Control of breathing when asleep

Question 1

How is sleep controlled when awake?

Answer 1

Ventilation causes change in PCO2/PO2
Feeds back to respiratory centre
Signal to respiratory muscles
Causes lung inflation (also feeds back to respiratory centre)

Question 2

How does sleep influence autonomic mechanisms?

Answer 2

• Doesn’t

Question 3

How does sleep influence voluntary mechanisms?

Answer 3

• No feedback from motor cortex

Question 4

How does sleep influence emotional mechanisms?

Answer 4

• No feedback from limbic system

Question 5

What are the nerual pathways for control of breathing awake?

Answer 5

Voluntary: corticospinal
Automatic: bulbospinal

Diaphragm–>cervical cord–>corticospinal tract–>pons–>medulla–>motor cortex

Diaphragm–>cervical cord–>respiratory neurones in medulla

Question 6

How does sleep influence ventilation?

Answer 6

Decreases slightly (10%)

Question 7

How does sleep influence respiratory muscles?

Answer 7

During REM get functional paralysis of skeletal muscle

Except diaphragm, cardiac and eye

Question 8

How does sleep influence lung inflation?

Answer 8

Decrease in tidal volume

Question 9

What are the sleep related changed in SaO2?

Answer 9

Decreases slightly (small change)

Question 10

What is the average sleep related increase in CO2?

Answer 10

Increases 0.5kPa in healthy people
Reduced sensitivity of central chemoreceptors to PaCO2 during sleep

Decreased ventilation and increased CO2 keeps you breathing when asleep

Question 11

What is the apneoic threshold?

Answer 11

Level above which the PaCO2 has to raise to maintain breathing during sleep

PaCO2 needed for breathing to occur during sleep - if tidal volume does not decrease, then PaCO2 will not decrease and will not breathe

Question 12

How does this increase in upper airway resistance influence breathing during sleep in a healthy young person?

Answer 12

reduced upper airway muscle activity during sleep

reduced extra luminal pressure (ELP) and negative intra luminal pressure (ILP)

Question 13

What are the consequences of influences of breathing on respiratory muscles?

Answer 13

occlusion of the phalangeal (everything above trachea - doesn’t have cartilage) airway –> obstructive sleep apnoea

Question 14

Name some of the factors that could cause the upper airway to collapse during sleep

Answer 14

if negative pressure generated during inhalation acts on floppy airways, can force shut rather than allow air to enter

exacerbated by excess adipose tissue because this applies external positive pressure that increases the problem

Question 15

What happens obstructive sleep apnoea?

Answer 15

1. apnoea leads to arousal and patent airway
2. increases ventilation that causes sleep to restart, but decreased accessory muscle function leads to hypercapnia and return of apnoea,
3. woken by effort of breathing against closed airway

Question 16

What is central sleep apnoea?

Answer 16

Failure of tidal volume to decrease due to stroke or central congenital hypoventilation syndrome that means PaCO2 does not decrease, and no effort is made to breathe

Question 17

What are the differences in airflow, thoracic effort, abdominal effort in central and obstructive apnoea?

Answer 17

Central Sleep Apnoea: no effort to breathe

Obstructive Sleep Apnoea: effort to breathe but ineffective

Question 18

What diseases are exacerbated during sleep and why?

Answer 18

COPD

Heart failure
- 50% of patients with heart failure hyperventilate (due to fluid in lungs) and therefore have a low PaCO2 (below the apnoeic threshold) which means they can experience central sleep apnoea

Pulmonary oedema: irritates receptors that causes hyperventilation, lowering PaCO2, hence causing cessation of breathing due to central sleep apnoea; affects 50% of heart failure patients and accelerates mortality (fluid results from pulmonary hypertension 2/2 heart failure)