POTS: When Your Brain Loses Its Balance

Your heart has a set rate that it wants to beat at. And it's not what you think. To understand what's going on in POTS, you have to understand how heart rate actually works in the first place.

Your Heart Has a Set Rate — And Your Brain Slows It Down

OK so here's something most people don't know. The resting rate of the heart is somewhere around 120, right? That's where it wants to be with no brain connected. Anybody that's had kids, you might have noticed that a kiddo's heartbeat beats much faster than an adult's. Even like a six-year-old — their heartbeat is a little bit faster. Why does that happen?

So once you start attaching the brain to it, what the brain does is it uses that parasympathetic output and it slows it down. Heart rate is a function of how well you maintain blood pressure. So if you're really efficient at it, you don't have to beat your heart as much to maintain pressure, which is pretty cool. And so you can have that parasympathetic system slow your heart down even more because that uses less energy and it's more efficient for your body.

Brakes and Gas Pedals

Now, if you want to get up real quick, you don't have to really do a lot to hammer down and hit the gas pedal and get the sympathetic system going. You don't really have to do that. All you can do is just let off the brakes of the parasympathetic system and that heart will be like, "let me run" — and it'll start to raise up toward that 100 to 120 mark, right? In that range, you don't really have to do much. You just back off the parasympathetic inhibition and that heart rate will naturally climb up into that range.

Then if you want to crank — you're back on the soccer field and you want to take it above that 120 mark — now you can shift over and push in that sympathetic drive and have that heart crank even more. That takes you from that 120 range up into the 170 range, let's call it.

So if we think about somebody with POTS, there's a difference between somebody who when they pop up is going from 70 to 120. That's still 50 points different, right? So it's still a big jump. But there's a little different physiology happening than if they take it to 150.

What Your Resting Heart Rate Tells You

Same thing if your heart rate is cruising around 100 at rest — that is a very different thing than if it starts at 65 or 70. It means that your ability to provide that inhibition to the heart is either not working, or your brain has decided that you shouldn't do that in order to maintain the state that you are in.

POTS Is Really an Energy Problem

At the end of it, the autonomic system really comes down to energy. How do we make it? How do we mobilize it? And how do we make it efficient and recoverable — so that when we expend energy, we can also replenish the system so we can spend it again?

I would move people away from thinking about it in terms of rest and digest and fight or flight. I would move it toward thinking about it in terms of: how much energy am I using? Is that efficient?

So if you're cranking 120 just to eat an orange on the couch, that's not efficient. And so then we have to back out of like, well, why does my body have to do that to maintain the status? Are there things that I can do so that my body can be more efficient — so that I'm not burning all of this energy in order to do really simple tasks?

The Norepinephrine Confusion

Does norepinephrine go up in POTS? We just talked about sympathetic nerves, right? So norepinephrine is what that nerve uses at the end. You send an electrical signal from one end of the nerve to the other, and then at the end of that it releases a little chemical to the next nerve, and that starts the electricity at the next nerve and then it goes. So that chemical that gets released where those two nerves butt up against each other in a sympathetic nerve — that one's called norepinephrine. It really only exists in this little cleft between the two.

But if you have to really crank that out in order to maintain blood flow to your head, then you're going to have more production or more utilization of norepinephrine at that nerve ending that we can measure, and you can see that go up. It's like if you were stomping on the gas pedal and you had more exhaust coming out of the tailpipe because you're burning more.

The thing that confuses people sometimes is we think of norepinephrine as the same thing as epinephrine — or adrenaline — that's produced in the adrenal glands, and they're not the same. Similar name. It's confusing, but it's not the same. One is a metabolic hormone — it helps us pull glucose out of the liver, out of the muscles, out of the blood supply and helps us use glucose. Whereas norepinephrine goes between those two nerve endings so that one sympathetic nerve can talk to the next one in the line.

They can go up and they should go up if we're seeing an acceleration of vasoconstriction, increases in heart rate, changes in respiration. All of those things may possibly yield higher levels of norepinephrine simply because you're trying to crank it out more.

Dual Tasking: When Thinking Makes Everything Worse

A dual task is basically a term we use to describe a cognitive task that is coupled to another context. We may do it when people are walking or doing a certain manual task, or in this case when they're on a tilt test. It's just a mental task, a cognitive task that we have you do so that we can see: when you're trying to think, does the system respond the same way, or does it change?

In some cases, the cerebral perfusion goes up during the dual task, which is great — it means when the brain demanded more energy, the body was able to fulfill that demand. But in some cases when you go to do that, we actually see it drop. And in that sense, we know that the metabolic capacity is not as good.

So What Actually Helps?

Underneath this is where we're seeing a proprioceptive error in the control of head and neck function. In this particular case, we're looking at doing a coordinated effort — it's not one thing. It's a combination of eye-head stimulus, coordinating eye and head movement, but also with proprioceptive stimulation through neck afference while we're creating that movement, so we can orient to the head better.

By recalibrating for that, improving that signal ratio, the brain is actually able to organize blood flow better — it controls it better.

The way to think about it: you could take someone that might have a problem with accurately putting their finger on their nose, or pinning the tail on the donkey. But by training the brain so they understand where their hand is better, it makes it way easier to do that task, right? Same idea. We want to make sure we're understanding where we are. And part of the benefit of that output is that it's tied to the reflexes of our autonomic outputs.

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