Respiratory Systems 16 - Control of Breathing While Asleep

Question 1

During sleep, how is breathing controlled?

Answer 1

• Only by the brainstem (automatic)

- No influence of motor cortex or limbic system

Question 2

Compare the pathways in the voluntary and automatic control of breathing

Answer 2

• Voluntary: corticospinal pathway

- Automatic: bulbospinal pathway

Question 3

How does minute ventilation change during sleep?

Answer 3

Decreases by 10%

Question 4

How does oxygen saturation change in sleep?

Answer 4

Decreases by 1% (very small change)

Question 5

Why does oxygen saturation only change slightly with sleep?

Answer 5

Due to the shape of the oxygen saturation curve - slight decrease despite large fall in PaO2

Question 6

How does CO2 change with sleep?

Answer 6

• PaCO2 increases by 0.5kPa in healthy people

- This is because tidal volume decreases

Question 7

How does sensitivity to CO2 change when asleep?

Answer 7

There is a reduced sensitivity of central chemoreceptors to PaCO2 which allows the increase in PaCO2

Question 8

Describe the mechanism of central sleep apnoea

Answer 8

• PaCO2 is important to ensure breathing during sleep.
• If PaCO2 does not raise above the apnoeic threshold during sleep, breathing will stop
• This is central sleep apnoea

Question 9

Define apnoeic thresold

Answer 9

The level above which the PaCO2 must raise to maintain breathing during sleep

Question 10

What can lead to obstructive sleep apnoea?

Answer 10

• A reduced upper airway muscle activity during sleep

- Extra luminal pressure and a negative intraluminal pressure results in occlusion of the phalangeal airway during sleep

Question 11

Describe the difference between central apnoea and obstructive apnoea

Answer 11

• In central apnoea, there is no thoracic or abdominal effort to breathe
• In obstructive apnoea, there is effort to breathe (abdominal + thoracic) but no airflow

Question 12

Describe the cycle of sleep that occurs in obstructive sleep apnoea

Answer 12

• Sleep
• Decreased upper airway muscle function
• Apnoea (hypoxia/ hypercapnia with increased effort)
• Arousal (and termination of apnoea)
• Airway opens (patent) and ventillation increases
• Sleep occurs again and the cycle begins

Question 13

What respiratory disease is exacberated by sleep related changes in the control of breathing.

Answer 13

• COPD

- This is due to a greater decrease in PaO2 during sleep, leading to decreased O2 saturation

Question 14

What cardiac disease is exasperated by sleep related changes in the control of breathing?

Answer 14

• 50% of patients with heart failure hyperventilate due to pulmonary oedema and therefore have a low PaCO2
• This is below the apnoeic threshold
• Patients may experience central sleep apnoea