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Year 1: Respiratory System > 7. Breathlessness and Control of Breathing > Flashcards

7. Breathlessness and Control of Breathing Flashcards

1
Q

What is most important function of the respiratory muscles?

A

Maintain arterial pH

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2
Q

What does breathing out rely on?

A

The elasticity of the lung and chest wall - This is a passive process
Therefore only breathing in counts towards respiration

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3
Q

Give the equation for Minute ventilation

A

V.E = VT x f

Minute ventilation = tidal volume x frequency

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4
Q

What does VT mean?

A

Tidal volume

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5
Q

What does V.E mean?

A

Minute ventilation

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6
Q

What is TTOT?

A

Duration of single respiratory cycle

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7
Q

What can TTOT be split into?

A

Inspiratory and expiratory

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8
Q

Define VT/TI

A

Mean inspiratory flow and shows how powerfully the muscles contract. This is called the neural drive

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9
Q

Define TI/TTOT

A

Inspiratory duty cycle - shows the proportion of the cycle actively ventilating (inspiring)

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10
Q

What happens in terms of VT, TI and TTOT when metabolic demands increase?

A

Increase in ventilation so - increase in VT/TI and decrease in TTOT hence there is an increase in frequency

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11
Q

What is normal tidal volume?

A

0.5L

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12
Q

What happens in terms of VT, V.E, VT/TI and frequency when artificial dead space is added?

A

The VT, V.E, VT/TI and frequency increases. The neural drive increases due to a need to satisfy more ventilation

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13
Q

How does chronic bronchitis and emphysema affect ventilation?

A

Narrows intrathoracic airways making expiration more difficult than inspiration. There is higher RV increasing the stiffness of the chest, hence increasing the work of breathing

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14
Q

What is the VT/TI of people with COPD?

A

They do not breathe any harder, as VT/TI is more or less the same

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15
Q

How do people with COPD breathe?

A

They take shorter an shallower breaths

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16
Q

How does shorter and shallower breathes affect the TV and TTOT?

A

The TV and TTOT decreases

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17
Q

How does exercise affect the TTOT?

A

It halves the TTOT hence doubling the frequency

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18
Q

In a healthy person how does the TI/TTOT change when exercising?

A

It increases - more time for inspiration

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19
Q

In a person with COPD how does the TI/TTOT change when exercising?

A

It decreases - more time for expiration as they have difficulty expiring

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20
Q

What controls involuntary breathing/metabolic centre?

A

Medulla (bulbo-pontine brain)

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21
Q

What controls voluntary breathing/behavioural centre?

A

Motor area of cerebral cortex

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22
Q

What centre will always override the other in terms of control of breathing?

A

The metabolic will always override the behavioural

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23
Q

What is the main driver of breathing?

A

Diaphragm

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24
Q

Where is the metabolic centre situated?

A

In the brain stem in the bulbopontine region

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25
Q

Where are the behavioural components situated?

A

Scattered throughout the mid and upper parts of the brain

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26
Q

What does the metabolic centre respond to?

A

Metabolic demands and production of CO2

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27
Q

What receptor lies in the metabolic controller?

A

H+ ion receptor

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28
Q

What nerves move the chest wall?

A

Phrenic nerves in the cervical region of the upper spinal cord

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29
Q

What is an important feedback to the metabolic controller?

A

Chemoreceptors in the carotid bodies. The detect H+ ion levels, pO2 and pCO2

30
Q

How does the metabolic controller control the upper airways muscles?

A

It dilates the pharynx and the larynx on inspiration and narrow them on expiration (to act as a break on expiratory flow)

31
Q

What is the pacemaker of breathing?

A

Made up from 10 groups of neurons in the medulla near the nuclei of cranial nerves IX and X

32
Q

What is the pre-Botzinger complex?

A

A group of pacemaker activity essential for generating the respiratory rhythm. Also called the ‘gasping centre’

33
Q

What is responsible for the generation of a tidal breath

A

6 groups of neurons in the medulla and brain stem. They discharge at different phases of the respiratory cycle

34
Q

How does early inspiratory neurons initiate inspiratory flow?

A

Via the respiratory muscles

35
Q

What do inspiratory augmenting neurons do?

A

Dilate pharynx, larynx and airways

36
Q

What are the important roles of pharyngeal an laryngeal muscles?

A

They open up the airways and act as brakes in breathing

37
Q

What is the lack of tone in the pharyngeal muscles cause?

A

Obstructive sleep apnoea syndrome

38
Q

What does the afferents of the 5th nerve come from?

