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How cooling your body could help fight small strokes

Aug 25 2020

Dr Kirsten Coupland is an early-career research fellow within the NHMRC Centre for Research Excellence in Stroke Recovery and Rehabilitation and is part of the stroke research group based at HMRI. 

For as long as she can remember, Kirsten has always asked 'Why?' - which is the ideal quality for someone trying to understand the brain. As you'll know from previous chats with our brain cancer researchers, despite many, many years of research, there's still so much we don't understand about this incredibly complex organ.

Kirsten's work involves trying to understand what happens ischemic stroke. In this type of stroke a blood vessel is blocked in the brain, which leads to intracranial pressure building up - and the best therapy is to release that pressure.

What Kirsten and her team have determined is that after a small stroke, there is a build-up in pressure, that's not caused by oedema (swelling of the brain). Traditionally a large stroke causes brain swelling, which drives the pressure up. We examine smaller strokes, which were thought to be too small to cause a pressure rise. We have shown that a pressure rise is occurring, but it isn’t happening due to brain swelling. Something else is going on and we are trying to figure out what it is.

But why do we care if the pressure goes up?

The pressure going up affects many systems in the brain, but the most important affected is blood flow. A stroke reduces the amount of blood that reaches the brain. Your brain has this amazing system of back-up blood supply called ‘collateral vessels’. When the pressure increases too much these blood vessels get squashed and can’t deliver blood to the area around the stroke. This leads to more cell death and worse outcomes for the stroke patient.

So what is driving this pressure increase?

Now, as you know, the skull is a finite space and can't expand. In a skull there's precise amounts of brain tissue, blood and cerebrospinal fluid. 

So far, all research seems to be pointing at the cerebrospinal fluid as causing the build-up in pressure after this stroke. 

But why?

Well after ruling out all other options Kirsten and the team are pretty sure that the cerebrospinal fluid moves in a certain way out of the skull and that's what's driving the pressure. However, in science, you answer one question only to raise five more...

The team are now looking at therapies in laboratory models to see what they can do to relieve the pressure, and hypothermia seems to be an option. In fact, Kirsten came to HMRI on a Fellowship funded by the Dalara Foundation to explore this very question. Over the past two years they've been exploring the subject, and they feel that reducing the body temperature to 32.5 degrees prevents the damaging intercranial pressure.

The challenge is how to reduce the body temperature safely. It's a procedure that's already used in patients who've had a heart attack, but they tend to be sedated and are closely monitored for negative side effects. With a stroke patient it's different as there's no sedation and it is always risky to sedate a patient unless absolutely necessary. To drop the body temperature you can use ethanol or fans, or just allow the body temperature to drop naturally. Our group is the first to demonstrate that short-duration (under an hour) exposure to hypothermia is sufficient to prevent an increase in pressure. This is big news, because the negative side-effects are much lower for shorter exposure to low temperatures.

We know that icing relieves inflammation with body parts (as anyone who's gone over on an ankle knows!) But why? (there's that question again!) How does it allow the body to regulate itself? Does it have an impact at a molecular level? Some research has shown that there is a molecular change in cerebrospinal fluid at lower temperatures - but we don't know why.

What we do know is that Kirsten and her teammates in the stroke team are working diligently to improve outcomes for people with stroke, still one of Australia's most debilitating conditions. 

Dr Kirsten Coupland spoke with ABC Newcastle's Kia Handley. Listen to the segment here