10. Control of Breathing - Asleep

Question 1

Define Apnoea?

Answer 1

The cessation of breathing

Question 2

What is the apnoeic threshold?

Answer 2

The threshold over which CO2 level has to be to make sure we breathe

Question 3

How can you measure sleep?

Answer 3

With an electeoencephalogram

Question 4

On an EEG what can be seen when you are awake?

Answer 4

High frequency, low voltage activity

Question 5

When you sleep what happens to your muscles?

Answer 5

The postural muscle activity falls and ocular muscle activity falls

Question 6

When do you dream?

Answer 6

REM sleep

Question 7

Describe the brain activity when you are asleep?

Answer 7

It is very active, like you’re awake. However you are functionally paralysed during REM sleep

Question 8

What muscles are spared functional paralysis during REM sleep?

Answer 8

Eye muscles
Diaphragm (for breathing)

It is more difficult to breath when you are sleep since you are functionally paralysed

Question 9

How many stages of sleep are there?

Answer 9

4

Stage 4 is deep sleep. Makes you feel better

Question 10

Describe the Hypogram in a healthy adult?

Answer 10

Fall asleep quickly and stay in deep sleep. After 90 mins you have a period of REM sleep. The cycle repeats through the night with deep sleep decreasing but REM sleep increasing

Question 11

What are the two ways in which breathing is controlled?

Answer 11

Brainstem (medulla) - reflex/automatic

Motor area of the cerebral cortex - Voluntary/behavoural

Question 12

When you are asleep which mechanism can not control breathing?

Answer 12

The motor area of the cerebral cortex - voluntary

Question 13

What is the Pre-Botzinger complex?

Answer 13

A cluster of respiratory nuclei essential for generating respiratory rhythm. If you knock them out you can’t breathe. The neurones in the pre-botzinger complex reciprocally inhibit each other.

Question 14

Give one way which we can measure breathing in humans?

Answer 14

Lesion deficit models. Patients with locked in syndrome have bleeds high up in the brain stem. Fully preserved sensory input but no motor output (except to the eye muscles)

Question 15

What changes when you sleep?

Answer 15

Blood gases - less input from respiratory centres so less output to respiratory muscles

Question 16

How does the ventilation change when you sleep?

Answer 16

10% reduction in ventilation

Question 17

How does the breathing depth change when you sleep?

Answer 17

Breathing becomes shallower - 350ml instead of 500ml

Question 18

What does not change when you sleep?

Answer 18

Oxygen saturation

Question 19

What is breathing driven by when you are awake?

Answer 19

PaCO2 NOT PaO2

Question 20

Why does oxygen saturation change very little when you sleep compared to being awake?

Answer 20

Most people live on the the flat part of the oxygen dissociation curve. So changes in partial pressure of O2 in your blood will not affect the O2 sat.

Question 21

How much can you change the ventilation without it affecting O2 saturation?

Answer 21

10%

Question 22

What happens to SO2 and PaO2 during REM sleep?

Answer 22

It drops a little

Question 23

What part of the oxygen dissociation curve do people with lung disease lie on?

Answer 23

The curved part - so decreases in ventilation will decrease oxygen levels. This will have a greater effect on the O2 sat and increase CO2 levels

Question 24

What rises when you sleep?

Answer 24

CO2

Question 25

What is the function of CO2 in sleep?

Answer 25

It has to increase to trigger breathing. The level of CO2 required to trigger breathing is higher when you are asleep

Question 26

How does the sensitivity to CO2 change when we sleep?

Answer 26

We become less sensitive because we have less cortical input going to the respiratory centres to make us breathe. As a result we allow CO2 levels to rise when we sleep

Question 27

What is central sleep apnoea?

Answer 27

CCHS (congenital central hypoventilation syndrome) is where the person asleep never reaches the apnoeic threshold so they don’t breathe. Or they can have a higher sensitivity to CO2. You treat this by artificial ventilation

Question 28

Where do you first get rings of cartilage?

Answer 28

larynx

Question 29

What happens to the muscle at the back of the throat?

Answer 29

It becomes relaxed and floppy - they close. If there is negative pressure at the back of the throat it causes the airways to get sucked close during inspiration

Question 30

Describe the luminal pressures when you are sleep?

Answer 30

You have a negative ILP and a positive ELP

Question 31

How does fat affect the ELP?

Answer 31

It increases the ELP more

Question 32

What can anatomical structure can decrease the size of an airway?

Answer 32

Recessed jaw

Question 33

What is the name for the condition where the airways in the larynx and pharynx close up?

Answer 33

Obstructive sleep apnoea - no airflow but they are still trying to breathe

Question 34

Describe the cycle of obstructive sleep apnoea

Answer 34

Sleep
Loss of upper airway muscle function
Apnoea
O2 levels fall, CO2 levels rise
Eventually hypoxia or hypercapnia wakes you up
Restart of normal ventilation

Question 35

What kind of problem is central sleep apnoea and obstructive sleep apnoea?

Answer 35

Central sleep apnoea - Chemosensitivity problem

Obstructive sleep apnoea - mechanical problem

Question 36

What disease is exacerbated by sleep?

Answer 36

COPD - They lie on the slope of the oxygen dissociation curve

Question 37

How does problems with breathing at night cause cardiac issues?

Answer 37

Sleep apnoea generates massive pressures in the chest - exacerbates cardiac conditions.

Question 38

What does heart failure cause?

Answer 38

Pulmonary oedema exacerbates hyperventilation and difficulty breathing