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Respiratory System > Mechanisms of Breathing I & II > Flashcards

Mechanisms of Breathing I & II Flashcards

1
Q

How does air move within the respiratory system?

A

The respiratory system achieves movement of air due to the ability of gases to naturally move from (connected) areas of higher to lower pressure, until an equilibrium is reached again

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2
Q

What are the two ways to quantify pressure?

A

PV = nRT

P ∝ n/v

if n remains constant, inc. volume = decreased pressure

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3
Q

Explain the effects of change in lung volume

A

Change in lung volume induces changes in alveolar pressure
=> generates pressure gradients between alveoli and
atmosphere, causing air flow

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4
Q

Describe the movement of the respiratory system during inspiration

A

Diaphragm contracts
Thoracic cavity expands
Alveolar pressure decreases
Air moves in

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5
Q

What movement occurs within the respiratory system during expiration?

A

Diaphragm relaxes
Thoracic cavity volume decreases
Alveolar pressure increases
Air moves out

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6
Q

How is lung pressure altered to create pressure gradients during the mechanism of breathing?

A

Inhalation: atm > lung
Exhalation: atm < lung

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7
Q

How is a pressure gradient created within the lungs?

A

Achieved by manipulating lung volume

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8
Q

What causes lung volume to be altered within the respiratory system?

A

Contraction of respiratory muscles induces volume changes in the thoracic cavity, causing pressure changes in the lungs
- pressure gradient created between atm and lungs
=> air moves

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9
Q

When is equal pressure reached in the respiratory system?

A

At the end of expiration, P(alveoli) = P(atm) so there is no movement of air as no pressure gradient

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10
Q

Describe the pressure gradient during inspiration

A

Outer (parietal membranes) surfaces of the lung are pulled outwards (expansion)

  • increases volume
  • decreases pressure

P(alveoli) < P(atm)
air flows in from atm to low pressure in lungs

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11
Q

Describe the pressure gradient during expiration

A

Air in the lungs is compressed

  • decreased volume
  • increased pressure

P(alveoli) > P(atm)
Air flows out of high pressure lungs to low pressure in atm

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12
Q

What is the role of the pleural cavity?

A

Indirectly attaches the lungs and chest wall

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13
Q

What is the pleural cavity?

A

Fluid filled space between membranes (pleura); lines each lung and the chest wall

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14
Q

What is the function of the pleura?

A

Help reduce friction to aid movement of the lungs

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15
Q

What causes negative pressure to build up in the pleural cavity?

A

The opposing elastic recoil of the chest wall (outwards) and lungs (inwards), generates negative pressure within the pleural cavity

sealed cavity + increased vol. = decreased pressure

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16
Q

What is the effect of the negative pressure in the pleural cavity?

A

Pulls the two membranes together

more negative the pressure = more force pulling pleurae together

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17
Q

What is the stability of pressure like between neighbouring spaces?

A

Differences in pressure between neighbouring spaces are unstable

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18
Q

What is the effect of insufficient opposing force in the pleural cavity?

A

Equilibrium will be re-established via either:
- movement of liquid / gas
- collapse / expansion of volume at the expense of
surrounding structures

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19
Q

What is negative pressure?

A

Lower no. of molecules per volume (relative to surroundings)
-> generates collapsing force by pulling surfaces of
contained spaces together

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20
Q

What is positive pressure?

A

Increased no. of molecules per volume (relative to surroundings)
-> generates an expanding force by pushing surfaces of
contained spaces apart

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21
Q

What is the effect of equal pressures?

A

Equilibrium reached

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22
Q

Explain the effect of increasing the volume of the pleural cavity

A

Decreases pressure further = negative pressure
- Collapsing force exerted on lung at expense of lung
volume; draws air in

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23
Q

What is the effect of positive pressure on on the lungs and pleural cavity?

A

Increasing pressure of the lungs (decreased vol.) compresses the pleural membrane
Expanding force exerted on the lungs (inwards) so air moves out

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24
Q

What determines the degree of expansion and retraction of the lungs?

A

Expansion and retraction of the lung is determined by the relative size of the opposing forces

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25
Q

What is the pressure gradient like at the end of expiration?

A

At the end of expiration, the system is in equilibrium

- forces are equal

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26
Q

Why is intrapleural pressure slightly negative after expiration?

A

At the end of expiration, the intra-pleural pressure is slightly negative due to minor stretching of the cavity by the opposing recoil forces acting on each pleura

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27
Q

What occurs in the intrapleural membranes for lung volume to change?

