When Palpitations Are Not About the Mind

In this piece, I take a step back.

The heart pounds, the hands tremble, heat becomes unbearable, sleep is shallow, anxiety comes for no reason, and weight has dropped. When a patient brings in this cluster, there are times I recommend a blood test before I even take the pulse.

This is because the list overlaps almost exactly with the symptoms of hyperthyroidism.

But There Is an Unexpected Point Here

Why does the heart race when thyroid hormone is in excess? It is easy to assume it is because more adrenaline is being released.

But an increase in circulating adrenaline alone does not explain it. When the blood concentration is directly measured, it comes out the same as normal, or even lower.

What has changed alongside it is the response on the heart's side. Thyroid hormone affects the contraction and relaxation of heart cells, the ion channels that set the rhythm, and several processes that respond to sympathetic nerve signals.

It is not only the amount of signal being sent that has changed. The property of the receiving side has changed along with it.

Change in the Receiving Side Has Been Measured in Humans

This is not something seen only in the thyroid. When a signal decreases, the receiving side turns up its ear (receptor up-regulation) — there is a study that actually measured this in people.

A study examined patients with a disease in which the sympathetic nerves degenerate (multiple system atrophy). The number of alpha-adrenergic receptors on their platelets had increased to nearly seven times that of healthy people. And when the same amount of signal was introduced, the sensitivity of the blood pressure response was ten to twenty times higher.

As the sending side grew quiet, the receiving side turned up its ear.

I have found this point interesting for a long time. If signal and response are thought of as one and the same, the question of why a normal number can still feel this hard goes unanswered. Even the same letter is read at a different size depending on the circumstances of the one receiving it.

The Baseline Itself Differs from Person to Person

The normal range is a line drawn by gathering many people together. But when it comes to thyroid hormone, the range within which a single person's level rises and falls is only half as wide as that population-based standard.

So a value that has already moved well outside a given person's own baseline can still register as normal on the population reference chart.

So being within the normal range does not mean "this is the same as usual for you." The very same number can be well within one person's usual range and quite far from another person's usual range.

The Same Thing Happens on a Monthly Timescale, Too

This property does not appear only in disease. Within a single person, the same thing comes and goes following the cycle.

After ovulation, core body temperature and heart rate variability can also shift somewhat. But the result depends on how precisely the phase of the cycle is identified and measured. This means individual differences and measurement conditions must be considered together.

Symptoms that cause difficulty before menstruation are not diagnosed from a single hormone value. They are assessed together with the pattern that repeats across the cycle and the impact on daily life.

I Cannot Change the Hormone Itself

I do not try to substitute for the hormone. That is not my role to play, and if it is needed, that care exists elsewhere.

What I look at is somewhere else: why, going through the same change, one patient is shaken badly while another passes through it.

I look at the same conditions I discussed in the timing of a racing heart and cold sweat — whether sleep and meals, breathing and pain, overlapped with the hormonal change at the same time.

Rather than setting out to change the hormone level directly, I look for what, among the bodily conditions overlapping with that change, can actually be addressed. I direct my medicine there.

When Testing Comes First

If the cluster described above continues for more than a few weeks, or if weight loss is pronounced, a blood test checking thyroid function comes first. Conversely, if a patient leans instead toward unusual fatigue, feeling cold, and swelling, that too is distinguished by the same test.

And if you are taking hormone medication, increasing or decreasing the dose is a decision for that specialty's care. What this piece has addressed is not that decision, but the point at which people, even on the same medication, experience it differently.

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The same number is experienced differently, person to person and time to time.

This is because both the sending side and the receiving side of the signal change together. And because the line called "normal" is drawn by gathering many people together, a person can be within it and still be far from their own baseline.

If treatment that directly regulates the hormone level is needed, that care comes first. What I can do stands alongside it. I look at how sleep, meals, and breathing overlapped during the period the level was fluctuating.

Written by Dr. Heo Ji-young (PhD in Korean Medicine Pathology, Kyung Hee University · former Research Professor of Herbology, Kyung Hee University)