An IST, Dysautonomia & Hyperadrenergic Health Update

If you’ve been following my health journey, you know I’ve spent a ridiculous amount of time trying to explain one very specific thing:

When I stand up, my body changes gears.

My heart rate climbs. My blood pressure climbs with it. The longer I’m upright, the more likely I am to become dizzy, nauseated, weak, heavy, lightheaded, or feel like the room and I have entered into some sort of disagreement about which direction gravity is supposed to work.

After months of tracking symptoms, watching heart-rate spikes, adjusting medications, drinking enough electrolytes to personally keep the industry afloat, and finally undergoing a tilt-table test, I now have the official report.

And somehow, the answer is both:

“Your tilt-table test was negative.”

and

“Your cardiovascular system absolutely did something.”

Welcome back to chronic illness, where apparently both things can be true at the same time.

What the Tilt Table Actually Showed

I started the test lying down with a blood pressure of 128/82 and a heart rate of 83 bpm.

Then they tilted me upright.

Instead of my blood pressure dropping, it began climbing.

Some of my recorded upright readings included:

• 143/95
• 141/103
• 139/115
• 153/89

My heart rate also increased, reaching a recorded high of 109 bpm during the passive portion.

That’s important because it represents an increase of 26 beats per minute from my baseline of 83.

The standard adult heart-rate criterion used in diagnosing POTS is an increase of at least 30 bpm within the appropriate testing window, without orthostatic hypotension.

I reached +26.

Four beats.

That’s how close the passive portion of my tilt came to meeting that particular heart-rate criterion.

So technically, and correctly according to those numbers, the report states:

“Passive phase does not demonstrate diagnostic criteria for POTS.”

That part isn’t something I’m disputing.

But it’s also not the end of the story.

Then Came the Isoproterenol

During the second portion of the test, they administered isoproterenol, a medication that stimulates the cardiovascular system.

And my body apparently interpreted that as a personal challenge.

My officially recorded heart rate reached 174 bpm.

But there’s an important detail that isn’t obvious when you simply read the table afterward: 174 was the highest heart rate documented before they stopped recording those individual data markers.

Immediately after the nurse took those final measurements, I watched my heart rate continue climbing until it was nearing 180 bpm. That’s when they began pulling me off the medication.

Because that near-180 number isn’t documented in the final data table, I’m not presenting it as an official recorded measurement. It is what I observed happening during the test.

What is officially documented is dramatic enough.

My heart rate remained around:

174 → 174 → 173 → 170 → 169 bpm.

I developed significant presyncopal symptoms and felt like I was going to pass out.

But here’s the part that continues to interest me:

My blood pressure didn’t crash.

It remained preserved and frequently elevated.

During that portion of the test, recorded blood pressures included:

159/94

127/109

144/118

128/87

139/106

And as I entered recovery, my blood pressure reached 177/103 while my heart rate was still 135.

My cardiovascular system wasn’t shutting down.

It looked much more like someone had slammed their foot onto the accelerator.

And the Report Actually Acknowledges That

The final interpretation describes what happened as a:

“Marked sinus tachycardic response.”

More importantly, it states:

“Findings may be consistent with an exaggerated adrenergic/sinus tachycardic response.”

Adrenergic refers to the sympathetic, adrenaline-driven side of the nervous system.

You know, fight or flight.

Except apparently mine occasionally chooses:

Fight, flight, run a marathon, fight a bear, flee the bear, become the bear.

The rhythm itself remained sinus tachycardia. In other words, my heart wasn’t flipping into an unrelated abnormal rhythm. My normal sinus rhythm was simply becoming extraordinarily fast in response to stimulation.

So What Did I Actually Test Negative For?

This is probably the most important clarification from this entire experience.

My tilt was negative for orthostatic hypotension.

My blood pressure didn’t fall significantly when I was upright.

It was also negative for a vasodepressor/neurocardiogenic hypotensive response.

Again, my blood pressure didn’t collapse.

And the passive portion did not meet the diagnostic heart-rate criteria for traditional POTS.

When I say traditional POTS, I’m making that distinction intentionally because POTS isn’t necessarily one identical physiological presentation in every patient. Different patterns or subtypes are commonly discussed, including neuropathic, hypovolemic, and hyperadrenergic POTS, and people can have overlapping features.

The massive heart-rate increase after isoproterenol cannot be used to turn my tilt into a positive POTS test. Isoproterenol itself increases heart rate, so those 170+ readings cannot count toward the required orthostatic HR increase.

That makes sense.

What I’m questioning now isn’t whether we should rewrite the results of the tilt.

