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Pulmonary physiology > Control of breathing > Flashcards

Control of breathing Flashcards

1
Q

When is breathing adjusted?

A

Changing metabolic rate and activities such as sneezing, swallowing, speech

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2
Q

What does control of breathing ensure?

A

Alveolar ventilation high enough to:

Get Hb close to full saturation

Maintain CO2 (and thus pH) since variations in CO2 vary pH

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3
Q

What are the changes in alveolar gas pp as ventilatory drive increases?

A

Gas moves in/out of alveolar space more quickly

PACO2 decreases and PAO2 increases

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4
Q

How do you work out CO2 breathed out?

A

Total amount of gas breathed out (alveolar ventilation) x fraction of gas that is actually CO2 (PACO2/Barometric pressure)

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5
Q

How do you work out inspired CO2?

A

Alveolar ventilation x (inspired CO2/barometric pressure) (aka total partial pressure)

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6
Q

How do you work out VCO2?

A

Amount of CO2 breathed out-amount of CO2 breathed in

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7
Q

What is VCO2?

A

Volume of CO2 produced per minute

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8
Q

What is VO2?

A

The volume of oxygen the body consumes.

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9
Q

How are VO2 and VCO2 different?

A

VO2 = equals amount of O2 breathed in - amount of O2 breathed out

VCO2 = amount of CO2 breathed out - amount of CO2 breathed in

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10
Q

Describe curve for alveolar ventilation and PAO2

A

Positive correlation, non linear and begins to turn into parabola under 20KPa

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11
Q

Describe curve for alveolar ventilation and CO2

A

Negative, correlation, non linear and begins to level off at around 5KPa

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12
Q

What sort of curves are both alveolar ventilation - PAO2/PACO2?

A

Hyperbolas

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13
Q

How is alveolar ventilation-alveolar partial pressure curve affected by varying inspired gas?

A

Shifts the asymptotes (up/down)

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14
Q

How is alveolar ventilation-alveolar partial pressure curve affected by varying metabolic rate?

A

Vary constant area (shape and position of metabolic hyperbola)

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15
Q

What does shape and position of metabolic hyperbola depend on (for alveolar ventilation/alveolar pp gases curve)?

A

Metabolic level and inspired gas concentration

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16
Q

Where do central chemoreceptors lie?

A

Ventrolateral surface of medulla, 0.2 mm within anterior surface of medulla

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17
Q

2 types of chemorecpetors?

A

Central (in brain)

Peripheral (outside brain)

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18
Q

What do central chemoreceptors respond to?

A

Changes in brain extracellular pH (which is determined by pH of blood and CSF)

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19
Q

Describe the BBB, why is it important in control of breathing?

A

Relatively impermeable to charged proton equivalents (e.g. H+ or HCO3-) but permeable to CO2 so pCO2 is main determinant of pH in brain interstitium

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20
Q

What is the main determinant of pH in brain interstitium?

A

Blood CO2 and thus pCO2 of CSF

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21
Q

Can ions such as H+ and HCO3- diffuse from the CSF into brain interstitium?

A

Yes

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22
Q

What is CO2 in interstitium determined by?

A

The CO2 will be determined by the ratio between the metabolic production of CO2 by the brain tissue and the blood flow.

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23
Q

How do increases in CO2 decrease pH?

A

CO2 + H2O H+ + HCO3-

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24
Q

How do central chemoreceptors respond to fall in pH?

A

Increasing the frequency of action potentials in their afferent nerve, resulting in an increase in ventilatory rate and reduction of pCO2

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25
Q

Do central chemoreceptors respond more to changes in pCO2 in blood or CSF?

A

Blood

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26
Q

Is the pH of the brain interstitium or CSF more sensitive to changes in pCO2, why?

A

CSF

Proton buffering capacity of the CSF is lower (fewer proteins).

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27
Q

What proportion of the ventilation response to CO2 is driven by central chemoreceptors?

A

80%

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28
Q

What is the effect on hypercapnia by cutting carotid sinus nerve, why?

A

Little effect on ventilatory response

central chemoreceptors mainly responsible

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29
Q

Why are responses by central chemoreceptors to arterial pCO2 slow?

A

Well buffered environment (glial cells)

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30
Q

When do central chemoreceptors becomes less sensitive?

A

When pCO2 persistently above/below normal levels

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31
Q

Describe how central chemoreceptors sense pCO2

A

H+ sensitive region, H+ predominantly determined by pCO2 in blood.

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32
Q

What is the brain interstitium?

A

Fluid surrounding cells of brain

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33
Q

Where are peripheral chemoreceptors located?

A

Carotid bodies: above carotid artery bifurcation

Aortic bodies: along arch of aorta

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34
Q

What do carotid bodies receive blood supply from, how does their location help with a response?

