September 10, 2016

Improved Helmets: Thinking about modelling the brain

So I’m doing some more thought exercises on this project. Yes, been a long time since I posted anything and I only just got around to having a look at the report into Phillip Hughes’ death.

In this case, the ball managed to strike a vertebral artery. There are typically two of these, and they flow to the basilar artery which feeds the brain stem. The other major route is via the carotid arteries . Both of these sets branch out into much finer blood vessels within the brain.

That, to my mind would have triggered a sharp impulse in the blood pressure in those arteries. The arteries are somewhat elastic, but they probably don’t appreciate that level of abuse: they have pretty thin walls in that part of the body and are quite small in diameter as they branch out from the brain stem. In the report, they talk about “traumatic basal subarachnoid haemorrhage“.

According to Wikipedia, that means blood is leaking out of vessels and into the protective layers that surround the brain. We often joke about the smoke escaping from an electronic component when we put too much current through it.

This would seem to be the blood vessel equivalent: a minor artery or three went “pop”.

It would appear that this is definitely one mode of failure in the brain that should be considered when designing protective gear. It’s particularly an issue for soldiers with IEDs. In their case, the helmet can work “perfectly”, but it’s the pressure wave hitting the body causing pressure up the blood vessels in the neck that do damage, as well as pressure waves in the cerebral fluid itself.

The other mode of failure seems to be in the neurons and their connections.

Thinking about this latter point, we know that the brain is a very delicate organ when taken out of its casing. It is described as having the consistency of tofu in some articles.

This makes me wonder whether the brain should be considered a solid at all. To my way of thinking, perhaps a very dense mesh of interconnected nodes is a more accurate representation of what’s going on.

As the head moves through space (which is what seems to do much of the damage), Newton’s First Law does its worst. If you consider a single node in this mesh travelling through a linear path, the node experiences a tension force from each connection to its neighbours.

These connections have a limit to the amount of tension they can withstand. When they break, that’s when brain damage takes place.

Now, under constant velocity, or at rest, these tension forces are within tolerance, nothing bad happens. However, when a sudden blow is experienced, it is this additional tension as individual nodes get jostled around from their own inertia and the transferred tensional forces from neighbouring nodes that may trigger these connections to break.

Modelling both of these situations is an interesting problem. The latter could be done with strain gauges, but they’d have to be sensitive ones. How sensitive? Not sure. 2AM isn’t a great hour to be answering such questions.

As for the vessels, perhaps piezo transducers at differing locations might give some insight into how much pressure is in different parts.

It may also be possible to have a tree-structure of tubes representing the arteries, and measure how much they expand as the pressure wave hits by measuring how much light is blocked between a LED and a photo diode with the “artery” running in the path: the fatter it is the less light hits the diode.

More food for thought I guess. 🙂