Control of Breathing (Asleep) Flashcards

1
Q

General Notes about Sleep

Define Apnoea?

What is the Apnoeic Threshold?

When you’re asleep, you are not normally responsive

The difference between sleep and other states (e.g. coma) is that it is ……………………..

Normally, we measure sleep using an …………………………………………….

When you’re wide awake and paying attention, there is ……… frequency, …….voltage activity

Usually, both parts of the brain do the same thing at the same time - dolphins, however, can put half the brain to sleep at a time

You go through a period of light sleep and then into Stage …. which is deep sleep - this is what makes you feel better and restored (in between is a semi-sleep stage)

When you are asleep, …………………….. muscle activity falls and …………………….. muscle activity falls

You dream during …………… sleep

If you measure brain activity during REM sleep, it looks like you’re wide awake

However, you are functionally paralysed during REM sleep (this has probably evolved to stop you acting out your dreams)

As you are functionally paralysed, there is more difficulty breathing

The two muscles that are spared the functional paralysis are:

………… …………………….. (this is what causes the rapid eye movements)

…………………….. (to allow you to breathe)

If a patient breathes a lot with the accessory muscles (e.g. intercostals) then they have more difficulty using these muscles as they are functionally paralysed

A

General Notes about Sleep

Apnoea is the cessation of breathing

Apnoeic Threshold - the level of blood gas you need to maintain breathing

When you’re asleep, you are not normally responsive

The difference between sleep and other states (e.g. coma) is that it is REVERSIBLE

Normally, we measure sleep using an electroencephalogram (EEG)

When you’re wide awake and paying attention, there is high frequency, low voltage activity

Usually, both parts of the brain do the same thing at the same time - dolphins, however, can put half the brain to sleep at a time

You go through a period of light sleep and then into Stage 4 which is deep sleep - this is what makes you feel better and restored (in between is a semi-sleep stage)

When you are asleep, postural muscle activity falls and ocular muscle activity falls

You dream during REM sleep

If you measure brain activity during REM sleep, it looks like you’re wide awake

However, you are functionally paralysed during REM sleep (this has probably evolved to stop you acting out your dreams)

As you are functionally paralysed, there is more difficulty breathing

The two muscles that are spared the functional paralysis are:

Eye Muscles (this is what causes the rapid eye movements)

Diaphragm (to allow you to breathe)

If a patient breathes a lot with the accessory muscles (e.g. intercostals) then they have more difficulty using these muscles as they are functionally paralysed

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2
Q

Sleep

We use sleep as a model to teach how breathing is controlled

Breathing is controlled by the ………………….. ………………. which sends information to the …………………. ………………

The muscle activity causes lung inflation –> ventilation –> changes in PCO2 and PO2

There are inputs to the respiratory centre directly from the …………………. ………………

If you suddenly breathe in deeply - there will be stretch receptor activity coming directly from the lungs as well as the change in chemosensitivity that the deep breath causes - these two inputs influence the respiratory centre

A

Sleep

We use sleep as a model to teach how breathing is controlled

Breathing is controlled by the respiratory centre which sends information to the respiratory muscles

The muscle activity causes lung inflation –> ventilation –> changes in PCO2 and PO2

There are inputs to the respiratory centre directly from the respiratory muscle

If you suddenly breathe in deeply - there will be stretch receptor activity coming directly from the lungs as well as the change in chemosensitivity that the deep breath causes - these two inputs influence the respiratory centre

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3
Q

Control of Breathing during Sleep

There are TWO ways in which breathing is controlled:

…………………. - reflex/automatic

…………… - voluntary/behavioural

It is possible to override the chemosensitivity to behaviourally control your breathing

Emotional Control of breathing comes from the ……………. ……………. which is a separate respiratory input

There is NO ………………… CONTROL when you’re asleep

Most of the time there is some input from the cortex unless you’re in deep sleep

A

Control of Breathing during Sleep

There are TWO ways in which breathing is controlled:

Brainstem - reflex/automatic

Cortex - voluntary/behavioural

It is possible to override the chemosensitivity to behaviourally control your breathing

Emotional Control of breathing comes from the limbic system which is a separate respiratory input

There is NO CORTICAL CONTROL when you’re asleep

Most of the time there is some input from the cortex unless you’re in deep sleep

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4
Q

Voluntary/Behavioural Control of Breathing: The Motor Cortex

If you look at the motor homunculus, the area in control of voluntary breathing is between the shoulder and the trunk

The hot spots seen on a PET scan tell us that there are some neurons in that region that are controlling breathing

A
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5
Q

Reflex/Automatic Control of Breathing: Brainstem Respiratory Neurones

These respiratory neurones are keeping you alive

There is a relatively small number of these neurones on either side of the brainstem

These neurons are found on the ………….- …………- ………… medullary surface

The name given to the cluster of respiratory nuclei is the ………… …………

If we inject these neurones and knock them out, then the animal is unable to breathe

