Matching lung ventilation and perfusion

Question 1

What is ventilation and how is it measured?

Answer 1

• Movement of gases in and out of the lungs
• Ventilation of the lungs occurs through airways
• Measured as change in volume per unit time

Question 2

What is perfusion, where does it occur and how is it measured?

Answer 2

• Blood flow through any organ e.g. lungs
• Perfusion occurs through blood vessels
• Measured as flow of blood/unit time e.g. 650 mL/min

Question 3

What are the regional differences in lung ventilation?

Answer 3

• Apical alveoli are about 4 times larger than basal alveoli in upright posture
• This is due to the effect of the gravity
• Basal alveoli can expand more than apical alveoli
• Basal regions of lungs have better ventilation than apical regions

Question 4

What is the functional supply for the pulmonary circulation?

Answer 4

Main blood supply to the lungs- RV to pulmonary arteries to lungs to pulmonary veins to body organs to RV

Question 5

What is structural supply of pulmonary circulation?

Answer 5

Nutrition to the lung tissues.
Also called Bronchial circulation
Bronchial artery from thoracic aorta 
Bronchial vein to superior vena cava
Only a small amount of blood.

Question 6

What is the equation for CO?

Answer 6

CO= SV x HR

Question 7

What is SV?

Answer 7

SV is amount of blood that comes out every ventricle

Question 8

Which ventricle is thicker and why?

Answer 8

Left ventricle 3 times thicker as pushing against more force- aorta has muscle and elastic tissue. P higher in LV and aorta.

Question 9

What structures does oxygen travel through to become oxygenated?

Answer 9

Pulmonary artery carry deoxygenated blood from right ventricle; split into right and left branches to supply respective side lung.

Each branch then successively split into smaller branches closely following airway divisions. They are called extra-alveolar vessels while running through lung parenchyma.

Question 10

What happens to the CO2 exchange when alveoli are damaged?

Answer 10

Can carry out CO2 exchange because it is easier as there are fewer barriers. Since alveoli are very badly damaged, they can’t always carry out oxygen exchange.

Question 11

Where does blood go when it passes through capillaries?

Answer 11

Beyond terminal bronchioles, blood vessels form capillary beds (starting with smaller arterioles) where gas exchange starts. Blood flowing through rich network of capillaries forms a ‘sheet’ of blood with huge surface area. Very efficient system of gas exchange.
Oxygenated blood flows in to pulmonary venules which unite to form four large veins emptying in to left atrium.

Question 12

What is emphysema?

Answer 12

– Widespread destruction and dilatation of distal airway (chronic inflammation)
– Regional destruction of vascular beds
– Poor gas exchange and hypoxia
– Chronic inflammation destroys alveoli

Question 13

Which blood vessel carries deoxygenated blood from heart to lungs?

Answer 13

Pulmonary artery

Question 14

Where in the pulmonary circulation does gas exchange start?

Answer 14

Small arterioles

Question 15

Which factor is predominantly responsible for highly efficient gas exchange in the lungs?

Answer 15

Large surface area of exposure between blood and alveolar gases

Question 16

Regional differences in lung perfusion- where is hydrostatic pressure the highest- top or bottom?

Answer 16

Max hydrostatic pressure at bottom

Question 17

Hydrostatic pressure definiton

Answer 17

Force exerted by weight of a fluid (blood/ water) due to gravity

Question 18

What is pulmonary circulation?

Answer 18

A column of blood exerting different hydrostatic pressure in different areas of lungs in relation to the position of the right ventricle – as that is where the blood is coming out of

Higher hydrostatic at the bottom of the lung compared to the top of the lung.
P above ventricle will be less, lower than the ventricle will be more.

Question 19

What are the extra alveolar vessels?

Answer 19

– Running through lung parenchyma
– Their diameter is affected by the lung volume (via pull of the lung parenchyma)
– When breathing they get bigger and are pulled

Question 20

Do the alveolar vessels get squashed?

Answer 20

– Diameter dependent

– They get smaller as they squashed

Question 21

If P upstream is smaller then P out but is larger than P downstream will blood flow through?

Answer 21

No as the alveolar P is greater than the upstream pressure so the capillary will collapse.

Question 22

If P upstream is larger then P out and is larger than P downstream will blood flow through?

Answer 22

Yes as the upstream P is greater than the alveolar P so capillary will stay open.

Question 23

What does P upstream, out and downstream relate to?

Answer 23

P us is the pressure in the arterials.
P out is the pressure in the alveoli.
P ds is P in the venous.

Question 24

What happens to the movement of blood when a patient bleeds?

