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BS - Respiratory System > Challenges to Normal Respiration > Flashcards

Challenges to Normal Respiration Flashcards

1
Q

How much oxygen is required per minute at rest?

What is this equivalent to?

A

250 ml of oxygen is required per minute at rest

This is equivalent to 1 MET

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2
Q

What are METs?

A

Metabolic equivalents

They are a multiple of the value for oxygen consumption at rest (250 ml/min)

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3
Q

Why is there not a single MET value for activities such as walking and swimming?

A

The METs consumed depends on the intensity of the exercise

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4
Q

How is minute ventilation increased?

What is the result of this?

A

The volume of air that is moved in and out of the lungs per minute is increased

This increases the quantity of oxygen that the body receives

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5
Q

How can oxygen delivery to the tissues be increased?

A
  1. through increased cardiac output

2. increased arterial O2 content

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6
Q

Why can arterial O2 concentration not really be increased in healthy individuals?

A

The haemoglobin is already around 98% saturated

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7
Q

Although arterial O2 concentration cannot be increased, what other factor can be changed when oxygen demand increases?

A

Oxygen extraction is increased

This is the amount of oxygen being taken out of the Hb by the tissues as it passes through

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8
Q

At 3 METs, by how many times has cardiac output increased?

A

4 times

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9
Q

How does minute ventilation compare to cardiac output at rest?

A

Minute ventilation is approximately the same as cardiac output - 5 L/min

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10
Q

At 2 METs, by how many times has minute ventilation increased?

A

10 times

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11
Q

When oxygen demand increases, is it easiest for the body to increase cardiac output?

A

No - the capacity to increase the amount of oxygen moved in and out of the body (MV) is much greater than the capacity to increase cardiac output

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12
Q

In what ways is the body’s ability to increase oxygen delivery limited?

A

The oxygen content of the blood cannot really be increased

Cardiac output can only be increased by around 5 times

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13
Q

What are the major responses of the body to increased oxygen demand?

A
  1. increased minute ventilation

2. increased oxygen extraction from Hb

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14
Q

How is mixed venous oxygen content measured?

A

A catheter is placed in one of the great veins of the neck or the femoral vein

It is then passed into the vena cava

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15
Q

Why is mixed venous oxygen content measured?

How does it vary?

A

It allows measurement of the oxygen saturation of the blood

70% saturated at rest

20% saturated during exercise

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16
Q

What is the difference between oxygen-requiring and non-oxygen-requiring processes?

A

Oxygen requiring processes are aerobic

Non-oxygen requiring processes are anaerobic

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17
Q

Why is aerobic respiration more efficient than anaerobic respiration?

A

Aerobic respiration, in the presence of O2, generates 36 ATP from 1 glucose

Anaerobic respiration, with no O2, generates 2 molecules of ATP per glucose

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18
Q

At the start of light exercise, what type of respiration is used and why?

A

Combination of both aerobic and anaerobic respiration

Because there are many different types of muscle in the body

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19
Q

Why do some muscles require more oxygen than others?

A

Some muscles depend almost entirely on oxygen as they have many mitochondria and generate ATP very efficiently

Some muscles have few mitochondria and little capacity for aerobic respiration

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20
Q

What do VO2 and VCO2 stand for?

A

VO2 - oxygen consumption

VCO2 - carbon dioxide production

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21
Q

During a period of light exercise, how does work done vary?

A

The work being done is constant

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22
Q

How do VO2 and VCO2 vary during a period of light exercise?

A

VO2 builds up after a few minutes and is closely followed by VCO2

The 2 variables plateau with VO2 being higher than VCO2

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23
Q

What do the values of VO2, VCO2 and lactate show about respiration during light exercise?

A

The majority of work is being done aerobically

Lactate in the blood increases very slightly showing some anaerobic respiration

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24
Q

During heavy exercise, how to the values of VO2, VCO2 and lactate vary compared to light exercise?

A

All 3 variables still reach a plateau

VCO2, VO2 and lactate concentrations are all higher, with a gap opening up between VCO2 and VO2

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25
Q

Why does the component of anaerobic respiration increase in heavy exercise?

