control of ventilation Flashcards
what nerves stimulate the muscles of inspiration
phrenic - diaphragm
intercostal nerves - external intercostal muscles
origin phrenic nerve
C3-5
what do respiratory centres do
- set automatic rhythm of breathing
- adjust rhythm in response to stimuli
PRG
pontine respiratory group
monitors what happens in DRG and VRG
DRG
dorsal respiratory group
predominantly assoc w inspiration
VRG
ventral respiratory group
predominantly assoc w expiration but also active during inspiration
resp centres have their rhythm modulated by
- emotion (via limbic system)
- voluntary override (voluntary brain centres)
- mechano-sensory input from thorax (stretch reflex)
- chemical composition blood: PCO2, PO2, pH (chemoreceptord)
what is the most dominant and important input to resp centres
chemoreceptor input
central chemoreceptors
medulla
respond directly to CSF H+ (directly reflects PCO2)
primary ventilatory drive
peripheral chemoreceptors
carotid and aortic bodies
repsond to plasma H+ and PO2 (less so PCO2)
2ry ventilatory drive
if plasma pH falls
H+ increases -> ventilation will be stimulated (acidosis) and CO2 is blowed off and H+ lowered
if plasma pH increases
H+ falls (alkalosis), ventilation inhibited and CO2 retained and H+ increases
how do barbituates and opioids affect resp centres
depress them - inhibit respiration
how do most gaseous anaesthetics affect resp centres
increase RR
but decrease TV and so decrease alveolar ventilation
how does nitrous oxide affect resp centres
blunts peripheral chemoreceptor response to falling PaO2.
problematic in chronic lung disease patients who are on hypoxic drive (giving O2 aggravates situation)
