The Mechanics of Breathing and Lung Function Testing Flashcards Preview

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

Flashcards in The Mechanics of Breathing and Lung Function Testing Deck (106):
1

How is air drawn into the lungs? 

By expanding the volume of the thoracic cavity 

2

What is work done during breathing doing? 

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

3

What is the pleural space? 

The space bewteen the lungs and thoracic wall 

4

What is the pleural space normally filled with? 

A few millimetres of fluid 

5

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

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

6

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

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

7

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

The lungs will tend to collapse

8

What happens in a pneumothorax? 

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

9

What is meant by lung compliance? 

The 'stretchiness' of the lungs

10

What is lung compliance defined as? 

The volume change per unit pressure change 

11

What does high compliance mean? 

Lungs are easy to stretch 

12

How is compliance measured? 

By measuring the change in lung volume for a given pressure 

13

What does a greater lung volume mean for compliance? 

Greater compliance 

14

What is it more usual to calculate than compliance? 

Specific compliance 

15

Why is it more usual to measure specific compliance? 

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

16

How is specific compliance calculated? 

Volume change per unit pressure change / Starting volume of lungs 

17

Draw a diagram illustrating the compliance for; 

  • Elastic lungs
  • Normal lungs
  • Stiff lungs

 

A image thumb
18

What do the elastic properties of the lungs arise from? 

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

19

What is meant by surface tension?

The interactions between molecules at the surface of a liquid

20

What is the effect of surface tension on stretchiness?

It makes the surface resistant to stretching 

21

What does a higher surface tension mean for compliance?

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

22

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

It is much lower than expected 

23

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

Due to the disruption of interactions between surface molecules by surfactant 

24

What produces surfactant in the lungs?

Type 2 alveolar cells 

25

What is surfactant?

A complex mixture of phospholipid and proteins, with detergent properties 

26

Where does the hydrophilic end of surfactant molecules lie?

In the alveolar fluid

27

Where does the hydrophobic end of surfactant molecules lie?

Projects into alveolar gas

28

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

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

29

When does surfactant reduce surface tension? 

When the lungs are deflated, but not when fully inflated 

30

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

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

31

What do the alveoli form? 

An interconnecting set of bubbles 

32

What is Laplace's law? 

Pressure is inversely related to the radius of a bubble 

33

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

Large alveoli would 'eat' small ones 

34

What happens as alveoli get bigger? 

With respect to surface tension

The surface tension in their walls increases

35

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

Because surfactant is less effective 

36

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

Pressure stays high and stops them from 'eating' smaller alveoli 

37

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

To force air through the airways 

38

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

It is laminar 

 

39

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

Poiseulle's Law 

 

40

What is Poiseulle's Law? 

The resistance of a tube sharply increases with a falling radius 

41

What is true of the combined resistance of small airways? 

It is normally low 

42

Why is the combined resistance of small airways normally low? 

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 

43

Where does most of the resistance to breathing reside? 

In the upper respiratory tract 

44

What is work done against in the lungs? 

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

 

45

What produces the elastic recoil of the lungs and thorax? 

  • Elastic properties of the lungs
  • Surface tension forces in the alveoli 

 

46

When is resistance to flow through airways important to consider? 

In disease, as it is often affected 

Of little significance in health 

47

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

0.1% - is very efficient 

48

What do the bronchioles do during inspiration? 

Use their smooth muscle to increase their radius 

49

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

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

50

What happens in spirometry?

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

51

What does simple spirometry allow for?

Measurement of many lung volumes and capacities 

52

What measurement taken from spirometry is particularly significant? 

Vital capacity 

53

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

Tables 

54

Why may vital capacity be less than normal? 

Because the lungs are not; 

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

 

55

What is meant by forced vital capacity? 

The maximum volume that can be expired from full lungs 

56

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

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

57

What is FEV1 affected by?

How quickly air flow slows down 

58

When is FEV1 low?

If the airways are narrowed

59

When may the airways be narrowed? 

Obstructive deficit 

60

Draw a diagram illustrating FVC and FEV1

A image thumb
61

How can restrictive and obstructive deficits be separated? 

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

62

What is maximal filling of the lungs determined by? 

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

63

When is a restrictive deficit produced? 

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

64

What is the effect of a restrictive deficit on FVC?

It reduces it 

65

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

FEV1 > 70% FVC

66

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

A image thumb
67

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

They are compressed 

68

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

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

69

What happens if the airways are narrowed? 

Expiratory flow is compromised much earlier in expiration

70

What is produced when the airways are narrowed? 

An obstructive deficit 

71

What is the effect of an obstructive deficit on FEV1?

It is reduced 

72

What is the effect of an obstructive deficit on FVC? 

It is relatively normal 

73

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

A image thumb
74

What a flow volume curves? 

A graph of volume expired against flow rate

75

What are flow volume curves derived from? 

A vitalograph trace

76

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

Q image thumb

  • 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

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

The resistance of large airways 

 

78

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

Severe obstruction of the smaller airways 

79

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

Asthma 

80

What does mild obstruction of the airways produce? 

A 'scooped out' expiratory curve 

81

What affect will a severe obstruction have on PEFR? 

It will reduce it 

82

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 image thumb
83

What is the Helium Dilution Test used to measure? 

Functional Residual Capacity (FRC)

84

What is FRC used to calculate? 

Residual volume

85

What is the advantage of using helium in tests? 

  • 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

How is a helium dilution test carried out? 

  • 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

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

Functional residual capacity 

88

What is FRC equal to? 

ERV+RV

89

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

4-7 minutes

90

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

C2

91

How is FRC calculated from a helium dilution test? 

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

 

92

What is residual volume equal too? 

FRC - ERV

93

How can ERV be measured?

Spirometry

94

What does the Carbon Monoxide Transfer Factor measure? 

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

95

What is the purpose of the CO transfer factor? 

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

96

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

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

97

Why is inhaled CO used in a transfer factor test? 

Because of its very high affinity for Hb

98

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

0

99

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

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

100

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

The concentration gradient between alveolar CO and capillary ppCO is maintained 

101

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

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

102

How is a CO transfer factor test carried out? 

  • 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

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

Because it is toxic

104

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

To make an estimate of total lung volume 

105

What does a nitrogen wsahout test measure? 

Serial (anatomical) dead space 

106

How is a nitrogen washout test carried out? 

  • 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