A

The work being done increases so more anaerobic respiration occurs to supplement the aerobic respiration

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26
Q

During severe exercise, how do the values of VCO2, VO2 and lactate vary compared to heavy exercise?

A

None of the variables reach a plateau

Lactate rises slowly

VCO2 and VO2 rise quickly at first and then continue to rise more slowly

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27
Q

What is the rate limiting factor in severe exercise?

Why do people stop exercising at this point?

A

Lactate accumulation

Cramp is caused by the build-up of lactate in the muscles

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28
Q

Why does lactate concentration act as a rate limiting factor in exercise?

A

When lactate reaches a concentration of 10 mmol/L, the body cannot tolerate the metabolic acidosis associated with increased lactate concentration

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29
Q

What pattern is shown by the increase in minute volume of ventilation during exercise?

A

Increase in ventilatory capacity during exercise is reasonably linear

It follows a linear pathway until it reaches Owles point

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30
Q

What is Owles point?

A

It describes the level of oxygen consumption at which the relationship with minute ventilation veers upwards

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31
Q

What do the limits of tolerance represent on the graph of oxygen consumption against minute volume of ventilation?

A

They represent the VO2 max in individuals of varying levels of physical fitness

32
Q

How can improving physical fitness affect the limit of tolerance?

A

Improving physical fitness increases the degree of oxygen consumption before the linear relationship changes

There is a limited capacity after the linear relationship ends, before the limit of tolerance is reached

33
Q

What is the VO2 max?

A

The amount of oxygen consumption which can be maximally generated

34
Q

At rest, what mechanism predominantly controls minute ventilation?

A

Contraction and recoil of the diaphragm

35
Q

As the demand for oxygen increases, how is the control of minute ventilation changed?

A

Different muscle groups are utilised to increase minute ventilation:

  1. accessory muscles of ventilation
  2. external intercostals on inspiration
  3. internal intercostals on expiration
36
Q

What is minute volume and the equation?

A

It is the product of the tidal volume and the respiratory rate

volume of breath x number of breaths per minute

37
Q

How do tidal volume and respiratory rate change during exercise?

A

Tidal volume and respiratory rate increase

This also increases minute volume

38
Q

At maximum exercise, by how much is tidal volume increased?

A

It is increased by 5-6 times the value of resting tidal volume

This is 50% of the vital capacity

39
Q

When exercising, at what point does minute ventilation begin to increase?

A

Instantaneously as exercise begins or even slightly before

Breathing instantly becomes harder and faster

40
Q

What are the 3 phases of minute volume change during exercise?

A

Phase I - rapid increase in minute ventilation at time 0

Phase II - Gradual increase in minute ventilation as exercise proceeds

Phase III - a plateau is reached and maintained

41
Q

What happens during the recovery phase after exercise?

A

There is an oxygen deficit which is compensated for

This is the oxygen debt

42
Q

What is the partial pressure of oxygen at sea level and why?

A

Atmospheric pressure is 100 kPa

pO2 is 21% of the atmospheric pressure

pO2 is 21 kPa at sea level

43
Q

What is the saturated vapour pressure of water at body temperature?

A

6.3 kPa

44
Q

What happens to oxygen as it is inhaled through the nose?

A

it takes up water vapour and becomes humidified

45
Q

As altitude increases, how does atmospheric pressure change?

How does this affect pO2 and saturated vapour pressure of water?

A

Atmospheric pressure decreases

pO2 in air decreases

saturated vapour pressure of water does not change

46
Q

What is PiO2 and why is it greater than alveolar pressure?

A

PiO2 - pO2 of air entering the trachea

Alveolar pressure is less as it is occupied with CO2 coming out of the pulmonary veins

47
Q

As altitude increases, what mechanism can be used to increase oxygen delivery?

A

Hyperventilation

48
Q

As altitude increases, what is the tolerance limit?

A

Tolerance limit is at 4 kPa

If pressure falls below 4 kPa, it is unsurvivable as the tissues are not receiving enough oxygen

Doubling the minute ventilation will not have an effect

49
Q

As altitude increases, how does this affect alveolar pressure, PiO2 and atmospheric pressure?

A

They all decrease as altitude increases

50
Q

What chemical mechanism triggers hyperventilation?

