Control of Ventilation Flashcards
Name/Describe the 4 respiratory centres
1) Emotion (via limbic system in brain)
2) Voluntary over-ride (via higher centres in brain)
3) Mechano-sensory input from thorax (e.g. stretch reflex)
4) Chemical composition of blood (PCO2, PO2 & pH) - detected by chemoreceptors
What are the DRG?
Dorsal Respiratory group via phrenic and intercostal nerves supply inspiratory muscles
What are VRG?
Ventral Respiratory group supply tongue, pharynx, larynx & expiratory muscles
What is the function of central chemoreceptors?
Found in the medulla, respond to changes in CSF [H+] - causes reflex stimulation of ventilation following rise in conc. Ventilation is inhibited by a decrease in arterial PCO2 (reduces CSF [H+]) (hyperventilation)
{does not respond to direct changes in [H+] in plasma}
Describe the mechanism of central chemoreceptors
- arterial PCO2 increases and crosses BBB
- central chemoreceptors monitor the PCO2 indirectly in CSF
- bicarbonate and H+ are formed and H+ is detected
- feedback via respiratory centres increases ventilation
What is the function of peripheral chemoreceptors?
In carotid and aortic bodies, detect changes in arterial PO2 and [H+], cause reflex stimulation of ventilation following significant fall in arterial PO2 (haemoglobin dissociation) or a rise in [H+]
Describe the transduction mechanism of peripheral chemoreceptors
No oxygen combined with oxygen sensor means KO2 channel closes, decreased K+ permeability, causes depolarisation, exocytosis of dopamine vesicles, causes AP in sensory neuron, signal to medullary centres to increase ventilation.
Changes in plasma pH will alter ventilation
How does plasma pH affect ventilation via peripheral chemoreceptors?
decrease pH (acidosis) (exercising muscle) = ventilation increase pH (alkalosis) (vomiting) = inhibits ventilation
How do barbiturates and opioids affect ventilation?
They depress the respiratory centre - can cause death as a result of overdose, normally cause drowsiness
How do anaesthetics affect ventilation?
Increase RR, decrease TV overall decrease AV
How does NO affect ventilation?
Blunts peripheral response in response to falling arterial PO2. Very safe in most individuals, problematic in chronic lung disease when individuals often on “hypoxic drive”. Administrating O2 aggravates the situation.
