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MRCEM Primary > Respiratory physiology > Flashcards

Respiratory physiology Flashcards

1
Q

Define tidal volume.

A

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

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2
Q

What is the normal tidal volume in a healthy male?

A

500mL (or 7ml/kg body mass).

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3
Q

Define inspiratory reserve volume.

A

The maximum volume of air that can be breathed in during maximal inspiration.

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4
Q

What is the usual inspiratory reserve volume in a healthy male?

A

3L

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5
Q

Define expiratory reserve volume.

A

The maximum volume of air that can be breathed out during maximal expiration.

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6
Q

What is the usual expiratory reserve volume in a healthy male?

A

1L

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7
Q

Define residual volume (reserve volume).

A

The volume of air remaining in the lungs after maximum expiration.

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8
Q

What is the usual residual volume in a healthy male?

A

1L.

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9
Q

How is residual volume measured?

A
  1. Nitrogen washout test (Fowler’s method)
  2. Helium dilution technique
  3. Body plethysmography

**Cannot be measured by spirometry.

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10
Q

What happens to the residual volume as age increases?

A

Residual volume increases.

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11
Q

Define vital capacity.

A

The maximum volume of air that can be breathed out following maximum inspiration.

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12
Q

How do you calculate vital capacity?

A

Inspiratory reserve volume + tidal volume + expiratory reserve volume.

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13
Q

What is the usual volume of vital capacity in a healthy male?

A

4.5L

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14
Q

Define total lung capacity.

A

The volume of air in the lungs at the end of maximal inspiration.

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15
Q

How do you calculate total lung capacity?

A

Vital capacity + residual capacity.

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16
Q

How is total lung capacity measured?

A

Helium dilution.

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17
Q

What is the usual total lung capacity in a healthy male?

A

5.5L

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18
Q

Define functional residual (reserve) capacity.

A

The volume of air present in the lungs at the end of a normal expiration.

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19
Q

How do you calculate functional reserve capacity?

A

Expiratory reserve volume + residual volume.

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20
Q

What is the usual functional reserve capacity in a healthy male?

A

2L

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21
Q

Give 2 factors that cause an increased functional residual capacity.

A
  1. Marked airway obstruction (severe asthma, COPD).
  2. Loss of elastic recoil (advanced age, emphysema).
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22
Q

Give 4 factors that cause decreased functional reserve capacity.

A
  1. Stiff, non-compliant lungs (restrictive disorders)
  2. Bilateral paralysis of diaphragm
  3. Lying in supine position
  4. Induction of anaesthesia (FRC falls by 15-20%)
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23
Q

What factor has the greatest influence on functional residual capacity?

A

Height

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24
Q

Define dead space.

A

The volume of inhaled air that does not take part in gas exchange.

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25
Q

Define anatomical dead space.

A

The portion of the airways that conducts gas to the alveoli where no gas exchange can take place.

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26
Q

How can anatomical dead space be measured?

A

Nitrogen washout test (Fowler’s test).

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27
Q

Define alveolar dead space.

A

The sum of the volumes of the alveoli with no blood flowing through their adjacent capillaries (alveoli that are ventilated but not perfused).

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28
Q

When can alveolar dead space increase?

A

In the presence of lung diseases such as pneumonia or a PE (Due to V/Q mismatch).

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29
Q

Define physiological dead space.

A

The sum of the alveolar and anatomical dead spaces.

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30
Q

How can physiological dead space be measured?

A

Bohr equation.

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31
Q

Physiological dead space can account for what percentage of the tidal volume?

A

30%.

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32
Q

Name the conducting airways of the respiratory tract.

A

Nasal cavity
Trachea
Bronchi
Brochioles

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33
Q

Name the non-conducting airways of the respiratory tract.

A

Larynx
Oropharynx
Laryngopharynx

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34
Q

What cells are the conducting airways of the respiratory system lined with?

A

Ciliated pseudo stratified columnar epithelium (known as the respiratory epithelium).

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35
Q

What cells are the non-conducting airways of the respiratory system lined with?

A

Stratified squamous epithelium

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36
Q

Name the 2 protective mechanisms of the airways.

A

Mucociliary clearance and the cough reflex

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37
Q

Name the 2 types of factor that can disturb mucociliary clearance.

A

Factors that increase the viscosity of mucous (CF/ asthma) and factors that reduce activity of the cilia (smoking).

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38
Q

What is the function of type 1 pneumocytes?

A

Form the gas exchange surface with the capillary endothelium.

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39
Q

What is the function of type 2 pneumocytes?

A

Secrete pulmonary surfactant.

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40
Q

What is the function of alveolar macrophages?