A

Peripheral chemoreceptors detect the decreased oxygen level of the blood

51
Q

Where are peripheral chemoreceptors found?

A

In the carotid body and the aortic arch

52
Q

What limits excessive hyperventilation?

A

Alkalosis

Respiratory alkalosis occurs due to a reduced level of CO2 in the blood

There is also a fall in [H+], especially in the CSF

53
Q

How does the body compensate for respiratory alkalosis?

What does this allow for?

A

Excretion of bicarbonate from the CSF

This allows for hyperventilation to continue

54
Q

What are the consequences of secreting bicarbonate by the kidneys?

A

Diuresis - more frequent urination

Hyponatraemia - sodium levels in the blood fall below normal

55
Q

What is acute mountain sickness predominantly caused by?

A

The hypoxic vasoconstriction response in the pulmonary arteries

56
Q

In acute mountain sickness, what happens when oxygen tension in the inspired area is low?

A

The pulmonary arteries constrict to try and move blood to regions of the lung which are better oxygenated

57
Q

In acute mountain sickness, what happens if all of the pulmonary arteries in the lung constrict?

A

Increased pressure on the right side of the circulation

This leads to increased fluid being shifted out of the pulmonary circulation and into the lungs

This causes pulmonary oedema

58
Q

What is a dangerous consequence of acute mountain sickness?

A

Fluid may come out into the brain and cause cerebral oedema

59
Q

What is erythropoiesis?

What is the mechanism involved?

A

Increase in the amount of RBCs, and consequently Hb

This involves an increase in erythropoietin (hormone) which stimulates production of RBCs

60
Q

By how much are Hb levels increased through erythropoiesis?

A

There is a 30 - 40% increase in haemoglobin by 5 g/dL

61
Q

Other than erythropoiesis, what are a further 2 examples of acclimatisation to high altitude?

A
  1. sustained hyperventilation and increase in cardiac output

2. less 2,3-DPG is produced which enables more oxygen to be released to tissues

62
Q

What happens to the pressure on the body as depth increases?

A

The pressure of the water above acts on the body, increasing the pressure on the body

63
Q

What is the “breaking-point” of breath-holding and how is it reached?

A

It determines how long someone can hold their breath

When someone holds their breath, pO2 falls and pCO2 rises until the breaking point is reached

64
Q

How can the time someone can hold their breath for be prolonged?

A

Inspiring air with a high oxygen concentration beforehand

Hyperventilation also gives a longer breath-holding period

65
Q

How much does pressure increase by when someone descends 10 m underwater?

A

For every 10m that someone descends, there is an increase in pressure of 1 atmosphere

This is 100 kPa

66
Q

How does the pO2 change as depth increases?

How does this affect the amount of oxygen needed?

A

As total pressure increases, pO2 also increases

The amount of oxygen that needs to be inspired is reduced

67
Q

How does nitrogen affect breathing?

A

Nitrogen limits the depth at which air can be breathed

68
Q

At what pressure is/does:

i - nitrogen detectable

ii - there serious impairment

iii - anaesthesia occurs

A

i - nitrogen is detectable at > 4 atm

ii - there is serious impairment > 10 atm

iii - anaesthesia occurs > 30 atm

69
Q

How does density affect breathing?

A

Density increases with high pressures which leads to an increased work of breathing

70
Q

What happens to nitrogen on ascent?

How is this overcome?

A

Nitrogen comes out of solution on ascent

This is overcome through using helium/oxygen mixtures for diving

71
Q

On descent, by how much is lung volume compressed and what does this lead to?

A

Lung volume of 6L is compressed to 600 ml at 10 atm

This leads to a loss of buoyancy

72
Q

On descent, how does alveolar CO2 compare to mixed venous CO2?

A

Alveolar CO2 > mixed venous CO2

73
Q

On ascent, how does alveolar pCO2 change?

A

Alveolar pCO2 decreases

74
Q

How is barotrauma brought about on ascent?

A

Expansion of air filled spaces

75
Q

What is involved in decompression sickness on ascent?

A

Bubbles form in the tissues and arterial gas embolism

BS - Respiratory System (20 decks)

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