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Cushing Reflex/Triad

Cushings Reflex occurs in response to cerebral ischemia cause by elevated intra-cerebral pressure.The triad are

  • Hypertension
  • Bradycardia
  • Irregular Respiration

The logic behind this is:

Increased cerebral pressure will cause hypo-perfusion of the brain so it will instruct the vasomotor center in the medulla to raise the sympathetic tone to elevate blood pressure in the periphery, this will drive more blood to the brain trying to correct hypo-perfusion.

The bradycardia is due to the sudden rise in BP. (Baroreceptor reflex)

Irregular Respiration is caused by impaired brainstem function due to high levels of PCO2.

Also refer to this thread:

Code:
http://www.usmle-forums.com/usmle-step-1-forum/40177-cushing-reaction.html
 

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Mechanism...

Increase ICT results in cerebral ischemia due to constriction of arterioles.. This results in decreased pH and increased pCO2...the effect of this is central reflex sympathetic rise in perfusion pressure (the mechanism for Hypertension)... This rise in Pressure stretches the baroreceptors which causes increased baroreceptor firing via CN IX, X resulting in increase in AV node refractory period(via Left vagus) resulting in Bradycardia...
Irregular respiration could be due to effect of Increases ICT/ pCO2...
Correct me if i missed something.. :)
 
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