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BS - Respiratory System > Lung Ventilation & Perfusion > Flashcards

Lung Ventilation & Perfusion Flashcards

1
Q

What is ventilation?

A

The movement of gases into and out of the lungs

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2
Q

Where does ventilation occur and how is it measured?

A

Ventilation of the lungs occurs through the airways

It is measured as a change in volume per unit time

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3
Q

What is perfusion?

A

The blood flow through any organ, such as the lungs

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4
Q

Where does perfusion occur and how is it measured?

A

It occurs through blood vessels

It is measured as the flow of blood per unit time

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5
Q

Why do the basal regions of the lungs have better ventilation than apical regions?

A

Before inspiration, there is already a large quantity of air in the apical alveoli

During inspiration, basal alveoli can expand more and take in more air than apical alveoli

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6
Q

How much bigger are apical alveoli than basal alveoli?

A

Apical alveoli are around 4 times larger than basal alveoli in the upright position

This is due to the effect of gravity

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7
Q

What are the 2 types of circulation in the lungs?

A

Functional supply and structural supply

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8
Q

What is functional supply involved in?

A

Oxygenation of venous blood

It is the main blood supply to the lungs

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9
Q

What is the role of pulmonary arteries and pulmonary veins?

A

Pulmonary arteries take deoxygenated blood from the right ventricle to the lungs

Pulmonary veins carry oxygenated blood back to the heart through the left atrium and ventricle

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10
Q

What is the role of structural supply?

A

Supplies nutrition to the lung tissue

Also known as bronchial circulation and accounts for only 2% of cardiac output

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11
Q

What blood vessels are involved in structural supply?

A

The bronchial artery comes from the thoracic aorta

The bronchial vein comes from the superior vena cava

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12
Q

How much blood do the lungs receive?

A

The full cardiac output of 3-5 L/min

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13
Q

How does pulmonary circulation differ to systemic circulation?

A

The blood is at a much lower pressure

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14
Q

Why is blood pumped by the left ventricle into systemic circulation at a much higher force?

A

Left ventricle has a much higher muscle mass and is around 3x thicker than the right ventricle

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15
Q

How much lower is pressure in the pulmonary blood vessels than systemic circulation and why?

A

pressure in the pulmonary vessels is 5-6 x lower than systemic vessels

systemic vessels have more elastic tissue and smooth muscle which provides more resistance to the flow of blood

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16
Q

Where are extra-alveolar vessels found?

A

they run through the lung parenchyma

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17
Q

How does the pulmonary artery split as it enters the lungs?

A

The pulmonary artery splits into the right and left branches as it enters the hilum

As it leaves the hilum it successively splits into smaller branches - extra-alveolar vessels

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18
Q

Where are alveolar vessels found and what is their role?

A

They are the capillaries which surround the alveolus

This creates a large surface area for efficient gas exchange at a fast rate

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19
Q

How long does the whole process of gas exchange take?

A

3/4 of a second

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20
Q

How many alveoli are in the lungs and how many capillaries supply each alveolus?

A

300 million alveoli in the lungs and 1,000 capillaries per alveolus

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21
Q

What generations of airway divisions make up the conducting and respiratory portions?

A

The first 16 generations of airway divisions make up the conducting portion

The last 7 generations of airway divisions make up the respiratory portion

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22
Q

In which blood vessels does gas exchange start?

A

Small arterioles

The blood vessels begin to form capillary beds beyond the terminal bronchioles which start with smaller arterioles

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23
Q

What is the combined surface area of the capillary network forming a ‘sheet’ of blood?

A

50 - 150 metres squared

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24
Q

What does emphysema result in?

A

widespread destruction and dilatation of the distal airway

due to the loss of elastic recoil and destruction of the lung parenchyma

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25
Q

what are the symptoms of emphysema?

A

poor gas exchange and hypoxia

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26
Q

What is hypoxia?

