Respiratory

Question 1

Describe the 4 west zones

Answer 1

VQ relationships in West’s zones:
* Zone 1:alveolar pressure is higher than arterial or venous pressure;
* Zone 2: alveolar pressure is lower than the arterial but higher than the venous pressure
* Zone 3: both arterial and venous pressure is higher than alveolar
* Zone 4: the interstitial pressure is higher than alveolar and pulmonary venous pressure (but not pulmonary arterial pressure)

2021 august Q10 deranged

Question 2

Regional differences in perfusion for the west zones

Answer 2

• Regional differences in perfusion
  o Perfusion of the lungs occurs at a low pressure
  o Hydrostatic pressure of the column of blood therefore has a significant influence
  o This is affected by:
   posture (upright vs supine)
   gravity
   Lung volume (atelectasis increases pulmonary vascular resistance)
   Hypoxic pulmonary vasoconstriction
   Gravity (affects the direction of the hydrostatic gradient)
   Pulmonary vascular architecture (some lung units are structurally advantaged)

2021 august Q10 deranged

Question 3

• Regional differences in ventilation for the west zones

Answer 3

• Regional differences in ventilation
  o Changes in the shape of the thoracic cavity occur unevenly (i.e. the base expands more than the apex)
  o Thus, regional ventilation differences develop (base usually better ventilated than apex)
  o This is affected by:
   Gravity (the weight of the lung) which produces a vertical gradient in pleural pressure
   Posture, which changes the direction of this vertical gradient
   Anatomical expansion potential (i.e. bases have more room to expand than apices)
   Lung compliance (more compliant lung regions, eg. lung bases, will be better ventilated at any given traspulmonary pressure
   Pattern of breathing (voluntary deep vs. automatic diaphragmatic vs. mechanical ventilation)

2021 august Q10 deranged

Question 4

Describe the ventilation / perfusion (V/Q) relationships in the upright lung according to West’s zones (40%). Explain the physiological mechanisms responsible for these relationships (60%).
.
examiners comments just read

Answer 4

This is a core aspect of respiratory physiology, and a detailed understanding of this topic is crucial to the daily practice of intensive care. As such the answers were expected to be detailed. Strong answers included precise descriptions of the zones of the lung as described by West and related these to the V/Q relationship in the upright lung. Generally, most candidates scored well in this section. Diagrams were of varying value. However, an impression from the examiners was that candidates spent too much time on this first section and ran out of time for a detailed answer in the second section. The answers to the second section seemed rushed and were often lacking in detail with many incorrect facts. This question highlights the importance of exam technique preparation in the lead up to the written paper.

2021 august Q10 examiners comments
Describe the ventilation / perfusion (V/Q) relationships in the upright lung according to West’s zones (40%). Explain the physiological mechanisms responsible for these relationships (60%).

Question 5

lung apex vs base

shape?

Answer 5

Shape Conical vs Irregular cylinder

deranged 2016 march Q3 - Compare the physiology of the apex of the lung with the base of the lung in the upright position.

Question 6

lung apex vs base

size?

Answer 6

Size

Relatively small fraction of the total lung volume

The bases represent the majority of the lung volume

deranged 2016 march Q3 - Compare the physiology of the apex of the lung with the base of the lung in the upright position.

Question 7

lung apex vs base

pleural pressure?

Answer 7

Pleural pressure Low (~ -7cm H2O) High (~ -3cm H2O)

deranged 2016 march Q3 - Compare the physiology of the apex of the lung with the base of the lung in the upright position.

Question 8

lung apex vs base

Anatomical boundaries

Answer 8

Anatomical boundaries

Ribcage, mediastinum, pleura superiorly, midzones of lung inferiorly

Ribcage, mediastinum, midzones of lung superiorly, diaphragm inferiorly

deranged 2016 march Q3 - Compare the physiology of the apex of the lung with the base of the lung in the upright position.

Question 9

lung apex vs base

Size Changes with respiratory cycle

Answer 9

Changes with respiratory cycle

Minimal expansion

Significant expansion due to increase in ribcage diameter and diaphragmatic contraction

deranged 2016 march Q3 - Compare the physiology of the apex of the lung with the base of the lung in the upright position.

Question 10

lung apex vs base

Alveolar size

Answer 10

Alveolar size

apex
Large, well-distended

base
Small, mid-collapsed

deranged 2016 march Q3 - Compare the physiology of the apex of the lung with the base of the lung in the upright position.

