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CTB Block 2 > B2 W1 - Mechanics of Breathing > Flashcards

B2 W1 - Mechanics of Breathing Flashcards

1
Q

What does Boyle’s Law state?

A

At a given temperature, the pressure and volume of an ideal gas are inversely proportional.

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2
Q

What happens to the pressure of a gas when its volume increases, according to Boyle’s Law?

A

The pressure decreases.

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3
Q

How does air move, in terms of pressure?

A

Air moves by bulk flow from an area of high pressure to an area of low pressure.

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4
Q

What is the relationship between volume and pressure according to Boyle’s Law?

A

As volume increases, pressure decreases, and vice versa.

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5
Q

What is required to move air into and out of the lungs?

A

A pressure gradient between the air outside the body (atmospheric pressure) and the air inside the lungs.

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6
Q

What happens when the pressure in the lungs falls below atmospheric pressure?

A

Air flows from the atmosphere into the lungs.

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7
Q

What happens when the pressure in the lungs rises above atmospheric pressure?

A

Air flows out of the lungs.

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8
Q

How are pressure changes in the lungs created during breathing?

A

By changing the volume of the lungs, utilising Boyle’s Law.

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9
Q

What happens to lung volume and pressure during inspiration?

A

Lung volume increases, causing pressure to decrease.

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10
Q

What happens to lung volume and pressure during expiration?

A

Lung volume decreases, causing pressure to increase.

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11
Q

Describe the relationship between the volume of a container and the frequency of gas molecule collisions with the container walls.

A

In a larger container, gas molecules have more space and collide less frequently with the walls, resulting in lower pressure.

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12
Q

Give an example illustrating the inverse relationship between pressure and volume.

A

If one container has twice the volume of another, it will have half the pressure, assuming the temperature and the amount of gas are constant.

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13
Q

What factor primarily affects atmospheric pressure, and how does this impact breathing?

A
  • Altitude primarily affects atmospheric pressure
  • At higher altitudes, atmospheric pressure is lower, which can make it more difficult to breathe due to the reduced pressure gradient between the atmosphere and the lungs.
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14
Q

How does Boyle’s Law relate to the mechanics of breathing?

A
  • Boyle’s Law states that at a given temperature, the pressure and volume of an ideal gas are inversely proportional.
  • This principle underpins airflow into and out of the lungs.
  • To move air into and out of the lungs, a pressure gradient must be created between the air outside the body and the air in the lungs.
  • By changing the volume of the lungs, we can change the pressure within them.
  • Increasing the volume of the lungs decreases the pressure inside, drawing air in.
  • Decreasing the volume of the lungs increases the pressure, forcing air out.
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15
Q

What is the primary function of the respiratory system?

A
  • Gas exchange between the air and the blood.
  • Specifically the uptake of oxygen and the removal of carbon dioxide
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16
Q

What are the two main divisions of the respiratory tract?

A

The upper and lower respiratory tracts.

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17
Q

Conceptually, what two systems can the respiratory system be divided into?

A
  • The bellows system (moves air in and out of the lungs
  • The gas exchange system (allows diffusion of oxygen and carbon dioxide).
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18
Q

What three main components make up the bellows system?

A
  • Chest wall
  • Pleura
  • Respiratory muscles.
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19
Q

Describe the concept of lung recoil.

A

The lungs have an inherent elastic recoil that tends to pull them inward toward collapse.

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20
Q

Explain chest wall recoil.

A

The chest wall has an outward elastic recoil, wanting to spring outwards.

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21
Q

How do lung recoil and chest wall recoil interact to influence the pleural space?

A

Their opposing forces create the negative pressure within the pleural space.

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22
Q

What are the opposing elastic recoils of the lungs and chest wall?

A

The lungs have an inward elastic recoil wanting to collapse, while the chest wall has an outward elastic recoil wanting to expand.

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23
Q

What is another term for quiet breathing?

A

Tidal breathing.

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24
Q

What is quiet breathing also known as?

A

Tidal breathing.

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25
Q

When does quiet breathing typically occur?

A

At rest.

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26
Q

What is tidal breathing?

A

The mode of breathing that occurs at rest, also known as quiet breathing.
It does not require conscious cognitive control.

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27
Q

What happens during quiet expiration?

A

The diaphragm and external intercostals relax, and the lungs recoil elastically.

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28
Q

How is quiet expiration achieved?

A
  • Passively
  • Through relaxation of the diaphragm and external intercostals
  • Elastic recoil of the lungs.
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29
Q

How do changes in pressure result in airflow during quiet breathing?

