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The vagaries of vascular ischemia : How is cerebral ischemia different from coronary ischemia ?

Posted Oct 22 2011 11:51pm

Is there  an  anginal equivalent  in cerebral circulation ?

Coronary Ischemia produce  angina . . . Cerebral  ischemia do not produce  corresponding   ischemic cerebral pain ! Why ?

Exertional angina  is the dominant  event when coronary artery is  stenosed  . When cerebral artery is stenosed   exertional  head ache do not occur .  So , how does brain respond to  exertional  ischemia ? (EST is also  a stress  to our  cerebral circulation  .  If only we record  EEGs  during treadmill we will  know the truth !)

But in the clinical setting  ,  we are not only surprised by lack of head ache during cerebral  ischemia   , even  exertional   giddiness  is not a common presentation . Instead ,  brain  primarily   respond to ischemia  with focal neurological  deficit instead  of  generating  pain within the skull. This is often referred  to as TIAs .

But,  chronic ischemia  has its effect in the form of lacunar  infarct with its  clinical counter part  – vascular  dementia.

Electrical rhythm  disturbance   like   Ischemic cerebral  arrhythmia are also  known to occur .

The reason for these coronary vs cerebral stenosis behavior is  not clear . Number of possible explanations can be offered.

  1. Paradoxically ,   in spite  of  brain  being a central neurological  command , by itself  has less pain receptors  especially to ischemia
  2. The hypoxic threshold for cerebral cells may exceed many fold to  that of myocytes.
  3. Cerebral  auto-regulation is more developed than coronary regulation.
  4. The circle of  Willis  , though   do not help  much when individual  cerebral arteries are  occluded  suddenly , it does  play  a role in balancing cerebral circulation  at times of chronic  low flow states and  ischemia .
  5. Finally , even in physiology  many of us are comfortable with  little  brain function. One estimate says we  hardly  use   2-3 % of  brain’s processing power (Like our computer  CPU) .Hence  intellectual , deterioration  are  very  late  phenomenon of cerebral ischemia.

 

Reference 

How often head ache occur in  acute stroke ?

It occurs in less than 15 %  in acute ischemia .( In chronic ischemia it is very rare ? non existent ?)

The exact source of pain is not clear .

A stretch induced pain , dull infarct zone pain, cerebral edema induced transient  ICT may also contribute .

It  was a real surprise ,  when I found this journal exclusive for  head aches !

 

What is the mechanism of vascular head ache ?

It is ironical  ,  more often an excess blood flow by inappropriate vasodilatation that cause many episodes of vascular head ache . These confirm the complexities of  ischemic vs non ischemic pain within the brain .


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