Pulmonary Circulation, Ventilation-Perfusion

Question 1

What are there variations in, in regards to lungs?

Answer 1

Lung ventilation

Lung perfusion

Question 2

What needs to occur for effective gas exchange?

Answer 2

Ventilation and perfusion need to be closely matched

Question 3

What is ventilation?

Answer 3

The change in volume through the respiratory cucle

Question 4

Is air evenly distributed through the lungs?

Answer 4

No

Question 5

Where does more gas end up in the lungs?

Answer 5

Base of the lung than the apex

Question 6

Why does the base of the lung change more in volume than the apex?

Answer 6

The lower ribs are more curved and mobile than the upper

This means the diaphragm extends the lower lobes more and as there is greater compliance

Gravity has a small role as the weight of the lung pulls down on pleura, so the apex has a more negative intrapleural pressure

Question 7

What two circuits nourish lung tissue?

Answer 7

Pulmonary

Bronchial

Question 8

What are bronchial arteries a branch of?

Answer 8

Descending aorta

Question 9

Where does the bronchial circulation join?

Answer 9

Joins with pulmonary veins thus diluting the oxygenated blood with deoxygenated blood

Question 10

What is the function of the bronchial circulation?

Answer 10

Supply oxygen to lung parenchyma

Airway smooth muscle

Pulmonary arteries and veins

Pleura

Warming inspired air

Question 11

How much blood enters the pulmonary circulation?

Answer 11

5L every minute

Question 12

What does one heart beat do?

Answer 12

Replaces entire pulmonary circulation

Question 13

What are the two keys to pressures in pulmonary circulation?

Answer 13

The pulmonary circulation is a low pressure, low resistance system

Able to recruit more vessels with only a small increase in arterial pulmonary pressure

Question 14

What is the mean arterial pressure in the pulmonary circulation?

Answer 14

15mmHg

Question 15

What is blood flow through the pulmonary circulation dependent on?

Answer 15

Balance between alveolar pressure and blood pressure

Called transmural pressure

Question 16

Slide 10

Answer 16

see if he talks about diagram

Question 17

Why is blood flow greater at the base than the apex of the lung?

Answer 17

Hydrostatic pressure difference between base and apex of the lung

Around 23mmHg

Or pressure in capillaries is lower at apex than at base of lung

Question 18

When will blood only flow?

Answer 18

If blood pressure is greater than alveolar pressure

Question 19

Slide

Answer 19

12

Question 20

When would there be no oxygen perfusion in the apex?

Answer 20

If the alveo

Question 21

When would there be no oxygen perfusion in the apex?

Answer 21

If the alveolar pressure is greater than the blood hydrostatic pressure

This forces the capillary to close

Question 22

Slide 14

Answer 22

lecture

Question 23

What is flow determined by in zone 2?

Answer 23

Arterial-alveolar pressure difference

This is because alveolar pressure is lower than systolic arterial pressure but may be higher than diastolic AP and venous pressure

Question 24

What blood flow occurs in zone 3?

Answer 24

Alveolar pressure is lower than both arterial and venous pressure

The capillaries are therefor distended as a consequence of the transmural pressure and there is continuous flow

Question 25

What is the ventilation and perfusion ratio in the whole lung?

Answer 25

0.85

Question 26

What is the ventilation and perfusion ratio in the base of lung?

Answer 26

0.6 (more perfusion than ventilation)

Question 27

What is the ventilation and perfusion ratio in the apex?

Answer 27

About 3

Question 28

What is the ventilation and perfusion ratio 2/3rds above the base?

Answer 28

1

Question 29

Describe perfect match between ventilation and perfusion

Answer 29

well ventilated alveoli with a good perfusion of blood | Blood will equilibrate with alveolar air and be rich in oxygen and low in CO2

Question 30

Describe poor ventilation alveoli with a rich blood supply

Answer 30

Alveolar air will equilibrate with the blood and the blood will tend towards the same composition as venous, as ↓fresh air is being brought in. Low PO2, high PCO2

Question 31

Describe well ventilated alveoli which are poorly perfused with blood

Answer 31

Blood leaving the alveoli will be low in CO2 (as there is a large concentration gradient, efficiently blown off), but as the haemoglobin is fully saturated, there will not be a significant increase in O2 levels

Question 32

Can different areas of the lungs compensate for each other?

Answer 32

No The lowered PO2 of blood leaving poorly ventilated parts of the lung is not compensated for by blood leaving well ventilated areas, because of the shape of the oxygen-haemoglobin dissociation curve

Question 33

What is the effect of low ventilation to perfusion ratios on CO2 concentration?

Answer 33

CO2 diffuses from blood to alveoli but not taken away as rapidly This CO2 accumulates in alveoli and higher steady rate of PCO2 occurs PCO2 may be 42mmHg, 40mmHg normally

Question 34

What is the effect of low ventilation to perfusion ratios on O2 concentration?

Answer 34

O2 diffuses from alveoli into blood but because ventilation is low the oxygen taken up by the blood is not fully replenished by new air entering the lungs Oxygen is therefore depleted in alveoli and new steady state low PO2 occurs 90mmHg, 100 normally

Question 35

What is the effect of high ventilation to perfusion ratio on CO2 concentration?

Answer 35

CO2 diffusing from blood is nearly all blown away, thus CO2 in alveoli is depleted until a new lower steady state level occurs PCO2 may be 28 mmHg (40 normally

Question 36

What is the effect of high ventilation to perfusion ratio on O2 concentration?

Answer 36

O2 diffusing from alveoli is not taken away by blood as much as normal because relative blood flow is lower. But as O2 is replenished with each breath O2 accumulates, diffusion carries on and a new higher PO2 level occursPO2 may be 130 mmHg (100 normally)

Question 37

Example of active control of blood flow to stop mismatching between ventilation and perfusion matching?

Answer 37

Hypoxic vasoconstriction The result diverts blood away from poorly ventilated areas

Question 38

When is the hypoxic vasoconstriction action important?

Answer 38

When born before 1st breath, lungs vasoconstrict and resistance is high, with 1st breath vasoconstriction decreases and so does resistance