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BS - Respiratory System > Energy Production & Oxygen Consumption > Flashcards

Energy Production & Oxygen Consumption Flashcards

1
Q

What drives oxygen to different places?

A

the partial pressure of oxygen

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2
Q

What drives oxygen towards the mitochondria and why?

A

The pressure gradient drives oxygen towards the mitochondria

pO2 is low in the mitochondria as oxygen is being consumed

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3
Q

What is the oxygen cascade?

A

the oxygen cascade describes the different stages of the partial pressure of oxygen from when it is breathed in to when it reaches the mitochondria

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4
Q

What are the stages of the oxygen cascade, from when it is breathed in?

A
  1. dry air
  2. humid air
  3. alveolar gas
  4. pulmonary capillary
  5. arterial blood
  6. venous blood
  7. cytoplasm
  8. mitochondria

pO2 decreases as it moves down the cascade

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5
Q

What is the pO2 of dry inspired air?

A

21 kPa

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6
Q

What is the first thing that happens to dry inspired air?

A

The air is humidified by adding a fixed amount of water at 37oC

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7
Q

What is the result of humidification of dry inspired air?

What is the pO2 of inspired humid air?

A

Humidification means oxygen is diluted slightly

pO2 = 19.9 kPa

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8
Q

What happens to air as it enters the lung?

A

It meets CO2 that is leaving the lung

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9
Q

What is pCO2 in the alveolus and how does this influence air entering the lung?

A

pCO2 = 5-6 kPa

Oxygen entering the lung becomes diluted by the same amount as the amount of CO2 present

Every time pCO2 increases by 1 kPa, pO2 will decrease by 1 kPa

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10
Q

What is the pO2 of alveolar gas?

A

14.9 kPa

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11
Q

What is the pO2 in the pulmonary capillaries?

A

14.9 kPa

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12
Q

Why is pO2 in the pulmonary capillaries very similar to the pO2 in alveolar gas?

A

Diffusion from the air space in the alveoli to the haemoglobin is very efficient

All the structures are very thin and there is a large surface area of lung

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13
Q

What is meant by an area of the lung having a ‘low ventilation to perfusion ratio’?

A

Some areas of the lung do not get enough ventilation for the amount of blood which flows through them

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14
Q

Which areas of the lung tend to have a low ventilation to perfusion ratio?

Why?

A

The less well ventilated areas are at the base of the lung

This is due to the effect of gravity

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15
Q

Why may there be a lower pO2 in arterial blood than in pulmonary capillaries?

A

If there is not enough O2 in the alveolus, the blood is not fully oxygenated

This blood mixes with oxygenated blood to provide a lower pO2 in arterial blood

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16
Q

What is the pO2 of arterial blood?

A

13.6 kPa

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17
Q

How is arterial pO2 measured?

A

A needle is inserted into the radial artery

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18
Q

What happens once the blood has entered the capillaries?

A

Oxygen diffuses out of the capillary and into cellular mitochondria

This is a long distance

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19
Q

What is mean tissue pO2?

A

5 kPa

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20
Q

What pO2 is required for the mitochondria to work efficiently?

A

0.15 kPa

There is an excess supply of oxygen to the mitochondria

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21
Q

What happens if pO2 is less than 0.15 kPa at the mitochondria?

A

The mitochondria develop anaerobic respiration

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22
Q

What does the Krogh model describe?

A

How oxygen gets from the capillary into the cells of a tissue

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23
Q

According to the Krogh model, how are tissues and their capillary supply arranged?

A

All tissues are arranged in a cylinder with one capillary supplying each cylinder

The capillary is in the centre of the cylinder, with tissue surrounding it

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24
Q

What happens to pO2 along the capillary, according to the Krogh model?

A

pO2 falls in an exponential manner

This occurs as oxygen diffuses away from the tissues exponentially

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25
Q

According to the Krogh model, how does pO2 differ at the arterial and venous ends of the capillary?

A

pO2 of cells at the venous end of the capillary will always be lower than pO2 of the cells at the arterial end of the capillary

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26
Q

What is the ‘lethal corner’ in the Krogh model?

