The number of very small capillaries drops in many tissues during a Covid-19 infection - and in long haulers, it does not go back up. This mechanism may be responsible for many of the symptoms in Long Covid.
“Persistent capillary rarefication in long COVID syndrome.” Angiogenesis, 11 Aug 2022. PMID 35951203
This change likely means less blood flow (nutrients and oxygen) to cells that are no longer close to very small capillaries. It might explain fatigue that comes with physical exertion, it might contribute to a state where vitality is generally lower. And the change is persistent, even at 18 months after the initial SARS2 infection.
It isn’t clear at this point how to restart the growth of the very small capillaries, but better understanding of the problem opens the door to trying different therapies with that goal.
There are a number of hormones in the body that are involved in growing new blood vessels. One of the most important is VEGF (Vascular Epithelial Growth Factor). Curiously, levels of VEGF are actually elevated in Long Covid patients according to this study:
“Data-Driven Analysis of COVID-19 Reveals Persistent Immune Abnormalities in Convalescent Severe Individuals.” Frontiers of Immunology, 19 Nov 2021, PMID 34867943.
So fixing the problem is not as simple as regular injections of VEGF. This situation may be analogous to what is seen with type II diabetes.
In type II diabetes, the pancreas is still making insulin - and insulin levels can be elevated above what is considered normal. But the insulin longer has its intended effect - cells are resistant to the signal it sends. The body produces more and more insulin to try to get the glucose under control, but the insulin does not trigger cells to open up and take the glucose into the cell.
In the case of VEGF resistance, there might be auto-antibodies. Or cells that are supposed to respond to VEGF might have had their surfaces altered by the infection, which might reduce receptors to the signal to grow new blood vessels.
So while there is no immediate treatment that comes out of this, we do have a better understanding of the chaos induced by the virus, and are a bit closer to being able to reverse the disorder.