10. Control of Breathing - Asleep Flashcards
Define Apnoea?
The cessation of breathing
What is the apnoeic threshold?
The threshold over which CO2 level has to be to make sure we breathe
How can you measure sleep?
With an electeoencephalogram
On an EEG what can be seen when you are awake?
High frequency, low voltage activity
When you sleep what happens to your muscles?
The postural muscle activity falls and ocular muscle activity falls
When do you dream?
REM sleep
Describe the brain activity when you are asleep?
It is very active, like you’re awake. However you are functionally paralysed during REM sleep
What muscles are spared functional paralysis during REM sleep?
Eye muscles
Diaphragm (for breathing)
It is more difficult to breath when you are sleep since you are functionally paralysed
How many stages of sleep are there?
4
Stage 4 is deep sleep. Makes you feel better
Describe the Hypogram in a healthy adult?
Fall asleep quickly and stay in deep sleep. After 90 mins you have a period of REM sleep. The cycle repeats through the night with deep sleep decreasing but REM sleep increasing
What are the two ways in which breathing is controlled?
Brainstem (medulla) - reflex/automatic
Motor area of the cerebral cortex - Voluntary/behavoural
When you are asleep which mechanism can not control breathing?
The motor area of the cerebral cortex - voluntary
What is the Pre-Botzinger complex?
A cluster of respiratory nuclei essential for generating respiratory rhythm. If you knock them out you can’t breathe. The neurones in the pre-botzinger complex reciprocally inhibit each other.
Give one way which we can measure breathing in humans?
Lesion deficit models. Patients with locked in syndrome have bleeds high up in the brain stem. Fully preserved sensory input but no motor output (except to the eye muscles)
What changes when you sleep?
Blood gases - less input from respiratory centres so less output to respiratory muscles
How does the ventilation change when you sleep?
10% reduction in ventilation
How does the breathing depth change when you sleep?
Breathing becomes shallower - 350ml instead of 500ml
What does not change when you sleep?
Oxygen saturation
What is breathing driven by when you are awake?
PaCO2 NOT PaO2
Why does oxygen saturation change very little when you sleep compared to being awake?
Most people live on the the flat part of the oxygen dissociation curve. So changes in partial pressure of O2 in your blood will not affect the O2 sat.
How much can you change the ventilation without it affecting O2 saturation?
10%
What happens to SO2 and PaO2 during REM sleep?
It drops a little
What part of the oxygen dissociation curve do people with lung disease lie on?
The curved part - so decreases in ventilation will decrease oxygen levels. This will have a greater effect on the O2 sat and increase CO2 levels
What rises when you sleep?
CO2
What is the function of CO2 in sleep?
It has to increase to trigger breathing. The level of CO2 required to trigger breathing is higher when you are asleep
How does the sensitivity to CO2 change when we sleep?
We become less sensitive because we have less cortical input going to the respiratory centres to make us breathe. As a result we allow CO2 levels to rise when we sleep
What is central sleep apnoea?
CCHS (congenital central hypoventilation syndrome) is where the person asleep never reaches the apnoeic threshold so they don’t breathe. Or they can have a higher sensitivity to CO2. You treat this by artificial ventilation
Where do you first get rings of cartilage?
larynx
What happens to the muscle at the back of the throat?
It becomes relaxed and floppy - they close. If there is negative pressure at the back of the throat it causes the airways to get sucked close during inspiration
Describe the luminal pressures when you are sleep?
You have a negative ILP and a positive ELP
How does fat affect the ELP?
It increases the ELP more
What can anatomical structure can decrease the size of an airway?
Recessed jaw
What is the name for the condition where the airways in the larynx and pharynx close up?
Obstructive sleep apnoea - no airflow but they are still trying to breathe
Describe the cycle of obstructive sleep apnoea
Sleep Loss of upper airway muscle function Apnoea O2 levels fall, CO2 levels rise Eventually hypoxia or hypercapnia wakes you up Restart of normal ventilation
What kind of problem is central sleep apnoea and obstructive sleep apnoea?
Central sleep apnoea - Chemosensitivity problem
Obstructive sleep apnoea - mechanical problem
What disease is exacerbated by sleep?
COPD - They lie on the slope of the oxygen dissociation curve
How does problems with breathing at night cause cardiac issues?
Sleep apnoea generates massive pressures in the chest - exacerbates cardiac conditions.
What does heart failure cause?
Pulmonary oedema exacerbates hyperventilation and difficulty breathing