Question 11

lung apex vs base

Alveolar compliance

Answer 11

Alveolar compliance

Poor compliance
(alveoli are almost maximally inflated)

Good compliance
(alveoli are mid-inflated)

deranged 2016 march Q3 - Compare the physiology of the apex of the lung with the base of the lung in the upright position.

Question 12

lung apex vs base

Airway resistance

Answer 12

Airway resistance

apex
Low
(traction pulls small airways open)

Base
High at expiration
(combination of alveolar deflation and pressure from weight of overlying lung)

Low with inspiration
(alveolar traction pulls small airways open)

deranged 2016 march Q3 - Compare the physiology of the apex of the lung with the base of the lung in the upright position.

Question 13

lung apex vs base

Ventilation

Answer 13

Ventilation

Comparatively low

50% higher than at the apex

deranged 2016 march Q3 - Compare the physiology of the apex of the lung with the base of the lung in the upright positio

Question 14

lung apex vs base

Pulmonary blood flow

Answer 14

Pulmonary blood flow

Low (due to gravity and increased vascular resistance)

High (due to gravity and low vascular resistance)

deranged 2016 march Q3 - Compare the physiology of the apex of the lung with the base of the lung in the upright position.

Question 15

lung apex vs base

Pulmonary vascular resistance

Answer 15

Pulmonary vascular resistance

High

Low (due to increased flow)

deranged 2016 march Q3 - Compare the physiology of the apex of the lung with the base of the lung in the upright position.

Question 16

lung apex vs base

Main source of resistance to blood flow

Answer 16

Main source of resistance to blood flow

Alveolar pressure
(i.e. Zone 1)

Pulmonary venous pressure
(i.e. Zone 3)

deranged 2016 march Q3 - Compare the physiology of the apex of the lung with the base of the lung in the upright position.

Question 17

lung apex vs base

V/Q ratio

Answer 17

Main source of resistance to blood flow

V/Q ratio

High (~3 in healthy lung)

Low (~0.6 in healthy lung)

deranged 2016 march Q3 - Compare the physiology of the apex of the lung with the base of the lung in the upright position.

Question 18

2016 march Q3 - Compare the physiology of the apex of the lung with the base of the lung in the upright position.

examiners comments just read

Answer 18

2016 march Q3 - Compare the physiology of the apex of the lung with the base of the lung in the upright position.

The majority of candidates gave extensive detail on West’s zones of the lungs and did not describe other parameters that vary from base to apex. Ventilation, resistance, compliance, alveolar and lung size all vary. Some candidates mixed up the changes at the apex versus the base.

Question 19

• V/Q ratios throughout the lung:

Answer 19

• V/Q ratios throughout the lung:
  o The upright lung has a V/Q gradient from top to bottom:
   The lung bases have a low V/Q ratio (~ 0.6)
   V/Q ratio reaches 1.0 at around the 3rd rib
   Lung apices have a high V/Q ratio (~ 3.0)

deranged 2017 august Describe the effects of Ventilation/Perfusion (V/Q) inequality on the partial pressure of oxygen (PaO2) in arterial blood.

Question 20

• The effect of changing V/Q ratio on gas exchange:

Answer 20

• The effect of changing V/Q ratio on gas exchange:
  o The lower the V/Q ratio, the closer the effluent blood composition gets to mixed venous blood, i.e. to “true” shunt.
  o The higher the V/Q ratio, the closer the effluent blood composition gets to alveolar gas.
  o The relationship between PaO2 and V/Q is steeper and more sigmoid than the relationship between PaCO2 and V/Q.

deranged 2017 august Describe the effects of Ventilation/Perfusion (V/Q) inequality on the partial pressure of oxygen (PaO2) in arterial blood.

Question 21

• The effect of low V/Q ratio on oxygenation:

o Low V/Q values (V/Q ratios between x and x) result in hypoxia

Answer 21

• The effect of low V/Q ratio on oxygenation:
  o Low V/Q values (V/Q ratios between 0 and 1) result in hypoxia
  o The hypoxia due to low V/Q ratio is reversible with increased FiO2
  o “True” shunt where V/Q = 0 does not improve with increased FiO2

deranged 2017 august Describe the effects of Ventilation/Perfusion (V/Q) inequality on the partial pressure of oxygen (PaO2) in arterial blood.