How is it clinically significant?

A

This is where the cells of a particular tissue cylinder have the lowest pO2

If there is a problem with oxygen delivery, these are the first cells to turn hypoxic

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27
Q

What is the definition of ‘oxygen delivery’?

A

The amount of oxygen leaving the heart in one minute

DO2

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28
Q

What is the equation used to calculate oxygen delivery?

A

DO2 = cardiac output x oxygen content of blood

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29
Q

What makes up the oxygen content of the blood?

A

Amount of dissolved oxygen and the amount of oxygen being carried by haemoglobin

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30
Q

What is the equation used to work out oxygen content of the blood?

What is normal oxygen content?

A

CO2 = (SO2 x [Hb] x 1.39) + 0.3

normal oxygen content is 19 ml/dl

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31
Q

In the oxygen content of the blood equation, what is normal SO2 and [Hb]?

A

SO2 = 0.97
This means the blood is 97% saturated with oxygen

[Hb] = 14 g/dl

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32
Q

When blood returns to the heart, what % of it is still oxygenated?

A

75%

33
Q

Why is cardiac output important in the DO2 equation?

A

Cardiac output determines the speed of blood flow and the amount of oxygen delivered to tissues

34
Q

In the oxygen delivery (DO2) equation, what are typical values for DO2, CO2 and CO?

A

DO2 = CO2 x CO

DO2 = 1000 ml/min
(oxygen delivery)

CO2 = 19 ml/dl
(oxygen content of blood)

CO = 5.25 L/min
(cardiac output)

35
Q

What is the definition of oxygen consumption?

A

The amount of oxygen used by the body in one minute (VO2)

36
Q

What is the basal metabolic rate and how is this related to oxygen consumption?

A

It is the minimum energy expenditure found in the body

This is oxygen consumption (VO2) at rest

37
Q

What is normal VO2 (oxygen consumption) at rest?

A

200 ml/min

38
Q

What are the values for BMR and VO2 when taking into account body size?

A

BMR is relative to body size so…

BMR = 45 W/m^2

VO2 = 4.8 ml/min/kg

39
Q

What is basal metabolic rate measured in and why?

A

BMR is measured per metre squared of body surface area

This is because larger people will have more tissues

40
Q

What is VO2 measured in?

Why is this not entirely accurate?

A

ml/min per kg of bodyweight

not entirely accurate as fat has a different oxygen concentration

41
Q

What are the 4 ways in which oxygen consumption may be measured?

A
  1. direct calorimetry
  2. indirect calorimetry
  3. arterio-venous CO2 (oxygen content of blood) difference
  4. inspired-expired O2 volume difference
42
Q

How is arterio-venous CO2 difference measured?

A

A sample of arterial and venous blood is taken

the oxygen concentration in each is measured

This allows you to see how much oxygen has been consumed by the tissues

43
Q

What is the drawback of measuring oxygen consumption through arterio-venous CO2 difference?

A

It is difficult to get a venous sample as different parts of the body are using different amounts of oxygen

A mixed blood sample from a pulmonary artery would be needed

44
Q

How is inspired-expired O2 volume difference performed?

A

The amount of oxygen inspired through a closed-system mask is measured

The amount that is expired is then measured

45
Q

How does calorimetry measure energy consumption?

A

By seeing how much heat is given off

All functions that require oxygen give off heat, so this shows baseline energy usage

46
Q

Which 3 factors affect oxygen consumption?

A
  1. age
  2. temperature
  3. exercise
47
Q

How does VO2 vary with age?

A

VO2 peaks at 2 years of age and then declines for the rest of life

48
Q

Why are older people more prone to hypothermia?

A

They have a lower basal metabolic rate

49
Q

Why do males and females have different metabolic rates?

A

There is a difference between the fat and muscle ratio in males and females

Fat has a low metabolic rate and muscle has a high metabolic rate

50
Q

How does temperature affect metabolism?

A

metabolism doubles (or halves) for every 10 degrees

51
Q

What is VO2 at rest?

How does this change with exercise and how is it measured?

A

VO2 at rest is 0.25 L/min

Oxygen consumption increases with intensity of exercise

It is measured in METs

52
Q

What are METs?