A

Nose and face (irritant)

39
Q

What does the afferents of the 9th nerve come from?

A

Pharynx and larynx (irritant)

40
Q

What does the 10th nerve come from?

A

Bronchi and bronchioles (irritant and stretch)

Herring-Breuer reflex

41
Q

What nerves are irritant receptors?

A

5th,9th and 10th nerves

42
Q

What do irritant receptors lead to?

A

Coughing and sneezing which are defensive

43
Q

What is the function of the Hering-Breuer reflex?

A

Used as a cut off signal for inspiration - comes from pulmonary stretch activated by large lung inflation

44
Q

Which nerve is responsible for the Hering-Breuer reflex?

A

10th

45
Q

What are the two parts of the metabolic controller?

A

Central part of the medulla SLOW- H+ conc

Peripheral part at the carotid bifurcation (carotid sinus) FAST - H+ conc

46
Q

What does H+ concentration correlate to?

A

Mirrors pCO2 changes

47
Q

What does a rise in arterial pCO2 cause?

A

A rise in minute ventilation

48
Q

How many L/min rise in minute ventilation for every 1kPa rise in arterial pCO2?

A

30 L/min - very sensitive system

49
Q

What effect does chronic metabolic acidosis have?

A

It increases the threshold but not the sensitivity. Shifts left

50
Q

Define chronic metabolic alkalosis?

A

Opposite of metabolic acidosis - shifts right. Still about threshold not sensitivity

51
Q

What happens to ventilation in sleep?

A

Ventilation would drop to zero but CO2 production continues. Within 10-60 seconds the arterial CO2 would have risen sufficiently above the apnoeic point to restart breathing

52
Q

What can cause depressed ventilatory response?

A

A disease affecting the metabolic control centre

53
Q

Define depressed ventilatory response to pCO2

A

Decrease in sensitivity to pCO2 - caused by affects on the metabolic control

54
Q

What is an important peripheral cause of a reduction in sensitivity to pCO2?

A

Respiratory muscle weakness leads to a raised arterial pCO2

55
Q

Where is the pre-Botzinger complex found?

A

Found in the ventro-cranial medulla near the 4th ventricle

56
Q

What may late inspiratory neurons signal?

A

The end of inspiration, and ‘brake’ the start of expiration

57
Q

What can expiratory decrementing neurons do?

A

They may ‘brake’ passive expiration by abducting the larynx and pharynx

58
Q

What do expiratory augmenting neurons do?

A

They may activate respiratory muscles when ventilation increases on exercise

59
Q

What do late expiratory neurons do?

A

They may sign the end of expiration and dilate the pharynx in preparation for inspiration

60
Q

What happens if you lower your arterial pCO2 to below the normal resting level (5.3kPa) ?

A

You don’t stop breathing - there is a minimal drive to breathe attributed to wakefulness

61
Q

What is not as tightly regulated compared to PaCO2 and H+?

A

PaO2 - rather oxygen saturation is better defended

62
Q

Usually, what does a fall in ventilation cause?

A

A fall in PaO2 and a rise in PaCO2

63
Q

What does the fall in PaO2 cause?

A

It increases the sensitivity of the carotid body to PaCO2 and H+. As a result the ventilation increases and so PaO2 increases

64
Q

What can inhibit the ventilatory response?

A

Hypoxic hyperventilation on going to altitude lowers the PCO2. This causes inhibition of the response. Several days of acclimatisation is required for the metabolic centre to adjust a lower O2 set point for increasing the sensitivity of PaCO2 and H+

65
Q

If the lung is unable to fully respond to metabolic acidosis and alkalosis what system also helps?

A

The renal excretion and retention of weak acids. The renal compensation is a slow responder

66
Q

What determines the H+ concentration in the blood?

A

The ratio of PaCO2:HCO3-

67
Q

Define metabolic acidosis

A

When the source of the excess hydrogen ions comes from metabolism rather than inadequate ventilation

68
Q

What are the compensatory mechanisms for acidosis?

A

Ventilatory stimulation lowers PaCO2 and H+
Renal excretion of weak acids
Renal retention of chloride to reduce strong ion difference

69
Q

What is metabolic alkolosis caused by?

A

Loss of H+ ion: vomiting, diuretics and dehydration

70
Q

What are the compensatory mechanisms for alkalosis?

A

Opposite of the compensatory mechanisms of acidosis

71
Q

What does breathlessness at rest imply?

A

Difficulty with inspiration and expiration

72
Q

What are the three types of breathlessness?

A

Tightness, Increases work and effort, Air hunger

Year 1: Respiratory System (19 decks)

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