A

Ingest foreign materials and destroy bacteria.

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41
Q

What is lung compliance?

A

A measure of the lung’s ability to stretch and expand, defined as the change in volume per unit change in distending pressure.

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42
Q

What is static lung compliance?

A

The change in volume for any given applied pressure (when there is not gas flow, such as during an inspiratory pause).

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43
Q

What is dynamic lung compliance?

A

Compliance at any given time during the movement of air (e.g. during inspiration when there is active gas flow).

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44
Q

How do you calculate lung compliance?

A

Lung compliance = change in volume/ change in pleural pressure.

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45
Q

Describe the relationship between static and dynamic lung compliance.

A

Dynamic compliance is always lower than or equal to static lung compliance.

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46
Q

What are lung compliance pressure volume loops?

A

A graphical representation between pressure and volume during inspiration and expiration.

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47
Q

When is static lung compliance reduced?

A

In the presence of fibrosis.

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48
Q

Describe the zone of atelectasis on a pressure volume loop.

A

Lungs are fully emptied to residual volume > a large proportion of alveoli are collapse > creates the zone of atelectasis.

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49
Q

Describe what happens at the lower inflection point on a pressure volume loop.

A

There is significant enough pressure to recruit sufficient alveoli to increase compliance and so the same change in pressure gives a larger increase in lung volume than before the LIP.

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50
Q

What does the upper inflection point mark on a pressure volume loop?

A

The zone of distension.

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51
Q

Describe the zone of distension on a pressure volume loop.

A

The point in inspiration where alveoli are maximally expanded and elastic recoil pressure is exerting significant force (these cause compliance to decrease).

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52
Q

What is the function of PEEP?

A

It holds alveoli open at the end of expiration.

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53
Q

What effect does PEEP have on the pressure volume loop?

A

Because alveoli are held open at the end of expiration, inspiration starts further along the pressure volume loop curve, closer to the LIP and steeper part of the curve (due to increased compliance).

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54
Q

Name the causes of reduced lung compliance.

A

Restrictive lung disease
Acute severe asthma
Supine position
Pneumothorax
Hydrothorax
Laparoscopic surgery

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55
Q

Give a cause of increased lung compliance.

A

Emphysema

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56
Q

How does pulmonary surfactant work?

A

It increases compliance by reducing the surface tension of the water at the alveolar air-fluid interface (blood-air barrier).

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57
Q

Which structures form the alveolar air-fluid interface (blood-air barrier)?

A

Type 1 pneumocytes
Capillary endothelial cells
The basement membrane

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58
Q

Which structure provides the strength of the alveolar air-fluid interface?

A

Type IV collagen

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59
Q

Describe Laplace’s law.

A

Laplace’s law shows that the pressure in a bubble (e.g. an alveolus) is proportional to the surface tension of the bubble and inversely proportional to the radius of the bubble.

Therefore, a smaller bubble will have a higher pressure than a larger one.

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60
Q

What is Laplace’s equation?

A

Pressure is proportional to surface tension / radius

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61
Q

Give the functions of pulmonary surfactant

A

Reduces surface tension in the alveoli
Maintains structural integrity and alveolar size
Increases pulmonary compliance
Prevents atelectasis
Keeps alveoli dry
Contributes to innate immunity

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62
Q

When during gestation is most pulmonary surfactant produced?

A

> 30 weeks gestation

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63
Q

Which nervous system is airway diameter determined by?

A

Autonomic nervous system.

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64
Q

What are the effects of the sympathetic nervous system on the airways?

A

Sympathetic innervation causes relaxation of bronchial smooth muscle = increased diameter of the airways.

This happens during exercise.

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65
Q

What are the effects of the parasympathetic nervous system on the airways?

A

Parasympathetic innervation increases smooth muscle contraction and reduces airway diameter.

This happens at rest.

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66
Q

Define peak flow.

A

The maximum flow rate generated during a forceful exhalation, starting from full lung inflation.

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67
Q

What are the 2 factors that peak flow depends upon?

A

Voluntary effort and muscular strength of the patient.

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68
Q

When does maximum airflow during a peak flow measurement occur?

A

During the effort-dependent portion of the expiratory manoeuvre.

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69
Q

What do peak flow readings depend on?

A

Height, sex and gender.

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70
Q

What is the appropriate normal PEFR range for a 20 year old male?

A

540-600

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71
Q

What is the appropriate normal PEFR range for a 30 year old male?

A

600-660

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72
Q

What is the appropriate normal PEFR range for a 40 year old male?

A

600-660

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73
Q

What is the appropriate normal PEFR range for a 50 year old male?