A

During quiet inspiration, the contraction of the diaphragm and external intercostal muscles increases the volume of the thorax, leading to an increase in the volume of the pleural space. As volume and pressure are inversely proportional, this leads to a decrease in intrapleural pressure, making it more negative.A more negative intrapleural pressure increases the transpulmonary pressure, causing the lungs to expand.As the lungs expand, the pressure within them decreases, becoming subatmospheric. This pressure gradient causes air to flow from the atmosphere into the lungs.This process continues until the alveolar pressure equals atmospheric pressure, at which point airflow stops.During tidal expiration, the diaphragm and external intercostals relax, and the elastic recoil of the lungs allows them to spring back to their resting position.The volume of the thoracic and pleural cavities decreases, leading to an increase in intrapleural pressure.The transpulmonary pressure decreases, and the elastic recoil of the lungs causes them to decrease in volume.As the volume of the alveoli falls, the alveolar pressure rises above atmospheric pressure, leading to airflow out of the lungs.This continues until the alveolar pressure once again equals the atmospheric pressure.

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30
Q

What is the driving force behind tidal expiration?

A

The elastic recoil of the lungs.

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31
Q

Does quiet breathing require conscious cognitive control?

A

No, it is an automatic process.

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32
Q

During quiet breathing, in what directions does the chest wall move?

A

Forwards and upwards, as well as laterally.

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33
Q

What is the primary muscle involved in inspiration during quiet breathing?

A

The diaphragm.

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34
Q

What action does the diaphragm perform during inspiration?

A

It contracts and flattens, increasing the volume of the thorax.

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35
Q

What is the approximate percentage of air intake and energy expenditure attributed to the diaphragm during quiet breathing in healthy adults?

A

75%

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36
Q

Besides the diaphragm, what other muscles play a role in quiet inspiration?

A

The external intercostals.

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37
Q

What role do the external intercostal muscles play during quiet inspiration?

A
  • They contract slightly to elevate the ribcage
  • Mainly to prevent deformation of the tissues between the ribs and maintain the volume of the thoracic cage.
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38
Q

Is quiet expiration an active or passive process?

A

Passive.

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39
Q

What three mechanisms contribute to quiet expiration?

A
  • Relaxation of the diaphragm
  • Relaxation of the external intercostal muscles
  • Elastic recoil of the lungs.
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40
Q

What happens to intrapleural pressure during tidal expiration?

A

It increases (becomes less negative).

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41
Q

How does the change in intrapleural pressure during tidal expiration affect transpulmonary pressure?

A

It decreases transpulmonary pressure.

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42
Q

What is forced breathing?

A

Breathing that occurs when there is a high demand for oxygenSuch as during exercise or disease states.

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43
Q

How is forced expiration achieved?

A

Through active contraction of abdominal muscles and internal/innermost intercostal muscles.

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44
Q

When does forced breathing typically occur?

A

When there is a high demand for oxygen, like during exercise, in certain disease states, or during actions that require controlled breathing, such as singing.

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45
Q

What happens during forced expiration?

A

Abdominal muscles contract, increasing intra-abdominal pressure and pushing the diaphragm upwards, while internal and innermost intercostal muscles contract to lower the ribs.

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46
Q

Which muscles are engaged during forced expiration?

A

Abdominal muscles and internal and innermost intercostal muscles.

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47
Q

How do the external intercostal muscles function during forced inspiration compared to quiet inspiration?

A

They are more active, raising the ribs to a greater extent to increase the volume of the thoracic cavity.

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48
Q

Describe the “water-pump” or “bucket-handle” effect of the ribs during forced inspiration.

A

The joints between the posterior ends of the ribs and the vertebrae allow the lower ribs to swivel upwards and outwards, increasing the lateral diameter of the chest.

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49
Q

Besides the diaphragm and external intercostals, what other muscles are recruited during forced inspiration?

A

Accessory muscles like the sternocleidomastoid, scalenes, pectoralis major, and latissimus dorsi.

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50
Q

How do the sternocleidomastoid and scalene muscles contribute to forced inspiration?

A

They contract to elevate the ribs, further expanding the chest cavity.

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51
Q

What is the “tripod sign”?

A

The tripod sign is observed when a person plants their arms to assist in expanding their chest during breathing. It involves fixing the shoulder girdle to allow the pectoralis major and latissimus dorsi muscles to pull the chest outwards. At rest, it is a sign of respiratory distress.

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52
Q

In athletes, when might you observe the use of accessory respiratory muscles?

A

At the end of a strenuous race, when oxygen demand is exceptionally high.

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53
Q

When do accessory muscles become involved in breathing?

A

During forced inspiration, when oxygen demand is high.

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54
Q

Is forced expiration an active or passive process?

A

Active.

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55
Q

What muscles are involved in forced expiration?

A

Abdominal musclesInternal intercostal musclesInnermost intercostal muscles.

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56
Q

Besides the diaphragm and external intercostals, what other muscles are involved in forced inspiration?

A

Accessory muscles such as:SternocleidomastoidScalenes (of the neck)Pectoralis majorLatissimus dorsi.

