Control of breathing when asleep Flashcards
How is sleep controlled when awake?
Ventilation causes change in PCO2/PO2
Feeds back to respiratory centre
Signal to respiratory muscles
Causes lung inflation (also feeds back to respiratory centre)
How does sleep influence autonomic mechanisms?
- Doesn’t
How does sleep influence voluntary mechanisms?
- No feedback from motor cortex
How does sleep influence emotional mechanisms?
- No feedback from limbic system
What are the nerual pathways for control of breathing awake?
Voluntary: corticospinal
Automatic: bulbospinal
Diaphragm–>cervical cord–>corticospinal tract–>pons–>medulla–>motor cortex
Diaphragm–>cervical cord–>respiratory neurones in medulla
How does sleep influence ventilation?
Decreases slightly (10%)
How does sleep influence respiratory muscles?
During REM get functional paralysis of skeletal muscle
Except diaphragm, cardiac and eye
How does sleep influence lung inflation?
Decrease in tidal volume
What are the sleep related changed in SaO2?
Decreases slightly (small change)
What is the average sleep related increase in CO2?
Increases 0.5kPa in healthy people
Reduced sensitivity of central chemoreceptors to PaCO2 during sleep
Decreased ventilation and increased CO2 keeps you breathing when asleep
What is the apneoic threshold?
Level above which the PaCO2 has to raise to maintain breathing during sleep
PaCO2 needed for breathing to occur during sleep - if tidal volume does not decrease, then PaCO2 will not decrease and will not breathe
How does this increase in upper airway resistance influence breathing during sleep in a healthy young person?
reduced upper airway muscle activity during sleep
reduced extra luminal pressure (ELP) and negative intra luminal pressure (ILP)
What are the consequences of influences of breathing on respiratory muscles?
occlusion of the phalangeal (everything above trachea - doesn’t have cartilage) airway –> obstructive sleep apnoea
Name some of the factors that could cause the upper airway to collapse during sleep
if negative pressure generated during inhalation acts on floppy airways, can force shut rather than allow air to enter
exacerbated by excess adipose tissue because this applies external positive pressure that increases the problem
What happens obstructive sleep apnoea?
- apnoea leads to arousal and patent airway
- increases ventilation that causes sleep to restart, but decreased accessory muscle function leads to hypercapnia and return of apnoea,
- woken by effort of breathing against closed airway
What is central sleep apnoea?
Failure of tidal volume to decrease due to stroke or central congenital hypoventilation syndrome that means PaCO2 does not decrease, and no effort is made to breathe
What are the differences in airflow, thoracic effort, abdominal effort in central and obstructive apnoea?
Central Sleep Apnoea: no effort to breathe
Obstructive Sleep Apnoea: effort to breathe but ineffective
What diseases are exacerbated during sleep and why?
COPD
Heart failure
- 50% of patients with heart failure hyperventilate (due to fluid in lungs) and therefore have a low PaCO2 (below the apnoeic threshold) which means they can experience central sleep apnoea
Pulmonary oedema: irritates receptors that causes hyperventilation, lowering PaCO2, hence causing cessation of breathing due to central sleep apnoea; affects 50% of heart failure patients and accelerates mortality (fluid results from pulmonary hypertension 2/2 heart failure)
