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ESA 3 - Respiratory System > The Mechanics of Breathing and Lung Function Testing > Flashcards

The Mechanics of Breathing and Lung Function Testing Flashcards

1
Q

How is air drawn into the lungs?

A

By expanding the volume of the thoracic cavity

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2
Q

What is work done during breathing doing?

A

Moving the structures of the lungs and thorax to overcome the resistance to flow of air through the airways

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3
Q

What is the pleural space?

A

The space bewteen the lungs and thoracic wall

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4
Q

What is the pleural space normally filled with?

A

A few millimetres of fluid

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5
Q

What is the purpose of the fluid in the pleural space?

A

The surface tension of which forms a pleural seal holding the outer surface of the lungs to the inner surface of the thoracic wall

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6
Q

What is the result of the pleural fluid holding the lungs to the thoracic wall?

A

The volume of the lungs changes with the volume of the thoracic cage

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7
Q

What happens if the integrity of the pleural seal is broken?

A

The lungs will tend to collapse

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8
Q

What happens in a pneumothorax?

A

Air gets in between the two layers of the pleura, fluid surface tension is lost and the lungs collapse

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9
Q

What is meant by lung compliance?

A

The ‘stretchiness’ of the lungs

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10
Q

What is lung compliance defined as?

A

The volume change per unit pressure change

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11
Q

What does high compliance mean?

A

Lungs are easy to stretch

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12
Q

How is compliance measured?

A

By measuring the change in lung volume for a given pressure

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13
Q

What does a greater lung volume mean for compliance?

A

Greater compliance

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14
Q

What is it more usual to calculate than compliance?

A

Specific compliance

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15
Q

Why is it more usual to measure specific compliance?

A

Becasue, even with the constant elasticity of lung structures, compliance will also depend on the starting volume from which it is measured

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16
Q

How is specific compliance calculated?

A

Volume change per unit pressure change / Starting volume of lungs

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17
Q

Draw a diagram illustrating the compliance for;

  • Elastic lungs
  • Normal lungs
  • Stiff lungs
A
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18
Q

What do the elastic properties of the lungs arise from?

A
  • Elastic tissue in the lungs
  • Surface tension forces of the fluid lining the alveoli
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19
Q

What is meant by surface tension?

A

The interactions between molecules at the surface of a liquid

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20
Q

What is the effect of surface tension on stretchiness?

A

It makes the surface resistant to stretching

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21
Q

What does a higher surface tension mean for compliance?

A

The higher the surface tension, the harder the lungs are to stretch and therefore the lower the compliance

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22
Q

What happens to the surface tension of the lungs at low lung volumes?

A

It is much lower than expected

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23
Q

Why is the surface tension of the lungs much lower than expected at low lung volumes?

A

Due to the disruption of interactions between surface molecules by surfactant

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24
Q

What produces surfactant in the lungs?

A

Type 2 alveolar cells

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25
Q

What is surfactant?

A

A complex mixture of phospholipid and proteins, with detergent properties

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26
Q

Where does the hydrophilic end of surfactant molecules lie?

A

In the alveolar fluid

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27
Q

Where does the hydrophobic end of surfactant molecules lie?

A

Projects into alveolar gas

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28
Q

What is the result of the position of the hydrophilic and hydrophobic ends of the surfactant molecule?

A

They float on the surface of the lining fluid, disrupting interaction between surface molecules

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29
Q

When does surfactant reduce surface tension?

A

When the lungs are deflated, but not when fully inflated

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30
Q

What is the result of surfactant only reducing surface tension when the lungs are deflated?

A

Little breaths are easy, and big breaths are hard, and it takes less force to expand small alveoli than it does large ones

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31
Q

What do the alveoli form?

A

An interconnecting set of bubbles

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32
Q

What is Laplace’s law?

A

Pressure is inversely related to the radius of a bubble

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33
Q

What would happen if Laplace’s law was applied to alveoli?

A

Large alveoli would ‘eat’ small ones

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34
Q

What happens as alveoli get bigger?

With respect to surface tension

A

The surface tension in their walls increases

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35
Q

Why does the surface tension in the walls of alveoli increase as they get bigger?

A

Because surfactant is less effective

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36
Q

What is the result of surface tension in the walls of large alveoli being higher?

A

Pressure stays high and stops them from ‘eating’ smaller alveoli

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37
Q

How must energy be expended in the lungs, in addition to work done against the elastic nature of the lungs?

A

To force air through the airways

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38
Q

What is true of the flow in most of the airways of the lungs?