Question 22

• The effect of low V/Q ratio on oxygenation:

o The hypoxia due to low V/Q ratio is X with increased FiO2
o “True” shunt where V/Q = 0 does X with increased FiO2

Answer 22

• The effect of low V/Q ratio on oxygenation:
  o Low V/Q values (V/Q ratios between 0 and 1) result in hypoxia
  o The hypoxia due to low V/Q ratio is reversible with increased FiO2
  o “True” shunt where V/Q = 0 does not improve with increased FiO2

deranged 2017 august Describe the effects of Ventilation/Perfusion (V/Q) inequality on the partial pressure of oxygen (PaO2) in arterial blood.

Question 23

• ???V/Q ratio units have excellent gas exchange but minimal blood flow

Answer 23

• High V/Q ratio units have excellent gas exchange but minimal blood flow
  o Only about 15% of the cardiac output circulates through lung units with a V/Q ratio of 5 and above
  o Therefore, these units cannot contribute enough oxygenated blood to compensate for the poor gas exchange occurring in low V/Q units

deranged 2017 august Describe the effects of Ventilation/Perfusion (V/Q) inequality on the partial pressure of oxygen (PaO2) in arterial blood.

Question 24

2017 august Describe the effects of Ventilation/Perfusion (V/Q) inequality on the partial pressure of oxygen (PaO2) in arterial blood.

examiners comments just read

Answer 24

2017 august Describe the effects of Ventilation/Perfusion (V/Q) inequality on the partial pressure of oxygen (PaO2) in arterial blood.
Overall answers lacked sufficient detail on a core area of respiratory physiology. Answers expected included a description of V/Q ratios throughout the lungs and an explanation of how V/Q inequality lowers PaO2.

Question 25

what is V/Q inequality?

Answer 25

• V/Q inequality:
  o Any ratio of ventilation (V) and perfusion (Q) which is not “ideal”, i.e. 1.0

2014 august Describe the effects of V/Q inequality on the partial pressure of oxygen (PaO2) and carbon dioxide (PaCO2) in arterial blood. (8% pass)

Question 26

• V/Q ratios throughout the lung are “scattered” between 0 and ∞ :
  o The upright lung has a V/Q gradient from top to bottom:?

Answer 26

• V/Q ratios throughout the lung are “scattered” between 0 and ∞ :
  o The upright lung has a V/Q gradient from top to bottom:
   V/Q = ∞ : “dead space”, where there is no perfusion
   V/Q > 1.0 : lung apices
   V/Q = 1.0 : ideal V/Q ratio: midzones (around the 3rd rib)
  V/Q < 1.0 : lung bases
   V/Q = 0 : or “true” shunt - collapsed regions of lung
  o The range of V/Q ratios in a normal healthy young person’s upright lung is around 0.6-3.0
  o This gradient virtually disappears when the subject is supine and the lung is horizontal.

2014 august Describe the effects of V/Q inequality on the partial pressure of oxygen (PaO2) and carbon dioxide (PaCO2) in arterial blood. (8% pass)

Question 27

• The effect of changing V/Q ratio on gas exchange:

Answer 27

• The effect of changing V/Q ratio on gas exchange:
  o The lower the V/Q ratio, the closer the effluent blood composition gets to mixed venous blood, i.e. to “true” shunt.
  o The higher the V/Q ratio, the closer the effluent blood composition gets to alveolar gas.
  o The relationship between PaO2 and V/Q is steeper and more sigmoid than the relationship between PaCO2 and V/Q.

2014 august Describe the effects of V/Q inequality on the partial pressure of oxygen (PaO2) and carbon dioxide (PaCO2) in arterial blood. (8% pass)

Question 28

• The effect of low V/Q ratio on oxygenation?

