11 - Control of Breathlessness (asleep) Flashcards
What is apnoea?
the (temporary cessation) of breathing
What is the apnoeic threshold?
the level of blood gas that you need to maintain breathing
What do we use to measure sleep?
EEG (electoencephalogram)
What does an EEG look like when awake and alert?
high frequency, low voltage activity
What happens to the pattern on EEG as you fall asleep?
higher voltage, lower frequency
What does an EEG look like for REM sleep?
looks like wakefulness- high frequency and low voltage
what happens to the muscles when you fall asleep?
postural muscle activity falls
ocular muscular activity falls
What is REM sleep?
where you have dreams - the EEG looks similar to that of wakefulness - the brain in very active
What happens to the muscles in REM sleep?
Which muscles are the exception?
You have functional paralysis (by brainstem). This is probably to stop us acting out our dreams.
The 2 muscles that are spared functional paralysis are the eye (causes rapid eye movement) and the diaphragm (allows for breathing).
what happens to the proportions of REM and non-REM sleep as you go through the night?
the amount of deep sleep decreases and the amount of REM sleep increases (hence, the first cycle is a very deep sleep)
Which centre controls breathing and what does it send signals to?
the respiratory centre, send signals to the respiratory muscles
What are the 3 inputs to the respiratory centre?
- brainstem - for reflexes
this involves chemosensitivity AND strech sensitivity from the lungs - motor cortex - voluntary/behavioural
- limbic system- emotional
During sleep, which input is no longer used?
corticol control (i.e. control of the motor cortex) - voluntary behaviour
Where are the neurones in the brainstem found?
on the rostral-lateral medullary surface
What is the Pre-Botzinger Complex?
What kind of neurones are present?
the name given to the cluster of respiratory nuclei in the brainstem
They have early and late firing neurones, which reciprocally inhibit each other
During sleep, there is less input from the respiratory centres, so there is less output to the respiratory muscles.
What changes does this result in during sleep?
- around 10% reduction in ventilation
- breathing becomes shallower
(- little change in oxygen saturation) - blood gases change
What gas level drives breathing when awake?
CO2 levels
What happens to the saturation of oxygen when asleep?
doesn’t change (this is dues to the shape of the ODC)
During REM sleep, what 2 measures decrease slightly?
- sO2 - dissolved oxygen
- PaO2 - partial pressure of oxygen in arterial blood
During sleep, what does change?
Why is this?
CARBON DIOXIDE LEVELS
they rise when you go to sleep (if they don’t we will die)
When you go to sleep, the chemosensitivity to CO2 decreases - the level of CO2 required to trigger breathing is higher when you are asleep (this is because there is less input into the respiratory centres)
If CO2 didn’t increase, the level wouldn’t be high enough to trigger breathing
What is the condition where the CO2 level does not exceed the apnoeic threshold?
How is it treated?
Central Sleep Apneoa
(if you are born with it) Congenital Central Hypoventilation Syndrome (CCHS)
Treated by artificially ventilating patients when they are asleep
What is obstructive sleep apneoa?
The brain is working, but the mechanics are failing
NOTHING TO DO WITH RESPIRATORY CONTROL
What are the changes in PaO2 and SaO2 during non-REM and REM sleep?
non-REM: breathing changes and partial pressure changes but the saturation remains the same because of the ODC
REM: SO2 and PaO2 drop slightly
What is a possible consequence of heart failure and sleep apnoea?
(blood not circulating properly)—–> pulmonary oedema —–> exacerbates hyperventilation and difficulty breathing
