8. Control of Ventilation

Question 1

What does ventilator control require?

Answer 1

Stimulation of the skeletal muscles of inspiration.

Question 2

How does stimulation of the muscles of inspiration occur?

Answer 2

Via the phrenic nerve and intercostal nerves

Question 3

Where does ventilator control reside?

Answer 3

Within ill defined centres located in the pons and medulla

Question 4

What is ventilator control entirely dependent on?

Answer 4

Signalling from the brain

Question 5

When will breathing cease?

Answer 5

If the spinal cord I severed above the origin of the phrenic nerve C3-5

Question 6

What is breathing normally?

Answer 6

Subconscious

Question 7

Although normally subconscious, what can breathing be subject to?

Answer 7

Voluntary modulation

Question 8

What are the 2 groups of neurons?

Answer 8

• Dorsal respiratory group

- Ventral respiratory group

Question 9

Respiratory centre have their rhythm modulated by…

Answer 9

• Emotion ( via limbic system in the brain)
• Voluntary over-ride (via higher centres in the brain)
• Mechano-sensory input from the thorax (e.g stretch reflex)
• Chemical composition of the blood (PCO2, PO2 and pH) detected by chemoreceptors

Question 10

What is the most significant stimulant affecting respiratory centre rhythm?

Answer 10

Chemoreceptor input

Question 11

What are the 2 types of chemoreceptors??

Answer 11

• Central

- Peripheral

Question 12

Where are central chemoreceptors located?

Answer 12

Medulla

Question 13

What do central chemoreceptors respond to?

Answer 13

Respond directly to H+

directly reflects PCO2

Question 14

What are the central chemoreceptors responsible for?

Answer 14

Primary ventilator drive

Question 15

Where are peripheral chemoreceptors located?

Answer 15

Carotid and aortic bodies

Question 16

What do peripheral chemoreceptors respond to?

Answer 16

Respond primarily to plasma [H+] and PO2

less so to PCO2

Question 17

What are the peripheral chemoreceptors responsible for?

Answer 17

Secondary ventilator drive

Question 18

What crosses the blood-brain barrier when arterial PCO2 increases?

Answer 18

Carbon dioxide

Question 19

What muscles does the dorsal respiratory group of neurons innervate?

Answer 19

Muscles of inspiration

Question 20

What muscles does the ventral respiratory group of neurones innervate?

Answer 20

Muscles of expiration

Question 21

What do the respiratory centres do?

Answer 21

• Set an automatic rhythm of breathing through co-ordinating the firing of smooth and repetitive bursts of action potentials in DRG- travel to inspiratory muscles.
• Adjust this rhythm in response to stimuli

Question 22

What do the central chemoreceptors in the medulla do?

Answer 22

• Detect changes in [H+] in CSF around brain

- Cause reflex stimulation of ventilation following rise in [H+] which is driven by hypercapnia (raise PCO2)

Question 23

What is ventilation reflexly inhibited by?

Answer 23

A decrease in arterial PCO2 (reduced CSF [H+]) (hyperventilation)

Question 24

What do the central chemoreceptors not respond to?

Answer 24

Do not respond to direct changes in plasma [H+]

Question 25

What monitors the PCO2 indirectly in the CSF?

Answer 25

Central Chemoreceptors

Question 26

What are formed when the chemoreceptors respond to an increase in PCO2?

Answer 26

Bicarbonate and H+

Question 27

What does feedback via the respiratory centres do in response to an increase in arterial PCO2?

Answer 27

Increase ventilation

Question 28

What slows ventilation rate?

Answer 28

Decrease arterial PCO2

Question 29

What do the peripheral chemoreceptors cause?

Answer 29

Reflex stimulation of ventilation following significant fall in arterial PO2 or a rise in [H+]

Question 30

What classifies as being a significant fall in arterial PO2?

Answer 30

A fall below 60mmHg

Question 31

What do peripheral chemoreceptors not respond to?

Answer 31

Oxygen content

Question 32

What does increased [H+] usually accompany?

Answer 32

A rise in arterial PCO2

Question 33

What will alter ventilation?

Answer 33

Changes in plasma pH

Question 34

What stimulates ventilation?

Answer 34

Acidosis

Plasma pH falls= increase in [H+]

Question 35

What inhibits ventilation?

Answer 35

Alkalosis
Plasma pH increases= decrease in[H+]
Can be caused by vomiting

Question 36

What allows a large degree of voluntary control over breathing?

Answer 36

Descending neural pathways from cerebral cortex to respiratory motor neurons

Question 37

What cannot be overridden?

Answer 37

Involuntary stimuli such as arterial PCO2 or [H+]

Question 38

What occurs during hyperventilation?

Answer 38

Ventilation id reflex inhibited by an increase in arterial PO2 or a decrease in arterial PCO2/[H+]

Question 39

What are some common drugs that can affect respiratory centres?

Answer 39

• Barbiturates
• Opioids
• Anaesthetics
• Nitrous oxide

Question 40

How do barbiturates and opioids affect respiratory centres?

Answer 40

Depress respiratory centres

Question 41

What can barbiturate and opioid overdose lead to?

Answer 41

Often leads to death as a result od respiratory failure

Question 42

What do most gaseous anaesthetic agents do?

Answer 42

Increase respiratory rate by decrease tidal volume so decrease AV

Question 43

What does nitrous oxide do?

Answer 43

Blunts peripheral chemoreceptor response to falling PaO2.

Question 44

What problems can arise surrounding nitrous oxide?

Answer 44

-Problematic in those with chronic lung disease
-Patients often have a hypoxic drive
Administering O2 to these patients often aggravates the situation

Question 45

Why is respiration inhibited during swallowing?

Answer 45

To avoid aspiration of food or fluids into the airways.

Question 46

Why is swallowing followed by an expiration?

Answer 46

In order that any particles are dislodges outwards from the region of the glottis