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57
Q

What is the role of accessory muscles during forced inspiration?

A

During forced inspiration, the external intercostal muscles raise the ribs to a greater extent than in quiet inspiration. They move the ribcage upwards and outwards, increasing the lateral and anteroposterior diameter of the thorax.The sternocleidomastoid and scalene muscles of the neck contract, helping to raise the ribs.In some cases, individuals may plant their arms, fixing the shoulder girdle and allowing the use of pectoralis major and latissimus dorsi to pull the chest outwards. This is known as the tripod sign and, at rest, can be a sign of respiratory distress.

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58
Q

What is the role of accessory muscles during forced expiration?

A

During forced expiration, the abdominal muscles contract. This increases intra-abdominal pressure, forcing the abdominal organs upwards against the diaphragm, and pushing the diaphragm upwards. This decreases the volume of the thoracic cavity.The internal and innermost intercostal muscles contract, pulling the ribs down and inwards to further decrease the volume of the thorax.

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59
Q

How do the abdominal muscles contribute to forced expiration?

A

They contract, increasing intra-abdominal pressure, forcing the abdominal organs upwards against the diaphragm, and pushing the diaphragm upwards to decrease the thoracic cavity volume.

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60
Q

What is the function of the internal and innermost intercostal muscles during forced expiration?

A

They contract to pull the ribs down and inwards (decompress), reducing the volume of the thoracic cavity.

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61
Q

What is the effect of the external intercostals raising the ribs during forced inspiration?

A

It increases the lateral and anteroposterior diameter of the thorax.

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62
Q

How do changes in the volume of the thorax lead to changes in lung volume?

A

The pleura, a serous membrane, connects the lungs to the thoracic cavity, allowing the lungs to move with the chest wall.

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63
Q

What is the pleura analogous to in the abdomen?

A

The peritoneal coverings.

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64
Q

What is the pleura?

A

A serous membrane covering the lungs and thoracic cavity.

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65
Q

What are the two layers of the pleura, and where are they located?

A

The visceral pleura covers the lungsThe parietal pleura lines the mediastinum, diaphragm, and ribcage.

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66
Q

What is the pleural cavity (or pleural space), and what does it contain?

A

The pleural space is found between the visceral and parietal pleural layers. It is a potential space, meaning that it is not a large area but it has the potential to become larger. It contains a few millimetres of pleural fluid, which acts as a lubricant.

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67
Q

What is the function of pleural fluid?

A

It acts as a lubricant between the visceral and parietal pleural layers.

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68
Q

Describe the movement of the pleural layers.

A

They can slide easily over each other but are difficult to separate.

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69
Q

What is the pressure within the pleural space, and what is its significance?

A

The pleural space is held at a negative pressure, which is crucial in preventing lung collapse.

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70
Q

What causes the pleural space to have a negative pressure?

A

The lungs have an inward elastic recoil, meaning that they naturally want to collapse, while the chest wall has an outward elastic recoil, meaning that it naturally wants to spring outwards. These two opposing forces pull the visceral and parietal pleural layers apart, resulting in a negative pressure in the pleural space.

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71
Q

Explain the concept of inward elastic recoil in the lungs.

A

The lungs naturally tend to collapse inwards due to their elastic properties.

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72
Q

Describe the elastic recoil of the chest wall.

A

The chest wall has an outward elastic recoil, wanting to expand outwards.

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73
Q

How do the opposing forces of lung recoil and chest wall recoil affect the pleural pressure?

A

The inward pull of the lungs and the outward pull of the chest wall create a negative pressure within the pleural space.

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74
Q

What are the four pressures involved in breathing?

A
  • Atmospheric pressure
  • Alveolar (intrapulmonary) pressure
  • Intrapleural pressure
  • Transpulmonary pressure.
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75
Q

What is atmospheric pressure?

A

Atmospheric pressure is the pressure exerted by the weight of the atmosphere. It is relatively constant and is often used as a reference point, considered as zero centimetres of water.

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76
Q

Define alveolar pressure.

A

Alveolar pressure, also known as intrapulmonary pressure, is the pressure within the alveoli of the lungs.

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77
Q

What is intrapleural pressure?

A

Intrapleural pressure is the pressure within the pleural space, between the visceral and parietal pleural layers.

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78
Q

Define transpulmonary pressure.

A

Transpulmonary pressure is the pressure difference across the lung wall, between the alveoli and the pleural space.It is calculated as the alveolar pressure minus the intrapleural pressure.

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79
Q

What is the function of a positive transpulmonary pressure?

A

It acts as an expanding pressure on the lungs, helping to keep them inflated.

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80
Q

How does transpulmonary pressure relate to lung volume?

A

As transpulmonary pressure increases, lung volume also increases, up to a certain limit.

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81
Q

How can the lungs be compared to balloons to understand the forces in the pleural space?

