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The Thorax > Respiratory Physiology > Flashcards

Respiratory Physiology Flashcards

1
Q

How is airflow through the airway calculated

A

Alveolar pressure - (atmospheric pressure / Resistance)

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2
Q

Function of airway cilia

A

To transport mucus from the airways to the pharynx where it is swallowed

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3
Q

What is the water vapour within the airways at 37 degrees

A

6.3kPa

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4
Q

What is the intrapleural pressure at the beginning of inspiration

A

-4cmH2O

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5
Q

What is the peak intrapleural pressure on inspiration

A
  • 9cmH20 during normal breathing

- 30cmH2O during exercise

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6
Q

What type of process is exhalation

A

Passive process from recoil of the chest wall

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7
Q

List the 3 forces acting on the lung

A
  1. Elastic nature of lungs = inward pull on visceral pleura
  2. Surfactant = inward pressure
  3. Negative intrapleural pressure = outward pull
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8
Q

What is Hysteresis

A

Unequal pressure required to maintain a given lung volume on inspiration and expiration

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9
Q

Where is surfactant produced

A

Type 2 alveolar cells

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10
Q

Describe surface tension

A
  • Occurs at all air-fluid interfaces
  • Water molecules are more attached to each other than the surrounding gas molecules
  • Creates an inward pressure
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11
Q

Biggest contributor to the elastic recoil of the lungs

A

Surface tension

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12
Q

What is the primary purpose of surfactant

A

Reduce surface tension at the pulmonary air-liquid interface to reduce work of breathing

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13
Q

Define the Law of Laplace

A

Alveolar distending pressure is proportional to surface tension / radius

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14
Q

What does the Law of Laplace imply

A

As alveoli decrease in size the pressure within them would increase and result in collapse (if surfactant were not present)

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15
Q

What is the relationship between alveolar radius and surfactant production

A

They increase or decrease in tandem

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16
Q

Describe lung compliance

A
  • The ease at which the lungs can be inflated

- Compliance = change in volume / change in pressure

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17
Q

What two factors govern lung compliance

A
  1. Elasticity of the lung parenchyma

2. Surface tension

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18
Q

List conditions that increase lung compliance

A

Emphysema

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19
Q

List conditions that reduce lung compliance

A
  • Scarring/fibrosis
  • Pulmonary oedema
  • Deficiency of surfactant e.g. prematurity
  • Decreased lung expansion e.g. paralysis
  • Supine position
  • Mechanical ventilation (due to reduced pulmonary blood flow)
  • Age
  • Breathing 100% O2
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20
Q

What class as non-elastic forces of chest wall movement

A
  • Airway resistance
  • Frictional forces
  • Inertia of the air and tissues
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21
Q

How is airway resistance divided throughout the respiratory tract

A
  • 1/3rd = upper airways

- 2/3rd = tracheobronchial tree (primarily the medium-sized bronchi)

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22
Q

Relationship between resistance and lung volume

A

Resistance falls as lung volumes increase as the elastic parenchyma pulls open the bronchioles

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23
Q

Describe the 4 phases of lung expansion

A
  1. Takes considerable pressure increase before there is change in volume
  2. Expansion of the lung is proportional to the increase in pressure
  3. Maximum capacity
  4. In the initial stage the lung volume is maintained until the pressure falls considerably
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24
Q

Shape of the lung inflation (compliance) curve

A

Sigmoid

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25
Q

How does tension pneumothorax develop

A

Lung injury forms a valve in which air leaks into the pleural cavity but closes during expiration leading to positive intrapleural pressure

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26
Q

When does a sucking pneumothorax develop

A

If defect in the chest wall is greater than 2/3rd the diameter of the trachea then air will enter via the chest wall as oppose to traditional airway

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27
Q

Define tidal volume

A

Air taken in and exhaled during quiet breathing

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28
Q

Define inspiratory reserve volume

A

Maximum volume of air that can be inspired in excess of normal inspiration

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29
Q

Define expiratory reserve volume q

A

Maximum volume of air that can be expired forcefully after normal expiration

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30
Q

Define functional residual capacity

A

Volume of gas left in the lungs. after expiration during normal breathing

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31
Q

How is functional residual capacity calculated

A

Using Helium dilution method

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32
Q

Define residual volume

A

Volume of air remaining after maximal expiration (FRC - ERV)

