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.
Paradoxically , in spite of brain being a central neurological command , by itself has less pain receptors especially to ischemia
The hypoxic threshold for cerebral cells may exceed many fold to that of myocytes.
Cerebral auto-regulation is more developed than coronary regulation.
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 .
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.
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 .