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ESA 3 > Respiratory Session 3- Gas Exchange And Lung Function Tests > Flashcards

Respiratory Session 3- Gas Exchange And Lung Function Tests Flashcards

1
Q

What is alveolar pO2 determined by?

A

Balance between rate of removal of O2 by the blood and rate of replenishment of O2 by alveolar ventilation

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2
Q

What is alveolar pCO2 determined by?

A

Balance between the rate at which CO2 enters the alveoli from blood and the rate at which it is removed from alveolar gas by ventilation

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3
Q

Why is the balance between perfusion and ventilation important?

A

Keeps the partial pressure of oxygen and carbon dioxide in the alveolar gas stable at its normal values of 13.3kPa and 5.3kPa respectively

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4
Q

What factors determine the rate at which gases exchange?

A

Area available for exchange
Resistance to diffusion
Gradient of partial pressure

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5
Q

What is the exchange area in a normal lung?

A

70m^2

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6
Q

From the alveoli, what must gas diffuse through to reach haemoglobin?

A 
Alveolar epithelial cell
Interstitial fluid
Capillary endothelial cell
Plasma
Red cell membrane
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7
Q

What property of a gas affects its rate of diffusion the most?

A

Solubility of the gas in water

More soluble= faster diffusion

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8
Q

Does CO2 or O2 diffuse faster and by how much?

A

CO2 diffuses 21 times as fast as oxygen

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9
Q

What are the normal partial pressures of O2 and CO2?

A 
O2 = 13.3kPa
CO2 = 5.3kPa
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10
Q

Are that partial pressures of O2 and CO2 in arterial blood the same as the partial pressures in alveolar gas?

A

YES! In a normal subject

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11
Q

How are the partial pressures of O2 and CO2 kept very close to their normal values?

A

Exchange of gas between alveolar gas and atmospheric air brought close to it through the airways of the lung by the process of ventilation

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12
Q

How long does full gas exchange take?

A

500ms

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13
Q

What are the 3 main diseases that cause diffusion defects and why?

A

Interstitial lung disease- excessive deposition of collagen in interstitial space and thickening of alveolar walls = lengthening of diffusion pathway
Pulmonary oedema- fluid in interstitium and alveolus increases length of diffusion pathway
Emphysema- destruction of alveolar walls = large air spaces which reduces total surface area available for gas exchange

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14
Q

How is diffusion resistance measured?

A

Carbon monoxide transfer factor- measuring CO uptake following single, maximal breath of a gas mixture containing air, 14% helium and 0.1% CO

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15
Q

Why is CO used to calculate diffusion resistance?

A

It has a very high affinity for Hb
All the CO entering blood binds to Hb so concentration gradient for pCO across alveolar capillary membrane is maintained for the entire time blood is in contact with alveolar gas

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16
Q

What is the anatomical or serial dead space?

A

The volume of the conduction airways (containing air that is not available for gas exchange)

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17
Q

How much dead space is there normally and how is it measured?

A

150ml- measured by the nitrogen washout test

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18
Q

What is the alveolar/distributive dead space?

A

The volume of air in alveoli not taking part in gas exchange

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19
Q

What is the physiological dead space and how is it determined?

A

Anatomical dead space and alveolar dead space

Can be determined by measuring pCO2/pO2 of expired and alveolar air

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20
Q

Define pulmonary ventilation rate

A

Total rate of movement of air into and out of the lungs

Dead space ventilation and alveolar ventilation

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21
Q

What is dead space ventilation?

A

Movement of air into and out of the dead space

22
Q

Is fewer deep breaths or many shallow breaths more effective and why?

A

Deeper breathing is more effective as at each breath the dead space is fully ventilated so the deeper the breath the higher the proportion of air available for gas exchange

23
Q

How is the movement of air during breathing measured?

A

Spirometry

24
Q

Define tidal volume

A

Volume of air that enters and leaves the lungs with each breath

25
Q

Define inspiratory reserve volume

A

Maximal amount of additional air that can be drawn into the lungs by determined effort after normal inspiration

26
Q

Define expiratory reserve volume

A

Additional amount of air that can be expired from the lungs by determined effort after normal expiration

27
Q

Define residual volume

A

Volume of air left in the lungs after forced expiration

28
Q

Can lung capacities change?

A

Nope

29
Q

How are lung capacities defined?

A

Fixed points in the breathing cycle- maximum inspiration, maximum expiration and end of quiet expiration

30
Q

Define inspiratory capacity

A

From the end of quiet expiration to maximum inspiration

31
Q

Define functional residual capacity

A

Volume of air in the lungs at the end of quiet expiration

32
Q

Define vital capacity

A

Inspiratory capacity and expiratory reserve OR

Inspiratory reserve volume and tidal volume and expiratory reserve volume

33
Q

How do you work out total lung volume?

A

Vital capacity and reserve volume

34
Q

Why can vital capacity be reduced?

A

Lungs not filled normally in inspiration, emptied normally in expiration or both

35
Q

What is maximal filling of the lungs determined by?

A

Balance between maximum inspiratory effort and the force of recoil of the lungs

36
Q

What can cause a ‘restrictive’ deficit?

A

Unusually stiff lungs

Inspiratory effort compromised by muscle weakness, injury or deformity

37
Q

How is an ‘obstructive’ deficit produced?

A

Expiratory flow compromised much earlier in expiration than normal is airways are narrowed

38
Q

How can restrictive and obstructive deficits be separated?

A

Asking patients to breathe out rapidly from maximal inspiration through a single breath spirometer which plots volume exhaled against time

39
Q

What is a vitalograph?

A

A time-volume plot generated during spirometry

40
Q

Describe a normal vitalograph

A

Rapid increase that slows down over time to a maximum volume

41
Q

What do you measure to distinguish between obstructive and restrictive defects?

A

Forced expiratory volume in one second

Forced vital capacity

42
Q

Describe the vitalograph findings in an obstructive defect

A

FVC is nearly normal
FEV1 is reduced markedly
FEV1/FVC ratio is <70%

43
Q

Describe the vitalograph findings in a restrictive defect

A

FVC is reduced
FEV1 is reduced proportionally
FEV1/FVC ratio is normal

44
Q

What is plotted on each axis in an expiratory flow volume loop?

A

X axis- lung volume

Y axis- expiratory flow rate

45
Q

When does the peak expiratory flow rate occur?

A

At the start of expiration, when the lungs are expanded and airways stretched open

46
Q

In normal individuals what affects peak flow the most?

A

Resistance of the large airways

47
Q

What can reduce PEFR?

A

Severe obstruction of small airways

48
Q

What dos the flow-volume curve look like with mild obstruction of the small airways?

A

It is scooped out- reduces very rapidly then slows as it reaches the minimum

49
Q

How can you measure residual volume?

A

Helium dilution test

50
Q

How can you measure dead space?

A

Nitrogen washout method

ESA 3 (18 decks)

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