A

The lungs can be thought of as a pair of balloons suspended in the thorax.Like balloons, the lungs have an inward elastic recoil and tend to collapse inwards.The chest wall, however, has an elastic recoil that is directed outwards. It wants to spring outwards but is held in place by the diaphragm.The pleural space lies between the lungs and the chest wall. The opposing forces of the inward recoil of the lungs and the outward recoil of the chest wall pull the visceral and parietal pleural layers apart. This results in the negative pressure within the pleural space.

82
Q

What is the relationship between pressure and volume according to Boyle’s Law?

A

At a given temperature, the pressure and volume of an ideal gas are inversely proportionalAs volume increases, pressure decreases, and vice versa.

83
Q

How does Boyle’s law relate to air movement in the lungs?

A

Air moves from areas of high pressure to areas of low pressure. By changing lung volume, we change the pressure within the lungs relative to atmospheric pressure, driving airflow in or out.

84
Q

What happens to lung pressure when lung volume increases?

A

Lung pressure decreases.

85
Q

How is a pressure gradient created to facilitate breathing?

A

By increasing or decreasing lung volume, utilizing Boyle’s Law.

86
Q

What happens to the pressure in the lungs when we increase their volume?

A

The pressure decreases, causing air to flow in.

87
Q

What happens to the pressure in the lungs when we decrease their volume?

A

The pressure increases, causing air to flow out.

88
Q

What causes air to flow into the lungs during inspiration?

A

The expansion of the lungs leads to a decrease in alveolar pressure, creating a pressure gradient between the atmosphere and the lungs.

89
Q

What units are used to measure pressure in the respiratory system?

A
  • Kilopascals (kPa) in the UK
  • Millimeters of mercury (mmHg) in the US
  • Centimeters of water (cmH2O) as a relative measure.
90
Q

What is atmospheric pressure and what is its approximate value at sea level?

A

Atmospheric pressure is the pressure exerted by the weight of the atmosphere, which is relatively constant except for changes in altitudeAt sea level, it has a mean value of 101.3 kilopascals (kPa).

91
Q

How is atmospheric pressure typically used as a reference point when discussing respiratory pressures?

A

Atmospheric pressure is often referred to as 0 centimetres of water (cmH2O), and other pressures are described as positive or negative relative to this baseline.

92
Q

What is alveolar pressure?

A

Alveolar pressure, also called intrapulmonary pressure, is the pressure inside the alveoli of the lungs.

93
Q

When is alveolar pressure equal to atmospheric pressure?

A

At the end of both inspiration and expiration, when there is no airflow.

94
Q

What is the state of the alveolar pressure relative to the atmospheric pressure at the end of both inspiration and expiration?

A

When there is no airflow, such as at the end of inspiration and expiration, the alveolar pressure is equal to the atmospheric pressure.

95
Q

What must be true about alveolar pressure at the end of both inspiration and expiration when there is no airflow?

A

Alveolar pressure must be equal to atmospheric pressure.

96
Q

What is intrapleural pressure?

A

The pressure within the pleural space.

97
Q

What is the typical value of intrapleural pressure, and how does it relate to atmospheric pressure?

A

Intrapleural pressure is typically negative, meaning it is lower than atmospheric pressure.

98
Q

Why is intrapleural pressure negative?

A

The lungs have an inward elastic recoil, wanting to collapse, while the chest wall has an outward elastic recoil. These opposing forces acting on the pleural space create a negative pressure.

99
Q

Explain the concept of a transmural pressure.

A

A transmural pressure is a pressure difference across the wall of a structure. The term “trans” means “across” and “mural” refers to a wall.

100
Q

What is transpulmonary pressure, and how is it calculated?

A

Transpulmonary pressure is the pressure difference across the lung wall, specifically between the alveolar pressure and the intrapleural pressure. It is calculated as alveolar pressure minus intrapleural pressure.

101
Q

What can transpulmonary pressure be thought of as?

A

The force resisting the inward elastic recoil of the lungs.

102
Q

What effect does a positive transpulmonary pressure have on the lungs?

A

It acts as an expanding pressure, helping hold the lungs partly expanded.

103
Q

What happens to the lungs as transpulmonary pressure increases?

A

They expand further.

104
Q

How does the change in intrapleural pressure during quiet inspiration affect transpulmonary pressure?

A

It increases transpulmonary pressure.

105
Q

How does the transpulmonary pressure relate to the inward elastic recoil of the lungs?

A

The transpulmonary pressure is the force that resists the inward elastic recoil of the lungs. The greater the transpulmonary pressure, the greater the volume of the lungs.

106
Q

What happens to intrapleural pressure during quiet inspiration?

A

It decreases (becomes more negative).

107
Q

Explain the balloon analogy used to describe the interaction between the lungs, chest wall, and pleural space.

