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Semester 3 - Respiratory > Session 3 - Mechanics of Breathing > Flashcards

Session 3 - Mechanics of Breathing Flashcards

1
Q

Why is work done during breathing?

A

• To move the structures of the lungs and thorax and to overcome the resistance to the flow air through the lungs

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2
Q

What is the pleural seal?

A

• A thin film of liquid which holds the outer surface of the lungs to the inner surface of the thoracic wall

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3
Q

What happens if the lung are removed from the chest cavity?

A

• The inward elastic recoil of the lungs causes them to collapse

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4
Q

How does a pneumothorax cause lungs to collapse?

A

• Breaks integrity of the pleural seal

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5
Q

In what direction do the lungs pull?

A

• In and up

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6
Q

In what direction does the thoracic cage pull?

A

• Out

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7
Q

In what direction does the passive stretch of the diaphragm go?

A

Down

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8
Q

What is the ‘default’ setting of the lungs

A

• The resting expiratory level (end of normal quiet respiration)

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9
Q

What is the function residual capacity?

A

• The lung volume that exists at the end of expiration

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10
Q

What does breathing in from the equilibrium position require?

A

• Contraction of the diaphragm and the external intercostal muscles

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11
Q

What does breathing out in quiet expiration require?

A

• Relaxation and passive recoil

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12
Q

What does forced breathing out require

A

• Abdominal muscles and the internal intercostal muscles

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13
Q

Give three examples of when passive exhalation is difficult due to an inability to flatten the diaphragm

A
  • Pregnancy
  • Obesity
  • Wearing a corset
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14
Q

What does an increase in the volume of the lungs cause?

A

The lungs to fall under atmospheric pressure, so air flows into them

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15
Q

How far does fresh atmospheric air reach?

A
  • The terminal and respiratory bronchioles

* Exchange of O2 and CO2 occurs via diffusion between atmospheric air and alveolar gas

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16
Q

What is lung compliance? What is it measured in?

A
  • The stretchiness of the lungs
  • Volume change per unit pressure change
  • Mesasured as volume vs pressure on graph (Y vs X)
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17
Q

What does higher compliance of the lungs mean?

A

Easier stretch

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18
Q

What is specific compliance?

A

• Compliance depends on starting volume from which it is measured

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19
Q

How is specific compliance measured?

A

• Volume change per unit pressure change/starting volume of the lungs

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20
Q

From what two sources do the elastic properties of the lungs arise from?

A

Elastic tissue

Surface tension

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21
Q

What is the key factor which reduces compliance?

A

• Surface tension of lining fluid

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22
Q

What is surface tension caused by?

A
  • Interactions between molecules at surface of a liquid

* The higher the surface tension, the harder the lungs are to stretch

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23
Q

Why is it easier to stretch lungs than expected, according to surface tension calculations

A

• Surfactant produced, which reduces surface tension when lungs are deflated

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24
Q

What is surfactant produced by?

A

• Type 2 alveolar cells

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25
Q

What are the limits of surfactant?

A
  • Reduces surface tension when lungs deflated, but not when fully dilated
  • Little breaths are easy
  • Big breaths are hard
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26
Q

Why is it hard to take big breaths?

A

• Detergent molecules get further and further spread out, reducing effect

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27
Q

What is hysteresis?

A
  • The energy put into stretchin a film of surfactant

* Decreases relaxing, energy lost (Hooke’s law in physics!)

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28
Q

Films want to reduce to smallest size - To what point will this continue?

A

• Until there is an equilibrium between tension and pressure

Pressure is inversely proportional to bubble size

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29
Q

Outline laplace’s law

A

• Pressure is inversely related to the radius of a bubble

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30
Q

Why don’t big alveoli eat little alveoli?

A
  • Surfactant becomes less effective as bubble size increases

* Surface tension increases, keeping pressure similar to small

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31
Q

What is respiratory distress syndrome?

A
  • Babies born prematurely have too little surfactant

* Breathing and gas exchange compromised

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32
Q

Outline the features of the lungs of a baby with respiratory distress syndrome

A
  • Lungs stiff

* Few, large alveoli

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33
Q

What is poiseulle’s law?

A

• Resistance of a tube increases sharply with a falling radius

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34
Q

What should resistance be like in airways?

A

• Small tubes have very high resistance

35
Q

Why is resistance not extortionately high in the lungs?

A
  • At each branch number of airways increases

* This causes a set of parallel resistors to be formed with relatively low resistance

36
Q

Where is the highest resistance in a normal breath?

A

• The trachea (the biggest tube, but least branches!)

37
Q

Why does resistance increase in forced expiration?

A
  • Small airways narrowed due to compression

* Resistance increases dramatically and air is trapped in alveoli

38
Q

What is work done against in the lungs?

A

• Elastic recoil of the lungs and thorax
○ Elastic properties of the lungs
○ Surface tension forces in the alveoli
• Resistance to flow through airways
○ Of little significance in health but often affected by disease

39
Q

What occurs in the lungs in terms of resistance in obstructive airway disease?

A
  • Small airways narrowed by disease (asthma, chronic bronchitis)
  • Resistance increases much earlier in expiration, making breathing out difficult
40
Q

How do small airways decrease resistance during inspiration?

A

• Decrease smooth muscle contraction

41
Q

What are lung function tests designed to assess?

A
  • The mechanical condition oft he lungs
  • Resistance of the airways
  • Diffusion across the alveolar membrane
42
Q

What factors can lung function be inferred from?

A
  • Volumes
  • Pressures/flows
  • Composition
43
Q

What does the spirometer measure?

A

• Vital capacity - Maximum inspiration to maximum expiration

44
Q

What is required before you can predict vital capacity of an indiviual?

