Whatcha talkin' 'bout, Circle of Willis?

If you haven’t heard (because, let’s say, you’ve been locked in a dungeon for a couple years), my day job is an engineer. Non-engineers may imagine that most of my days are spent standing in front of whiteboards filled with equations. The truth: a huge majority of my time is writing. See, I work in the heavily regulated medical field and it can months of writing and revising in order to gain approval for a report that the actual testing took a few minutes of time. It’s interesting because the mechanics of engineering writing are different (passive voice only), one thing remains common between my fiction and my reports…I strive to explain complex things (for example, character emotions or arterial motion due to the respiratory cycle) with clarity and brevity. And today, for your pleasure (?) will attempt such a feat for you. Stand back kids. Don’t try this at home.

 

Specifically, I design and test medical devices. In my career, I’ve had the hand in getting a number of surgical products into operating rooms. From a line of gynecological instruments (which is as glamorous as it sounds) to a system which reversed blood flow through the brain to prevent strokes during carotid stenting procedures…

“WHAaAaA?” you ask. “Reverse blood flow through the brain while doing what?”

Ok, I’ll clarify…since you asked:

Most of you know that a stent is a device that gets installed in a person’s artery to help fix a blood flow problem. One common use of stents is when an artery gets plugged up with plaque. The stent is supposed to smash the gunk against the arterial wall and help open up the flow. Contrary to what people may picture, it’s not a delicate procedure and there are instances when bits of plaque break off and take to the bloodstream. For a stent in aorta (the artery in the belly…which is gigantic as far as blood vessels go), nobody cares if a little piece of plaque gets loose since it’ll be easily filtered out later. However, if the artery in question is the carotid (the vessel in the neck that supplies blood to the head/brain/face), even a tiny piece of plaque can clog the flow in the delicate capillary beds downstream, preventing oxygen to some vital areas of the brain (a.k.a it causes a stroke). In summary, there’s a risk that stenting the carotid may end up causing the much more serious issue of a stroke.

So the system I worked on is used to prevent these particles from going downstream and causing a stroke while the docs are stenting the carotid. We do this by…wait, here’s the clever part…reversing the blood flow through the brain.

The idea being that if the little chunks of plaque go away from the brain instead of into it, the danger of stroke has been nullified. If the blood has reversed flow, there’s no chance of stroke.

Now, before you throw up your hands and scream, “What kind of Sci-Fi BALONEY is this?!” Allow me to explain. It’s a matter of two important attributes.

First, liquids (such as blood) will flow from high pressure to lower pressure. And it happens that the venous half of the cardiovascular system (the part that returns deoxygenated blood to the heart) is lower in pressure than arterial system.

Second, as vital of an organ as they come, the brain has several redundant blood supply channels. Once they all get into the brain, they mesh and combine in what’s called, “The Circle of Willis.”

So, how does the flow reversal work?

Basically, at a point just upstream of the plaque, we use a fancy tube to connect the carotid being stented into a major vein. This makes the blood want to flow from the higher pressure in the brain through our tube and into the lower pressure vein. And because the Circle of Willis, there’s plenty of blood to do this. So the flow reverses over the part we’re planning to stent. The brain stays oxygenated and blood-filled because of the redundant supply. Once the stent is in place, the flow is restored to normal.

“Jeez,” you say. “Is there any harm to the patient by doing all this mumbo jumbo?”

In most patients, the answer is simply, “No, harm at all.” Many of the people getting these treatments already have diminished blood supplied to the brain through the plaque heavy parts anyway. Again, there’s an amazing amount of blood getting pumped into the brain through several routes.

Sorry, to have geeked out on you like that. As you can tell, I can be as passionate about my day job as I am about my writing. Thanks for indulging me.