A

Hypoxia is a condition in which a region of the body is deprived of adequate oxygen supply at the tissue level

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27
Q

What is hydrostatic pressure and where is it greatest?

A

the force exerted by the weight of a fluid due to gravity

it is greater at the bottom

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28
Q

How can pulmonary circulation be considered in terms of hydrostatic pressure?

A

A column of blood exerting different hydrostatic pressures in different areas of the lungs

This occurs in relation to the position of the right ventricle

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29
Q

What is the diameter of the extra-alveolar vessels dependent on?

A

Diameter is affected by lung volume

This is due to the pull of the lung parenchyma

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30
Q

What is the diameter of the alveolar vessels dependent on?

A

it is dependent on many factors

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31
Q

What is Starling’s resistor comprised of?

A

upstream and downstream pipes connected by a soft, flexible pipe that is responsive to pressure changes

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32
Q

How is flow through the collapsible segment in Starling’s resistor determined?

A

It is determined by the difference of two out of the three largest pressures

Pus, Pds, Pout

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33
Q

What is upstream pressure equivalent to?

A

arterial pressure

hydrostatic pressure of the blood at the arterial end of the capillary

34
Q

What is the downstream pressure equivalent to?

A

venous pressure

the hydrostatic pressure of the blood at the venous end of the capillary

35
Q

What is P(out) equivalent to?

A

alveolar pressure

this is the gaseous pressure inside the alveoli

36
Q

What is zone 1 of the lungs?

A

alveolar dead space

37
Q

what is the perfusion and ventilation like in zone 1 of the lungs?

A

There is no perfusion under any circumstances

There is good ventilation

38
Q

What is gas exchange like in zone 1?

A

No gas exchange occurs due to poor blood flow

39
Q

Where is the alveolar dead space found in the lung?

A

It is very small and comprises the apices of the lungs in healthy people

The apex of the lung is 15cm above the right ventricle

40
Q

How is blood flow determined in zone 1 of the lungs and why is there no blood flow?

A

Blood flow is determined by the difference in alveolar and arterial pressure

There is no blood flow as P(alveolar)>P(arterial)>P(venous)

41
Q

What is zone 2 of the lungs and why?

A

Recruitment zone

More blood vessels are being recruited and there is recruitment of more alveolar units

42
Q

What is perfusion like in zone 2?

A

Perfusion is sporadic

43
Q

Why is arterial pressure greater in zone 2 than 1?

A

This is due to the increase in hydrostatic pressure which increases as you move towards the basal surface of the lung

44
Q

How is blood flow determined in zone 2 and why does more blood flow through zone 2 than 1?

A

determined by the difference in arterial and alveolar pressures

more blood flows through the system as P(arterial)>P(alveolar)>P(venous)

45
Q

What is zone 3 of the lungs?

A

Distension zone which is below the level of the right ventricle

46
Q

How does pressure change in zone 3 of the lungs?

A

As it is below the level of the right ventricle, hydrostatic forces raise alveolar and venous pressure above alveolar

47
Q

What is the state of the alveoli in zone 3?

A

They are collapsed and do not contain much air

48
Q

How is blood flow through zone 3 determined?

A

P(arterial)>P(venous)>P(alveolar) so blood flow is determined by the difference in arterial and venous pressures

49
Q

What is blood flow like in zone 3 of the lungs?

A

Blood flow is continuous through this zone

Efficient gas exchange occurs as the alveoli fill with oxygen during inspiration

50
Q

In which lung diseases is there a pathological expansion of zone 1?

How does it affect blood flow?

A

emphysema, pneumonia and acute respiratory distress syndrome

it interferes with blood flow in zone 2

51
Q

What is the definition of dead space?

A

the volume of air that is inhaled and does not partake in gas exchange

52
Q

Where does the air that does not partake in gas exchange reside?

A

it either remains in the conducting airways or it reaches alveoli that are not/poorly perfused

53
Q

How does haemorrhage affect hydrostatic pressures?