A

570-630

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74
Q

What is the appropriate normal PEFR range for a 70 year old male?

A

490-540

75
Q

What is the appropriate normal PEFR range for a 60 year old male?

A

540-590

76
Q

What is the appropriate normal PEFR range for a 20 year old female?

A

410-450

77
Q

What is the appropriate normal PEFR range for a 30 year old female?

A

420-460

78
Q

What is the appropriate normal PEFR range for a 40 year old female?

A

420-460

79
Q

What is the appropriate normal PEFR range for a 50 year old female?

A

400-440

80
Q

What is the appropriate normal PEFR range for a 60 year old female?

A

370-410

81
Q

What is the appropriate normal PEFR range for a 70 year old female?

A

350-390

82
Q

Define forced vital capacity.

A

The volume of the lungs from full inspiration to forced maximal expiration expressed as a percentage of the predicted normal.

83
Q

Define slow vital capacity.

A

The maximal amount of air exhaled steadily from full inspiration to maximal expiration.

84
Q

Define forced expiratory volume in 1 second (FEV1).

A

The volume of air expelled in the first second of a forced expiration.

85
Q

Define forced expiratory ratio.

A

The percentage of FVC expelled in the first second of a forced expiration.

86
Q

What happens to FEV1 and FVC in obstructive airway disease?

A

FEV1 will be <80%
FVC will be reduced but to a lesser extent than FEV1.

87
Q

What happens to the FEV1/FVC ratio in obstructive airways disease?

A

It is reduced to <0.7.

88
Q

Give the 4 lung volumes/ capacities that are increased in obstructive lung disease.

A

Total lung capacity
Residual volume
Functional residual capacity
Residual volume/ total lung capacity ratio

89
Q

Give the 4 lung volumes/ capacities that are decreased in obstructive lung disease.

A

Vital capacity
Inspiratory capacity
Inspiratory reserve volume
Expiratory reserve volume

90
Q

Which measurement is used to classify airflow obstruction severity?

A

FEV1.

91
Q

What is the FEV1 in mild airflow obstruction?

A

> 80% in the presence of symptoms.

92
Q

What is the FEV1 in moderate airflow obstruction?

A

50-79%

93
Q

What is the FEV1 in severe airflow obstruction?

A

30-49%

94
Q

What is the FEV1 in very severe airflow obstruction?

A

<30%

95
Q

What is the FEV1/FVC ratio in restrictive lung disease?

A

> 0.7

96
Q

Define partial pressure.

A

The pressure of any single type of gas in a mixture of gases.

97
Q

What is meant by total pressure?

A

The sum of all the partial pressures in a gaseous mixture.

98
Q

What is meant by atmospheric pressure?

A

The pressure exerted by the combination of the partial pressures of molecules present in the atmosphere.

99
Q

What is the partial pressure of nitrogen in room air?

A

597.4

100
Q

What is the partial pressure of oxygen in room air?

A

158.8

101
Q

What is the partial pressure of water in room air?

A

3.o

102
Q

What is the partial pressure of carbon dioxide in room air?

A

0.3

103
Q

What does Henry’s law describe?

A

The behaviour of gases when they come into contact with liquids.

104
Q

What does Henry’s law state?

A

That the concentration of gas in a liquid is directly proportional to the solubility and partial pressure of that gas.

Therefore, the greater the partial pressure of a gas, the greater the number of gas molecules that will dissolve in a liquid.

105
Q

Is the amount fo water vapour present higher I alveoli or in air?

A

In alveoli (as the respiratory system humidifies incoming air).

106
Q

Describe the concentration of oxygen and carbon dioxide in alveoli compared to their concentrations in air.

A

Greater CO2 and less oxygen in the alveoli as gas exchange removes oxygen and adds CO2 to alveolar air.

107
Q

What is the partial pressure of nitrogen in alveolar air?

A

569

108
Q

What is the partial pressure of oxygen in alveolar air?

A

104

109
Q

What is the partial pressure of water in alveolar air?

A

40

110
Q

What is the partial pressure of carbon dioxide in alveolar air?

A

40

111
Q

What is gas transfer factor a measure of?

A

Gas diffusion across the alveolar membrane into the capillaries.

112
Q

How is gas transfer factor measured?

A

TLCO (the diffusion of carbon monoxide).

113
Q

Name the causes of decreased transfer factor.

A

COPD
Acute asthma
ILD
Pulmonary oedema
Pneumonia
Pneumothorax
Pulmonary vascular disease
Pneumonectomy
Anaemia

114
Q

Name the causes of decreased transfer factor.

