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S1, R > Ventilation and compliance > Flashcards

Ventilation and compliance Flashcards

1
Q

What is residual dead space?

A

RV
Volume of gas in the lungs at the end of maximal expiration
No matter how hard you try, you can’t get rid of this volume from your lungs

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2
Q

Approx. what is the volume of residual dead space?

A
  • Approx. 1200ml
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3
Q

Why have residual dead space?

A

It’s easier to inflate your alveoli to full capacity from a partially inflated state
Provides reservoir of air to allow for gas exchange

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4
Q

What is expiratory reserve volume?

A

ERV

Maximum volume of air which can be expelled from the lungs at the end of normal expiration

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5
Q

Approx. what’s the expiratory reserve volume?

A

Approx. 1100ml extra volume can be expired

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6
Q

What is tidal volume?

A

V_T

Volume of air breathed in and out of the lungs at the end of normal inspiration

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7
Q

Approx. what is the tidal volume?

A

Average is 500ml

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8
Q

What is inspiratory reserve volume?

A

IRV

Maximum volume of air which can be drawn into the lungs at the end of a normal inspiration

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9
Q

Approx. what is the inspiratory reserve volume?

A

Approx. 3l addition capacity

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10
Q

What is vital capacity?

A

VC
Breathe in and force all air out
Tidal volume + inspiratory reserve volume + expiratory reserve volume

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11
Q

What is total lung capacity?

A

TLC

TLC = vital capacity + residual volume

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12
Q

Functional residual capacity

A

Amount of air in lungs after a normal, relaxed expiration

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13
Q

Which lung capacity is impacted upon by a number of anaesthetics?

A

Functional residual capacity

Helps to stop collapse of smaller airways

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14
Q

What is inspiratory capacity?

A

IC

Tidal volume + inspiratory reserve volume

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15
Q

FEV1/FVC

A

Fraction of forced vital capacity expired in one second

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16
Q

Anatomical dead space

A

Volume of gas occupied by the conducting airways
Air that doesn’t participate in gas exchange
Usually fixed for an individual

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17
Q

Approx. what is the volume of the anatomical dead space?

A

Approx. 150ml

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18
Q

What is ventilation?

A

Movement of air in and out of the lungs

Measured in l/min

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19
Q

What is pulmonary ventilation?

A

Total movement of air into and out of the lungs

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20
Q

What is alveolar ventilation?

A

Fresh air that gets to the alveoli and is available for gas exchange

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21
Q

How efficient is breathing at rest?

A

Only 70% due to dead space

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22
Q

What is normal alveolar pressure?

A

P_alv = 4.2 l/min

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23
Q

How can we use normal alveolar pressure as a measure of hyper/hypoventilation?

A

If you are greater than alveolar pressure then you’re hyper ventilating
If you’re lower than normal alveolar pressure then you’re hypoventilating

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24
Q

What is Dalton’s Law?

A

Pressure of a gas in a mixture of gases is equivalent to the percentage of that particular gas in the entire mixture, multiplied by the pressure of the whole gaseous mixture

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25
Q

What’s the symbol for partial pressure in alveoli?

A

P_A

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26
Q

What’s the symbol for partial arterial pressure?

A

P_a

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27
Q

What’s the normal partial pressure in alveoli of O2 and CO2?

A

O2 - 13.3 kPa
CO2 - 5.3 kPa
These remain fairly constant throughout normal conditions

28
Q

If the atmospheric pressure of O2 is 21 kPa then why is partial pressure lower?

A

The O2 is diluted by:

  • residual volume in lungs and dead space
  • air being humidified to allow the oxygen to become fully saturated
  • partial pressure of air being in equilibrium with arterial pressure
29
Q

What does hyperventilation and hypoventilation depend on?

A
  • Depth of the breath is far more influential on gas exchange than rate of breathing
  • So someone with a low breathing rate could be hyperventilating and someone with a high breathing rate could be hypoventilating
30
Q

Hyperventilation in relation to partial pressure

A
  • Partial pressure of O2 increases to about 120 mmHg

- Partial pressure of CO2 decreases to about 20 mmHg

31
Q

Why is it difficult to keep hyperventilating?

A

Body will want to stop breathing for a while so there is no impetus to remove CO2
Body is far more interested in removing CO2 than acquiring oxygen

32
Q

Hypoventilation in relation to partial pressure

A
  • Partial pressure of O2 drops to about 30 mmHg

- Partial pressure of CO2 increases to about 20 mmHg

33
Q

Why are patient breathless in respiratory pathology?

A
  • Responding to rise in CO2 rather than fall in O2
34
Q

What is the pulmonary surfactant?

A

Type II Alveolar cells:

Detergent like fluid produced

35
Q

What does the pulmonary surfactant do?