A

Loss of blood results in a large decrease in blood pressure

This is characterised by a drop in arterial pressure

54
Q

Why does gas exchange not occur efficiently in haemorrhage?

A

the alveoli are open but the arterioles are shut

there is lots of air but no blood to perform the gas exchange

55
Q

What happens to patients who suffer from haemorrhage?

A

They become hypoxic as the blood is not being sufficiently oxygenated

56
Q

How is positive pressure ventilation characterised?

A

A rise in alveolar pressure

57
Q

What is positive pressure ventilation?

A

If the patient is not breathing there is no negative pressure in the chest

A ventilation unit may be used to force air into the lungs by positive pressure

58
Q

What is used to describe the ventilation perfusion mismatch?

A

the ventilation-perfusion ratio (V/Q)

59
Q

Under what circumstances would the V/Q ratio be equal to 1?

A

If the amount of ventilation (V) to an area of the lung is equal to the amount of perfusion (Q)

60
Q

How does V/Q ratio vary in different parts of the lung?

A

V/Q ratio varies from 3.3 at the apex of the lung to 0.6 at the base of the lung

61
Q

What is the normal average V/Q ratio?

A

0.8

62
Q

What is the V/Q ratio value in the dead space of the lung?

A

V/Q is infinite

perfusion is zero and anything divided by zero is equal to infinity

63
Q

How is ventilation and perfusion in the dead space of the lungs?

A

There is good ventilation as the alveoli are open

there is no/very poor perfusion

64
Q

what is anatomic dead space?

what is the average volume?

A

the amount of air that remains in the conducting airways

150 ml

65
Q

Why does the air in the anatomic dead space remain deoxygenated?

A

The anatomic dead space fills with inspired air at the end of each inspiration but this air is exhaled unchanged

66
Q

What is alveolar dead space?

A

the amount of air contained in unperfused or poorly perfused alveoli

67
Q

What is physiological dead space?

A

the volume of air in each breath that does not participate in gas exchange

anatomical + alveolar = physiological

68
Q

What is a pulmonary embolism?

A

A blood clot from a deep vein of the leg/pelvis or a fat emboli

69
Q

What does the pulmonary embolism do?

A

It travels to the lungs and blocks the large or intermediate pulmonary arteries

70
Q

What are the symptoms of pulmonary embolism?

A

Severe hypoxia due to a lack of blood supply in one region of the lung

71
Q

How does a pulmonary embolism affect alveolar dead space?

A

It enlarges alveolar dead space as a particular region of the the lung becomes poorly perfused

72
Q

What is a shunt?

A

Blood is shunted from the right to the left side of the heart without any oxygenation

It bypasses the lungs or fails to get oxygenated

73
Q

Where does a shunt occur in the lungs and why?

A

Base of the lung due to the alveoli being collapsed

74
Q

How is perfusion and ventilation at the shunt?

A

Good perfusion but there is no ventilation

No air available for gas exchange

75
Q

What is the V/Q value at a shunt?

A

V/Q is 0 or very low

76
Q

What are the 3 main reasons for a shunt?

A

Pneumothorax, bronchial veins and age-related changes

With increased age, areas of the lung change to have a low V/Q ration

77
Q

How can pneumonia lead to formation of a shunt?

A

Inflammatory fluid can fill up an area of the lungs and lead to consolidation

All the alveoli in a certain area are filled with fluid

There is sufficient blood flow but insufficient ventilation for gas exchange

78
Q

How is a pneumothorax brought about?

A

Usually, inspiration creates a negative pressure

Pressure inside the chest wall becomes equal to atmospheric pressure

The lung cannot withstand this so collapses

79
Q

Why is a pneumothorax an example of a shunt?

A

The lung still has a good blood supply but it contains no air

Gas exchange cannot occur

80
Q

What is the V/Q value in other alveolar units and why?

A

There is good ventilation and perfusion

V/Q is closer to 1 and there is efficient gas exchange

BS - Respiratory System (20 decks)

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