A Painful Place Tilts Acidic

"It is nothing much. Why does it hurt this way?"

There is no great bruise and no visible swelling, yet the place cannot be touched. And the other way round — a much worse injury can hurt less than expected.

How much something hurts is not set by the size of the injury alone. The circumstances that place is in have their say too. Among those circumstances, one that is seldom spoken of is acid-base.

What tilting acidic means

The body makes acid for as long as it is alive. Energy is spent, carbon dioxide is left over, and when that meets water hydrogen ions appear. More hydrogen ions is what we mean by tilting acidic.

So the body clears them diligently. It breathes carbon dioxide out, and the kidneys discard acid while holding on to bicarbonate. The breath works within minutes to hours; the kidneys work over days.

All of this is about the blood as a whole. And that value is held within a narrow range.

But the body has channels that read acidity

It is easy to treat acid-base as waste left over from metabolism. It is not.

Sensory nerve endings carry doors that open when hydrogen ions arrive — acid-sensing ion channels, or ASICs. Not some other stimulus: the acidity itself is the key. When a place tilts acidic, these doors open and the nerve sends that up as a signal.

The body is reading acidity. That it keeps a dedicated instrument for a value says something about how much that value matters.

So pain speaks of the circumstances of that place

Inflamed tissue, tissue that blood does not reach well, muscle that has worked long — each tilts acidic in that place alone. The acid-base numbers in a blood test stay perfectly normal. The test measures the whole; the pain speaks of the place.

And as acidity falls, other channels that carry pain have their thresholds lowered too. A stimulus that would ordinarily pass unnoticed becomes a signal. This is part of why a painful place is so exquisitely sensitive. The nerve is not being peculiar; the environment of that place has lowered the threshold. (Calcium Is Not Only for Bones)

The breath is the regulator

Here the breath returns. The acid-base state of the blood is set by the relation between how much carbon dioxide is sent out and how much bicarbonate remains — the relation physiology calls the Henderson–Hasselbalch equation.

So how you breathe is acid-base regulation. Breathe shallow and fast under tension and too much carbon dioxide leaves, and that is when hands and feet tingle or the mouth goes numb around the edges. (Tingling Hands and Frequent Cramps When the Tests Are Normal)

Acidity does not move nerves alone

Acid-base does not stop at pain.

The speed at which enzymes work follows acidity, and so do the thresholds at which ion channels in the membrane open and close. A compound entering the body takes on different activity depending on how acidic that place is.

So I read acid-base as a condition, not a result. Not a number left behind once the body's chemistry is done, but a value that sets what happens next.

So in practice

Looking at a painful place, I look first at whether blood is moving in and out of it. A common reason for tilting acidic is simply that the traffic has slowed. What is made and not carried away stays there.

I look at how the person breathes as well. Many breathe shallowly, from the shoulders only. Correcting posture and restoring circulation to the place often serves better than working on the sore spot alone.

When to be seen first

If breathlessness comes with clouded consciousness, or deep laboured breathing sets in suddenly, the acid-base state may genuinely be disturbed and examination comes first. All the more so with diabetes or kidney disease.

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We have come round the place that hurts out of all proportion to its injury.

Korean medicine, looking at a painful place, always asked about the circumstances of that place. Is there heat, what happens on pressure, does cool or warm ease it. It never asked about the size of the pain alone.

Today those circumstances can be given names. There is acidity, there are doors on nerve endings that read it, and when those open the thresholds of other doors come down with them.

The two were looking at the same place in different words. I lay those words over one another to find where the patient's own trouble sits.

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Sources

• A review of how inflammation, ischaemia and injury lower local pH, and how acid-sensing ion channels on sensory neurons turn that into pain signals — Pharmaceuticals, 2010
• A physiology account of how blood acid-base is held narrow, with the lungs compensating in minutes to hours and the kidneys over days — StatPearls, 2022

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