Microcirculatory Disorders
A five-minute self diagnosis detecting blockages in microcirculation:
Microcirculatory Disorders During Septic Shock
Primary and Secondary Microcirculatory Disorders in Essential Hypertension
Three major pathological processes in microcirculation:
- Hyperemia – local increase of blood supply (and/or content)
- Ischemia – local decrease of blood supply and content
- Stasis – local stop of blood flow in vessels
All can occur separately, or as mosaic elements within a structure of bigger, more complicated pathological processes. For example, hyperemia and stasis are embedded, as elements, into the structure of inflammation. Or for example, in thrombosis of arteriolae, a person is going to have ischemia. In thrombosis of venulae, a person is going to have venous hyperemia, and so on. So, three major, typical pathological processes. Hyperemia, local increase of blood supply and/or blood content in organ or in portion of tissue. Ischemia, local decrease of blood supply and blood content in organ or tissue portion. Stasis, local stop of blood flow in vessels, obligatory and within vessels.
Various parameters which we need to take into consideration interpreting the microcirculatory disorders. The first group of parameters most essential. It is related to inflow of blood and outflow of blood. As soon as you understand what happened to inflow and outflow, you can understand the whole dynamic of hyperemia, or ischamia, orvenous congestion, or stasis.
The next thing to evaluate is diameter of the major microvessels. What happens to arteriolae diameter, venulae diameter, capillaries, as regards to its diameter and its number per square millimeter of tissue?
The next group of parameters is biophysical. It belongs to pressure characteristics. What happens to blood pressure in arteriolae, what happens to blood pressure in venulae? What is the difference in pressure between arteriolae and venulae, and how it changes in certain microcirculatory disorders?
Also, we are interested in blood velocity, blood speed, what happens to volume speed of blood, what happens to linear speed of blood, and how blood flow looks. Is there some separation of blood layers visible in microscope? Or the blood flow is turbulent without delineation of plasma layer and blood cell layer.
The next group of parameters characterizing the disorders of microcirculation belongs to chemistry. It is partial pressure of oxygen in tissue, how it changes during disorder. Also, oxygen difference between arteriolae and venulae.
Also, a very important parameter is pH parameter, how the acidity of tissue changes when a certain microcirculatory disorder develops.
And finally, we evaluate temperature,how it changes.
Tissue fluid formation, is it changed or not? Lymph drainage, is it altered or not? Presence of edema, if a certain disorder can produce edema or cannot produce it.
And maybe of great importance for practical medicine is a visual habitus of involved organ or tissue. Its color, its warmth or coldness, and different visible growth consequences of hyperemia or ischemia.
Now we can compare all this set of parameters in three major Microcirculatory disorders in active hyperemia, in passive hyperemia, and in ischemia. And you can see that virtually all of them are different in these different disorders. Arterial inflow of blood is increased in active hyperemia, not changed in passive hyperemia, and decreased in ischemia.
Then we will look to the venous end of the system. What about venous outflow?
In arterial hyperemia, venous outflow is equal to inflow, and it is also increased. But in venous condition or passive hyperemia, the situation is different. Venous outflow is always smaller than arterial inflow, so it is decreased compared to inflow. And in ischemia, inflow and outflow are both decreased and equal to each other. The same thing with all other parameters. For example, if you will look on the lumen of, Vessels, you can see that arterial hyperemia, active one is characterized by increase in our arteriole diameter, equal increase in venule diameter, and the total number of functioning capillaries is also increased.
The situation is a little bit different in passive hyperemia, because arterial diameter in pure classic passive venous hyperemia is not changed. An absolutely different situation with venous diameter, because venules are distended by the increased amount of venules blood. And their diameter in passive hyperemia used to increase, sometimes greatly increased.
What about capillaries? Total number of capillaries in venous hyperemia is not changed, but the venous portion of capillary is distended. And its diameter may be increased if you will look on similar set of parameters in ischemia. You can notice that the diameters of both arterial and venule are decreased in the total number, as well as lumen of capillaries is also decreased. If you study the above table you'll understand what sets these disorders apart.
Besides the biophysical aspect, there is also pathophysiological aspect. And active hyperemia, passive hyperemia, and ischemia have close consequences. The remote consequences, it has also some defensive value in certain situations, and some pathogenic potential for other situations. And you need to evaluate the remote and close sequels, defense or pathogenic roll of active hyperemia, passive hyperemia, ischemia in every particular case.