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BS - Respiratory System > Principles of Gas Exchange > Flashcards

Principles of Gas Exchange Flashcards

1
Q

What areas of the lung participate in gas exchange?

A

the alveoli and the respiratory bronchioles

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2
Q

What law governs the rate of diffusion?

A

Fick’s Law

the rate of diffusion is proportional to surface area multiplied by pressure gradient

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3
Q

What is the equation for Fick’s Law?

A

Rate of diffusion = A x delta P

A = surface area
delta P = pressure gradient

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4
Q

What other factors is diffusion dependent on?

A

the physicochemical properties of the gas and the nature of the membrane

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5
Q

What type of cells is are the alveoli walls made from?

What is the problem with this?

A

It is made from simple squamous epithelia cells and is only one cell thick

This means disease progress can rapidly change lung function

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6
Q

What is the pressure gradient?

A

the difference in partial pressures of the respective gases in the alveolus and the blood

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7
Q

What is the partial pressure of a gas?

A

the partial pressure of a gas in a mixture of gases is the pressure it would exert if it was the only gas in the equation

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8
Q

What does Dalton’s Law state?

A

The partial pressure of a gas in a gas mixture is equal to the total pressure multiplied by the fractional concentration of the gas

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9
Q

What is the Dalton’s Law equation?

A

Partial pressure of gas A = total pressure x fractional concentration of gas A

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10
Q

What is the fractional concentration, partial pressure at sea level and partial pressure at 5,000m of oxygen in the air?

A

fractional concentration - 21%

partial pressure sea level - 21.3 kPa

partial pressure 5,000m - 11.8 kPa

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11
Q

What is the fractional concentration, partial pressure at sea level and partial pressure at 5,000m of carbon dioxide in the air?

A

0

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12
Q

What is the fractional concentration, partial pressure at sea level and partial pressure at 5,000m of nitrogen in the air?

A

fractional concentration - 79%

partial pressure sea level - 80 kPa

partial pressure 5,000m - 44.2 kPa

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13
Q

What is atmospheric pressure in kPa, mmHg and cmH2O?

A

1 atmosphere

101.3 kPa

760 mmHg

1033 cm of water

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14
Q

Why does partial pressure decrease with higher altitudes?

A

In a given volume of air, there are fewer molecules present

The % of the gas is the same as at sea level but there are fewer molecules of every gas present

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15
Q

How does partial pressure of oxygen differ in the alveoli and the atmosphere?

A

partial pressure of oxygen in the alveoli is lower than in room air

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16
Q

Why is partial pressure of oxygen in the alveoli lower than room air?

A
  1. inspired air is humidified in the upper airway
  2. in the alveoli, oxygen is taken up while CO2 is released
  3. the body consumes more oxygen molecules than it produces CO2
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17
Q

Why is nasal breathing encouraged at rest?

A

The nose is highly efficient at humidifying inspired air

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18
Q

With how much water is the air humidified with?

A

the air is humidified with around 6.3 kPa of water

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19
Q

Why does the air need to be humidified before it reaches the lungs?

A

Dry air reaching the lungs would lead to rapid loss of fluid from the lungs

the lungs would stop working efficiently and would need higher pressures to expand and recoil

breathing becomes more difficult

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20
Q

How much more oxygen is consumed by the body than CO2 produced and why?

A

The body consumes 1.25 x as much oxygen than it produces CO2

This is due to the respiratory quotient

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21
Q

What is the body’s respiratory quotient? How could it be made to be closer to 1?

A

0.8

a diet of pure carbohydrate and no fat would produce a RQ closer to 1

this is because fats are oxygen poor and carbohydrates are oxygen rich

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22
Q

What is the saturated vapour pressure of water at 37oC?

A

6.3 kPa

this is the partial pressure of water vapour

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23
Q

What is the partial pressure of oxygen in fully humidified air at 37oC?

A

19.95 kPa

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24
Q

How is arterial blood gas CO2 related to the CO2 in the capillaries?

A

Arterial blood gas CO2 is the same as the capillaries

The blood has already passed out of the lungs at this point

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25
Q

What is the normal alveolar partial pressure of CO2?

A

5 kPa

The healthy range is 4.5 - 6kPa

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26
Q

What is the partial pressure of oxygen in the blood?

A

13.3 kPa

27
Q

What is the expected partial pressure of oxygen in the blood?

Why is the actual value lower?

A

13.7 kPa

It is lower due to shunting where blood passes straight from the arterial to venous system without participating in gas exchange

28
Q

What term is used to describe how molecules move around?

A

Brownian motion

They move in a random manner

29
Q

What happens when molecules hit the surface of a solution?

A

Their motion is not changed but it is slowed down

Molecules diffuse in and out of the solution at a slower pace

It is a dynamic equilibrium across the surface of a solution

30
Q

How does the partial pressure of a gas in solution relate to its solubility?

A

The partial pressure of a gas in solution is inversely proportional to its solubility

31
Q

Why does a more soluble gas have a lower partial pressure in solution?

A

The lower solubility gas will equilibrate more quickly and generate its partial pressure

The greater the solubility, the more molecules can be accommodated for a given partial pressure

32
Q

How many times more soluble is CO2 compared to O2?

What does this mean?

