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Respiratory Physiology, Medicine and Critical Care > Control of Ventilation > Flashcards

Control of Ventilation Flashcards

1
Q

How is respiratory rhythm at rest maintained?

A

Inspiratory neurons are activated for a short period, in what is thought to be a rapid positive feedback loop. Their activity then shuts off, and passive expiration takes place due to the elastic recoil of the lung

Basal activity in the inspiratory muscles during inspiration is directed towards the larynx, pharynx and tongue to maintain airway patency.

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3
Q

Where are peripheral chemoreceptors found?

A

Aortic and carotid bodies

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4
Q

What are the different types of chemoreceptors involved in modulating respiratory effort?

A
  • Central chemoreceptors
  • Peripheral chemoreceptors
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6
Q

What is the downstream effect of peripheral chemoreceptor activation?

A

Stimulus inactivates K+ channels, causing the receptor cell to depolarise and send signals to the medullary centres to increase ventilation

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7
Q

What are peripheral chemoreceptors sensitive to?

A

Decreases in:

  • PO2
  • pH

Increases in:

  • PCO2
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8
Q

What is the ventilatory response if the system becomes alkalotic?

A

Ventilation will be inhibited, causing the body to retain CO2 and thus increase H+ concentration

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9
Q

What acts to control changes in ventilatory response to changes in PO2 or PCO2?

A

Increase in PO2 and decrease in PCO2 act as negative feedback for the response system

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10
Q

What stimulates central chemoreceptors?

A

H+ in the CSF

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11
Q

How low does PO2 have to fall for peripheral chemoreceptors to be stimulated?

A

<60 mmHg

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12
Q

How does CO2 go from being in the arterial circulation to stimulating central chemoreceptors as H+ ions?

A

It crosses into the cerebrospinal fluid, where it is combined with H2O by carbonic anhydrase to carbonic acid, where it then dissociates to H+ and HCO3-. H+ ions then stimulate central chemoreceptors

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14
Q

What is the response to decreased pH or increased PCO2?

A

These both stimulate ventilation in response to the system becoming acidotic. This blows off CO2, resulting in a decrease in H+ ions.

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18
Q

Where are central chemoreceptors found?

A

Located in the medulla

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20
Q

Of peripheral and central chemoreceptors, which is regarded as being the primary ventilatory drive mechanism?

A

Central chemoreceptors

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21
Q

Of peripheral and central chemoreceptors, which is regarded as being the secondary ventilatory drive mechanism?

A

Peripheral chemoreceptors

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22
Q

Under what circumstances would stimulation of central chemoreceptors result in normal respiration?

A

Chronic stimulation of central chemoreceptors e.g. in COPD

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23
Q

What do you need to bear in mind with those with anaemia (who are properly ventilated) with regards to respiratory drive?

A

It is not the oxygen content that determines haemoglobin saturation; PaO2 does this.

In anaemic patients who are properly ventilated, they will not stimulate O2 receptors in aortic and carotid bodies, and their respiratory rate and depth will remain the same

24
Q

What factors affect respiratory drive during rest and when exercising?

A

Rest

  • Emotion
  • Voluntary override
  • Mechanosensory input from the thorx
  • Chemical composition of blood

Exercise

  • Temperature
  • Plasma adrenaline concentration
25
Q

What are the main physiological factors which influence respiratory rate (and therefore you should consider from a clinical perspective as causes of altrered resipiratory rate)?

A
  • pH
  • pCO2
  • pO2
  • Voluntary control/emotional drive
  • Stretch/proprioception receptors in bronchial tissue
  • Temperature
  • Hypoglycaemia
26
Q

What are the main senosry organs involved in control of respiratory function?

A
  • Carotid body glomus (type 1 cells)
  • Aortic Glomus cells
  • Central Chemoreceptors - ventral medullary sensing body
  • Mechanoreceptors (stretch and proprioceptive) in bronchial and lung tissue
27
Q

How do carotid body cells sense hypoxia?

A

Oxygen sensitive K channels are inhibited by hypoxia.This reduction in the membrane potential opens voltage-gated calcium channels, which causes a rise in intracellular calcium concentration. This causes exocytosis of vesicles containing a variety of neurotransmitters, including acetylcholine, noradrenaline, dopamine, adenosine, ATP, substance P, and met-enkephalin. These act on receptors on the afferent nerve fibres which lie in apposition to the glomus cell to cause an action potential.

Depolarisation of these cells also occurs with:

  • pH changes
  • Temperature
  • PaCO2 changes
  • Glucose changes (specifically, hypoglycaemia)
28
Q

Which chemoreceptors respond quicker to changes in PaCO2 - central or peripheral chemoreceptors?

A

Peripheral chemoreceptors - enact response to immidiate changes in PaCO2. Central chemoreceptors are responsible for most of hte steady-state response to sustained hypercapnia

29
Q

What is the difference in terms of chemosensory action between aortic and carotid bodies?

A

Aortic bodies sense oxygen content (to do with arterial oxygen delivery), whereas Carotid bodies sense oxygen tension. However, Aortic Bodies have fairly blunted respinse to oxygen content

30
Q

When do mechanoreceptors in the lung stimulate respiratory activity?

A

When lungs deflate

31
Q

When do mechanoreceptors suppress respiratory activity?

A

When tissues are overstretched

32
Q

What non-respiratory functions do the lungs have?

A
  • Trap for airborne particles/Antimicrobial functions
  • Reservoir of blood
  • Route of drug administration/elimination
  • Metabolism
  • Modulator of acid/base balance/clotting cascade
  • Filter of the bloodstream
  • Modulation of body temperature
33
Q

How does PaCO2 influence minute volume?

A

Increased PaCO2 increases minute volume - mediated by peripheral chemoreceptros over a timescale of seconds, and by central chemoreceptors

34
Q

How much does the rate of minute volume increase by per 1 mmHg increase of PaCO2?

A

2-5L/min

35
Q

How is the CO2/ventilation response curve influenced by hypoxia?

A

Shifted to the left - increase in minute ventilation is increased per unit rise of CO2. Hypoxis tends to make you more sensitive to changes in PaCO2

36
Q

How is the CO2/ventilation response curve influenced by metabolic acidosis?

A

Shifted to the left - increase in minute ventilation is increased per unit rise in CO2

37
Q

How do sleep, sedation, anaeasthesia and opiates influence the CO2/ventilation curve?

A

Shifts curve to the right and decreases the slope of the curve - the increase in minute ventilation is reduced per unit rise of CO2

41
Q

How does age influence ventilatory response?

A

Decreases ventilatory response

42
Q

How quickly does the change in minute volume increase in response to raised PaCO2?

A

About 75% of maximum occurs within minutes

Respiratory Physiology, Medicine and Critical Care (42 decks)

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