A

External carotid arteries, so chemoreceptors are close to arterial composition of blood -rapid response

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35
Q

Which type of peripheral chemoreceptor is more important for a response?

A

Carotid

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36
Q

What innervates the carotid body?

A

Sinus nerve (branch of glossopharyngeal)

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37
Q

What innervates aortic bodies?

A

Vagus nerve

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38
Q

What does carotid body detect?

A

Changes in composiiton of arterial blood flowing through it

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39
Q

What changes in arterial blood does carotid body detect?

A

Mainly pO2

also pCO2, pH and temp

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40
Q

What is aortic body mainly sensitive to?

A

pO2 and pCO2

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41
Q

What are the main effects of aortic bodies?

A

Vascular not respiratory effects

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42
Q

Are the carotid and aortic bodies organs?

A

Yes

43
Q

What is blood supply to carotid body?

A

20 l/kg/min

44
Q

What do peripheral chemoreceptors mainly monitor?

A

pO2, pCO2 and pH

45
Q

How do peripheral chemoreceptors respond to low pH, low paO2 or high paCO2?

A

Afferent fibres running in carotid sinus fibre fire more frequently, leads to increased rate/depth of ventilation

46
Q

Which peripheral chemoreceptor is responsive to pH?

A

Carotid body

47
Q

How does lowered pH affect ventilation rate?

A

Hyperventilation (e.g. in patients in anaerobic exercise and diabetic ketoacidosis)

48
Q

How does rate of firing through afferent fibres in carotid sinus nerve change with lowered paO2?

A

Firing rate increases gently as PaO2 falls below 60mmHg but relatively insensitive to changes above this value

49
Q

What does curve for ventilatory drive - pO2 correlate with, why?

A

Nerve impulse frequency in carotid sinus nerve

Becasue only peripheral chemoreceptors able to elicit ventilatory response to hypoxia.

50
Q

How does increased paCO2 affect carotid bodies?

A

Through increase in pH

51
Q

What is more important quantitatively for peripheral chemoreceptors to respond to?

A

pO2>pCO2

52
Q

How does sensitivity of peripheral chemoreceptors change?

A

Increasing pCO2, increases sensitivity to decreased oxygen (pCO2) and vice versa

53
Q

When are peripheral chemoreceptors more sensitive to hypoxia in asphyxia?

A

When high pCO2

54
Q

What is the natural stimulus of carotid body?

A

Asphyxia

55
Q

What are type 1 cells of peripheral chemoreceptors called, what are they and what do they do?

A

Glomus cells, afferent nerve fibres synapse onto these.

Chemosensing occurs

56
Q

What do type 1 cells contain?

A

Vesicles with neurotransmitter

57
Q

What are type 2 cells called, what do they do, describe their chemosensing capaity?

A

Glial cells, supportive cells with no chemosensing capacity

58
Q

How does low oxygen lead to increase in ventilaiton?

A

Increased rate of firing of action potentials in nerves

These APs go into brain, phrenic nerve to diaphragm increases neural activity to breathe more

59
Q

What is more important for overall ventilatory response, CO2 or O2?

A

paCO2

60
Q

Why is PaCO2 most important for determining ventilatory response?

A

Both central/peripheral chemoreceptors response to pCO2

Small increase in pCO2 greatly increases ventilation (unlike little decrease in pO2 for values above 60mmHg)

Slight decrease in pO2 doesn’t significantly reduce Hb saturation because of curve (but slight decrease in pCO2 can significantly decrease blood pH)

61
Q

Describe how changes in pO2 and pCO2 affected Hb saturation and pH respectively above 60mmHg, why?

A

Above 60mmHg

Slight decrease in pO2 doesn’t significantly reduce Hb% saturation due to sigmoidal dissociation curve

Slight increase in pCO2 can significantly decrease blood pH

62
Q

What do both types of chemoreceptor respond to?

A

pCO2

63
Q

Describe and explain the curves for pCO2: ventilation at low O2 and high O2

A

At high O2, less steep curve (less ventilation for given pCO2 compared to at low O2) - response by both central and peripheral

At low O2, curve steeper and mainly have peripheral chemoreceptors responding

64
Q

At low CO2, describe effect on ventilation as pO2 varies?

A

Little effect on ventilation (linear line)

65
Q

Where is respiratory rhythm generated?

A

Brain stem (in respiratory centres in medulla and pons)

Pre-Botzinger complex (cluster of interneurons which have been identified as pacemaker of breathing rhythm)

66
Q

What happens as you section above brainstem?

A

Abolish voluntary/cortical control of breathing but leave normal rhythm intact

67
Q

What if you section through brain stem?

A

Stop breathing

68
Q

What are the 2 groups of upper respiratory neurones in the pons?

A

Dorsal + ventral respiratory group

69
Q

Where are the dorsal and ventral respiratory group mainly located?