A
  • Reduces surface tension on alveolar surface -> reducing tendency for alveolar collapse
  • Increases lung compliance
  • Reduced lung’s tendency to recoil
  • Makes work of breathing easier
36
Q

Is pulmonary surfactant more effective in small or large alveoli?

A
  • Small because the surfactant molecules come closer together and are therefore more concentrated
37
Q

What is surface tension?

A

Attraction of one water molecule to another

38
Q

Why do alveoli have an air-water interface?

A

Alveoli are in a water vapour

39
Q

Why do the alveoli want to collapse?

A

Surface tension
There is an inward pressure as all the water molecules are attracted to each other
Surfactant overcomes this inwardly directed pressure

40
Q

What is the Law of LaPlace?

A

P = 2T/r

T is surface tension

41
Q

What does LaPlace have to do with alveoli?

A

The surface tension would be lower if the radius was larger, so all the small alveoli would collapse
Surface area would be small, that would be bad
Surfactant overcomes this

42
Q

When does surfactant production start and finish in pregnancy?

A

Starts at 25 weeks, ends at 36 weeks

43
Q

Why are premature babies a concern with Infant Respiratory Distress Syndrome?

A
  • Might not have enough surfactant

- May be fighting the small alveoli collapsing with every breath

44
Q

What are surfactants stimulated by in pregnancy?

A

Thyroid hormones and cortisol

45
Q

What is compliance?

A
  • Change in volume relative to change in pressure
  • Represents the stretchability of the lungs
  • Shows how easy it is for air to get into the lungs, not about how easy it is to get out of the lungs
46
Q

What is high compliance?

A
  • Large increase in lung volume for small decrease in ip pressure
47
Q

What is low compliance?

A
  • Small increase in lung volume for large decrease in ip pressure
  • Never healthy
  • Lungs of inspiration are having to work hard to increase the volume
48
Q

Why would lung compliance change?

A
  • Disease states

- Age

49
Q

How do you measure compliance?

A

Pressure-volume relationship
Steeper curve: high compliance
Shallower curve: low compliance

50
Q

What has a greater change in pressure from FRC to get to a particular lung volume, inspiration or expiration?

A

Inspiration because in expiration the work is passive as the work of inspiration is recovered through elastic recoil
-Also in inspiration you have to fight surface tension, initiate momentum

51
Q

How does the lung vary in compliance

A
  • Greatest at base of lung
  • due to gravity
  • Alveoli are more squashed at bottom of lung, more range to expand and contract
52
Q

Obstructive lung disease characteristics

A
  • Obstruction of airflow, especially on expiration

- Increased airway resistance

53
Q

Basic characteristics of COPD

A
  • Chronic bronchitis
  • Emphysema: elastase degrades the elastic fibres around the alveoli, alveoli destroyed
  • Intrapleural pressure can become positive, need to invest energy in expiration
  • Transpulmonary pressure can become negative
54
Q

Restrictive lung disease characteristics

A
  • Restriction of lung expansion

- Loss of lung compliance, stiff lungs, incomplete expansion

55
Q

Main test for abnormal lung function

A

Spirometry

56
Q

What is a static measurement in spirometry?

A

Only consideration made is the volume exhaled

57
Q

What is a dynamic measurement in spirometry?

A

Time taken to exhale a certain volume

58
Q

What can you measure in spirometry?

A
  • Tidal volume
  • Inspiratory reserve volume
  • Inspiratory capacity
  • Vital capacity
  • Expiratory reserve volume
59
Q

What can’t you measure in spirometry?

A

Residual volume

FRC

60
Q

What are the units of spirometry?

A

FEV1/FVC

61
Q

Whats the normal forced expiratory volume in 1 second in a healthy male?

A

4l

62
Q

Whats the normal forced vital capacity in a healthy male?

A

5l

63
Q

What’s FEF?

A

Forced expiratory flow
FEF (FEF_25-75)
Average expired flow over the middle of an FVC

64
Q

How can FEF help make an early diagnosis?

A
  • Looking at how long it takes for them to expire a set value in l/s
  • In restrictive or normal you might get a similar value of around 3.5/ls
  • Obstructive could be 1.4l/s, so a lot lower
65
Q

Spirometry in obstructive lung disease

A
  • Rate at which air is exhaled is much slower
  • Total volume is also reduced
  • FEV is reduced, to a greater extent than FVC
  • Ratio reduced
66
Q

Spirometry in restrictive lung disease

A
  • Absolute rate of airflow is reduced
  • Less air inhaled in first place
  • Total volume is reduced due to limitations in lung expansion
  • Ratio remains constant or can increase as large proportion of air can be exhaled in first second
67
Q

Limitations to spirometry

A
  • FEV1/FVC ratio being normal doesn’t always indicate health

- Ratio can remain same in restrictive lung disease

S1, R (5 decks)

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