A

It is laminar

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39
Q

What determines the resistance of an airway to flow, when flow is laminar?

A

Poiseulle’s Law

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40
Q

What is Poiseulle’s Law?

A

The resistance of a tube sharply increases with a falling radius

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41
Q

What is true of the combined resistance of small airways?

A

It is normally low

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42
Q

Why is the combined resistance of small airways normally low?

A

Because they are connected in parallel over a branching structure, where the total resistance to flow in the downstream branches is less than the resistance of the upstream branch

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43
Q

Where does most of the resistance to breathing reside?

A

In the upper respiratory tract

44
Q

What is work done against in the lungs?

A
  • The elastic recoil of the lungs and thorax
  • Resistance to flow through airways
45
Q

What produces the elastic recoil of the lungs and thorax?

A
  • Elastic properties of the lungs
  • Surface tension forces in the alveoli
46
Q

When is resistance to flow through airways important to consider?

A

In disease, as it is often affected

Of little significance in health

47
Q

What % of oxygen consumption does the work of breathing consume at rest?

A

0.1% - is very efficient

48
Q

What do the bronchioles do during inspiration?

A

Use their smooth muscle to increase their radius

49
Q

What is the purpose of bronchioles increasing their radius during inspiration?

A

It decreases their resistance (due to Poiseulle’s Law), allowing air to be drawn easily through them into alveoli

50
Q

What happens in spirometry?

A

The patient fills their lungs from the atmosphre, and breathes out as far and fast as possible through a Spirometer

51
Q

What does simple spirometry allow for?

A

Measurement of many lung volumes and capacities

52
Q

What measurement taken from spirometry is particularly significant?

A

Vital capacity

53
Q

What can be used to predict the vital capacity of an individual of known age, sex, and height?

A

Tables

54
Q

Why may vital capacity be less than normal?

A

Because the lungs are not;

  • Filled normally in inspiration
  • Emptied normally in expiration
  • Both
55
Q

What is meant by forced vital capacity?

A

The maximum volume that can be expired from full lungs

56
Q

What is meant by forced expiratory volume in one second (FEV1)?

A

The volume expired in the first second of expiration from full lungs

57
Q

What is FEV1 affected by?

A

How quickly air flow slows down

58
Q

When is FEV1 low?

A

If the airways are narrowed

59
Q

When may the airways be narrowed?

A

Obstructive deficit

60
Q

Draw a diagram illustrating FVC and FEV1

A
61
Q

How can restrictive and obstructive deficits be separated?

A

By asking patients to breathe out rapidly from maximal inspiration through a single breath spirometer, which plots volume expired against time

62
Q

What is maximal filling of the lungs determined by?

A

The balance between the maximum inspiratory effort and the force of recoil of the lungs

63
Q

When is a restrictive deficit produced?

A

If the lungs are unusually stiff, or inspiratory effort is compromised by muscle weakness, injury, or deformity

64
Q

What is the effect of a restrictive deficit on FVC?

A

It reduces it

65
Q

What will be true of FEV1 in a patient with a restrictive deficit?

A

FEV1 > 70% FVC

66
Q

Draw a graph illustrating the difference between normal lungs, and lungs with a restrictive deficit

A
67
Q

What happens to small airways during expiration, particularly when forced?

A

They are compressed

68
Q

What is the result of the compression of small airways during expiration?

A

It increases flow resistance, eventually to the point where no more air can be driven out of the alveoli

69
Q

What happens if the airways are narrowed?

A

Expiratory flow is compromised much earlier in expiration

70
Q

What is produced when the airways are narrowed?

A

An obstructive deficit

71
Q

What is the effect of an obstructive deficit on FEV1?

A

It is reduced

72
Q

What is the effect of an obstructive deficit on FVC?

A

It is relatively normal

73
Q

Draw a graph illustrating the difference between normal lungs, and lungs with a obstructive deficit

A
74
Q

What a flow volume curves?

A

A graph of volume expired against flow rate

75
Q

What are flow volume curves derived from?

A

A vitalograph trace

76
Q

What is happening at points A-D on this flow volume curve?

A
  • A - When the lungs are full, the airways are stretched so resistance is at minimum, so flow is therefore at peak expiratory flow rate (PEFR)
  • B-D - As the lungs are compressed, more air is expired and the airways begin to narrow, so resistance increases and flow rate decreases
77
Q

In normal individuals, what is peak flow most affected by?

A

The resistance of large airways

78
Q

In disease processes, what can peak flow be affected by?

