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BS - Respiratory System > Mechanics of Breathing 2 > Flashcards

Mechanics of Breathing 2 Flashcards

1
Q

What is functional residual capacity (FRC) and what is it dependent on?

A

It is the volume of air present in the lungs after passive expiration

It is dependent on the compliance of the lungs and chest wall

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2
Q

What happens at FRC?

A

The opposing elastic recoil forces of the lungs and chest wall are in equilibrium

There is no exertion by the diaphragm or other respiratory muscles

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3
Q

What is compliance?

A

The change in lung volume per unit change in intrathoracic pressure

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4
Q

What does compliance measure?

A

It is a measurement of the ability of the lungs and chest wall to stretch and expand

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5
Q

What are the 2 types of compliance?

A

static compliance and dynamic compliance

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6
Q

What is the equation for compliance?

A

C = change in volume/change in pressure

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7
Q

What is static compliance?

A

The change in volume for any given applied pressure when there is no air flow

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8
Q

What is static compliance a function of?

A

A function of elastic recoil of the lung and surface tension of the alveoli

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9
Q

What is dynamic compliance?

A

The compliance of the lung at any given time during the actual movement of air

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10
Q

Why is dynamic compliance always less than static compliance?

A

Dynamic compliance includes the pressure required to generate flow by overcoming resistance forces

There is always a degree of airway resistance

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11
Q

What is an oesophageal balloon used to measure?

A

Intrathoracic pressure

This is the pressure that is present between the 2 layers of pleura

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12
Q

What is the assumption made when measuring intrathoracic pressure?

A

It is measured indirectly by assuming that the pressure in the thorax and the pressure in the chest wall are equal, at the end of either inspiration or expiration

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13
Q

Why are the lungs both compliant and elastic?

A

They are elastic to recoil and push air out during expiration

They are compliant to fill with air during inspiration

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14
Q

At the start and end of expiration, what is alveolar pressure?

A

At the start and end of expiration, alveolar pressure is in equilibrium with atmospheric pressure

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15
Q

What is recoil pressure of the lung?

A

The pressure that drives the lung to collapse

The lung has a natural tendency to collapse on itself

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16
Q

How is recoil pressure determined?

A

Determined by the different between alveolar pressure and intrapleural pressure

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17
Q

At maximal expiration, what is alveolar pressure and why?

A

Breathing all the way out keeps the glottis open so alveolar pressure is zero

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18
Q

What is maximal intrapleural pressure and recoil pressure after maximal expiration?

A

Maximum intrapleural pressure is -3 cm of water

Recoil pressure is +3 cm of water

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19
Q

What is the equation for recoil pressure?

A

Alveolar pressure - intrapleural pressure

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20
Q

At maximal expiration, what lung volume is present?

A

+3 cm of water is at the residual volume

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21
Q

After expiration and during normal tidal breathing, what lung volume is present?

A

Functional residual capacity is the volume of air left in the lungs

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22
Q

After expiration and during normal tidal breathing, what is intrapleural pressure?

A

around -5 cm of water

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23
Q

After expiration and during normal tidal breathing, what is recoil pressure?

A

alveolar pressure is still 0 as the glottis is open so

0 - - 5 = +5

recoil pressure is +5 cm of water

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24
Q

At peak inspiration, what is the intrapleural pressure?

A

A very negative pressure is generated in the chest during maximal inspiration

intrapleural pressure is -30 cm of water

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25
Q

What is recoil pressure at peak inspiration and what lung volume is this equivalent to?

A

+30 cm of water

total lung capacity

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26
Q

Which 3 points are needed to draw a lung compliance curve?

A
  1. residual volume
  2. functional residual capacity
  3. total lung capacity
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27
Q

When is compliance low and high and what does this mean?

A

It is low when the lung is expanded - a lot of effort is required to expand the alveoli more

It is high after expiration meaning less effort is needed to expand the alveoli

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28
Q

Which pressures determine chest wall compliance?

A

Intrapleural pressure and barometric pressure

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29
Q

How is recoil pressure of the chest wall calculated?

A

intrapleural pressure - barometric pressure

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30
Q

What is the value of atmospheric pressure?

A

It is zero unless the altitude is altered

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31
Q

How do you remove the effect of the lung when measuring chest wall compliance?

A

Breathe all the way out, close the glottis and relax the muscles

Closing the glottis prevents air from entering the lungs

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32
Q

After maximal expiration, what is the recoil pressure of the lungs?

