19. Control of breathing (asleep) Flashcards
The body becomes functionally paralysed during REM sleep. What 2 muscles are spared?
What implications does this have for breathing?
Eye muscles
Diaphragm
The accessory muscles (e.g. intercostals) are no longer active so it becomes more difficult to breathe
How does the control of breathing change when asleep compared to when awake?
When asleep, cortical and emotional control of breathing is inactive.
It’s solely regulated by the respiratory centre.
Describe the changes that can be seen between wakefulness and sleep
Hypoventilation Decrease in tidal volume Decrease in minute ventilation Decrease in alveolar ventilation Oxygen saturation remains ~unchanged
Name a complex in the medulla that is involved in regulating the respiratory rhythm.
Pre-Botzinger Complex
What plays the biggest role in the control of breathing when awake?
PCO2 levels
How does oxygen saturation change when asleep?
Oxygen saturation remains the same: because you are at the flat part of the ODC so despite a decrease in PaO2, oxygen saturation stays the same.
How does oxygen saturation change during REM sleep?
PO2 and SO2 drop slightly
How does oxygen saturation change when asleep in someone with COPD?
Their awake saturation is lower (on the steeper part of the ODC) so a reduction in PaO2 during sleep can cause a marked reduction in oxygen saturation and can push them into respiratory failure
How do carbon dioxide levels change when you go to sleep?
PaCO2 increases (as tidal volume decreases)
What mechanism keeps you breathing when asleep?
Reduction in tidal volume and increase in PaCO2
How does sensitivity to carbon dioxide change when you go to sleep?
Sensitivity to CO2 decreases when asleep: there is a smaller change in minute ventilation per 1 kPa rise in PCO2
What increases likelihood of becoming hypercapnic?
Low CO2 sensitivity
As more likely to retain CO2 and not blow it off
What is the apnoeic threshold?
The minimum PaCO2 required to trigger breathing during sleep
What happens if you prevent the carbon dioxide levels from exceeding the apnoeic threshold?
You stop breathing
Describe the structure of the upper airways (pharynx).
It is a muscular, collapsible tube with no cartilage rings holding it open.
Describe what causes obstructive sleep apnoea.
Relaxation of the muscular parts of the upper airways
Generates negative intraluminal pressure downstream
Airways close
What can contribute to airway collapse and obstructive sleep apnoea?
If in addition there is positive extralumenal pressure e.g. fat around airway
Describe characteristics that predispose to obstructive sleep apnoea
Fat tissue around tongue and neck
Shorter airways anatomically
Older (lose muscle tone in airways, airways become more compliant)
What causes snoring?
Turbulent air passing over vocal cords (caused by slight closure of the airways)
What defines central sleep apnoea?
No airflow, but no effort to breath
What defines obstructive sleep apnoea?
No airflow, but effort to breath
Describe the cycle that takes place in someone suffering from obstructive sleep apnoea.
Fall asleep Decrease in upper airway muscle activity Apnoea High CO2, low O2, still trying to breath Wake due to effort of trying to breath against closed airway Cycle repeats
How do sleep-related changes in breathing exacerbate heart failure?
Patients hyperventilate
Therefore have a low PaCO2 (below apnoeic threshold) which means they can experience central sleep apnoea
How does central sleep apnoea differ from obstructive sleep apnoea?
This is a chemosensitivity issue rather than a mechanical obstruction
List 2 causes of central sleep apnoea
Stroke / central lesion
Congenital hypervenilation syndome.
What is the main cause of obstructive sleep apnoea
Obesity
