Control of breathing during sleep

Question 1

What are some things that happen when you sleep?

Answer 1

• Can still hear during light sleep
• First thing to happen is that postural muscles weaken and then you eyes roll
• Brain is active during REM sleep – muscles are functionally paralysed
• Diaphragm and ocular muscles are spared

Question 2

What is unique about the respiratory system?

Answer 2

The respiratory system is the only one that can be done by both voluntary and automatic control

Question 3

What are the two ways in which breathing is controlled and where from?

Answer 3

• Brainstem: reflex/automatic
• Cortex: voluntary/behavioural
• There is no cortical control when you’re asleep (some input from the cortex unless you’re in deep sleep )

Question 4

Which part of the brain is responsible for voluntary breathing?

Answer 4

Motor cortex

Question 5

Where are the areas in the medulla that control breathing and what is the complex called?
How does the complex know to adjust breathing rate?

Answer 5

• There is a relatively small number of these neurones on either side of the brainstem
• Found on the rostral-ventral-lateral medullary surface (outside)
• Cluster of respiratory nuclei is the Pre-Botzinger Complex
• Bathed in CSF so they can detect the pH and adjust breathing rate

Question 6

How do the neurones fire?

Answer 6

They reciprocally inhibit each other - when one set fires, the other doesn’t
There are early and late firing neurones

Question 7

Give an example of a potential pathway through which voluntary control from the cortex gets to the respiratory muscles.

Answer 7

Neural pathway going from the motor cortex, through the brainstem and then to the spinal cord and to the respiratory muscles

Question 8

Why does breathing become more shallow during sleep?

Answer 8

During sleep you have less input from the respiratory centres and less motor effect so breathing becomes more shallow

Question 9

What happens to oxygen and carbon dioxide levels during sleep?

Answer 9

• No change/little change in oxygen saturation

- Carbon dioxide concentration increases (controls breathing)

Question 10

Why can we change our breathing rate during sleep without it affecting oxygen saturation?

Answer 10

• You can change your breathing quite a lot (10%) while you’re asleep without changing your oxygen saturation - this is because of the ODC
• Most normal people are on the flat part of the ODC

Question 11

What must happen to carbon dioxide levels when you sleep, and why?

Answer 11

• CO2 has to increase when you go to sleep or else you will die
• Your chemosensitivity to CO2 decreases when you sleep (less cortical input) and so CO2 levels must rise when you sleep to trigger breathing

Question 12

Is carbon dioxide sensitivity uniform in everyone?

Answer 12

Carbon dioxide sensitivity varies between individuals

Question 13

What is the apnoeic threshold?

Answer 13

The threshold over which CO2 levels must be to ensure we keep breathing

Question 14

What is central sleep apnoea?

Answer 14

When you cannot breathe whilst sleeping due to problems with chemosensitivity - problem with respiratory control

Question 15

What is obstructive sleep apnoea?

Answer 15

Patients fall asleep and they lose muscle function -the blood gases are stimulating breathing but there is a mechanical obstruction preventing breathing

Question 16

Congenital Central Hypoventilation syndrome

Answer 16

When individuals have central sleep apnoea from birth

Question 17

Why is the upper airway poorly designed for breathing

Answer 17

• The back of the throat is a muscular tube (no cartilage until the larynx)
• When you’re asleep, the muscles relax and become floppy
• If negative pressure is produced at the back of the throat, this sucks the airway and it closes during inspiration

Question 18

What happens to people with sleep apnoea?

Answer 18

The uvula comes in and blocks the airway so there is no airflow

Question 19

Why do people with obstructive sleep apnoea wake up suddenly during sleep?

Answer 19

• Without breathing the oxygen levels fall and carbon dioxide levels increase
• As they try to breathe, the pressure in the thorax increases.
• Eventually, hypoxia /hypercapnia (elevated CO2) wakes them

Question 20

What is the main difference between obstructive and central sleep apnoea in terms of how thoracic/abdominal effort vary?

Answer 20

In obstructive sleep apnoea, there may not be any airflow but they are still trying to breathe so there is thoracic/abdominal effort. But in central sleep apnoea this is not the case.

Question 21

How does heart failure affect breathing?

Answer 21

Patients with sleep apnoea generate massive pressures in the chest when they are trying to breathe which can exacerbate cardiac conditions.
If you have heart failure and hence the blood is not circulating properly through the lungs then you will get more pulmonary oedema. This irriatetes J receptors in the lungs which makes you breathe more quickly and hence CO2 levels decrease even more. The lag in pulmonary circulation, low heart rate and so low CO2 causes cheyne stoked repsiration.

Question 22

How does having COPD affect breathing?

Answer 22

If you have lung disease and you’re on the steep part of the oxygen dissociation curve, even going to sleep is dangerous because it is going to decrease ventilation, decrease oxygen levels and increase carbon dioxide levels. COPD patients already have low CO2 levels and they go even lower on the curve whilst sleeping so just sleeping alone is very dangerous and they can go into respiratory failure.

Question 23

What can worsen sleep apnoea by affecting the airways?

Answer 23

If you have lots of adipose tissue around your neck then the extraluminal pressure is higher and airway is more likely to close

Question 24

What is Cheyne-stoked respiration?

Answer 24

This is gaps in between breathing which is known as sleep apnoea by respiratory doctors.