A

Imagine the lungs as balloons suspended within the thorax. The balloons (lungs) want to collapse inward due to their elastic recoil, while the thorax (chest wall) wants to spring outward. The pleural space acts as the interface, and the opposing forces create a negative pressure within this space, preventing the “balloons” from collapsing.

108
Q

What is the effect of a positive transpulmonary pressure on the lungs?

A

It acts as an expanding pressure, keeping the lungs inflated and counteracting their inward elastic recoil.

109
Q

How does transpulmonary pressure relate to lung volume?

A

As transpulmonary pressure increases, lung volume increases until a certain point.

110
Q

What does the term “transmural pressure” mean?

A

A transmural pressure is the pressure difference across the wall of a structure.Transpulmonary pressure, which is the difference between the alveolar pressure and intrapleural pressure, is an example of a transmural pressure.

111
Q

How does inspiration affect intrapleural pressure and transpulmonary pressure?

A

During inspiration, the volume of the thoracic cavity increases, leading to a more negative intrapleural pressure. This, in turn, increases the transpulmonary pressure, causing the lungs to expand.

112
Q

What happens to alveolar pressure during inspiration, and how does this drive airflow?

A

As the lungs expand during inspiration, alveolar pressure drops below atmospheric pressure. This pressure gradient causes air to flow from the atmosphere into the lungs.

113
Q

How does expiration affect intrapleural pressure and transpulmonary pressure?

A

During expiration, the volume of the thoracic cavity decreases, leading to a less negative intrapleural pressure. This decreases the transpulmonary pressure, allowing the lungs to recoil.

114
Q

What happens to alveolar pressure during expiration, and how does this drive airflow?

A

As the lungs recoil during expiration, alveolar pressure rises above atmospheric pressure. This pressure gradient causes air to flow from the lungs out to the atmosphere.

115
Q

What happens to the diaphragm during inspiration?

A

It contracts and flattens, increasing the volume of the thorax.

116
Q

How does contraction of the diaphragm and external intercostal muscles lead to inspiration?

A

It increases thoracic volume, which decreases intrapleural pressureThus increasing transpulmonary pressure and causing lung expansionLeading to airflow into the lungs.

117
Q

How does relaxation of the diaphragm and elastic recoil of the lungs lead to expiration?

A

It decreases thoracic volume, increasing intrapleural pressureThus decreasing transpulmonary pressure and causing the lungs to recoilLeading to airflow out of the lungs.

118
Q

Is there a limit to how much the lungs can expand?

A

Although lung volume increases as transpulmonary pressure increases, there is a limit to how much the lungs can expand.

119
Q

What is lung compliance?

A

Lung compliance is a measure of how easily the lungs can be stretched or distended.

120
Q

What is the relationship between lung compliance and elasticity?

A

Lung compliance and elasticity are inversely related. High compliance means low elasticity and vice versa.

121
Q

What two components contribute to the elastic properties of the lungs?

A

Lung tissue (specifically elastin and collagen fibres) and surface tension.

122
Q

What is the name of the phenomenon where the pressure and volume curve is different for inspiration and expiration?

A

Hysteresis.

123
Q

Where in the lungs is ventilation greater, the base or the apex?

A

The base of the lungs.

124
Q

Besides protection, what are two functions of the alveolar fluid?

A

It supports immune function and mediates gas exchange.

125
Q

What is surface tension?

A

Surface tension is the cohesive force at the surface of a liquid that resists external forces.

126
Q

According to Laplace’s law, how is the pressure inside a bubble related to its radius?

A

The pressure inside a bubble is inversely proportional to its radius.

127
Q

About what proportion of lung elasticity is due to surface tension?

A

About two-thirds.

128
Q

What are the two main types of work involved in breathing?

A

Elastic work and resistive work.

129
Q

What is the primary cause of resistive work during breathing?

A

Airway resistance.

130
Q

What are the two main factors affecting airway resistance?

A

Turbulent airflow and changes in airway radius.

131
Q

Under what conditions can airflow become turbulent in the bronchi?

A

During peak inspiratory flow or when the velocity of gas flow increases.

132
Q

Besides bronchoconstriction, what are two factors that can reduce airway radius?

A

Low lung volume and dynamic airway compression.

133
Q

How does the compliance of the lungs change as they expand?

A

Compliance is not constant. It is low at very low and very high lung volumes, and highest at mid-range volumes.

134
Q

Briefly describe the difference in lung compliance between the apex and the base.

A

At the end of expiration, the base of the lung has greater compliance than the apex because it is less distended.

135
Q

What is the function of the pores of Kohn and the canals of Lambert?

A

They connect adjacent alveoli and help equalise pressure, opposing alveolar collapse.

136
Q

Where is pulmonary surfactant produced?

A

Pulmonary surfactant is produced by cuboidal type two pneumocytes in the alveoli.

137
Q

What is the composition of pulmonary surfactant?