A

Exercise
Polycythaemia
Pulmonary haemorrhage
Asthma (not during acute attacks)
Left to right shunts

115
Q

How is oxygen transported in the blood?

A

Binds to haemoglobin to form oxyhaemoglobin.

116
Q

Describe the rate of diffusion as an equation.

A

Rate of diffusion = permeability x area x difference in partial pressures.

117
Q

Give the factors affecting the rate of diffusion.

A

Membrane thickness
Membrane surface area
Solubility of gas in the membrane
Partial pressure difference across the membrane
Molecular weight of the gas

118
Q

Give 3 conditions that can affect the rate of diffusion.

A

Pulmonary fibrosis (thickened membrane)
Pulmonary oedema (fluid in interstitial space interferes with diffusion)
Emphysema (destruction of alveoli reduces available surface area and rate of diffusion)

119
Q

Describe the relationship between haemoglobin and oxygen.

A

The more oxygen that is bound to haemoglobin, the higher the affinity for oxygen (cooperative binding).

120
Q

How can the rate of change for oxygen binding to haemoglobin be visualised?

A

Oxygen dissociation curve.

121
Q

What happens to haemoglobin at high partial pressures of oxygen?

A

It binds to oxygen.

122
Q

What happens to haemoglobin at low partial pressures of oxygen?

A

It releases oxygen (normally at tissues that are deprived of oxygen).

123
Q

Why does the oxygen dissociation curve have a sigmoid shape?

A

Due to the cooperate binding of oxygen to the 4 polypeptide chains.

124
Q

What does a right shift of the oxygen dissociation curve indicate?

A

Indicates decreased oxygen affinity of haemoglobin, allowing more to be available to tissues.

125
Q

What does a left shift of the oxygen dissociation curve indicate?

A

Indicates an increased oxygen affinity of haemoglobin, meaning less oxygen is available to tissues.

126
Q

Describe what happens to the oxygen dissociation curve when the following factors decrease:

  1. pH
  2. CO2
  3. Temperature
  4. 2,3-DPG
A

All have left shift apart from pH which causes right shift when it decreases.

127
Q

Describe what happens to the oxygen dissociation curve when the following factors increase:

A

All have right shift apart from pH which has left shift when it increases.

128
Q

By what factor does carbon monoxide have a better affinity for haemoglobin than oxygen?

A

240 times.

129
Q

The presence of carboxyhemoglobin (CO bound to Hb) causes the oxygen dissociation curve to shift which way?

A

Left (it interferes with the unloading of oxygen).

130
Q

The presence of methaemoglobin causes the oxygen dissociation curve to shift which way?

A

Left (methaemoglobin does not unload oxygen from haemoglobin).

131
Q

How long does foetal haemoglobin persist for after birth?

A

About 6 months.

132
Q

What allows the foetus to extract oxygen from the maternal circulation?

A

The haemoglobin have 2 alpha and 2 gamma subunits which make the foetal haemoglobin have a greater affinity for oxygen so it can extract oxygen from maternal circulation.

133
Q

What is the effect of foetal haemoglobin on the oxygen dissociation curve?

A

Left shift (higher affinity for oxygen at lower partial pressures).

134
Q

Where does the oxygen dissociation curve lie for myoglobin?

A

Even further to the left than foetal haemoglobin (acts as an oxygen storage molecule so has a very high affinity).

135
Q

What is the function of myoglobin?

A

Provides additional oxygen to muscled during periods of anaerobic respiration.

136
Q

Where are the neutrons forming the central pattern regulator for respiration found?

A
137
Q

Which respiratory control neurones are located in the medulla?

A

Dorsal and ventral respiratory groups.

138
Q

Where do the dorsal and ventral respiratory groups receive input from?

A

Chemoreceptors and lung receptors.

139
Q

How does the dorsal respiratory group send impulses?

A

Via the phrenic nerve.

140
Q

How does the ventral respiratory group send impulses?

A

Via intercostal nerves.

141
Q

What respiratory centre is located in the upper pons?

A

Pneumotaxic centre.

142
Q

Where does the pneumotaxic centre receive inputs from?

A

Hypothalamus (+ other areas).

143
Q

How can respiration be affected voluntarily?

A

Voluntary control is mediated by higher brain centres (cortical motor neurone in the pyramidal tract) which van bypass respiratory neurones in the brainstem.

144
Q

Where are peripheral chemoreceptors located?

A

Carotid bodies and aortic bodies.

145
Q

Where are carotid bodies located?

A

At the bifurcation of the common carotid arteries.

146
Q

What are carotid bodies innervated by?

A

Carotid sinus nerve and glossopharyngeal nerve.