A

CO2 is 24 x more soluble than O2

A lot more CO2 molecules are needed in solution than oxygen molecules to generate the same partial pressure

33
Q

Why is CO2 transfer more efficient than O2 transfer?

A

Carbon dioxide has a higher relative diffusing capacity (20.5)

34
Q

What are the partial pressures of oxygen and carbon dioxide in venous blood entering the alveolus?

A

pO2 - 5.3 kPa

pCO2 - 6.1 kPa

35
Q

What are the partial pressures of O2 and CO2 within the alveolus?

A

pO2 - 13.7 kPa

pCO2 - 5.3 kPa

36
Q

What are the partial pressures of O2 and CO2 in venous blood exiting the alveolus?

A

pO2 - 13.3 kPa

pCO2 - 5.3 kPa

37
Q

How long does it take for the partial pressure of oxygen to increase when passing through the alveoli?

A

0.25 seconds

This is the time taken for the blood to equilibrate with the alveolus

38
Q

How long does it take for CO2 to equilibrate when passing through the alveoli?

A

0.1 seconds

39
Q

Why does CO2 equilibrate more quickly than oxygen?

A

CO2 diffusion is more efficient

There is less partial pressure to equilibrate

There are more molecules of CO2 as it is more soluble than oxygen

40
Q

What happens to blood flow during exercise?

A

The blood passes through the lungs more quickly

It doesn’t have as much time to equilibrate as it passes through the alveoli

41
Q

During exercise, how long does the blood take to pass through the alveolus and what does this mean?

A

0.25 seconds

There is still enough time for oxygen to equilibrate

CO2 still equilibrates in good time as it takes less than 0.25 seconds

42
Q

How would oxygen deficit be caused?

A

If the blood passed through the alveoli any quicker than in 0.25 seconds, it would not have enough time to equilibrate properly

43
Q

What is the pO2 in pulmonary fibrosis patients and why?

A

They do not have enough time during exercise to equilibrate their oxygen across the alveoli

pO2 can only reach 9.5 kPa

44
Q

What happens to CO2 equilibration in pulmonary fibrosis patients and what does this lead to?

A

CO2 still has enough time to equilibrate

Type I respiratory failure as there is not adequate oxygenation but there is adequate expiration of CO2

45
Q

How is oxygen diffusing capacity measured clinically?

A

oxygen uptake is divided by (alveolar pO2 - mean pulmonary capillary pO2)

46
Q

Why is direct measurement of oxygen diffusing capacity not used in practice?

A

pulmonary capillary pO2 is very difficult to measure

47
Q

What mechanism is used in practice to measure diffusing capacity?

A

Carbon monoxide diffusing capacity

transfer factor

48
Q

How is carbon monoxide diffusing capacity measured?

A

Carbon monoxide uptake is divided by alveolar pCO

49
Q

What is the value for mean pulmonary capillary pCO?

A

0

Hb has a very high affinity for CO, so when bound to Hb the CO cannot exert a partial pressure as it is not in solution

50
Q

How is carbon monoxide diffusing capacity measured in practice?

A

A concentration of carbon monoxide is given to a patient and the amount of CO taken up is measured

51
Q

What happens in alveolar fibrosis and how does this impact diffusion?

A

Thickening the alveolar wall increases the diffusion distance

Decrease in diffusion capacity which can lead to respiratory problems

52
Q

What happens in pneumonia?

A

Consolidation pneumonia involves the creation of a shunt

The alveolus no longer participates in gas exchange even though blood flows through it

53
Q

What happens to oxygen concentration in pneumonia patients?

A

venous blood pools with the arterial blood that was successful in gas exchange

This leads to a dilution of the oxygen concentration

54
Q

What happens in pulmonary oedema?

A

Frothy secretions within the alveolus

Works in a similar way to consolidation pneumonia

Patients cough up pink frothy sputum

55
Q

What happens in interstitial oedema?

A

Fluid around the base of the alveolus, between the alveolus and the capillary

56
Q

What happens in emphysema?

A

Reduction in the number of alveoli leads to a reduction in the total surface area for gas exchange

The lungs are less able to oxygenate the blood

57
Q

What is atelectasis?

A

Collapse of the alveoli

58
Q

How is atelectasis related to age?

A

As you get older, the elasticity of the lungs and thoracic wall is lost

The lungs begin to close and can no longer participate in gas exchange

59
Q

how does atelectasis affect gas exchange?

A

As more and more alveoli begin to collapse, there is less capacity to oxygenate the blood

60
Q

What is a common cause of pulmonary oedema?

A

Left heart failure leads to a lot of back pressure in the pulmonary vein

The right heart is still working efficiently

A lot of fluid is being pumped into the lungs but this is not being efficiently removed

61
Q

How can pulmonary oedema lead to respiratory failure?

A

Thickening of the basement membranes and the alveoli filling with fluid means oxygen transfer is not as efficient

62
Q

What happens in adult respiratory distress syndrome?

A

Lungs are filled with water which prevents gas from entering the lungs, and consequently the blood

63
Q

how does obesity affect FRC?

A

A large mass on top of the chest prevents the thorax from springing out and reduces FRC

64
Q

What can obesity lead to?

A

The chest is pulled inwards due to the decrease in FRC, leading to closure of alveoli

This is atelectasis

BS - Respiratory System (20 decks)

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