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3 - Respiratory > Mechanics of Breathng > Flashcards

Mechanics of Breathng 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 tissueSurface 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

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 expirationBoth

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 maximallyCannot 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 (

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 does mild obstruction of the airways cause?

A

• A scooped out expiratory curve• More severe obstruction will cause reduced PEFR (peak expiratory flow rate)

64
Q

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

A

Peak then rapid decline

65
Q

What can’t be measured by spirometer?

A

• Functional Residual Capacity

66
Q

What can measure residual volume?

A

Helium dilution

67
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

68
Q

Why is helium used to detect lung function?

A

• Not present in normal air• Insoluble in blood, so not remains in alveolia

69
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

70
Q

How is Transfer Factor calculated?

A

• Carbon Monoxide Transfer Factor

71
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

72
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

73
Q

Why is only a small amount of CO used?

A

• Toxic

74
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 sampleCan detect con of CO and inert gas

75
Q

What does nitrogen washout measure?

A

• Serial dead space and ventilation perfusion

76
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

77
Q

What do you measure in nitrogen washout test?

A

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

78
Q

What are you measuring in a diffusion conductance test?

A

• Measure how easily CO crosses from alveolar air to blood

79
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

80
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

81
Q

Give an example of a restrictive airway disease

A

Pulmonary fibrosis

82
Q

Give two examples of obstructive airway disease

A

COPDBronchial Asthma

3 - Respiratory (20 decks)

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