Answer 24

If patient bleeds they lose blood and drop BP- P out will be more than P us- drop BP upstream P will drop below alveolar P- that zone that was zone of recruitment will turn into a zone where air is still there but no blood passes through.

Question 25

What happens in zone 1 of the lungs?

Answer 25

Zone 1: Alveolar dead space
• Good ventilation but no perfusion
• No gas exchange
• Poor blood flow (lung apex 15 cm above right ventricle)
• Apices of the lungs, very small area in healthy people
• P alveolar >P arterial > P venous ( P out > P us > P ds)
• Blood flow determined by difference in Palveolar & Parterial

Question 26

What happens in zone 2 of the lungs?

Answer 26

Zone 2: Recruitment zone- more and more blood is going through it as more capillaries
• Lower down the lung than zone 1
• Higher Parterial due to higher hydrostatic pressure
• Recruitment of more alveolar unit especially in systole
• Parterial > Palveolar > Pvenous ( P us > P out > P ds)
• Blood flow determined by difference in Parterial & Palveolar

Question 27

What happens in zone 3 of the lungs?

Answer 27

Zone 3: Distension zone
• Lung bases
• Hydrostatic forces raise P arterial and P venous above P alveolar
• P arterial > P venous > P alveolar (P us > P ds> P out )
• Continuous blood flow
• Blood flow determined by difference in Parterial & Pvenous (because they are larger P- biggest difference= largest flow)

Question 28

What happens when a haemorrhage occurs?

Answer 28

Drop in Parterial- loss of blood BP drops- area of lung that was participating in gas exchange, no participating in gas exchange anymore- patient gets hypoxic-more alveoli in recruitment zone as in arterial P higher than alveolus P- dynamic will change- recruitment zone will change into dead space

Question 29

What happens during positive pressure ventilation?

Answer 29

Rise in P alveolar- when patient is asleep and mechanically ventilating- patient not able to make negative pressure- so air is forced through lungs through positive pressure- pressure in alveolus will be higher than normal. Some of the alveolus which were participating in gas exchange will not be because of pressure dynamic exchange.

Question 30

What is Ventilation(V)- perfusion(Q) mismatch?

Answer 30

• The ventilation-perfusion (V/Q) ratio is commonly used to describe this mismatch
• If the amount of ventilation (VA) to an area of lung is equal to the amount of perfusion (Q) the ratio of VA/Q would be 1 (ideal situation)
• VA/Q ratio varies from 3.3 at the apex of the lungs to 0.6 in the base
• Normal average V/Q ratio is 0.8

Question 31

What is anatomic dead space?

Answer 31

Conducting airways; no gas exchange

Question 32

What is alveolar dead space?

Answer 32

Unperfused or poorly perfused alveoli

Question 33

What is physiological dead space?

Answer 33

Part of each breath that does not take part in gas exchange

Question 34

What is the equation for physiological dead space?

Answer 34

Physiological dead space = Anatomic dead space + Alveolar dead space

Question 35

What is a pulmonary embolism?

Answer 35

– Medical emergency, potentially fatal
– Blood clot from deep veins of leg/pelvis or fat emboli
– Large/intermediate pulmonary arteries
– Severe hypoxia
– Lack of blood supply to that part of lung
– Enlarged alveolar dead space
– Areas where they is no blood but air is still there

Question 36

What is a shunt? Give examples

Answer 36

– Deoxygenated blood reaching left side of the heart either bypassing lungs or failing to get oxygenated in the lungs
– Examples
• bronchial veins
• pneumothorax
• Age related changes: areas low V/Q ratio in the lungs
– Minimal effect of oxygen supplementation on a very large shunt
– Blood going to R to L side of heart picking up no oxygen

Question 37

What is a pneumothorax?

Answer 37

A collapsed lung. Occurs when air leaks into the space between your lung and chest wall. This air pushes on the outside of your lung and makes it collapse. Lung collapses- no air in lung but same amount of blood is passing through

Question 38

What is treatment for a pneumothorax?

Answer 38

• immediate needle decompression

* Chest drain connected to an underwater sealed system

Question 39

What is the V/Q for dead space?

Answer 39

Dead space has good ventilation, no perfusion so V/Q ratio is infinite.

Question 40

What is the V/Q for a shunt?

Answer 40

No ventilation, good perfusion. V/Q is 0.

Question 41

What is alveolar dead space?

Answer 41

No perfusion, good ventilation.

Question 42

What is the value of V/Q ratio in shunt?

Answer 42

Ventilation/perfusion ratio (V/Q)= 0- no ventilation

Question 43

Which abnormality of oxygenation are you most likely to see in pneumonia?

Answer 43

Shunt- air being replaced but blood is still flowing through