A

minimum recoil pressure is generated after maximal expiration

this is -30 cm of water and is residual volume

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33
Q

Once the glottis is open, what is the recoil pressure (&intrapleural pressure) of the chest wall?

A

-5 cm of water

this is the functional residual capacity

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34
Q

During maximal inspiration, how is total lung capacity reached?

A

The glottis is closed and the muscles are relaxed

The volume of air in the lung is retained by closing the g,lottis

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35
Q

What is recoil pressure of the chest wall at maximal inspiration?

A

The highest possible intrapleural pressure of +3 cm of water is reached

Chest wall compliance is +3 cm of water

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36
Q

What does the overall effect of compliance take into account?

A

Both chest wall and lung compliance

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37
Q

What is the overall effect of compliance at maximal expiration?

A

the lungs are compliant

the resistance to compliance caused by the chest wall overrides the stretchiness of the lungs

38
Q

What is significant about functional residual capacity on the compliance curve?

A

It is a relaxation and equilibrium point

The chest wall and lung recoil pressures are equal but opposite

39
Q

Where does FRC appear on the compliance curve?

A

where the curve crosses the zero pressure point on the y axis

40
Q

What is the problem with having a lower FRC?

A

Normal tidal breathing becomes closer to residual volume

There is less expiratory reserve volume so if there is a need to increase ventilation, the capacity to increase the volume of ventilation is diminished

41
Q

During tidal breathing, why is there a difference between compliance during inspiration and expiration?

A

It is not caused by a difference in compliance as the lung elasticity is the same

It is caused by changes in the calibre of the airways

42
Q

Why does hysteresis occur?

A

the elastic nature of the tissues and airway resistance

43
Q

What is hysteresis?

A

any process where the future state of a system is dependent on its current and previous state

it means that the compliance of the lung is different in inspiration and expiration

44
Q

What is the difference in lung volumes during inspiration and expiration?

A

Lung volume at any given pressure during inspiration is less than the lung volume at the same pressure during expiration

45
Q

Why does hysteresis occur in dynamic compliance curves?

A

It occurs due to airway resistance, which is a function of flow rate

46
Q

In a dynamic compliance curve, when is flow rate maximal?

A

flow rate (and resistance) is maximal at the beginning of inspiration and the end of expiration

47
Q

Why does hysteresis occur in a static compliance curve?

A

There is no resistive component

Hysteresis occurs due to viscous resistance of surfactant and the lungs

48
Q

how is a heavy smoker defined?

A

someone who smokes at least 1 cigarette each day

49
Q

What happens in pulmonary fibrosis?

A

elastic tissue becomes replaced with fibrous scar tissue

this causes lung tissue to become thickened and stiff

50
Q

Where does scarring normally occur in pulmonary fibrosis?

A

A network of tissue called the interstitium, which surrounds the alveoli

51
Q

What is the effect of scar tissue developing in pulmonary fibrosis?

A

Scar tissue is not elastic

Lungs lose their ability to transfer oxygen into the bloodstream as they cannot take in as much oxygen from the air during inspiration

52
Q

what are the main symptoms of pulmonary fibrosis?

A

Breathing requires more effort so patients are breathless just from walking

a persistent cough

feeling tired all the time

53
Q

what are the main causes of pulmonary fibrosis?

A
  1. being exposed to certain types of dust including wood, metal dust or asbestos
  2. being exposed to allergens
  3. side effect of a drug
  4. for most cases, a specific cause cannot be found
54
Q

What is kyphoscoliosis?

What is it caused by?

A

caused by a decrease in chest wall compliance

restrictive lung disease that causes extrapulmonary restriction of the lungs

55
Q

What do the terms “kyphosis” and “scoliosis” describe?

A

Kyphosis - anterior-posterior curvature of the spine

Scoliosis - lateral displacement of the spine

56
Q

What is the effects of kyphoscoliosis?

A

restriction of the lungs leads to an impairment of pulmonary functions and respiratory failure

the ribs cannot articulate properly with the spinal column

57
Q

What is the main cause of kyphoscoliosis?

A

80% of cases are idiopathic - the cause is unknown

58
Q

What is a circumferential burn?

A

a burn that goes all the way around the body

59
Q

what happens to the tissue after a circumferential burn?

A

the tissue becomes burnt and forms scar tissue

this is not elastic and restricts the expansion of the chest

60
Q

What is the effect of a circumferential burn?

A

reduced chest wall compliance which hinders ventilation

61
Q

How is scar tissue removed in a circumferential burn?

