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BS - Respiratory System > Mechanics of Breathing 1 > Flashcards

Mechanics of Breathing 1 Flashcards

1
Q

What % of deaths are attributable to respiratory disease?

A

36%

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2
Q

What is ventilation?

A

The process of moving gases in and out of the lungs

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3
Q

What is “mechanics of breathing”?

A

The structural and physiological bases of ventilation

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4
Q

What are the 2 categories of diseases that affect breathing?

A

obstructive and restrictive conditions

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5
Q

What is an obstructive lung condition?

A

There is increased resistance to the flow of air into and out of the lungs due to airway obstruction

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6
Q

What are the 3 most well known obstructive lung conditions?

A

asthma

chronic obstructive pulmonary disease (COPD)

lung cancer

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7
Q

What is a restrictive lung condition?

A

Lung expansion is restricted leading to a decreased lung volume and inadequate ventilation and/or oxygenation

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8
Q

Why does a restrictive lung condition come about?

A

Due to a loss of elasticity of the lungs and/or chest wall

It is harder for them to expand so a greater effort is required to move the less elastic structures

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9
Q

How are restrictive lung conditions divided?

A

Intrinsic and extrinsic conditions

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10
Q

What is an intrinsic lung condition?

A

A result of a problem within the lungs themselves

e.g. pulmonary fibrosis

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11
Q

What is an extrinsic lung condition?

A

These happen when lung problems occur from disorders outside of the lungs

e.g. pneumothorax

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12
Q

What factors determine the direction of gas flow?

A

The pressure gradient between atmospheric and alveolar pressure

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13
Q

What is the pressure constant?

A

Atmospheric pressure outside the body has a constant pressure

This is P(b) - pressure constant

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14
Q

What is another name for atmospheric pressure?

A

barometric pressure

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15
Q

What is the pressure variable?

A

The alveolar pressure can be changed

This is the pressure variable - P(a)

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16
Q

How does breathing occur relating to pressure?

A

Breathing is brought about by changes in alveolar pressure

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17
Q

How do the pressure variable and pressure constant related to each other during inspiration and expiration?

A

Inspiration - P(b) > P(a)

Expiration - P(a) > P(b)

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18
Q

What equation is used for flow that shows airway obstruction has a major effect on flow?

A

Flow = (k. delta P. r^4) / L

delta p - change in pressure
r - radius of tube
L - length of tube
k - constant

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19
Q

What is delta P dependent on?

A

Atmospheric pressure is constant so it is dependent on a cycle of pressure changes in the chest

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20
Q

What type of tube would have a lower pressure?

A

One where the tube is longer and has a larger diameter

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21
Q

If the radius of the tube is reduced by half, how much is the flow reduced by?

A

factor of 16

the relationship between flow and radius is not linear

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22
Q

What does Boyle’s Law show?

A

The relationship between pressure and volume

P = 1/v

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23
Q

How does changing the calibre of the airways affect gas flow?

A

Relatively small changes in the calibre of the airways can have profound effects on the flow of gas into and out of the lungs

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24
Q

Which muscles are involved in quiet breathing?

A

Contraction of the diaphragm only

External intercostal muscles contract to stabilise the rib cage

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25
Q

Which muscles are involved when the effort of breathing is increased?

A
  1. contraction of diaphragm
  2. contraction of external intercostal muscles
  3. accessory muscles
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26
Q

How do the 4 accessory muscles move the rib cage during inspiration?

A

Muscles in the neck pull it upwards

Sternocleidomastoids elevate the sternum

Scalenus major and minor muscles elevate both the first 2 ribs and the sternum

the shoulder girdle muscles pull the ribcage outwards

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27
Q

How does expiration differ to inspiration ?

A

There is little muscular effort involved in expiration

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28
Q

How is expiration achieved during quiet breathing?

A

through the elastic recoil of tissues

during inspiration, lungs and thoracic cage are stretched which generates elastic energy that gives a large elastic recoil

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29
Q

How is effort increased in forced expiration?

A

Internal intercostal muscles and abdominal wall muscles contract

This increases pressure in the abdomen to push the diaphragm back up again

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30
Q

How are the diaphragm and intercostal muscles innervated?

A

Diaphragm innervated by the phrenic nerve that is supplied by the 3rd, 4th and 5th cervical nerve

Intercostals are supplied by segmental thoracic nerves in the intercostal bundle

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31
Q

How can spinal cord injury affect respiration?

A

Lead to ventilatory muscle paralysis

32
Q

What is quadriplegia and how is it compatible with life?

A

Paralysis of all 4 limbs

Cervical nerves are not affected so you can continue to breathe

33
Q

What happens if the neck is fractured above C5?

A

Death

Breathing is no longer possible as the diaphragm is paralysed

34
Q

Why are the pleura important in respiration?

A

They transmit thoracic cage expansion into lung volume expansion

Thoracic cage expansion exerts an increasing negative pressure on the intrapleural space

35
Q

How is pressure expressed?

A

Pressure is expressed relative to atmospheric pressure

36
Q

How does intrapleural pressure change during respiration?

A

Intrapleural pressure is negative compared to atmospheric

It will decrease during inspiration and increase during expiration

37
Q

How does alveolar pressure change during respiration and why?

A

It will decrease during inspiration and increase during expiration

The decrease in intrapleural pressure causes the alveolar pressure to decrease

38
Q

What happens to alveolar pressure during inspiration?

What happens to the muscles of inspiration?

A

As air moves into the lungs, it normalises alveolar pressure with atmospheric pressure until they are equal

At this point, muscles causing inspiration will relax

39
Q

What happens to intrapleural pressure once alveolar pressure equals atmospheric pressure?

