In order to discuss about edema, it is important to know which districts are involved in its genesis.
They are three: the blood capillaries, the lymphatic vessels and the interstitial tissue.
What is their role in the edema genesis?
Let’s start with capillaries.
Capillaries transport the oxygenated blood to the cells, tissue and organs transferring oxygen and nutrients. In exchange, the waste from the cells, including carbon dioxide, are transferred into the blood. So capillaries are very essential for the cell viability.
But what happens in case of edema like after a sprain or a trauma?
A greater amount of blood arrives in the capillaries resulting in an internal pressure much higher than normal (hydrostatic pressure). The increased hydrostatic pressure alters the vessel walls, impairing the endothelial cells adhesion; the liquid portion of the blood flows through the space between two endothelial cells and inundates the cells and the surrounding interstitial tissue.
If the stimulus persists, the distance between the endothelial cells increases and larger molecules like mineral salts, proteins like fibrinogen or even red blood cells pass through the endothelial barrier collecting in the interstitial spaces and causing edema. In the latter case, edema becomes hematoma or hemorrhagic edema.
But let’s focus our attention only on edema.
The liquid leaks towards the interstitial tissue inevitably leads to swelling like an ankle after a sprain.
How does the tissue react to this excessive leak of liquid?
Firstly it triggers a defensive inflammatory phenomenon, but inflammation triggers, in turn, edema because it attracts more blood in situ, maintains the increased hydrostatic pressure, facilitates the leakage of liquid from the capillaries and, in the end, it triggers a positive feedback which sustains edema
And what about the lymphatic vessels?
Physiologically, the lymphatic system is responsible for the drainage of the liquid from the interstitial tissue to the blood stream. But in case of edema, it isn’t able to transport all that excessive liquid and so it must work more and hardly causing a lymphatic failure and a persistent edema.
It is just in this moment that is very important a therapeutic approach, for example intervening on the capillaries, on the lymphatic vessels or only on the interstitial tissue.
But what would happen if we work on all the three districts at the same time?
We would obtain the resolution of edema in a shorter time.
Because the action on the capillaries may reduce the permeability, and may get closer the endothelial cells stopping the excessive liquid leak from the vessels. In addition, the activity of the lymphatic system may enhance the drainage and drains faster the liquid already leaked. The intervention on the interstitial tissue may reduces inflammation and thus may reduce the continuous stimulus to the leakage of additional liquid.