A

a surgical method called an escharotomy

62
Q

what occurs in emphysema?

A

the alveolar membranes are destroyed causing the alveoli to fuse together

this means there is less lung tissue

63
Q

How does emphysema affect gas exchange?

A

surface area of the alveoli are reduced so the volume of oxygen diffusing into the blood is also reduced

64
Q

how does emphysema affect compliance of the lung?

A

elasticity and compliance are increased

65
Q

Why is compliance in different parts of the lung not the same?

A

due to the effect of gravity

66
Q

Why is compliance greatest at the base of the lung?

A

the same pressure is applied to every part of the lung as intrapleural pressure is the same

the bottom of the lung has a greater increase in volume as ventilation is greater at the bottom

67
Q

What is closing capacity of the lung?

A

It is the point during expiration when small airways begin to close

it increases with age and decreased pulmonary blood flow

68
Q

What affect does age have on the alveoli?

A

as you get older, some of the alveoli become closed during expiration

closed alveoli have low compliance

69
Q

What happens if closing capacity exceeds FRC?

A

Alveoli in dependent parts of the lung are poorly ventilated

They will be closed or collapsed during normal tidal breathing

70
Q

What is the problem with increased closing capacity?

A

It decreases the compliance of the lung

71
Q

What would happen to the alveoli if there was no surfactant and why?

A

The alveoli are interconnected by bronchioles so all of the air would empty into the larger alveolus

All the alveoli are different sizes

72
Q

What is the Law of Laplace?

A

P = 2t/r

P = pressure
t = surface tension
r = radius of alveolus
73
Q

What does the Law of Laplace state?

A

The pressure needed to be applied to a sphere to prevent it from collapsing is inversely proportional to the radius

74
Q

What is the role of surface tension?

A

Surface tension opposes pressure and acts inwards to create a collapsing force

A greater surface tension leads to a greater collapsing motion

75
Q

What is the role of surfactant?

A

There is a tendency for smaller alveoli to collapse and empty into larger alveoli

This motion is overcome by altering the surface tension within the alveolus by producing surfactant

76
Q

What cells produce surfactant?

A

specialised alveolar epithelial cells called type II cells

77
Q

What is surfactant made from?

A

It comprises 90% phospholipid and 10% protein

78
Q

Which disease shows a deficiency in surfactant?

What happens?

A

infant respiratory distress syndrome

collapsing pressure is not equalised so the smaller airways collapse

79
Q

What are the 3 roles of surfactant?

A
  1. increases pulmonary compliance
  2. prevents atelectasis
  3. aids alveolar recruitment and minimises alveolar fluid
80
Q

What happens in atelectasis?

A

there is collapse or closure of a lung resulting in reduced or absent gas exchange

the alveoli are deflated down to no or little volume

81
Q

How does surfactant prevent alveolar collapse in alveoli of different sizes?

A

each alveolus produces the same amount of surfactant

the surfactant becomes more dispersed as alveolar volume increases

it equalises pressure between alveoli of different sizes

82
Q

In which size alveoli does surfactant have the greatest effect on reducing surface tension?

A

smaller alveoli

in larger alveoli, the surfactant is more dispersed around the inner wall

83
Q

How is the potential energy of the lungs generated?

A

the energy used to overcome elastic forces in inspiration is stored as potential energy

potential energy is dissipated in expiration

84
Q

How is work expended during breathing?

A

Work is expended in the form of heat to overcome resistance forces of air passing through the airways

85
Q

How is the work of breathing calculated?

A

work = volume x pressure

86
Q

What is airway resistance?

A

The opposition to the flow os air caused by forces of friction

87
Q

What is the resistance to flow like in laminar flow?

A

resistance is quite low

only a small driving pressure is required to produce a certain flow rate

88
Q

What is the resistance to flow like in turbulent flow?

A

resistance is much larger

a much larger driving pressure is required to produce the same flow rate

89
Q

What factors increase resistance to air flow?

A

reducing the radius of the airway

when the airways begin to branch

90
Q

What % of energy expenditure is taken up by breathing in a healthy person?

A

2 - 5 %

91
Q

At maximal hyperventilation, what % of energy expenditure is taken up by breathing?

A

30%

92
Q

how is the work of breathing minimised in restrictive and obstructive lung conditions?

A

restrictive - taking rapid shallow breaths

obstructive - taking large volume, slow breaths

BS - Respiratory System (20 decks)

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