These neurones also have ………… firing and ………… firing neurones

As some neurones fire and stop firing, the other neurones start firing - they reciprocally ………… each other (when one set fires, the other doesn’t)

NOTE: we don’t know where these neurones exist in humans

A

Reflex/Automatic Control of Breathing: Brainstem Respiratory Neurones

These respiratory neurones are keeping you alive

There is a relatively small number of these neurones on either side of the brainstem

These neurons are found on the rostral-ventral-lateral medullary surface

The name given to the cluster of respiratory nuclei is the Pre-Botzinger Complex

If we inject these neurones and knock them out, then the animal is unable to breathe

These neurones also have early firing and late firing neurones

As some neurones fire and stop firing, the other neurones start firing - they reciprocally inhibit each other (when one set fires, the other doesn’t)

NOTE: we don’t know where these neurones exist in humans

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6
Q

Explain the effect of sleep on the following parameters in a healthy person

State if there is an increase or decreases

Minute ventilation

Alveolar ventilation

Frequency

Tidal Volume

Oxygen Saturation

A

Sleep- breathing just becomes a bit shallower

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7
Q

What happens to oxygen saturation during sleep

A

It doesn’t change at all

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8
Q

Does CO2 change in sleep. if so how?

A

When you go to sleep your CO2 goes up-REMEMBER

Because your sleeping decreases

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9
Q
A
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10
Q

Changes in CO2 with Sleep

REMEMBER: CARBON DIOXIDE LEVELS ………… WHEN YOU GO TO SLEEP

CO2 has to increase when you go to sleep or else you will die

The CO2 level required to trigger breathing when you’re awake is ……… than the CO2 required to trigger breathing when you’re asleep

If CO2 didn’t increase when you go to sleep, it will not be sufficient to trigger breathing

A

Changes in CO2 with Sleep

REMEMBER: CARBON DIOXIDE LEVELS RISE WHEN YOU GO TO SLEEP

CO2 has to increase when you go to sleep or else you will die

The CO2 level required to trigger breathing when you’re awake is lower than the CO2 required to trigger breathing when you’re asleep

If CO2 didn’t increase when you go to sleep, it will not be sufficient to trigger breathing

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11
Q

Ventilatory Sensitivity to CO2

In this experiment you get people to keep breathing in their own air

You expire more carbon dioxide than you inspire

At the beginning the VT is around 500 mL at 12 breaths per minute which gives you a minute ventilation of around 5 or 6 - this maintains your carbon dioxide level

If you breathe in your own carbon dioxide, blood carbon dioxide levels will increase and you will try to breathe more to get rid of the carbon dioxide - and by breathing more you breathe in more carbon dioxide and carbon dioxide levels continue to rise

If you keep doing this you will eventually pass our or asphyxiate

Some people’s slopes (sensitivity to carbon dioxide) are flat whilst others are steep

For people with steep slopes, if they get sick they will try to blow the carbon dioxide off whereas people with flatter slopes will retain carbon dioxide more and slip in to respiratory failure quicker

On the other hand, if you are doing elite performance sport, there is evidence to suggest that a steeper slope (hence brisk CO2 response) favours certain exercises compared to a flatter slope

What happens to CO2 sensitivity when we sleep and how does this happen?

A

When we sleep we become LESS SENSITIVE TO CARBON DIOXIDE because we have less cortical input going to the respiratory centres to make us breathe - is a reduced sensitivty ( of the central chemoreceptors) to PaCO2 during sleep.

As we are less sensitive to carbon dioxide when we breathe, we allow our carbon dioxide levels to rise when we sleep

We think this happens because we know that sleep is important for the brain so by allowing ourselves to be less sensitive to carbon dioxide when we’re asleep, it gives us more blood gas range before we wake ourselves up

If we are extremely sensitive to carbon dioxide, every time there is a slight change in carbon dioxide level our body would wake us up

Therefore, it could be an adaptive system that allows us to maintain our brain in the sleeping state

Apnoeic Threshold - the threshold over which CO2 level has to be to make sure we breathe

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12
Q

Define Apnoeic Threshold?

Hypercapnia is …………………… for breathing during sleep

This is an illustration of the apnoeic threshold

In this experiment, you have stopped the carbon dioxide from exceeding the apnoeic threshold so when the person is asleep they are not breathing

There is a condition in which this happens - ……………… ………………. ……………..

Central Sleep Apnoea is also known as Congenital Central Hypoventilation Syndrome (CCHS)

You treat this by artificially ventilating the patients when they are asleep

A

Apnoeic Threshold - the threshold over which CO2 level has to be to make sure we breathe

Hypercapnia is MANDATORY for breathing during sleep

This is an illustration of the apnoeic threshold

In this experiment, you have stopped the carbon dioxide from exceeding the apnoeic threshold so when the person is asleep they are not breathing

There is a condition in which this happens - Central Sleep Apnoea

Central Sleep Apnoea is also known as Congenital Central Hypoventilation Syndrome (CCHS)

You treat this by artificially ventilating the patients when they are asleep

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13
Q

Respiratory muscle control during sleep

We are badly designed for breathing - the upper airway is well designed for eating and drinking

The bit at the back of the throat is a muscular tube

At the front you have the tongue and you have the ………………….. …………………..muscles around the back - the airway at this point is a muscular tube

You do NOT get cartilage rings until you get to the ………………..