A

Intrapleural pressure becomes less negative and squeezes air out of the respiratory system

This causes an increase in alveolar pressure above atmopsheric pressure

40
Q

How are intrapleural pressure and alveolar pressure related?

A

A greater change in intrapleural pressure is required to give relatively subtle changes in alveolar pressure

41
Q

What units are used to measure intrapleural and alveolar pressure?

A

centimetres of water

they are small changes so require a sensitive unit

42
Q

When does pneumothorax occur?

A

It occurs when there is gas within the thorax

A penetrating injury causes air to get between the layers of pleura

43
Q

What happens in a pneumothorax and why?

A

Air between the pleura disrupts the tight connection between the 2 layers

The lung no longer sticks to the pleura so it collapses

44
Q

What occurs during a tension pneumothorax?

A

The heart is pushed further to the left hand side due to loss of tissue on the right hand side

Pressure on the heart prevents it from functioning normally and leads to severely low blood pressure, fainting, death

45
Q

how is pneumothorax relieved?

A

sticking a sharp hollow tube between the 1st and 2nd rib which allows the gas to leave

46
Q

What is a pleural effusion and what are the effects?

A

Fluid accumulates in the pleural space which reduces the ability of the lung to expand

47
Q

How is pleural effusion identified on a chest X-ray?

A

A meniscal fluid level can be observed

There is not a sharp angle between the diaphragm and the chest wall

48
Q

How can pneumothorax and pleural effusion be diagnosed without a chest X-ray?

A

Assessment of chest expansion can allow detection of differential expansion

49
Q

How are lung volumes measured and what are they dependent on?

A

Measured using a spirometer

Dependent on age, sex and height

50
Q

What is tidal volume?

A

The volume of air moved in and out of the lungs during normal breathing

51
Q

What is normal tidal volume at rest and during exercise?

A

At rest - 6-7 ml per kg of bodyweight

exercise - 15 ml/kg

52
Q

What is inspiratory reserve volume?

A

the additional air that can be forcibly inhaled after the inspiration of a normal tidal volume

53
Q

How is inspiratory reserve volume measured?

A

After normal expiration, take as deep a breath in as possible

It is the maximum inspiration that can be taken on top of tidal volume

54
Q

What is normal IRV?

A

for a typical 70kg male it is 3,000 ml

55
Q

What is expiratory reserve volume?

A

the additional amount of air that can be expired from the lungs by determined effort after normal tidal expiration

56
Q

How is expiratory reserve volume measured?

A

After normal inspiration, breathe out as deeply as possible

57
Q

What is normal ERV?

A

for a typical 70kg male it is around 1,500 ml

58
Q

What is residual volume?

A

the amount of air that remains in a person’s lungs and respiratory system after forced expiration

59
Q

Why does residual volume exist?

A

The rigid nature of the thorax and pleural attachments of the lungs to the chest wall prevent complete emptying of the lungs

60
Q

What is normal residual volume and how is it measured?

A

for a typical 70kg male it is 1,000 ml

it cannot be measured by spirometry

61
Q

What is total lung capacity?

A

It is the sum of all 4 lung volumes

TV + IRV + ERV + RV = TLC

62
Q

What is vital capacity?

A

The maximum volume of air that can be moved into and out of the lungs

TV + IRV + ERV = VC

63
Q

How is vital capacity achieved and what is a typical value?

A

Achieved by making a maximal expiration after a maximal inspiration

for a typical 70 kg male it is 5,000 ml

64
Q

What is functional residual capacity?

A

the volume of air present in the lungs at the end of passive expiration

ERV + RV = FRC

65
Q

What are lung volumes used for?

A

Used in diagnosis

Monitoring progression of disease and effectiveness of treatment

66
Q

How do lung volumes change in restrictive lung conditions?

A

Restrictive diseases are associated with reduced volumes

Reduced RV, FRC, VC and TLC

67
Q

How do lung volumes change in obstructive lung conditions?

A

Increase in residual volume

TLC reduced in COPD

TLC and FRC increased in emphysema

68
Q

Why do obstructive lung conditions lead to an increase in residual volume?

A

There is more air in the lungs that is not being moved

Ventilation becomes less efficient

69
Q

What is a Vitalograph spirometer used to measure?

A

Forced vital capacity (FVC)

Forced expiratory volume in 1 second (FEV1)

70
Q

What is used to measure peak expiratory flow rate (PEFR)?

A

a peak flow meter

71
Q

How is the FEV1/FVC ratio used to distinguish between obstructive and restrictive lung conditions?

A

Ratio < 0.7 - obstructive

Ratio > 0.7 - restrictive

72
Q

What is PEFR used to measure?

A

It is used to measure airway obstruction

Patients use a peak flow meter at home to monitor COPD or asthma

73
Q

How does PEFR compare to FEV1?

A

PEFR is less dependent on effort than FEV1 but will only measure expiratory flow rate

74
Q

What is PEFR measured in and how does it vary?

A

measured in L/min or L/s

wide diurnal variations as highest readings are taken in the evening and the lowest in the early hours of the morning

75
Q

How can you distinguish between asthma and COPD?

A

Measurements of FEV1 and PEFR are made before and after inhalation of a bronchodilator

e.g. salbutamol

76
Q

After salbutamol, what would be seen in asthma patients?

A

FEV1 and PEFR are restored to normal after taking salbutamol

In asthma the airway constriction is reversible

77
Q

After salbutamol, what is seen in COPD patients?

A

There is less than 15% improvement in FEV1 and FVC

The airway constriction is irreversible or nearly irreversible

BS - Respiratory System (20 decks)

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