Control of Breathing during sleep

Question 1

What happens in sleep

Answer 1

Loss of postural muscle tone
Rapid eye movement (REM) or non-REM sleep
REM - paralysis of the postural muscles

Question 2

What are the 3 inputs into the respiratory centre

Answer 2

Voluntary / behavioural (motor cortex) - corticospinal pathway
Emotional (limbic system)
Reflex/ automatic (brainstem) - bulbospinal pathway

Question 3

What is the input during sleep

Answer 3

Reflex/automatic

Question 4

What is the function of the PreBotzinger complex

Answer 4

Generates the rhythm of breathing.

Close to the surface which allows it to sense changes in pH on the rostroventrolateral surface of the medulla

Question 5

What happens to ventilation during sleep

Answer 5

Hypoventilation
Rate remains the same 
Alveolar ventilation decreases (-16%)
Minute ventilation decreases (-10%)
Tidal volume decreases (-11%)
SaO2 decreases
PaCO2 increases

Question 6

Explain the change in PaCO2 during sleep

Answer 6

Increase in PaCO2
Central chemoreceptor become less sensitive to CO2
Hypercapnia is mandatory for breathing in sleep

Question 7

What causes central sleep apnoea

Answer 7

PaCO2 does not raise above the apnoeic threshold (pCO2 the must be exceeded during sleep)
Stroke/central lesion
Congenital hyperventilation syndrome

Question 8

Describe obstructive sleep apnoea

Answer 8

Airway become obstructed

Affects the upper airway above the trachea where there is no cartilage

Question 9

What is the effect of obstructive sleep apnoea on the respiratory muscles

Answer 9

REM sleep influence
Intraluminal pressure increases -> negative pressure
Gravitational factors and adipose tissue causes the trachea to close/decrease in diameter
Loss of muscle tone

Question 10

What is snoring caused by

Answer 10

Turbulent air flow over the vocal cords

Question 11

Compare central and obstructive sleep apnoea

Answer 11

Central - no effort to breathe (no airflow)

Obstructive - Effort to breathe, but not effective

Question 12

How does sleep apnoea affect waking up

Answer 12

Patients wake up 4 times an hour due to the effort needed to breathe
Patients with severe sleep apnoea are woken every minute

Question 13

What is the effect of sleep on COPD

Answer 13

COPD is exacerbated during sleep
Accessory muscles paralysed in REM sleep (need more effort inspiring and expiring)
Can push into respiratory failure as a small change in pressure will cause a large change in oxygen saturation
(healthy people - O2 saturation doesn’t change much)

Question 14

What is the effect of sleep on heart failure

Answer 14

Can be exacerbated by the sleep-related changes in breathing
About 50% of patients with heart failure hyperventilate and therefore have a low PaCO2 (below the apnoeic threshold) which means they can experience central sleep apnoea

Heart failure -> pulmonary congestion -> irritation of receptors in the lung -> chronic hyperventilation -> apnoeic threshold

Question 15

Describe REM slepe paralysis

Answer 15

Tongue, levator palatini, tensor palatine in the throat relax -> obstruction
Stiffening of the pharynx
Pharyngeal resistance increases
Caused by obesity