular resistance is increased

Question 25

What effect does gravity have on ratio of ventilation to perfusion.

Answer 25

When in the upright position the ratio within the lung changes from the base to the apex due to gravity

Question 26

What is a perfectly matched ratio?

Answer 26

Ventilation: perfusion = 1.0

Question 27

What are mismatched ratios?

Answer 27

• Ventilation> perfusion> 1.0

- Ventilation< perfusion <1.0

Question 28

Where does the majority of mismatch take place?

Answer 28

Apex

Question 29

What happens if ventilation decreases in a group of alveoli?

Answer 29

PCO2 increases and PO2 decreases. Blood flowing past those alveoli does not get oxygenated

Question 30

Shunt

Answer 30

Passage of blood through areas of the lung that are poorly ventilated

Question 31

What is shunt the opposite of?

Answer 31

Alveolar dead space

Question 32

What does alveolar dead space refer to?

Answer 32

Alveoli that are ventilated but not perfused

Question 33

What does anatomical dead space refer to?

Answer 33

Air in the conducting zone of the respiratory tract unable to participate in gas exchange as walls of airways in this region are too thick.

Question 34

Physiological dead space

Answer 34

Alveolar DS + Anatomical DS

Question 35

What tries to keep ventilation and perfusion matched?

Answer 35

Local control mechanisms

Question 36

What happens when there is decreased tissue PO2?

Answer 36

Causes the arterioles of under ventilated alveoli to constrict, diverting blood to better ventilated alveoli.

Question 37

What can cause mild bronchial dilation?

Answer 37

Increased PCO2

Question 38

What is constriction in response to hypoxia particular to?

Answer 38

Pulmonary vessels (systemic vessels dilate)

Question 39

When does autoregulation take place?

Answer 39

when alveolar dead space occurs

Question 40

In what ay is autoregulation opposite to shunt?

Answer 40

• Increase in alveolar PO2 causes pulmonary vasoldilation

- Decreases in alveolar PCO2 causes bronchial constriction

Question 41

What does autoregulation ultimately lead to?

Answer 41

Increases in perfusion and to a lesser extent a decrease in ventilation bringing the ratio back towards 1.