It’s:

What explains everything else?

Enter Inappropriate Sinus Tachycardia

My cardiologist feels strongly that Inappropriate Sinus Tachycardia, or IST, is part of what is happening.

The report also specifically states:

“Inappropriate sinus tachycardia remains a clinical consideration in the appropriate setting.”

IST could explain quite a bit of what I’ve experienced.

But there’s still another piece of my pattern that I want investigated.

My resting heart rate generally isn’t sitting at 110 or 120 all day.

It’s usually somewhere around 75–90 bpm, with my average resting heart rate around 88.

When I’m upright, however, I routinely see:

115–140 bpm.

And my blood pressure tends to rise along with my heart rate.

That’s the piece that keeps waving its little flag at me.

This Morning Was Another Example

The morning after receiving all of this information, I woke up at approximately 9:27 a.m.

I hadn’t taken my morning medication yet.

While sleeping/resting, my wearable showed my heart rate roughly around the 80s.

I woke up.

I stood up.

And almost immediately, my graph climbed into approximately the 110–118 bpm range.

That’s much closer to what I experience in ordinary life:

Resting: approximately 75–90

Upright: approximately 115–140

And when these episodes happen, my blood pressure frequently rises too.

That doesn’t diagnose POTS.

A wearable graph certainly doesn’t diagnose POTS.

But it does provide another piece of evidence showing that posture appears to matter to what my cardiovascular system is doing.

So Now I’m Asking About Hyperadrenergic POTS

To be crystal clear:

I have not been diagnosed with hyperadrenergic POTS.

My passive tilt did not meet the heart-rate criterion required to establish POTS during that study.

But hyperadrenergic physiology is something I want explored because several pieces of this puzzle keep pointing toward excessive sympathetic activation.

My heart rate and blood pressure increase while I’m upright.

The tilt objectively documented elevated blood-pressure readings while standing.

The isoproterenol challenge produced an enormous sinus-tachycardic response while my blood pressure remained preserved or elevated.

And the physician interpreting the test literally described the findings as potentially consistent with an exaggerated adrenergic response.

So my question going forward isn’t:

“Do I have IST or hyperadrenergic POTS?”

I’m beginning to think the better question is:

“Does IST explain the entire picture, or is there also an overlapping hyperadrenergic orthostatic disorder?”

Those are very different questions.

And sometimes bodies don’t read medical textbooks closely enough to realize they’re only supposed to pick one box.

Where We Go From Here

The recommendations from the tilt-table report are to continue correlating these findings with my symptoms and previous ambulatory monitoring, continue metoprolol as tolerated, maintain adequate hydration and conservative measures, avoid excessive caffeine and other tachycardia triggers, and consider an electrophysiology evaluation if my symptoms remain significant despite medication.

For me, that means continuing to document what happens outside the doctor’s office.

Not just:

“My heart rate was 135 today.”

But:

What was it lying down?

What happened when I stood?

How long had I been standing?

What did my blood pressure do at the same time?

What symptoms appeared?

Because that’s where the pattern lives.

And if my doctors believe it’s appropriate, I also want to discuss whether additional autonomic testing, including testing aimed specifically at a hyperadrenergic response, would help distinguish IST alone from IST combined with an orthostatic autonomic problem.

“Negative” Doesn’t Always Mean Normal

That’s probably my biggest takeaway from this whole experience.

When someone hears:

“Your tilt-table test was negative,”

it sounds reassuring.

It sounds like nothing happened.

But my test documented a heart rate in the 170s, presyncope, significant hypertension, and what the physician himself characterized as an exaggerated adrenergic/sinus tachycardic response.

That’s not nothing.

The test simply didn’t demonstrate the specific physiological criteria required to diagnose traditional POTS or orthostatic hypotension during the passive phase.

And there’s an enormous difference between:

“We didn’t find anything.”

and

“We found something, but we still have to determine exactly what it means.”

Right now, I’m living in the second sentence.

We have IST strongly on the table.

We have dysautonomia.

We have an objectively documented exaggerated adrenergic response.

We have repeated real-world episodes where standing sends both my heart rate and blood pressure upward.

And we still have questions about whether there’s a hyperadrenergic orthostatic component sitting underneath or alongside everything else.

So the puzzle isn’t finished.

But at least now we’re finally holding some pieces that actually fit together.

And I’ll take progress wherever I can get it. 🖤

Until next time,

Mrs. B 🖤🌙

Still chronically complicated, still asking questions, and still refusing to let the word “negative” be the end of the conversation when my body is very clearly saying otherwise.