Control of Breathing (Asleep) Flashcards
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
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
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
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
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
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
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
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
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
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
Sleep- breathing just becomes a bit shallower
What happens to oxygen saturation during sleep
It doesn’t change at all
Does CO2 change in sleep. if so how?
When you go to sleep your CO2 goes up-REMEMBER
Because your sleeping decreases
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
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
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?
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
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
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
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
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
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
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
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
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
When does sleep apnoe become life threatening?
Respiratory patients who already have low CO2 levels- COPD
Heart Failure
