control of breathing when asleep Flashcards

1
Q

what is apnoea?

A

the cessation of breathing

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2
Q

what is the apnoetic threshold?

A
  • the level of blood gas you need to maintain breathing
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3
Q

how can we measure sleep?

A

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

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4
Q

what happens to muscle activity during sleep?

A
  • postural and ocular muscle activity falls

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

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5
Q

how much control is there whilst we are asleep?

A
  • emotional and voluntary/behavioural control is eliminated

- NO cortical control when in deep sleep.

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6
Q

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

A

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

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7
Q

where does the automatic control come from?

A
  • 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.
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8
Q

how can we measure breathing?

A
  • use a lesion deficit model
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9
Q

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

A

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

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10
Q

how does breathing change when you are asleep?

A
  • 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
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11
Q

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

A
  • SO2 drop and PO2 drops
  • ventilation decreases but oxygen saturation stays the same
  • the CO2 levels do change
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12
Q

how do CO2 levels change during sleep?

A
  • 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
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13
Q

why do we need more CO2 when asleep?

A
  • there is a reduced sensitivity of chemoreceptors to CO2

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

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14
Q

so what is the apneoic threshold?

A
  • the threshold over which the CO2 level has to be in , in order to allow us to breath
    when asleep
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15
Q

what is hypercapnia?

A

the retention of extra CO2

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16
Q

what is central sleep apnoea?

A
  • 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
17
Q

what happens to respiratory muscle control when you are asleep?

A
  • 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
18
Q

what else can pre dispose us to obstructive sleep apnoea?

A
  • a recessed jaw
19
Q

how to classify obstructive sleep apnoea and central sleep apneoa?

A
  • 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
20
Q

what happens in obstructive sleep apnoea?

A
  • 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
21
Q

how does heart failure cause sleep apneoa?

A
  • 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