A

Severe obstruction of the smaller airways

79
Q

Give an example of a disease where there may be severe obstruction of the small airways

A

Asthma

80
Q

What does mild obstruction of the airways produce?

A

A ‘scooped out’ expiratory curve

81
Q

What affect will a severe obstruction have on PEFR?

A

It will reduce it

82
Q

Draw a graph of flow against volume for inspiration and expiration that would be seen in;

  • A normal person
  • Early small airways obstruction
  • Chronic obstructive disease
  • Fixed large airway obstruction
  • Variable extrathoracic large airway obstruction
  • Restrictive disease
A
83
Q

What is the Helium Dilution Test used to measure?

A

Functional Residual Capacity (FRC)

84
Q

What is FRC used to calculate?

A

Residual volume

85
Q

What is the advantage of using helium in tests?

A
  • It is an inert, colourless, odourless, tasteless gas that is not toxic
  • It cannot transfer across the alveolar-capillary membrane, and therefore is not contained within the lungs
86
Q

How is a helium dilution test carried out?

A
  • At the normal tidal expiration, the patient is connected to a circuit, which is connected to a container containing a gas mixture with a known helium concentration (C1) and volume (V1)
  • The patient continues to rebreathe into the contained until equilibrium occurs
87
Q

What is lung volume equal to at the end of tidal expansion?

A

Functional residual capacity

88
Q

What is FRC equal to?

A

ERV+RV

89
Q

How long does it usually take for equilibrium to occur in a helium dilution test?

A

4-7 minutes

90
Q

What is the new concentration of helium at equilibrium termed in a helium dilution test?

A

C2

91
Q

How is FRC calculated from a helium dilution test?

A
  • C1 x V1 = C2 x V2
  • V2 = V1 + FRC
  • Since C1, V1, and C2 are known, FRC can be calculated
92
Q

What is residual volume equal too?

A

FRC - ERV

93
Q

How can ERV be measured?

A

Spirometry

94
Q

What does the Carbon Monoxide Transfer Factor measure?

A

The rate of transfer of CO from the alveoli to teh blood in ml per minute per kPa (ml/min/kPa)

95
Q

What is the purpose of the CO transfer factor?

A

It is a way of measuring the diffusion capacity of the lung

96
Q

Why is the CO transfer factor a way of measuring the diffusion capacity of the lung?

A

Because the amount transferred will depend on how well gas diffusion takes place

97
Q

Why is inhaled CO used in a transfer factor test?

A

Because of its very high affinity for Hb

98
Q

In a CO transfer factor test, what can we assume the ppCO is?

A

0

99
Q

Why can we assume the ppCO is 0 in a CO transfer factor test?

A

Because almost all of the CO entering the blood binds to Hb, very little remains in the plasma

100
Q

What is the result of the ppCO being 0 in a CO tranfer factor test?

A

The concentration gradient between alveolar CO and capillary ppCO is maintained

101
Q

What is the result of the maintainence of the concentration gradient between alveolar ppCO and capillary ppCO?

A

The amount of CO transferred from the alveolli to the blood is limited only by the diffusion capacity of the lung

102
Q

How is a CO transfer factor test carried out?

A
  • The patient performs a full expiration, followed by a rapid maximum inspiration of a gas mixture composed or air, a tiny fraction of CO and a fraction of inert gas such as helium
  • The breath is held for 10 seconds
  • The patient exhales, and gas is collected mid-expiration, to gain an alveolar sample
  • Concentration of CO and inert gas is measured
  • From these measurements, the CO Transfer Factor is measured
103
Q

Why is only a tiny fraction of CO used in a transfer factor test?

A

Because it is toxic

104
Q

Why is a fraction of inert gas used in a CO transfer factor test?

A

To make an estimate of total lung volume

105
Q

What does a nitrogen wsahout test measure?

A

Serial (anatomical) dead space

106
Q

How is a nitrogen washout test carried out?

A
  • The patient takes a maximum inspiration of 100% oxygen
  • The oxygen that reaches the alveoli will mix with alveolar air, and the reslting mix will contain nitrogen (there is 79% nitrogen in air)
  • However, the air in the conducting airways (dead space) will still be filled with pure oxygen
  • The person exhales through a one way valve that measures the percentage of nitrogen in and volume of air expired
  • Nitrogen concentration is initially zero, as the patient exhales dead space oxygen
  • As alveolar air begins to move out and mix with dead space air, nitrogen concentration gradually climbs, until it reaches a plateau where only alveolar gas is being expired
  • A graph can be drawn to determine the dead space, plotting nitrogen % against expired volume

ESA 3 - Respiratory System (14 decks)

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