The Inner Surface of a Vessel Feels the Flow

"They tell me my vessels are clear, but it still feels like nothing is circulating."

I hear this often in the clinic.

First, clear vessels are good news. That test checks whether the large vessels have narrowed or become blocked, and if nothing showed up there, one large worry has been set aside.

Still, the question that test answers and the place where the heaviness is felt may not be the same. What a person actually feels happens in vessels far finer than the large roads.

Today let me follow those finer ones through.

A blood vessel is not a hollow pipe

A single layer of cells lines the inside of a blood vessel. It is called the endothelium. And on top of that sits one more layer — sugars and proteins woven together, standing up like fine down. It is called the glycocalyx.

When blood flows, what it actually touches is not the wall but this downy layer.

This layer feels the flow

Here is where it gets interesting. This layer works as a sensor for flow.

When blood moves evenly, that force lays the down over, and the force of it is carried through to the cell's inner skeleton. The endothelium then releases nitric oxide. That substance relaxes the muscle of the vessel and widens the road, and at the same time keeps the blood from clotting readily.

If you strip heparan sulfate, hyaluronic acid, and sialic acid out of that downy layer, the nitric oxide does not come even when you give it flow. The flow is unchanged, but with nothing there to feel it, there is no response.

So circulation is not only a matter of whether blood passes through. Whether the surface that feels it and answers is intact stands alongside.

When flow weakens, that surface changes character

This relationship runs both ways.

When flow stays weak for long, the endothelium crosses into a different state — from the side that keeps things open and sliding, to the side that sticks and clots readily. A narrowed road means less flow, and less flow in turn changes the surface. Neither is first; they pull each other along.

The way your legs feel lighter after standing up from a long sit is not unrelated to this layer. When posture changes and flow returns, the signals that had been swelling the tissue fall away quickly.

What leaks out is also decided here

The explanation we were long taught went like this. Water leaves for the tissue at the front of the capillary and is drawn back in at the far end.

We see it differently now. In most tissues that drawing-back is not sustained. The membrane that actually divides inside from outside is less the vessel wall than that downy layer, and the water that left for the tissue returns mainly through the lymph. (I have written separately about legs that swell in the afternoon.)

So when this layer is worn away, things tip toward leaking. Inflammation wears it, high blood sugar wears it, oxidative stress wears it, and blood stopping and then flowing again wears it too. What does the wearing has names as well. Reactive oxygen species, and enzymes that cut this layer away — heparanase and matrix metalloproteinases.

I work on the layer that feels the flow

Once you know this layer, there is one more place to work on. When I hear about circulation, I think about the state of this surface alongside the calibre of the vessel.

First, there are medicines that protect the surface itself. Coptis (hwangnyeon) is one. In mice given endotoxin-induced inflammation and in human vascular endothelial cells, its compound reduced the shedding of syndecan-1 and heparan sulfate, the two mainstays of this downy layer. The reactive oxygen species, heparanase, and matrix metalloproteinase mentioned above came down along with it. Reduce what does the wearing, and the layer remains.

Medicines that open the way in are a separate matter. Cinnamon twig (gyeji) is one. It opens the fine arteries at the periphery and pushes blood through, and the same material also works toward keeping this downy layer from being worn away. One material doing separate work at different layers.

There are also medicines that help the way back out. Astragalus (hwanggi) works toward raising the force with which veins and lymph gather things up. Flow runs in one direction only when the pushing force and the gathering force are both there. Push alone and it pools in the tissue; gather alone and there is nothing to push in.

There is something to be careful about here, though. Increasing supply because something looks short is not the answer. Push it suddenly into tissue that is not ready to receive it and it becomes a burden rather than a recovery. (Filling it back up does not bring it back to life)

And in an actual body these strands do not run separately. Where the way in is weak, the way back out has usually slowed as well, and where the surface is damaged, both are difficult. That is why working on one place alone tends not to hold. (Cold dull pain and hot swollen pain)

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Look at a vessel only by its width and there is a place you miss. Inside it lies a thin layer that feels flow and answers it, and that layer changes character according to the flow. It stays intact because things flow, and things flow because it is intact.

What herbal medicine does in this place is less a matter of manufacturing flow that was not there than of making the conditions under which the body's own response can happen again. The pushing hand and the gathering hand are each placed somewhere different, and the moments at which they land differ a little too.

Circulation is of course not the whole of the body. Chemistry, metabolism, and immunity stand alongside it, and circulation is one among them. But when you look at this one, taking in the inner surface as well rather than only whether the road is open, more comes to be explained.

If one leg swells suddenly, if swelling comes with heat and pain, or if you are short of breath — that is a different matter. Please have it seen first.

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Sources

• The glycocalyx senses flow and mediates nitric oxide production — Biochemical and Biophysical Research Communications, 2007
• Tissue fluid balance revisited — lymph rather than reabsorption — The Journal of Physiology, 2004
• Berberine reduces glycocalyx degradation and promotes its restoration — International Immunopharmacology, 2018

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