control of breathing when asleep

Question 1

what is apnoea?

Answer 1

the cessation of breathing

Question 2

what is the apnoetic threshold?

Answer 2

• the level of blood gas you need to maintain breathing

Question 3

how can we measure sleep?

Answer 3

measured using an electroencephalogram (EEG) and awake gives a high frequency and a low voltage.

Question 4

what happens to muscle activity during sleep?

Answer 4

• postural and ocular muscle activity falls

- During REM, only 2 unparalysed muscles are diaphragm and eye muscles.

Question 5

how much control is there whilst we are asleep?

Answer 5

• emotional and voluntary/behavioural control is eliminated

- NO cortical control when in deep sleep.

Question 6

where does the voluntary control of breathing whilst asleep come from?

Answer 6

Voluntary breathing (when awake) comes from the motor homunculus (located in the brain between motor areas for the shoulder and the trunk)

Question 7

where does the automatic control come from?

Answer 7

• in the brain stem
• The respiratory neurones are found on the rostral-ventral-lateral medullary surface
• it is called the pre botzinger complex
  (names after the wine they were drinking)
• These neurones reciprocally inhibit each other (when one fires, the other stops) which allows breathing to take place.

Question 8

how can we measure breathing?

Answer 8

• use a lesion deficit model

Question 9

how can we used locked in syndrome patients to learn about how resp neurones are connected in the body?

Answer 9

locked in syndrome patients have bleed in the brain so they have sensory function but no motor output
- this syndorme proves that the limbic system (emotional) has an effect on the breathing rate

Question 10

how does breathing change when you are asleep?

Answer 10

• during sleep there is less input from the resp centre
• there is less output to the resp muscles so blood gas levels change
• there is a 10% reduction in ventilation

Question 11

how does SO2 and PO2 change in the REM part of sleep? in healthy people

Answer 11

• SO2 drop and PO2 drops
• ventilation decreases but oxygen saturation stays the same
• the CO2 levels do change

Question 12

how do CO2 levels change during sleep?

Answer 12

• CO2 levels rise during sleep
• this is crucial
• the CO2 level required to trigger breathing is lower when awake compared to sleep so more CO2 is needed

Question 13

why do we need more CO2 when asleep?

Answer 13

• there is a reduced sensitivity of chemoreceptors to CO2

- peoples sensitivity to CO2 is variable and determines why some people might have steeper slopes

Question 14

so what is the apneoic threshold?

Answer 14

• the threshold over which the CO2 level has to be in , in order to allow us to breath
  when asleep

Question 15

what is hypercapnia?

Answer 15

the retention of extra CO2

Question 16

what is central sleep apnoea?

Answer 16

• when the CO2 levels do not raise above the apnoeic threshold so the breathing stops
• happens with Congenital Central Hypoventilation Syndrome
• treated by artificial ventilation

Question 17

what happens to respiratory muscle control when you are asleep?

Answer 17

• before the cartilage rings of the trachea there is a MUSCULAR TUBE
• the muscles relaxes
  (genioglossus and leator palatini muscles )
• Positive extra-luminal pressure is present
• Negative intra-luminal pressure is present
  these can predispose you to airway collapse which is known as obstructive sleep apnoea
• a partial collapse is why we snore

Question 18

what else can pre dispose us to obstructive sleep apnoea?

Answer 18

• a recessed jaw

Question 19

how to classify obstructive sleep apnoea and central sleep apneoa?

Answer 19

• in obstructive sleep apneoa there might be no airflow but they are trying to breathe so there is thoracic and abdominal effort
• Central Sleep Apnoea is due to changes in sensitivity of the chemoreceptors while obstructive sleep apnoea has healthy chemoreceptors

Question 20

what happens in obstructive sleep apnoea?

Answer 20

• patient falls asleep and lose muscle function
• there is a mechanical obstruction
• no breathing so O2 levels fall and Co2 levels rise
• eventually either hypoxia or hypercapnia wake you up
• cycle begins again
• often patients are sleepy and tired

Question 21

how does heart failure cause sleep apneoa?

Answer 21

• Heart failure can be exacerbated by the sleep-related changes in breathing because about 50% of patients with heart failure hyperventilate (and therefore have a LOW PaCO2 below the apnoeic threshold
• this means they suffer from central sleep apnoea