A

METs show how many multiples of resting oxygen consumption are being used

53
Q

If someone was using 10 METs whilst exercising, what would this mean?

A

They are using 10 times as much oxygen than they would be using at rest

54
Q

Why does anaemia of chronic diseases occur?

A

The bone marrow is not working as well as it should, so is not producing enough red blood cells

55
Q

How does the O2-Hb curve shift in anaemia and why?

A

It shifts to the right due to an increase in 2,3-DPG

This means Hb will give up its oxygen more easily to the tissues

56
Q

What physiological mechanism means that anaemia patients often look pale?

A

The autonomic nervous system reduces blood flow to non-essential organs

There is reduced blood flow to the skin

57
Q

How does the saturation of Hb in venous blood vary in anaemia patients and why?

A

There is increased oxygen extraction from the blood

Hb in venous blood falls to 50% saturation

58
Q

How does the heart modify its behaviour in response to anaemia?

A

Increased cardiac output to maintain oxygen delivery

59
Q

Why must cardiac output be doubled in anaemia patients?

A

Oxygen carrying capacity of the blood falls from 19ml to 8ml

doubling CO means the same amount of oxygen is reaching the tissues as a a healthy person

60
Q

What is the potential negative outcome of increasing cardiac output in anaemia patients?

A

Doubling CO puts a lot of extra strain on the heart

This can lead to ischaemic heart disease and angina

61
Q

How does partial pressure of oxygen vary with altitude?

A

pO2 decreases with increasing altitude

62
Q

How does oxygen saturation of Hb change with increasing altitude?

What is the critical value?

A

It decreases

It is incompatible with life if oxygen saturation falls below 60%

63
Q

How does [Hb] change with altitude?

What does this allow for?

A

At increasing altitudes, Hb concentration increases

This allows arterial oxygen content to remain reasonably normal

64
Q

What is the respiratory exchange ratio (RER)?

What is the name for the RER at rest?

A

It is the ratio of carbon dioxide production (VCO2) to oxygen consumption (VO2)

The RER at rest is the respiratory quotient

65
Q

What is the normal value for RER?

What 3 factors may affect this?

A

Normal value = 1

  1. acid-base balance
  2. hyperventilation
  3. metabolic fuel
66
Q

What is cardio-pulmonary exercise testing used for?

A

It is used in clinical medicine to get an objective measure of how often a patient exercises

67
Q

What graph is plotted from the results of cardio-pulmonary exercise testing?

A

VCO2 is plotted against VO2

68
Q

What does the gradient of the line in the cardio-pulmonary exercise test graph show?

A

A value for RER

69
Q

How would you identify the anaerobic threshold from the cardio-pulmonary exercise test graph?

A

It appears where the graph starts to curve

70
Q

What is the anaerobic threshold?

A

The pO2 at which the patient begins to respire anaerobically

Oxygen consumption does not change, but more CO2 begins to be produced

71
Q

When is cardio-pulmonary exercise testing used in practice?

A

To see how well a patient will respond to major surgery

It is a way of quantifying risk so that a patient can make an informed decision

72
Q

What are the 3 fundamental causes of cellular hypoxia?

A
  1. anoxic
  2. stagnant
  3. anaemic

all 3 causes can overlap in a Venn diagram type way

73
Q

What does anoxic mean in terms of hypoxia?

A

There is a lack of O2 in the blood, meaning insufficient oxygen is delivered to the cell

74
Q

What type of condition usually leads to anoxic conditions?

A

A lung problem such as respiratory failure

75
Q

What is meant by stagnant in terms of hypoxia?

A

There is a lack of blood flow to the tissue

76
Q

What conditions often cause stagnant hypoxia?

A

cardiac problems

e.g angina, heart failure, arrhythmia

77
Q

What is meant by anaemic in terms of hypoxia?

A

There is not enough haemoglobin in the blood, which reduces oxygen delivery

78
Q

Why do anaemic patients often experience their angina becoming worse?

A

The causes of hypoxia overlap - stagnant & anaemic

BS - Respiratory System (20 decks)

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