Answer 28

• The effect of low V/Q ratio on oxygenation:
  o Low V/Q values (V/Q ratios between 0 and 1) result in hypoxia
  o The hypoxia due to low V/Q ratio is reversible with increased FiO2
  o “True” shunt where V/Q = 0 does not improve with increased FiO2

2014 august Describe the effects of V/Q inequality on the partial pressure of oxygen (PaO2) and carbon dioxide (PaCO2) in arterial blood. (8% pass)

Question 29

• The effect of low V/Q ratio on CO2 removal:

Answer 29

• The effect of low V/Q ratio on CO2 removal:
  o The same change in V/Q (from 1.0 to 0.1) has a significant effect on oxygenation, but a minimal effect on CO2 removal
  o This is because the relationship of CO2 clearance to V/Q ratio is more flat and linear than the relationship of O2 uptake

2014 august Describe the effects of V/Q inequality on the partial pressure of oxygen (PaO2) and carbon dioxide (PaCO2) in arterial blood. (8% pass)

Question 30

• ?? V/Q ratio units have excellent gas exchange but minimal blood flow?

Answer 30

• High V/Q ratio units have excellent gas exchange but minimal blood flow
  o Only about 15% of the cardiac output circulates through lung units with a V/Q ratio of 5 and above
  o Therefore, these units cannot contribute enough oxygenated blood to compensate for the poor gas exchange occurring in low V/Q units

2014 august Describe the effects of V/Q inequality on the partial pressure of oxygen (PaO2) and carbon dioxide (PaCO2) in arterial blood. (8% pass)

Question 31

2014 august Describe the effects of V/Q inequality on the partial pressure of oxygen (PaO2) and carbon dioxide (PaCO2) in arterial blood. (8% pass)

examiner comments just read

Answer 31

2014 august Describe the effects of V/Q inequality on the partial pressure of oxygen (PaO2) and carbon dioxide (PaCO2) in arterial blood. (8% pass)

Very few candidates demonstrated understanding of this core topic. Candidates did not accurately define V/Q inequality and the physiological factors causing this phenomenon. V/Q scatter as well as true shunt (V/Q=0) and dead space (V/Q=∞) needed to be considered. The inability of high V/Q areas to compensate for low V/Q zones owing to the relatively small contribution of blood flow from these high V/Q units was not discussed. The differential effect of FiO2 on true shunt versus V/Q scatter was seldom explained. The shape of the oxy-Hb dissociation curve and CO2-dissociation curve were sometimes mentioned but their effect on arterial gas tensions not well explained. Often graphs were reproduced inaccurately and contradictory statements made, leaving the impression that candidates did not understand the basic concepts. It is core knowledge for Intensive Care Specialists managing respiratory failure. A sophisticated knowledge based on the chapter in Nunn is a minimum standard expected for this topic

Question 32

2008 feb
Question 6 – Compare the effect on arterial blood carbon dioxide and oxygen levels of ventilation / perfusion inequalities.

examiners comment just read

Answer 32

examiners comment
2008 feb Compare the effect on arterial blood carbon dioxide and oxygen levels of ventilation / perfusion inequalities
Compare the effect on arterial blood carbon dioxide and oxygen levels of ventilation / perfusion inequalities.

Question 6 – Compare the effect on arterial blood carbon dioxide and oxygen levels of ventilation / perfusion inequalities.

The main points expected for a pass were:
* Range, regional pulmonary differences and gradients of V/Q ratios.
* Definitions of shunt (V/Q = 0) and dead space (V/Q = ).
* Explanation of why and how V/Q mismatch lowers arterial PaO2 (majority of pulmonary blood flow being from basal regions, shape of haemoglobin disassociation curve).
* Explanation of why and how V/Q mismatch lowers arterial PaCO2 (majority of pulmonary blood flow being from basal regions, predominately linear shape of CO2 disassociation curve within the physiological range of PaCO2 values).

Again, the use of illustrations would be very useful aids as part of a good answer. Candidates often failed to frame their answer to the question that was asked and deviated to areas not directly sought after by the question. This resulted in wasted time and opportunities for marks. Syllabus B1g Reference Nunn 4 th edition page 165-187

Question 33

I keep forgetting so need a summary slide

Explain V/Q in relation to lungs

Answer 33

so top of lungs are well ventilated, thus have a high V/Q and are closer to infinity and has dead space

bottom of lungs, have high blood , thus have e a low V/Q and closer to zero, and closer to shunt

Question 34

I keep forgetting so need a summary slide

Explain V/Q in relation to lungs

Answer 34

so top of lungs are well ventilated, thus have a high V/Q and are closer to infinity and has dead space

bottom of lungs, have high blood , thus have e a low V/Q and closer to zero, and closer to shunt

Question 35

2021 aug, 2016 aug and 2013 sept and 2009 feb
Explain the physiological factors that affect airway resistance