A

Pulmonary surfactant is a mix of phospholipids, neutral lipids, fatty acids, and proteins.

138
Q

How does pulmonary surfactant increase lung compliance?

A

It reduces surface tension more in smaller alveoli than larger ones, making the lungs easier to inflate.

139
Q

What proportion of the work of breathing is typically used for quiet tidal breathing?

A

Less than 2% of the basal metabolic rate.

140
Q

What can happen to the work of breathing in lung pathology?

A

It can increase substantially, leading to respiratory muscle fatigue and respiratory failure.

141
Q

In normal tidal breathing, where does turbulent airflow typically occur?

A

In the trachea.

142
Q

How does dynamic airway compression occur?

A

During forced expiration, positive intrapleural pressure can exceed airway pressure, compressing the bronchioles and increasing airway resistance.

143
Q

What does Boyle’s Law state?

A

At a constant temperature, the pressure and volume of a gas are inversely proportional.

144
Q

How does Boyle’s Law apply to breathing?

A

When we inhale, lung volume increases, decreasing pressure and drawing air in. When we exhale, lung volume decreases, increasing pressure and pushing air out.

145
Q

What is transpulmonary pressure?

A

The difference between alveolar pressure (pressure inside the alveoli) and intrapleural pressure (pressure in the pleural space).

146
Q

What is the relationship between transpulmonary pressure and lung expansion?

A

When transpulmonary pressure is positive, the lungs expand.

147
Q

How does airway resistance affect breathing effort?

A

When airway resistance is increased, a greater pressure gradient is needed to maintain airflow, requiring more effort to breathe.

148
Q

What is the effect of emphysema on lung compliance?

A

Emphysema, which involves the loss of elastic lung tissue, increases lung compliance.

149
Q

What is the effect of pulmonary fibrosis on lung compliance?

A

Pulmonary fibrosis, where scar tissue replaces normal lung tissue, decreases lung compliance.

150
Q

How does the compliance curve relate to the work of breathing?

A

Normal tidal breathing occurs at the steepest part of the compliance curve, where compliance is highest, minimizing the work of breathing.

151
Q

What is tissue resistance?

A

Tissue resistance refers to the friction encountered as tissues move against each other during breathing. It usually constitutes a small proportion of the total resistive work.

152
Q

What is the effect of emphysema on lung compliance?

A

Emphysema increases lung compliance. Emphysema is characterized by the loss of elastic lung tissue, making the lungs easier to stretch.

153
Q

What is the effect of pulmonary fibrosis on lung compliance?

A

Pulmonary fibrosis decreases lung compliance. In pulmonary fibrosis, scar tissue replaces normal lung tissue. This scar tissue is stiffer and less stretchy, making the lungs harder to inflate.

154
Q

What is an analogy used to describe the change in lung compliance during inflation?

A

Inflating the lungs can be compared to blowing up a balloon. Initially, considerable pressure is required to start inflating the balloon. As the balloon expands, it becomes easier to inflate, but then it becomes difficult again as it approaches its maximum capacity. This illustrates how lung compliance changes throughout the breathing cycle.

155
Q

Why is the base of the lungs better ventilated than the apex?

A

Several factors contribute to this:Compression: The base of the lung is compressed by the weight of the lung tissue above it, leading to lower volume at the end of expiration.Intrapleural Pressure: The weight of fluid in the pleural cavity increases the intrapleural pressure at the base, making it less negative than at the apex.Compliance: As a result of the compression, the base has a lower volume at the end of expiration. Because compliance is higher at lower lung volumes, the base expands more during inspiration.

156
Q

What are the functions of alveolar fluid?

A

Alveolar fluid serves several important roles:Protection: It acts as a physical barrier to protect the alveoli from inhaled particles.Immune Support: It dissolves antimicrobial peptides and cytokines and provides an environment for alveolar macrophages.Gas Exchange: It forms part of the diffusion barrier for gas exchange.

157
Q

What are the limitations of Laplace’s Law in relation to alveoli?

A

While useful, Laplace’s Law has limitations:Shape: Alveoli are not perfect spheres.Surfactant: The role of surfactant is complex and goes beyond a simple reduction in surface tension.

158
Q

What are the two components of resistive work?

A

Resistive work, the work done to overcome friction during breathing, consists of:Tissue Resistance: This refers to the friction as tissues move against each other. It usually constitutes a small portion of resistive work.Airway Resistance: This is the major component of resistive work and arises from the frictional forces on gas molecules as they interact with each other and the airway walls.

159
Q

What are some specific examples of conditions that can cause upper airway obstruction?

A

Conditions leading to upper airway obstruction and increased turbulent airflow:Laryngeal oedema: Swelling in the larynx can obstruct airflow.Foreign body: A foreign object lodged in the airway can cause obstruction.

160
Q

How does lung pathology affect the work of breathing?