A

Knowledge of age, sex and height

45
Q

What causes vital capacity to be less than normal?

A
  • Filled normally in inspiration
  • Emptied normally in expiration

Both

46
Q

What is vital capacity?

A

• Maximum inspiration to maximum expiration

47
Q

What limits vital capacity?

A 
• Maximum inspiration
	○ Compliance of the lungs
	○ Force of inspiratory muscles
• Maximum expiration
	○ Increasing airway resistance as the lungs are compressed
48
Q

What may be the reason if vital capacity is less than normal?

A

• Cannot breathe in maximally

Cannot breath out maximally

49
Q

What is single breath spirometry?

A

• Subject fills lungs from atmosphere and breathes out as far and fast as possible through spirometer

50
Q

What is a vitalograph trace?

A
  • Plot of volume expired vs time

* Will show an initial rapid rise which tails off to a plateau

51
Q

What is the forced vital capacity?

A
  • The maximum volume that can be expired from full lungs

* Typically 5l in normal adults

52
Q

What is the FEV 1.0

A
  • Volume expired in first second of exhalation
  • Affected by how quickly air flow slows down
  • Less if airways narrows
  • > 70%
53
Q

How can obstructive and restrictive deficits be separated?

A

By asking patients to breathe out rapidly from maximal inspiration

54
Q

What does a single breath spirometer do?

A

Plots volume expired

55
Q

What is a restrictive deficit?

A

If lungs are difficult to fill

56
Q

What is an obstructive deficit?

A
  • If airways are narrowed and lungs will be easy to fill

* Resistance will increase in expiration

57
Q

What factors would cause the lungs to be difficult to fill?

A
  • Stiff
  • Weak muscles
  • Problems with chest wall
58
Q

What will an vitalograph show with a restrictive deficit?

A
  • FVC will be reduced

* FEV will be normal (>70% FVC)

59
Q

What will a vitalograph show with an obstructive deficit?

A
  • FEV 1.0 will be reduced (<70% FVC)

* FVC will be relatively normal

60
Q

What is a flow volume curve?

A

• Plot of volume expired against flow rate, derived from a vitalograph tract

61
Q

Why is expiratory flow rate highest at state of expiration?

A
  • Airways stretched, so resistance at a minimum

* Known as peak expiratory flow rate

62
Q

What are the two types of graphs we can us for flow volume?

A
  • Volume expired against time

* Flow against volume expired

63
Q

What happens at point A?

A

• Airways are stretched so resistance at a minimum

64
Q

What happens at points b-d?

A

• As the lungs are compressed, more air is expired and airways begin to narrow, so resistance increases and flow rate decreases

65
Q

What does mild obstruction of the airways cause?

A
  • A scooped out expiratory curve

* More severe obstruction will cause reduced PEFR (peak expiratory flow rate)

66
Q

What does restrictive disease show on a flow-expiratory graph?

A

Peak then rapid decline

67
Q

What can’t be measured by spirometer?

A

• Functional Residual Capacity

68
Q

What can measure residual volume?

A

Helium dilution

69
Q

What is helium dilution?

A
  • Patient breathes in helium of known concentration at end of quiet expiration
  • See how much conc reduced by mixing with air already in lungs
70
Q

Why is helium used to detect lung function?

A
  • Not present in normal air

* Insoluble in blood, so not remains in alveolia

71
Q

Outline exactly what happens in Helium Dilution Test (Use equation!)

A

• Patient inhales gas with known Helium Concentration (C1) and Volume (V1)
• End of tidal expiration
○ Lung volume = Functional Residual Capacity = Expiratory Reserve Volume + Respiratory Volume
• Patient keeps breathing until equalised
• Functional Residual capacity - Expiratory reserve volume = Residual Volume

72
Q

How is Transfer Factor calculated?

A

• Carbon Monoxide Transfer Factor

73
Q

What is CO transfer factor?

A
  • Rate of transfer of CO from the aveoli to the Blood in ml/min/kPa
  • Way of measuring diffusion capacity of the lung
74
Q

Why is CO used?

A
  • High affinity for haemoglobin
  • Concentration gradient between blood plasma and alveoli constant as CO removed immediately by RBC
  • Thus, only limiting factor is diffusion capacity of lung
75
Q

Why is only a small amount of CO used?

76
Q

What exactly occurs in a CO Transfer Factor?

A
  • Gas containing CO inhaled
  • Held for 10 seconds
  • Patient exhales and gas collected mid expiration to gain an alveolar sample

Can detect con of CO and inert gas

77
Q

What does nitrogen washout measure?

A

• Serial dead space and ventilation perfusion

78
Q

What happens in nitrogen washout test?

A
  • Takes one normal breath of pure oxygen
  • Breathes out via meter measuring %nitrogen
  • Initially only oxygen expired from airways
  • Then mixture of o2 and air from aveoli
79
Q

What do you measure in nitrogen washout test?

A

• Time it takes for nitrogen to appear in mixture is amount of dead space

80
Q

What are you measuring in a diffusion conductance test?

A

• Measure how easily CO crosses from alveolar air to blood

81
Q

Why is CO used in the diffusion conductance test?

A

• Uses CO because binding to Hb means no partial pressure in mixed venous blood

82
Q

What four things are found in a lung function report?

A
  • Vital capacity
  • FEV 1.0
  • Ratio FEV1.0/FVC
  • Peak expiratory flow
  • FRC
  • RV
  • TLC
  • RV/TLC
  • Transfer factor
  • CO conductance
83
Q

Give an example of a restrictive airway disease

A

Pulmonary fibrosis

84
Q

Give two examples of obstructive airway disease

A

COPD

Bronchial Asthma

Semester 3 - Respiratory (18 decks)

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