Factors which affect airway resistance
Main categories

Answer 35

Factors which affect airway resistance

• Gas properties which affect the type of flow
• Factors which affect airway diameter
• Factors which affect airway length
• Factors which affect flow rate

Question 36

2021 aug, 2016 aug and 2013 sept and 2009 feb
Explain the physiological factors that affect airway resistance

Factors which affect airway resistance
* Gas properties which affect the type of flow

Answer 36

• Gas properties which affect the type of flow
  o Gas density (increased density leads to increased turbulence and hence increased resistance)
  o Gas viscosity (increased viscosity promotes laminar flow and hence decreases resistance)

Question 37

2021 aug, 2016 aug and 2013 sept and 2009 feb
Explain the physiological factors that affect airway resistance

Factors which affect airway resistance
* Factors which affect airway diameter

Answer 37

• Factors which affect airway diameter

o Lung volume (resistance decreases with higher volume)

o Physiological variation in airway diameter

o Pathological conditions which affect airway diameter:
 Mechanical obstruction or compression
 Extrinsic, eg. by tumour
 Dynamic compression, eg. due to gas trapping or forceful expiratory effort
 Artificial airways and their complications, eg. endotracheal tube becoming kinked
 Decreased internal crossection
 Oedema
 Mucosal or smooth muscle hypertrophy
 Encrusted secretions
 Decreased smooth muscle tone
 Bronchodilators
 Sympathetic nervous system agonists
 Increased smooth muscle tone
 Bronchospasm
 Irritants, eg. histamine
 Parasympathetic nervous system agonists

Question 38

2021 aug, 2016 aug and 2013 sept and 2009 feb
Explain the physiological factors that affect airway resistance

o Pathological conditions which affect airway diameter:

Answer 38

o Pathological conditions which affect airway diameter:

• Mechanical obstruction or compression
   Extrinsic, eg. by tumour
   Dynamic compression, eg. due to gas trapping or forceful expiratory effort
   Artificial airways and their complications, eg. endotracheal tube becoming kinked
• Decreased internal crossection
   Oedema
   Mucosal or smooth muscle hypertrophy
   Encrusted secretions
• Decreased smooth muscle tone
   Bronchodilators
   Sympathetic nervous system agonists
• Increased smooth muscle tone
   Bronchospasm
   Irritants, eg. histamine
   Parasympathetic nervous system agonists

Question 39

2021 aug, 2016 aug and 2013 sept and 2009 feb
Explain the physiological factors that affect airway resistance

Factors which affect airway resistance
* Factors which affect airway length

Answer 39

• Factors which affect airway length
  o Lung volume (increasing volume stretches and elongates the bronchi)
  o Artificial airways (increase the length in the case of an ETT, or decrease it in the case of a tracheostomy)

Question 40

2021 aug, 2016 aug and 2013 sept and 2009 feb
Explain the physiological factors that affect airway resistance

Factors which affect airway resistance
* Factors which affect flow rate

Answer 40

• Factors which affect flow rate
  o Respiratory rate (increased respiratory rate produces an increase in the flow rate for each breath)
  o Inspiratory and expiratory work (eg. voluntary forced expiration for spirometry)
  o Inspiratory flow pattern generated by a mechanical ventilator

Question 41

2021 aug, 2016 aug and 2013 sept and 2009 feb
Explain the physiological factors that affect airway resistance

Other factors which affect respiratory resistance as a whole:

Answer 41

Other factors which affect respiratory resistance as a whole:
* Resistance from deformation of the tissues (important at all flow rates)
o Tissue resistance from lung parenchyma (~70%)
o Tissue resistance from chest wall (~30% )
* Inertance of air and thoracic tissues (important at high respiratory rates)
* Compression of intrathoracic gas (important mainly with high respiratory pressures)

Question 42

Deranged exact same as 2021 but has a preamble
2016 august
6 Describe the factors that affect airway resistance.

