Saturday, January 21, 2017

Cushing's Reflex in Meningitis : Mnemonic and Explanation


Hello everyone !
Another short post on a very important triad. Cushing's!

Cushing's reflex
It occurs in response to raised Intracranial Pressure (ICP/ICT)

Mnemonic

HIB

H - Hypertension
I   - Irregular Breathing
B - Bradycardia

Mechanism :
So just imagine :
Due to some reason you develop an increase in the ICT.
We know that blood flows from High Pressure to Low Pressure. Generally , the CSF pressure is lower than the BP.
However after a point , the ICT is bound to become equal to or even more than the systemic BP!
If that happens , the blood flow to the brain is decreased and the Brain can get ischemic (cause the Cranial pressure would be higher. So the body won't be able to pump the blood into it.)

Thus, in order to compensate for this , the sympathetic system is activated. The body's peripheral vessels undergo constriction to raise the BP. This would keep them at a higher pressure than the Cranium thus keeping the blood flow intact for a while at least. This causes the Systemic Hypertension.

In a way it's the last ditch effort to save the brain!
Due to sympathetic stimulation the respiratory centers get stimulated too and it's all weird so it causes Irregular Respiration.

Now you'd expect Tachycardia when there is so many Sympathetic juices flowing through your body.
But no. Things aren't as simple as that.

The aortic baroreceptors sense the increased BP and end up decreasing the Heart Rate. Resulting in Bradycardia. So in a way that's the 2nd phase of this Reflex!

The Reflex serves as a marker of raised ICT as that is the event that puts the whole cycle into place.
This generally occurs as the body's last resort to restore blood to the brain.
What a wonderful Homeostatic mechanism !!

Hope this helped !
Stay awesome !

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