The muscular tube is distensible so it is good for swallowing but it is bad to breathe through

When you’re asleep, your muscles relax and this applies to the muscles at the back of your throat as well - instead of being open and rigid, the are floppy

If we produce negative pressure at the back of the throat, this makes the floppy airway get sucked closed during inspiration

When you’re asleep there is negative intraluminal pressure (ILP) and positive extraluminal pressure (ELP) pressing down on the muscular tube

If you are FAT around the neck, then you have even more extraluminal pressure

The difficulty is in trying to maintain the airway while sucking air into the lungs

If someone has a recessed jaw - they already have quite a small airway at the back of the throat

So if you have a narrow tube to begin with and you start putting on fat then you’re going to have problems

The person on the right has a much narrower airway so is more likely to suffer from obstructive sleep apnoea

Notes from video showing obstructive sleep apnoea:

In the patient with sleep apnoea - whenever they try to breathe in, the uvula comes in and blocks the airway so there is no airflow (in or out)

This is very suffocating because very time they breathe in, they can’t take any air in

A

Respiratory muscle control during sleep

We are badly designed for breathing - the upper airway is well designed for eating and drinking

The bit at the back of the throat is a muscular tube

At the front you have the tongue and you have the pharyngeal constrictor muscles around the back - the airway at this point is a muscular tube

You do NOT get cartilage rings until you get to the larynx

The muscular tube is distensible so it is good for swallowing but it is bad to breathe through

When you’re asleep, your muscles relax and this applies to the muscles at the back of your throat as well - instead of being open and rigid, the are floppy

If we produce negative pressure at the back of the throat, this makes the floppy airway get sucked closed during inspiration

When you’re asleep there is negative intraluminal pressure (ILP) and positive extraluminal pressure (ELP) pressing down on the muscular tube

If you are FAT around the neck, then you have even more extraluminal pressure

The difficulty is in trying to maintain the airway while sucking air into the lungs

If someone has a recessed jaw - they already have quite a small airway at the back of the throat

So if you have a narrow tube to begin with and you start putting on fat then you’re going to have problems

The person on the right has a much narrower airway so is more likely to suffer from obstructive sleep apnoea

Notes from video showing obstructive sleep apnoea:

In the patient with sleep apnoea - whenever they try to breathe in, the uvula comes in and blocks the airway so there is no airflow (in or out)

This is very suffocating because very time they breathe in, they can’t take any air in

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14
Q

Obstructive Sleep Apnoea

Patients fall asleep and they lose muscle function (particularly in the upper airway)

If you lose this muscle function, you stop breathing

NOTE: this has nothing to do with RESPIRATORY CONTROL - the blood gases are stimulating breathing but there is a mechanical obstruction preventing breathing

If you don’t breathe, oxygen levels fall and carbon dioxide levels increase

If you block off your nose and mouth and you try to breathe, you are increasing the pressure in your thorax

Eventually, either the ………….. or …………………. will wake you up

Because there is nothing wrong with the chemosensitivity, the patients will eventually wake up

Waking up allows them to clear their airways and the cycle starts again

A

Obstructive Sleep Apnoea

Patients fall asleep and they lose muscle function (particularly in the upper airway)

If you lose this muscle function, you stop breathing

NOTE: this has nothing to do with RESPIRATORY CONTROL - the blood gases are stimulating breathing but there is a mechanical obstruction preventing breathing

If you don’t breathe, oxygen levels fall and carbon dioxide levels increase

If you block off your nose and mouth and you try to breathe, you are increasing the pressure in your thorax

Eventually, either the hypoxia or hypercapnia will wake you up

Because there is nothing wrong with the chemosensitivity, the patients will eventually wake up

Waking up allows them to clear their airways and the cycle starts again

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15
Q

Classification of Sleep Apnoea

In ………………… ……………….. …………………., there may not be any airflow but they are still trying to breathe

They will have a continuous cycle of breathing and then not breathing and then breathing again (they wake up to clear their airway)

These patients will be ………….. throughout the day because they have disrupted sleep

Central sleep apnoea occurs because of the …………………………. changing when you go to sleep

…………….. ……………. ……………….. is a chemosensitivity problem and it is very rare

A

Classification of Sleep Apnoea

In obstructive sleep apnoea, there may not be any airflow but they are still trying to breathe

They will have a continuous cycle of breathing and then not breathing and then breathing again (they wake up to clear their airway)

These patients will be tired throughout the day because they have disrupted sleep

Central sleep apnoea occurs because of the chemosensitivity changing when you go to sleep

Central sleep apnoea is a chemosensitivity problem and it is very rare

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16
Q

When does sleep apnoe become life threatening?

A

Respiratory patients who already have low CO2 levels- COPD

Heart Failure