A

Either forces acting on one of the pleura needs to become greater than the other

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28
Q

Describe the events occurring during inspiration in the pleural cavity and lungs

A 
Muscular contraction (e.g. diaphragm)
Parietal pleura pulled outwards 
Cavity stretches - inc. vol, decreased P(intrapleural)
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29
Q

What is the effect of decreased P(intrapleural)?

A

The decreased (more negative) P(intrapleural) creates a greater level of force acting to pull the visceral pleura outwards

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30
Q

What enables the parietal pleura to be held outwards?

A

Parietal pleura held outwards by muscular contraction

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31
Q

What causes the parietal pleura to pulled outwards?

A

Outward force generated by P(intrapleural) > Inward force generated by lung recoil, expanding the lung

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32
Q

Describe the events occurring during passive expiration

A

Relaxation of previously contracted muscles
Reduces outwards force on parietal pleura
Reduces degree of cavity stretch
P(intrapleural) increases

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33
Q

Explain the effect of the increased P(intrapleural)

A 
Increased P(intrapleural) no longer generates sufficient force to overcome elastic recoil of visceral pleura inwards
Lung volume decreases - air moves out
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34
Q

What happens during a forced expiration?

A

Other respiratory muscles also contract (e.g. abdominal and intercostal)
provide further inward force on parietal pleura
Pleural cavity compressed further increasing P(intrapleural) forcing an increased lung volume decline

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35
Q

How is movement of air into / out of lungs achieved?

A

By altering the volume of the thoracic cavity

36
Q

Outline the events within the thoracic cavity during inspiration

A
  • Respiratory muscles contract
  • Thoracic cavity volume increases
  • P(intrapleural) = more negative
  • Outward force on visceral pleura > inward recoil force
  • Lungs expand, increasing Volume
  • Palv < Patm
  • air moves into alveoli expanding lungs
37
Q

Which mechanisms are involved in expiration?

A

Involves the elastic recoil of lungs and muscle relaxation

38
Q

What causes lung compression during expiration?

A

Increased P(intrapleural) - during forced expiration

39
Q

Why does passive expiration not require an increased P(intrapleural)?

A

Elastic recoil is sufficient enough to decrease lung volume

40
Q

What is an open pneumothorax?

A

an unsealed opening in the chest wall impairing respiratory mechanisms => air moves in from atm

41
Q

What is the atmospheric pressure value?

A

100kPa

42
Q

What is the normal intrapleural pressure, relative to atmospheric pressure?

A

Intrapleural pressure is naturally sub-atmospheric ~99.5 kPa due to opposing elastic recoil of chest wall and lungs

43
Q

What is the consequence of piercing either of the pleural membranes?

A

Will cause air to enter pleural cavity from either the lungs (closed) or the atmosphere (open) depending on the injury => pneumothorax

44
Q

What is a closed pneumothorax?

A

When air / gas enters pleural cavity from lungs, without any external injury - normally occurs in CF / cancer patients (when lung already damaged)

45
Q

What is the consequnece of pneumothorax?

A

Negative P(intrapleural) lost
Chest wall and lungs no longer indirectly attached
- will recoil in opposing directions causing lung tissue
collapse => atelactasis

46
Q

Describe the effect of entry of air into a pneumothorax

A

Increased pleural cavity volume
at expense of lung volume (decreases)
Reduces P(intrapleural) changes during inspiration
- prevents proper lung expansion

pneumothorax causes lung collapse - limits gas exchange

47
Q

Outline how breathing occurs

A
  1. Lung volume increases
  2. Palv < Patm
  3. air moves into lungs
48
Q

Why is the difference in pressure between atm and alveoli not negated immediately ?

A

The difference in pressure aren’t instantly negated as there’s a delay due to the time taken for air to move

49
Q

What is speed of airflow increased by?

A
  • Decreased resistance
  • Increased Radius
  • Increased Pressure

R ∝ 1/r⁴

50
Q

How does air reach gas exchange surfaces?

A

To reach gas exchange structures, air must pass through a series of increasingly narrow and numerous airways

51
Q

What causes impaired airway function?

A

Due to insufficient ventilation

52
Q

What does rate of airflow depend upon?

A

The rate of airflow depends on the pressure gradients and level of airway resistance

53
Q

Outline Ohm’s Law

A

Airflow = ΔP / resistance

↑ΔP = ↑ airflow
↑ resistance = ↓airflow

54
Q

Explain how a reduction in airway radius effects airflow

A

As airway radius decreases, Resistance increases, reducing airflow dramatically

55
Q

What type of airflow increases resistance?

A

Turbulent flow

56
Q

How does turbulent airflow increase airway resistance?