147
Q

What 2 types of cells are the carotid bodies made up of?

A

Type 1 cells (gloms cells)
Type 2 cells (sheath cells)

148
Q

Where are the aortic bodies located?

A

In the aortic arch.

149
Q

What nerve innervates the aortic bodies?

A

Vagus nerve.

150
Q

What do peripheral chemoreceptors detect?

A

Large changes in PO2 as the arterial blood leaves the heart.

151
Q

Where are central chemoreceptors located?

A

Ventrolateral medullary surface in close proximity to the exit points of cranial nerves IX and X.

152
Q

What do central chemoreceptors detect?

A

Changes in the pH of the CSF (indirectly respond to PCO2 levels by detecting this).

153
Q

How do central chemoreceptors act?

A

They initiate negative feedback loops that act to control the respiratory system (i.e. increase or decrease respiration).

154
Q

What happens when PCO2 levels remain abnormal over a substantial period of time (3 days)?

A

Choroid plexus cells in the BBB allow HCO3- ions to enter CSF and reset the baseline to a different PCO2 by manipulating the pH.

155
Q

Name the 3 types of lung receptor.

A

Stretch receptors
Juxtacapillary (J) receptors
Irritant receptors

156
Q

Where are stretch receptors located?

A

In the bronchial walls.

157
Q

Where are juxtacapillary receptors located?

A

Within alveolar walls next to pulmonary capillaries of the lung.

158
Q

Where are irritant receptors located?

A

Within the respiratory epithelium.

159
Q

What happens when stretch receptors are initiated?

A

The Hering-breuer reflex and increased production of surfactant.

**Hering-breuer = reduces resp rate and delays next respiratory cycle.

160
Q

What happens when juxtacapillary receptors are initiated?

A

Increased breathing rate (cause the sensation of dyspnoea).

161
Q

Which nerve innervates J receptors?

A

Vagus nerve.

162
Q

How are J receptors activated?

A

By physical engorgement of pulmonary capillaries or increased pulmonary interstitial volume.

163
Q

What happens when irritant receptors are initiated?

A

Initiation of coughing response ( + bronchoconstriction in susceptible individuals).

164
Q

What does ventilation refer to?

A

The flow of air into and out of the alveoli.

165
Q

What does perfusion refer to?

A

The flow of blood that reaches the alveoli via the capillaries.

166
Q

When do ventilation defects occur?

A

When perfusion is adequate but ventilation is inadequate.

167
Q

When do perfusion defects occur?

A

When there is adequate ventilation but impaired perfusion.

168
Q

What do perfusion defects produce?

A

Pathological dead space where lung alveoli are ventilated adequately but not perfused = impaired gas exchange.

169
Q

What is the normal V/Q ratio in an average 70kg male?

A

V is about 5 and Q is about 5, so the ideal ratio is 1.

170
Q

How do ventilation and perfusion change from the apex of the lung to the base?

A

They increase from apex to base but perfusion rises at a greater rate.

171
Q

Where in the lung is the V/Q ratio the highest?

A

Apices of lungs (3.3)

172
Q

Where in the lung is the V/Q ratio lowest?

A

Bases of lungs (0.63)

173
Q

What is the overall average V/Q value?

A

0.8.

174
Q

Why is perfusion greater at the bases of the lungs?

A

Gravity distends the pulmonary blood vessels = increased blood flow.

175
Q

Why is ventilation greater at the bases of the lungs?

A

Gravity increases intrapleural pressure at the bases = alveoli are more compliant.

176
Q

What will the V/Q ratio be if there is a ventilation defect?

A

<1

177
Q

What will the V/Q ratio be if there is a perfusion defect?

A

> 1

178
Q

If the alveoli were ventilated but there was no perfusion at all, what would the V/Q ratio be?

A

Infinity (for example, in the presence of a PE that has blocked a pulmonary artery).

179
Q

If the alveoli were perfused but not ventilated at all then what would the V/Q ratio be?

A

0 (for example, if there was inhalation of. foreign body).

180
Q

How can the body respond to a low V/Q ratio?

A

Hypoxic vasoconstriction to re-direct blood to non-affected areas of the lung (reducing perfusion to the hypoxic region and raising the V/Q ratio).

181
Q

How can the body respond to a high V/Q ratio?

A

Bronchoconstriction to decrease ventilation to the area that is not well perfused (reduces the alveolar dead space and lowers V/Q ratio).

182
Q

What is chloride shift?

A

Movement of chloride ions into RBCs from the plasma in exchange for bicarbonate ions.

183
Q

Central chemoreceptors detect changes in what?

A

pH of CSF

MRCEM Primary (39 decks)

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