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33
Q

Define vital capacity

A

Volume of air that is expelled from maximal inspiration to maximal expiration

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34
Q

Define anatomical deadspace

A

Volume of gas that does mix with air in the alveoli

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35
Q

Define physiological deadspace

A

Volume of gas that may reach air in the alveoli but due to lack of perfusion does not take part in gas exchange (includes anatomical deadspace)

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36
Q

How is anatomical deadspace calculated

A

Fowler’s method - uses nitrogen analyser

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37
Q

How is physiological deadspace calulated

A

Bohr equation - based on principle that all expired CO2 comes from the alveoli

38
Q

What factors increase anatomical dead space

A
  • Increasing size of patient
  • Standing position
  • Increased lung volume
  • Bronchodilatation
  • Ventilation
39
Q

Factors increasing physiological deadspace

A
  • Hypotension
  • Hypoventilation
  • Emphysema and PE
  • Positive pressure ventilation
40
Q

Define closing capacity

A

The volume of the lungs at which small airways at the base of the lungs start to close (usually 10% of vital capacity)

41
Q

What factors increase closing capacity

A
  • Increasing age
  • Supine posture
  • Anaesthesia
42
Q

How is diffusion capacity measured

A
  1. Inhalation of CO

2. Measurement of arterial CO

43
Q

What reduces diffusion capacity

A
  • Increase in diffusion distance e.g. pulmonary oedema

- Loss of alveolar surface area e.g. emphysema

44
Q

Describe hypoxic pulmonary vasoconstriction

A

Hypoxia or hypercapnia result in constriction of the small alveolar vessels to divert blood to better oxygenated areas of the lung

45
Q

What is the typical pulmonary artery pressure

A

25/8mmHg

46
Q

What 3 factors determine pulmonary blood flow

A
  • Hydrostatic pressure in the pulmonary arteries
  • Pressure in the pulmonary veins
  • Pressure of air in the alveoli
47
Q

Where in the lung is pulmonary blood flow the worst

A

Apex of the lung - alveolar pressure is similar to PA pressure causing small vessels to be compressed

48
Q

What happens to pulmonary resistance when Cardiac output increases and why

A

Reduces:

  • Distension of already open vessels
  • Recruitment of additional vessels
49
Q

What does V/Q equal in alveoli that are ventilated but not perfused

A

Infinity

50
Q

What does V/Q equal in alveoli that are not ventilated but well perfused

A

0

51
Q

Where is the ideal V/Q of 1 found in the lung

A

Approximately 2/3rd the way up the chest

52
Q

List the causes of PE

A
  • DVT
  • Fat embolism
  • Amniotic fluid embolism
  • Air embolism
  • Tumour fragments
53
Q

List the physiological changes associated with PE

A
  • Increased pulmonary vascular resistance
  • Pulmonary HTN
  • Increased RV afterload
  • Reduced LV output
  • Impaired gas exchange
  • Decreased lung compliance from reduced surfactant
54
Q

Normal volume of fluid in the lung interstitium

A

20-30ml

55
Q

List the three stages of pulmonary oedema

A
  1. Interstitial oedema
  2. Alveolar oedema
  3. Airway oedema
56
Q

List the physiological effects of pulmonary oedema

A
  • Decreased lung compliance

- Increased airway resistance

57
Q

What are the 2 phases of ARDS

A
  1. Acute exudative

2. Late organisation

58
Q

What forms during the acute exudative phase of ARDS

A

Hyaline membranes

59
Q

What occurs in the organisation phase of ARDS

A
  1. Regeneration of type 2 pneumocytes

2. Hyaline membranes organise with pulmonary fibrosis

60
Q

What 3 factors affect the diffusion of gasses in the lungs and peripheral tissues

A
  1. Pressure gradient
  2. Diffusion coefficient
  3. Tissue factors
61
Q

What does oxygen have to cross to reach the circulation in the lungs

A
  1. Pulmonary surfactant
  2. Alveolar epithelium
  3. Alveolar epithelium basement membrane
  4. Pulmonary capillary endothelium
62
Q

