Lecture - Resp (Bevin Physiol 4 Gas Exchange)

Question 1

Ventilation

1. What does ventilation deliver and remove? (this is piss easy)
2. For air movement (flow) to occur, what do you need to develop between the alveoli and atmosphere?
3. How do you achieve the pressure grandients that allow flow to occur?
4. When the lungs expand and air flows, what two things do they need to over? These two things are “Work of Breathing”

Answer 1

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Question 2

1: To breathe, we need to have compliance

1. What is lung compliance a measure of?
2. What four things does lung compliance vary with?

Answer 2

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Question 3

2 To breathe, we need to overcome airways resistance

1. Air flow is mainly laminar flow during quiet breathing so what can we use to calculate the resistance?
2. Where in the airway tree do you get the main area of airway resistance?

Answer 3

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Question 4

Factors determining airway resistance

1. What can cause bronchoconstriction?
2. What can cause bronchodilation?
3. What is the third thing that increases airway resistance?

Answer 4

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Question 5

Factors determining airway resistance #2

1. So we’ve figured that dynamic compression of airways can happen because some airways are very collapsible. Can you explain this in more detail to me? Aka summarise slide 6
2. Limits airlflow in normal subjects during when?
3. This dynamic compression is exaggerated in some lung diseases by reduced what and loss of what?
   - eg in e_____
4. May occur in diseased lungs at relatively low…….what does this mean for exercise ability?
5. How do these people with dynamic compression of airways counteract the problem? (Like those with ephysema). How does this help?

Answer 5

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Question 6

Work of breathing

1. Work is done to overcome two things - what are they and how are they overcome or exacerbated?
2. For each of these, tell me is it ‘stiff lungs’ or ‘narrow pipes’ and why
   - Restrictive Lung Disease
   - Obstructive Lung Disease
   - Pulmonary oedema

Answer 6

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Question 7

Work of breathing again

1. Fall in intrapleural pressure during inspiration equates with ______ done to move the air
2. Has two components- what are they and what are they on this graph

Answer 7

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Question 8

Go and explain slides 13, 14, 15 and 16 about the volume and pleural pressure graph

Answer 8

Okay so we can think of the pleural pressure as the work done by the lungs and the volume is just the volume of the lungs.

So the lung compliance is going to be a straight line - there is a direct relationship between overoming the elastic forces and the volume that it expands.

But we have pipes and that means we have airway resistance to overcome when we inspire. That turns the straight line into a curved one.

Looking at the graph itself, it’s like: “If we didnt have pipes then changing the pleural pressure to -6 would increase the lung volume to eg +0.2 but since we have airway resistance, if we change the pleural pressure to -6, then the lung volume will only increase +0.16 etc……dont get hung up on the pleural pressure but rather think of it as ‘work’ so for the same work, we can’t have the same change in volume since we have to do extra work to overcome the airway resistance”

So the curved line is the line which we use when we have to also overcome airwar ressitance

When it comes to expiration, the energy that was stored by the elastic forces in inspiration is used to expire (when expiring, only have to overcome airway resistance and that comes from the recoil)

In asthma people, there is increased resistance of airways so they need extra inspiratory muslce activity to inspire and that no longer covers the expiration energy so they also need to do more work by the expiratory muscles to expire

Question 9

Hypoventilating pateint

1. What happens to their PCO2?
2. What are the three reaosns for why this might be? Think logically for why you wont get enough CO2 out and accumulate it…..

Answer 9

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Question 10

Gas exchange

1. How much in general is O2 consumption (VO2)?
2. How much CO2 do we generally produce? (VCO2)
3. We need to exchange these amounts of gases across alveolar membrane for homeostasis and be able to what?
4. What is the respiratory ratio
   - what’s the usual number
   - what is it dependent on
5. Diffusion across alveolar membrane - what do you need for this? (Large…)
6. It is driven by what?
   - So what pressures are important in Fick’s Law (like, which side?)
7. What else is gas exchange also dependent on?
   - what do you need the right balance of?

Answer 10

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Question 11

PAO2 and PACO2

1. Set the ______ ‘end’ of partial pressure diffusion gradient
2. What four things are these partial pressues determined by (in list form)
3. What are the three things that affect the PAO2 and PACO2 in equation form?
   - think bank balance

Answer 11

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Question 12

PACO2 = PlCO2 + (VCO2/VA)

1. What can you rearrange that to? Aka what’s the equation in red that you should measure that calculates VA (alvelolar ventilation) for you?
2. What sort of relationship is there between VA and PACO2

Question 13

Okay so you have memorised an equation for calculating the alveolar ventilation using the alveolar CO2

Now tell me the equation that’s termed “Alveolar Gas equation” for measuing alveolar O2

i) the original (like freshly driven)
ii) what R starts for
iii) What the final eqation you need to know is

Question 14

Alright, so why bother to calculate the PAO2 and measure PaO2? Like, what can you identify? I.e. determine this cool thing called an _____-_____ gradient

Answer 14

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Question 15

So okay the A-a gradient

1. What is the equation?
2. What is normally the value?
3. What does an increased A-a gradient?

Question 16

Slide 34:

Okay so where does the ‘150’ come from? What is it?

Answer 16

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