Answer 42

The question asked specifically for airways resistance, and the candidates would have probably not earned any marks if they discussed other contributing elements (eg. inertance, tissue resistance and the effect of gas compression). Ergo, only airway stuff is listed here:
A main determinant of airway resistance is whether the flow is laminar or turbulent. This depends on the Reynolds number, which is a dimensionless metric determined by:
* Tube diameter
* Tube length
* Flow rate
* Gas density
* Gas viscosity

Question 43

Deranged exact same as 2021 but has a preamble
2016 august

o Physiological variation in airway diameter

Answer 43

o Physiological variation in airway diameter
 The “paradox” alluded to by the college is probably referring to the fact that the airways get narrower, and one might expect the resistance to increase because of this, but because their total crossectional area becomes exponentially greater the flow in them slows down to the point where all the airways distal to Generation 10 contribute less than 16% to the total airway resistance.

note; I find this really confusing, but I think the point is you would expect resitenace to increase as you go down the airways because individual ones get smaller, but resistance is actually very little because what actually actually matters is total cross sectional area

Question 44

2013 September Q23
What factors affect airway resistance? (80% of marks) Briefly outline how it may be measured and/or changes in flow are detected. (20% of marks)

• Measurement of respiratory resistance:

Answer 44

Measurement of respiratory resistance …and/or… detection of .. flow changes? It is hard to tell exactly what the examiners wanted by reading the question, even if one stares at it for a really long time without blinking. From the examiners’ comments, it would appear that they were looking for a list of methods of measuring respiratory resistance and detecting gas flow in the respiratory system. It is unclear what is meant by “poorly understood”, as one would not have enough time to demonstrate a good understanding of these matters in a question weighing only 20%. Ergo, one might surmise that they were looking for a regurgitated list, such as this one:

• Measurement of respiratory resistance:
  o Direct measurement of air flow, airway pressure and alveolar pressure or less invasive surrogate (eg. oesophageal pressure
  o Body plethysmography
  o Forced oscillation technique
  o Airway interrupter resistance measurement
  o Inspiratory hold (in a mechanically ventilated patient)
  o Rhinomanometry
• Methods of determining flow and detecting increased resistance to flow:
  o Spirometry
  o Mechanical ventilator data (eg. flow and volume waveforms), detected by:
   Hot wire anemometry
   Variable orifice flowmeters
   Screen pneumotachography
   Ultrasonic flowmeters
  o End-tidal gas monitoring (eg. EtCO2 monitoring)

Question 45

2013 September Q23
What factors affect airway resistance? (80% of marks) Briefly outline how it may be measured and/or changes in flow are detected. (20% of marks)

2009 march 18 Describe the factors that affect airway resistance.

Additionally, for extra marks, it may be mentioned that airway resistance ??? markedly with growth from infancy to adulthood

Answer 45

Additionally, for extra marks, it may be mentioned that airway resistance decreases markedly with growth from infancy to adulthood. Marciniak (2019) lists a resistance of 19 to 28 cm H2O/L per second in neonates, whereas the figure is closer to 2 cm H2O/L per second in adults.

Question 46

examiner comments

2013 somewhat unique

Answer 46

2021 august Q12 Explain the physiological factors that affect airway resistance.

College Answer
It was expected candidates cover the breadth of the factors that affect airway resistance. Generally, as a concept the type of flow (laminar vs turbulent) was answered well by most candidates, however many failed to mention the other factors that affect airway resistance. Airway diameter as a primary determinant of airway resistance was commonly omitted. Better answers which covered the factors affecting airway diameter classified them broadly and included examples such as physical compression/external obstruction, broncho-motor tone and local cellular mechanisms. Some answers did not explain these factors in enough detail and often with incorrect facts.

2016 august 6 - Describe the factors that affect airway resistance.
Candidates who used a structured approach of using formulae that describe resistance fluid
flow scored well. Poiseuille’s law describes the determinates of resistance to laminar fluid flow
and provides a useful answer structure. The most common mistakes were confusion between
resistance and compliance as well as failure to describe turbulent as well as laminar flow.

2013 September Q23
What factors affect airway resistance? (80% of marks) Briefly outline how it may be measured and/or changes in flow are detected. (20% of marks)

This topic required a definition and understanding of airways resistance. It was expected candidates could identify that issues around the nature of flow (turbulent vs. laminar) and airway diameter were central determinants. It was expected candidates would describe the determinants of turbulent flow.The provision of formula and comments about Reynolds number helped demonstrate an understanding of this. Better answers discussed the transitional point in the airway and the paradox about size vs. total cross sectional area and its influence on total resistance. Several candidates confused pulmonary vascular resistance with airways resistance. Using graphs to help illustrate certain concepts would have been helpful. Measurement of resistance (indirectly via measurement of flow and pressure difference by a body plethysmography, spirometry) and detection of flow (spirometry, capnography) was in general poorly understood.