A

Medulla

70
Q

What do the upper respiratory neurones fire?

A

APs with frequency that corresponds to respiratory cycle

71
Q

What are dorsal respiratory group neurones for?

A

Initiate inspiration by synapsing with neurons of contralateral phrenic nerve

72
Q

What do DRG neurones send input to?

A

Ventral group

73
Q

What does DRG receive?

A

Neurones arrive here from peripheral chemoreceptors in lung

74
Q

What do VRG compromise?

A

Inspiratory/expiratory neurones, which synapse with neurones of contralateral phrenic/intercostal nerve regulating muscle

75
Q

Describe which respiratory group is mainly afferent and which is efferent?

A

DRG afferent

VRG efferent

76
Q

What modifies the rhythmic activity of respiratory neurones?

A

Inputs from higher brain centres (i.e. cortex, hypothalamus)

Afferent fibres from chemoreceptors + mechanoreceptors in ariways/lungs

77
Q

What do pulmonary stretch receptors adapt to?

A

Respond mainly to stretch, with slow adaptation

78
Q

How do pulmonary stretch receptors respond?

A

As you increase tidal volume + rate of inspiration

Stretch lung

Stimulate receptors and APs sent along vagal afferent fibres to brain

79
Q

What is the reflex of pulmonary stretch receptors?

A

Inhibition of inspiration (Hering Breuer reflex)

80
Q

Where are pulmonary stretch receptors located?

A

Between SMC in large airways

81
Q

What do pulmonary stretch receptors join with?

A

Large myelinated fibres within vagus

82
Q

What innervates bronchi?

A

Pulmonary branches of vagus nerve (autonomic)

83
Q

How do VRG neurones have different roles in normal and forced breathing?

A

Inactive during normal breathing

Activated by signals from the dorsal respiratory group during heavier breathing and in turn stimulate the muscles of forced exhalation

84
Q

What part of medulla oblongata are inspiratory neurones found?

A

Dorsal surface

85
Q

Are the cells of the central respiratory centre chemoreceptors?

A

Yes, nowhere near as sensitive as central chemo ones

86
Q

Describe what state the expiratory cells/ neurones are in in normal quiet breathing

A

Quiescent

87
Q

How is breathing changed in anaemia, why?

A

No change, anaemia causes no change in pO2

88
Q

Describe responses of aortic and carotid bodies to pH?

A

Only carotid bodies respond

89
Q

What does stimulation of chemoreceptors do to airways?

A

Bronchoconstriction

90
Q

Why are peripheral chemoreceptors active in haemorrhage?

A

Local vasoconstriction causes hypoxaemia and hypercapnia

91
Q

What does stimulation of peripheral chemoreceptors do to systemic and pulmonary vessels?

A

Constricts

92
Q

How much of a role do peripheral chemoreceptors have in normal quiet breathing?

A

Little

93
Q

What is the effect of acidosis on the response to hypoxia of peripheral chemoreceptor?

A

Increased sensitivity

94
Q

Do the peripheral chemoreceptors have role in hyperventilation during moderate exercise?

A

No, blood arterial gases remain same after moderate exercise

95
Q

Where are the receptors that stimulate Herring Breuer reflex?

A

Between smooth muscle of bronchial tree (not respiratory mucosa)

96
Q

What is the effect of Herring Breuer reflex on respiratory rate?

A

Decreases, by prolonging expiatory time

97
Q

What stimulates cough reflex

A

Mechanical stimuli and chemical stimuli

98
Q

How can tissue hypoxia occur without arterial hypoxaemia?

A

Septic shock and histotoxic hypoxia

99
Q

Where abouts in the carotid is carotid body?

A

At birfucation

100
Q

If respiratory activity is not allowed to change during chemoreceptor stimulation (asphyxia/ artificial ventilation at a fixed rate), then what is the effect on HR and systemic vessels?

A

Chemoreceptor activation causes bradycardia and coronary vasodilation (both via vagal activation) and systemic vasoconstriction (via sympathetic activation).

Blood pressure rise

101
Q

If respiratory activity increases in response to the chemoreceptor reflex, what is the effect?

A

Increased sympathetic activity

Stimulates both the heart and vasculature to increase arterial pressure.

(rapid breathing - lung inflation reflex - initiates tachycardia that overrides the chemoreceptor reflex)

102
Q

How does chemoreceptor activity, also affect cardiovascular function?

A

Directly (by interacting with medullary vasomotor centers)

Indirectly (via altered pulmonary stretch receptor activity).

103
Q

Hypoxia vasodilation/constriction?

A

Acute: some vasodilation facilitated by adenosine and adrenaline (locally)

BUT vasodilation is restrained by chemoreceptor reflex vasoconstriction.

104
Q

What can activate pulmonary stretch receptors?

A

Pulmonary oedema

Pulmonary physiology (3 decks)

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