A

Lung diseases can significantly increase the work of breathing:Normal Breathing: In healthy individuals, quiet tidal breathing utilizes less than 2% of the basal metabolic rate.Disease State: In individuals with lung pathology, the work of breathing can increase to up to 30% of the basal metabolic rate. This can lead to respiratory muscle fatigue and respiratory failure.

161
Q

What is compliance in the context of the lungs?

A

Compliance is a measure of how easily the lungs can be stretched or distended.

162
Q

What is the relationship between compliance and elasticity in the lungs?

A

Elasticity is the tendency of the lungs to return to their original shape after being stretched and can be thought of as the opposite of compliance.

163
Q

What two components contribute to the elastic properties of the lungs?

A

The elastin and collagen fibres within the lung tissue and the surface tension of the alveolar fluid contribute to the elastic properties and tendency of the lungs to recoil.

164
Q

How does emphysema affect lung compliance?

A

Emphysema, which involves the loss of elastic lung tissue, increases lung compliance.

165
Q

How does pulmonary fibrosis affect lung compliance?

A

Pulmonary fibrosis, which involves the replacement of normal lung tissue with scar tissue, decreases lung compliance.

166
Q

What is the shape of the curve that represents the relationship between lung volume and transpulmonary pressure?

A

The relationship between lung volume and transpulmonary pressure is non-linear, as represented by a curve that is initially shallow, then steep, and then flattens.

167
Q

At what point in the respiratory cycle is lung compliance the highest?

A

Lung compliance is highest at low lung volumes, meaning the lungs are more easily stretched when they are relatively empty.

168
Q

Why is ventilation greater at the base of the lungs compared to the apex?

A

The base of the lung has a greater initial compliance than the apex because it is less distended at the end of expiration, resulting in greater expansion during inspiration.

169
Q

What is surface tension?

A

Surface tension is the inward pulling force created by the attraction of water molecules at the air-liquid interface in the alveoli.

170
Q

How does surface tension contribute to the elastic recoil of the lungs?

A

Surface tension acts to reduce the surface area of the alveolar fluid, pulling the alveoli inwards and contributing to the lungs’ tendency to collapse.

171
Q

How does Laplace’s law relate to alveolar pressure?

A

Laplace’s law states that the pressure within a bubble (or alveolus) is proportional to the surface tension and inversely proportional to the radius, implying smaller alveoli require greater pressure to stay inflated.

172
Q

What is the approximate proportion of elastic recoil attributed to lung tissue versus surface tension?

A

The elastic tissue of the lungs contributes to about one-third of the elastic recoil, while the surface tension of the alveolar fluid contributes to about two-thirds.

173
Q

What is hysteresis in the context of lung compliance?

A

Hysteresis refers to the phenomenon where the pressure-volume curve for inspiration is different from the curve for expiration.

174
Q

What are three problems that surface tension presents for the lungs?

A

Surface tension makes smaller alveoli harder to inflate, can cause smaller alveoli to collapse into larger ones, and tends to draw fluid from the interstitium into the alveoli.

175
Q

What are the two mechanisms that act to reduce surface tension in the lungs?

A

Structural interdependence of the alveoli and the presence of surfactant act to reduce surface tension.

176
Q

What is surfactant and what is its function?

A

Surfactant is a mixture of phospholipids and proteins secreted by type II pneumocytes that reduces surface tension in the alveoli, particularly in smaller alveoli.

177
Q

How does surfactant stabilise alveoli?

A

Surfactant reduces surface tension more in smaller alveoli than larger ones, helping to equalise pressure and prevent smaller alveoli from collapsing.

178
Q

What are the two components of the work of breathing?

A

The work of breathing consists of elastic work, used to overcome the elastic forces of the lungs and chest wall, and resistive work, used to overcome friction.

179
Q

What are the two main types of resistive work?

A

Resistive work is comprised of tissue resistance, which arises from tissues moving against each other, and airway resistance, which results from friction encountered by airflow.

180
Q

What two factors primarily affect airway resistance?

A

Airway resistance is primarily affected by turbulent airflow and changes in airway radius.

181
Q

What can cause turbulent airflow in the airways?

A

Turbulent airflow can be caused by high airflow velocity, upper airway obstruction, and increased respiratory rate.

182
Q

What factors can lead to a reduction in airway radius?

A

Airway radius can be reduced by bronchoconstriction, low lung volume, and dynamic airway compression.

183
Q

What is dynamic airway compression?

A

Dynamic airway compression occurs during forced expiration when increased intrapleural pressure compresses the airways, further increasing airway resistance.

184
Q

What factors can influence lung compliance?

A

Lung compliance can be affected by factors such as disease (e.g., emphysema increases compliance, pulmonary fibrosis decreases it), lung volume (compliance is higher at lower volumes), and surface tension.