A

Air moves in different directions increasing resistance reducing speed of airflow

57
Q

Describe the structure of alveoli in healthy individuals

A

Elastin in surrounding alveoli provides radial traction to splint bronchioles against positive Palv

58
Q

How does COPD affect alveoli structure and airflow?

A

Without radial traction, bronchioles collapse causing obstruction

59
Q

What causes a loss of airway patency in COPD?

A

Loss of airway patency due to degradation of structure causing airway obstruction
Airways collapse due to lack of structural integrity

60
Q

How can we calculate the total % of lung capacity an individual can exhale in the first second?

A

100 x FEV₁ / FVC = %

FEV₁ - Forced expiratory volume (in 1 sec)
FVC - Forced vital capacity

(<80% is indicative of obstructive airways disease)

61
Q

Describe the results for a patient with obstructive COPD

A

FEV₁ / FVC < 70%

e. g. asthma
- increased resistance

62
Q

What would the results of a patient with restrictive COPD look like?

A

FEV₁ / FVC > 70%
FVC < 80%
e.g. Fibrosis
- decreased compliance

63
Q

Outline how you’d calculate Transpulmonary pressure Pₜₚ

A

Pₜₚ = Pₐₗᵥ - Pᵢₚ

64
Q

What is transpulmonary pressure?

A

The level of force acting to expand the lung

65
Q

What is lung compliance?

A

Lung compliance is the relationship between transpulmonary pressure and lung volume (higher lung CL, steeper gradient)

66
Q

How does scoliosis muscular dystrophy + obesity affect lung CL?

A

Decreases lung compliance interfering with chest wall mechanisms

67
Q

How does NRDS (newborn respiratory distress syndrome) affect compliance?

A

Affects alveolar surface tension - decreasing CL

68
Q

What is the effect of fibrosis and COPD on lung compliance?

A

Affect the elastin fibres:

  • Fibrosis : ↓CL due to collagen deposition
  • COPD: ↑CL due to elastin degradation
69
Q

How does emphysema affect lung compliance?

A

↑CL due to elastin degradation

70
Q

How do air liquid interfaces resist inflation?

A

Generate surface tension which resist inflation

71
Q

Give examples of air liquid interfaces

A

Alveoli are lined with fluid to enable gas exchange - the gas molecules dissolve into the water before diffusing.

72
Q

Why does tension arise within the bubble formed by water-air interfaces?

A

Tension arises due to H-bonds between water molecules exerting a collapsing force towards the centre of the bubble

73
Q

How does Laplace’s law relate to the respiratory system?

A

Describes the pressure generated by surface tension within a bubble
- collapsing force generates pressure, the amount within
a specific bubble is described by Laplace’s

74
Q

Outline the equation used by Laplace’s Law to calculate pressure generated

A

P = 2T/r

p - pressure
2T - surface tension
r - bubble radius (alveoli)

75
Q

How does the size of alveoli affect the pressure generated at air liquid interfaces?

A

if T remains constant, P ∝ 1/r

  • smaller the alveoli, the larger the pressure generated
76
Q

How is alveolar surface tension reduced?

A

Reduced by the presence of pulmonary surfactant, secreted by type II pneumocytes

77
Q

What is the role of pulmonary surfactant?

A

Pulmonary surfactant act to equalise pressure and volume across varying alveoli

78
Q

How does [surfactant] change as gas exchange occurs?

A

As alveoli expand, the [surfactant] decreases - increasing surface tension

79
Q

How are the lungs kept inflated?

A

Larger alveoli tend to collapse into smaller ones, helping consistent inflation of the lungs

80
Q

What role does pulmonary surfactant play in alveolar oedema?

A

Pulmonary surfactant help prevent alveolar oedema by reducing surface tension

81
Q

How does surface tension affect alveolar oedema?

A

Surface tension produced at air-liquid interface also reduces hydrostatic pressure
- fluid pulled out of surrounding capillaries -> alveoli

82
Q

What is NRDS?

A

neonatal respiratory distress syndrome

83
Q

What causes NRDS?

A

Insufficient surfactant production often due to:

  • premature birth
  • maternal diabetes
  • congenital development issues
84
Q

Explain the effects of NRDS and how they occur

A 
Premature birth / congenital defects 
↓
Insufficient surfactant production 
↓
Stiff (low CL), alveolar collapse, oedema 
↓ 
Respiratory failure 
↓
Pulmonary vasoconstriction, endothelial damage, acidosis, pulmonary &amp; cerebral haemorrhage
85
Q

How is NRDS treated?

A
  • artificial surfactant supplementation

- maternal glucocorticoid supplementation

Respiratory System (10 decks)

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