control of ventilation Flashcards
how are respiratory motor movements affected by the central nervous system?
requires stimulation of skeletal muscles via phrenic and intercostal nerves, at rest no expiration takes place so no neural input is required
where do respiratory centres reside?
pons and medulla
what is ventilatory control dependant on?
signalling from the brain
severing the spinal cord above the phrenic nerve (C3-C5) ceases breathing
what do respiratory centres have their rhythm modulated by?
emotions (via limbic system in brain)
voluntary override (via higher centres in brain)
mechano-sensory input from the thorax (eg. stretch reflex)
chemical composition in the blood (PCO2, PO2, pH)- detected by chemoreceptors
what are the 2 main neurons inside respiratory centres?
DRG- dorsal respiratory group
VRG- ventral respiratory group
in what muscles does the ventral respiratory group stimulate contraction?
tongue, pharynx, larynx and expiratory muscles
in what muscles does the dorsal respiratory group stimulate contraction?
inspiratory muscles via phrenic and intercostal nerves
what are the two types of chemoreceptors ?
central- medulla, responds directly to H+ and is the primary ventilatory drive
peripheral- carotid & aortic body, responds to PO2 & plasma H+ and is the secondary ventilatory drive
what do central chemoreceptors in the medulla detect?
changes in [H+] in the CSF around the brain
what is hypercapnea ?
raised PCO2
what happens in the blood brain barrier when arterial PCO2 increases ?
CO2 crosses the barrier but H+ don’t
what do central chemoreceptors do?
measure PCO2 indirectly in CFS
what happens to arterial PCO2 levels in patients with chronic lung disease ?
becomes chronically elevated, patient becomes desensitised to PCO2 and relies on changes in arterial PO2 to stimulate ventilation
patient goes into hypoxic drive
what will happen to the respiration rate in an anaemic patient with normal lung function, who has blood oxygen level half the normal amount ?
it will stay the same because is lungs are working normally, diffusion takes place normally and the PaO2 will be normal
what do most gaseous anaesthetic agents increase and decrease?
increase- respiration rate
decrease- tidal volume and alveolar ventilation