How does alveolar air composition differ from room air composition

A

Addition of water vapour and constant removal of O2

63
Q

Define shunting

A

Passage of blood through the lungs without coming into contact with ventilated alveoli

64
Q

Causes of shunting

A
  • Pneumonia
  • ASD
  • VSD
  • PDA
65
Q

Describe the structure of Hb

A
  • Consists of 4 peptide chains = 2 alpha and 2 beta chains
  • Each chain has a haem group
  • Haem group = protoporphyrin ring surrounding ferrous (Fe2+) molecule
66
Q

How much oxygen can each gram of Hb carry

A

1.34ml

67
Q

What does the oxygen dissociation curve illustrate

A

Relationship between the partial pressure of O2 and the concentration of O2 in the blood

68
Q

What does a right shift of the oxygen dissociation curve demonstrate

A

Reduced affinity for oxygen of haemoglobin and thus oxygen will be released at a higher pO2 (Bohr Effect)

69
Q

What does a left shift of the oxygen dissociation curve demonstrate

A

Increased affinity for oxygen of haemoglobin

70
Q

List the causes of a left shift of the oxygen dissociation curve

A
  • Alkalosis
  • Reduced temperature
  • Reduced 2,3-DPG
  • Carbon monoxide
  • Fetal Hb
71
Q

List the causes of a right shift of the oxygen dissociation curve

A
  • Acidosis
  • Increased temperature
  • Increased 2,3-DPG
  • Carbon dioxide
  • Altitude
72
Q

Describe the Bohr effect

A

Right shift of the oxygen dissociation curve, the factors causing this are present in active tissues, it represents ma mechanism to increase oxygen extraction

73
Q

Does anaemia affect the oxygen dissociation curve

A

No

74
Q

Describe the structure of fetal Hb (differences from adult Hb)

A

Different globin chains = 2 alpha and 2 gamma

75
Q

Purpose of fetal Hb

A

Has a greater affinity for O2 and allows the foetus to extract blood from the circulation

76
Q

What is the function of myoglobin

A

Acts a storage molecule for oxygen - provides additional O2 in muscles during periods of anaerobic respiration

77
Q

List the 3 methods of CO2 transport

A
  1. Carbamino groups
  2. Dissolved CO2 - 10%
  3. HCO3 - 60-70%
78
Q

Outline the process by which CO2 is transported as HCO3

A
  1. CO2 diffuses into RBC
  2. Reacts with water to form carbonic acid
  3. Carbonic acid dissociates into H+ and HCO3-
  4. H+ binds to Hb and the HCO3- diffuses out of the cell into plasma
  5. To maintain balance CL- diffuses into the RBC (chloride shift)
79
Q

Define the Haldane Effect

A

The amount of CO2 carried increases as the oxygen level falls

80
Q

Where is the respiratory centre located

A

Medulla oblongata (contain inspiratory and expiratory nerurons)

81
Q

What is the role of the Apneustic centre in the pons

A

Prolongs inspiration and results in short expiratory efforts

82
Q

What is the role of the pneumotaxic centre in the pons

A

Inhibits inspiratory neurons and shortens inspiration

83
Q

Where controls the ability to hold a breath

A

Cerebral cortex

84
Q

Where are central chemoreceptors located

A

In the CNS, close to the respiratory centre of the medulla

85
Q

How are central chemoreceptors stimulated

A

Sensitive to changes in arterial CO2:

  1. CO2 reacts with water in the brain to produce H+
  2. pH falls and directly stimulates the receptor
86
Q

What is the most important stimulus to respiration

A

CO2

87
Q

Where are the peripheral chemoreceptors located

A
  1. Carotid body

2. Aortic bodies

88
Q

What stimulates peripheral chemoreceptors

A
  1. Hypoxia <8kPa

2. Changes in arterial pH

89
Q

Describe the Hering-Breur reflex

A

Prevents lung overinflation - stretch receptors in the lung send inhibitory signals via the vagus

90
Q

Define hypoxia

A

Deficiency of oxygen in the tissues

91
Q

Define hypoxaemia

A

Reduction in the concentration of oxygen in the arterial blood

92
Q

Define histotoxic hypoxia

A

Poisoning of the enzymes involved in cellular respiration. Oxygen is available but cannot be utilised. e.g. Cyanide poisoning

The Thorax (5 decks)

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