Resp 11 - control of breathing during sleep

Question 1

How is the EEG activity when you are wide awake?

Answer 1

High frequency, low voltage

Question 2

The body becomes functionally paralysed during REM sleep. What two muscles are spared? What implications does this have for breathing?

Answer 2

Eye muscles (REM)
Diaphragm
The accessory muscles (e.g. intercostals) are no longer active so it becomes more difficult to breathe

Question 3

What centre controls breathing and where is it located?

Answer 3

Respiratory Centre - medulla

The respiratory centre receives information from the respiratory muscles, lung inflation and blood gases.

Question 4

How does the control of breathing change when asleep compared to when awake?

Answer 4

When awake, 3 things affect respiratory muscles: brainstem, motor cortex (voluntary) and limbic system (emotional).
When asleep, cortical and emotional control of breathing is inactive. It is solely regulated by the respiratory centre.

Question 5

Where is the area that controls breathing on the homunculus motor?

Answer 5

In between the shoulder and the trunk. We just don’t know how this is connected to diaphragm.

Question 6

Name a complex in the medulla that is involved in regulating the respiratory rhythm.

Answer 6

Pre-Botzinger Complex (we don’t know where these neurons are in humans)

Question 7

How do minute ventilation and tidal volume change when asleep?

Answer 7

Breathing becomes shallower
Minute Ventilation = DECREASES (10% reduction in minute ventilation)
Tidal Volume = DECREASES
NOTE: frequency remains roughly the same so no rate change just shallower

Question 8

What plays the biggest role in the control of breathing when awake?

Answer 8

PCO2 levels

Question 9

How does oxygen saturation change when asleep? Explain your answer.

Answer 9

Oxygen saturation remains the same - because you are at the flat part of the oxygen dissociation curve meaning that despite a decrease in PO2, oxygen saturation stays the same.
NOTE: During REM sleep, you PO2 and SO2 drop slightly

Question 10

Why might this be different for someone with lung disease?

Answer 10

People with lung disease live on the steeper part of the ODC so a reduction in PO2 during sleep can cause a marked reduction in oxygen saturation.

Question 11

How do carbon dioxide levels change when you go to sleep?

Answer 11

Carbon dioxide levels rise when you go to sleep.

Question 12

How does the level of carbon dioxide required to trigger breathing change when you go to sleep?

Answer 12

INCREASES - a higher PCO2 is required to trigger breathing

If they don’t you die

Question 13

How does sensitivity to carbon dioxide change when you go to sleep?

Answer 13

Sensitivity to carbon dioxide decreases when you go to sleep - there is a smaller change in minute ventilation per 1 kPa rise in PCO2 - this is because you have less cortical input going to respiratory muscles during sleep

Question 14

What is the apnoeic threshold?

Answer 14

The minimum PCO2 required to trigger breathing

It is lower when awake

Question 15

What happens if you prevent the carbon dioxide levels from exceeding the apnoeic threshold?

Answer 15

You stop breathing

Question 16

Describe the structure of the upper airways (pharynx).

Answer 16

It is a muscular collapsible tube with no cartilage rings holding it open (until you get to larynx)
-> well designed for eating and drinking but not breathing

Question 17

Describe what causes obstructive sleep apnoea.

Answer 17

Relaxation of the muscular parts of the upper airways (= reduced upper airway muscle activity; throat is made of muscular tube until larynx), negative intraluminal pressure and positive extraluminal pressure (caused by fat) can lead to collapse of the airways.

Question 18

What is the disease in which someone stops breathing during sleep because CO2 levels are under the apnoeic threshold?

Answer 18

Central Sleep Apnea aka Congenital Central Hypoventilation syndrome

Question 19

Describe the cycle that takes place in someone suffering from obstructive sleep apnoea.

Answer 19

Sleep –> decrease in upper airway muscle function –> apnoea (hypoxia or hypercapnia will trigger arousal)–> arousal (termination of apnoea) –> patent airway –> ventilation (induces the next apnoea)
All starts again

Question 20

How does central sleep apnoea differ from obstructive sleep apnoea?

Answer 20

This is a chemosensitivity issue rather than a mechanical obstruction

Question 21

What are the major cardio-respiratory diseases exacerbated by sleep-related diseases (one cardiac, one respiratory)? Why is sleep detrimental to these patients?

Answer 21

Cardiac: Heart failure (HF)
Why? Patients with sleep apnoea have to generate massive pressures in their chest to allow them to breathe and this can exacerbate heart conditions.
50% of patients with HF will hyperventilate and therefore have a low PaCO2 (below apnoeic threshold) and so can experience central sleep apnoea.

Respiratory: COPD
Why? You O2 levels are lower so you are on the steeper part of the ODC. With sleep, you get even lower so during sleep patients with COPD go into respiratory failure.