Physiological Consequences of Respiratory Centre Depression Flashcards
What is the purpose of the respiratory system?
To keep blood oxygen at 100mmHg, carbon dioxide at 40mmHg and pH at 7.40
How is the respiratory system controlled?
By controlling the respiratory muscles, chest wall and airways to alter ventilation
Can gas exchange be controlled?
No - because it is a passive process but it is altered indirectly via ventilation
Where is the central controller of the respiratory system?
The brain stem (pons and medulla) and the cortex
What is the role of the neurons in the brain stem?
To generate a an automatic rhythm of inspiration
What is the major output of the respiratory centre?
The phrenic nerves
What is the role of the cortex in the respiratory centre?
To give voluntary control to alter the output of the brainstem
What receptors feed in to the central controller?
Central chemoreceptors, peripheral chemoreceptors, stretch receptors in the lung, irritant receptors in the lung, stretch receptors in the muscle, joint position receptors in the muscle, receptors for touch, temperature and pain, emotional stimuli acting through the limbic system
Where are the central chemoreceptors located?
on the ventral surface of the medulla where they are in contact with the CSF
What do central chemoreceptors respond to?
CSF H+
Where are the peripheral chemoreceptors located?
in the carotid bodies at the bifurcation of the common carotid and in the aortic bodies at the arch of the aorta
What do peripheral chemoreceptors respond to?
H+, CO2 and O2
What is the result of a small increase in CO2?
Rapid increase in ventilation
What is the result of a small fall in O2?
No change in ventilation
What O2 pressure is required to influence ventilation?
<60mmHg
What is the relationship between work and minute ventilation?
Linear - match ventilation with oxygen consumption
What is the relationship between PaO2, PaCO2 and pH with work?
Blood gases remain constant while work increases
What happens at high levels of work?
There is anaerobic metabolism which generates extra acid, so to compensate there is a further increase in ventilation - this leads to a decrease in CO2 and an increase in O2 to allow pH to return to just below normal
What happens to breathing in anxiety?
There is excessive ventilation for oxygen consumption and CO2 production so the result is respiratory alkalosis
What is hypoventilation?
When ventilation is not meeting the metabolic requirements for oxygen consumption and carbon dioxide production
What is the result of acute hypoventilation?
respiratory acidosis
What is the result of chronic hypoventilation
metabolic alkalosis?
What are the causes of hypoventilation?
Reduced respiratory centre activity, neuromuscular disease, chest wall deformity, gross obesity, sleep disordered breathing
What are the 3 types of sleep disordered breathing?
obstructive sleep apnoea, central sleep apnoea, obesity hypoventilation syndrome
What is obstructive sleep apnoea?
A transient obstruction to the throat during sleep which prevents breathing
Why does the obstruction occur in OSA?
airway muscles relax in sleep, the throat is already narrowed e.g. by obesity and the tongue falls backward if supine
What makes you wake up in OSA?
Reduced O2 and increased CO2
What is the management for OSA?
weight loss, CPAP, lying on side, mandibular advancement splint, surgery
What is the long term consequence of sleep disordered breathing?
The brainstem will start to accept higher levels of CO2 and lower levels of O2 so that sleep can continue without being disrupted - leads to chronic hypercapnea with normal pH and high bicarbonate (compensated respiratory acidosis)
What will happen to respiratory drive in long term sleep disordered breathing?
Will become dependent on hypoxic drive - more dependent on PaO2
What will happen if you give someone with hypoxic drive supplementary oxygen?
They will develop acute hypoventilation