2009 march 18 Describe the factors that affect airway resistance.
Important factors to be discussed in this answer were anatomical site, laminar versus
turbulent flow, airway calibre and factors that affect it such as oedema and sympathetic tone.
The effect of lung volume on airway resistance is usefully described in a diagram.
The differences in infants earned extra marks
Syllabus B1d, 2h
Reference: Nunn 6th edition p39-47.

Question 47

2021 march question 2
Describe the work of breathing and its components

• Work is the product of x
• In respiratory physiology, work is the product of x

Answer 47

2021 march question 2
Describe the work of breathing and its components

• Work is the product of force and distance, and is measured in Joules (1J = 1N per 1m)
• In respiratory physiology, work is the product of pressure and volume

Work = Force x distance
j = n x m

pressure is F/A
so n/m2

so pressure times volume
n x m3 divided by m

-deranged

Question 48

2021 march question 2
Describe the work of breathing and its components

Several components contribute to the total work of breathing:

Answer 48

2021 march question 2
Describe the work of breathing and its components

Elastic work
Resistive work

-deranged

Question 49

2021 march question 2
Describe the work of breathing and its components

Elastic work

Answer 49

2021 march question 2
Describe the work of breathing and its components
-

Work done to overcome elastic recoil of the lung
This increases with increasing inspiratory volume
–
Work done to overcome elastic recoil of the chest
subtracted from the work done to overcome the elastic recoil of the lung; i.e. elastic recoil of the chest wall does work to inflate the lung
With small volumes, work is actually done to reduce the chest wall volume down to FRC
With larger tidal volumes, the energy for expiration increases beyond stored potential energy and work must be done to overcome both the elastic recoil of the lungs and the chest wall

-deranged

note; I Dont really get this

Question 50

2021 march question 2
Describe the work of breathing and its components

Resistive work

Answer 50

2021 march question 2
Describe the work of breathing and its components
.
Resistive work
.
Work done to overcome tissue resistance otherwise referred to as viscous resistance:
Chest wall resistance
Lung resistance
Displacement of abdominal organs
Compression of mediastinal structures
Normally accounts for no more than 10-20% of the total work of breathing
Increased with raised intraabdominal pressure, pleural disease, mediastinal masses, etc
.
Work done to overcome airway resistance, which includes:
Airway resistance
Resistance of airway devices and circuits
Usually minimal contribution to the total work of breathing
Increased in scenarios where flow rate is increased (eg. with increased respiratory rate) or where airway diameter is decreased (eg. small ETT, bronchospasm)
Work done to overcome respiratory inertance
Work done to compress intrathoracic gas

-deranged

Question 51

2021 march question 2
Describe the work of breathing and its components

Resistive work, 2 main categories

Answer 51

2021 march question 2
Describe the work of breathing and its components

Resistive work

Work done to overcome tissue resistance otherwise referred to as viscous resistance:

AND

Work done to overcome airway resistance, which includes:

-deranged

Question 52

2021 march question 2
Describe the work of breathing and its components

examiner comment

Answer 52

2021 march question 2
Describe the work of breathing and its components

2021 march question 2

This is a core topic within respiratory physiology. There was a very low pass rate for this question. Expected components of the answer included: a definition of WOB as a product of pressure and volume or force and distance including the units of measurement; followed by a detailed explanation of the following three broad components – elastic resistance, viscous resistance and airflow resistance. Further marks were awarded to situations where the energy for expiration increases beyond stored potential energy as well as the impact of respiratory rate and tidal volume on different aspects of the WOB. For example, the changes in TV will have relatively greater impact on the elastic component, whereas RR will impact the resistance component. Additional marks were awarded for describing the efficiency of breathing. A common area where candidates missed out on marks was producing a diagram of WOB without a description; many diagrams were often incorrectly drawn or had no axes labelled. There were many incorrect definitions or respiratory equations provided without any link to the written answer. Factual inaccuracy and limited depth of knowledge were also prevalent in poorly performing answers. Marks were not awarded for a description of the control of breathing.

-deranged

Question 53

summary slide just read

Answer 53

just to organize thoughts

work 2 main categories; elastic and resistance

elastic; chest and lung

resistance; tissue (viscous) and airway (has 4 main properties)