185
Q

Why is understanding hysteresis in lung compliance not considered crucial at this stage?

A

While the difference between inspiratory and expiratory pressure-volume curves (hysteresis) is observed, the source suggests that the detailed mechanism is not essential for a basic understanding at this point.

186
Q

How does surfactant contribute to alveolar stability, and why is its role particularly important in smaller alveoli?

A

Surfactant reduces surface tension, and this effect is greater in smaller alveoli, where surfactant molecules are more concentrated. This helps to equalise pressure between alveoli of different sizes, preventing the collapse of smaller alveoli into larger ones.

187
Q

What is the impact of lung diseases on the work of breathing, and what can this potentially lead to?

A

Lung pathologies can significantly increase the work of breathing, potentially demanding up to 30% of the basal metabolic rate. This increased workload on respiratory muscles can result in fatigue and respiratory failure.

188
Q

Why does increased airway resistance necessitate increased respiratory effort?

A

When airway resistance is high, the respiratory muscles have to work harder to generate a larger pressure gradient, which is required to maintain airflow. This translates to increased effort during breathing.

189
Q

How do conditions like asthma and emphysema exacerbate the effects of dynamic airway compression?

A

In asthma, narrowed airways are more prone to collapse during forced expiration, while in emphysema, the loss of elastic tissue reduces the radial traction that helps keep airways open. Both conditions worsen the effects of dynamic airway compression, making it harder to exhale and potentially trapping air in the lungs.

190
Q

What is the role of Boyle’s Law in respiration, and how does it relate to the movement of air?

A

Boyle’s Law states that the pressure of a gas is inversely proportional to its volume at a constant temperature. During inspiration, the volume of the thoracic cavity increases, leading to a decrease in intrapulmonary pressure, causing air to flow into the lungs. During expiration, the opposite happens: thoracic volume decreases, intrapulmonary pressure increases, forcing air out.

191
Q

How does intrapleural pressure contribute to transpulmonary pressure and lung expansion?

A

The intrapleural pressure, which is negative, pulls on the lungs outwards, while the lungs’ natural elasticity causes them to recoil inwards. The difference between the pressure inside the alveoli (intrapulmonary pressure) and the intrapleural pressure is the transpulmonary pressure. A positive transpulmonary pressure results in lung expansion.

192
Q

How does the source illustrate the concepts of compliance and elasticity?

A

The source uses the analogy of thick and thin rubber bands. A thick rubber band (low compliance, high elasticity) requires more force to stretch but snaps back strongly. A thin rubber band (high compliance, low elasticity) stretches easily but has a weaker recoil.

193
Q

What is the difference between static and dynamic lung mechanics?

A

Static lung mechanics refers to measurements taken at a single point in time, without considering airflow. Dynamic lung mechanics, on the other hand, considers how airflow changes over time. The pressure-volume curves discussed in the source represent static mechanics.

194
Q

Why does the base of the lung receive more ventilation than the apex?

A

Several factors contribute to this:Gravity compresses the base of the lung more than the apex.The weight of pleural fluid creates a less negative intrapleural pressure at the base.As a result, the transpulmonary pressure is lower at the base at the end of expiration.Since compliance is higher at lower lung volumes, the base expands more during inspiration.

195
Q

What is the role of alveolar fluid in surface tension?

A

The thin layer of alveolar fluid lining the alveoli creates an air-liquid interface.At this interface, water molecules attract each other more strongly, creating an inward-pulling force known as surface tension which contributes to the lungs’ tendency to recoil.

196
Q

How does Laplace’s law relate to alveolar stability?

A

Laplace’s law states that the pressure inside a bubble (or alveolus) is directly proportional to surface tension and inversely proportional to its radius (P=2T/r).This means smaller alveoli would have a higher collapsing pressure if surface tension remained constant.Surfactant helps to overcome this by differentially reducing surface tension, especially in smaller alveoli.

197
Q

Are there any criticisms of the surfactant explanation for alveolar stability?

A

The source acknowledges that the traditional model, which describes alveoli as perfect spheres, has limitations.The actual role of surfactant might be more complex than this simplified model suggests.

198
Q

What are the two main components of the work of breathing?

A

Elastic work: The energy needed to overcome the elastic recoil of the lungs and chest wall during inspiration.Resistive work: The energy used to overcome frictional forces in the airways and tissues.

199
Q

What are the factors that can contribute to turbulent airflow in the respiratory system?

A

Increased velocity of airflow, such as during exercise or with upper airway obstruction.The large diameter of the trachea, which makes it harder for airflow to remain laminar.

200
Q

Why are even small changes in airway radius significant for airflow?

A

Airflow is proportional to the fourth power of the radius of the airway.This means a small decrease in radius, such as with bronchoconstriction, leads to a disproportionately large increase in resistance and reduces airflow.

CTB Block 2 (5 decks)

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