Hemodynamic disorders part 1

 

Hyperemia and congestion:

Hyperemia:

Øhyperemia and congestion both are the terms for the increase in blood within the tissues

Ø But they have different mechanisms.

Ø Hyperemia is an active process that causes arteriodilation and increases blood flow as in inflammation sites or in exercise.

Ø In hyperemia, increased inflow leads to engorgement with oxygenated blood, resulting in erythema.

Congestion;

Ø While congestion is a passive process resulting from impaired venous drainage from tissue.

Ø Congestion can occur systemically like in cardiac failure or it can occur locally too like a venous obstruction

Ø Congested tissues have abnormal blue-red color which is the result of the accumulation of deoxygenated hemoglobin in that affected area.

Ø Now if congestion is persistent or long-standing so it can lead to severe hypoxia and more pressure building which can lead to necrosis and injury by rupturing capillaries and hence the edema, localized hemorrhage, and secondary tissue fibrosis.

Ø In congestion, diminished outflow leads to a capillary bed swollen with deoxygenated venous blood and resulting in cyanosis

 

 Difference between hyperemia and congestion

Hyperemia	congestion
Active process	Passive process
Involved oxygenated blood accumulation	Involve deoxygenated blood accumulation in capillaries bed
Erythema occurs	No erythema
Tissues are red	Tissues are blude-red in color

EDEMA;

Ø Edema is the accumulation of interstitial fluids within the body tissues, which results from the net outward movement of water into extravascular spaces or interstitial spaces.

Ø Approximately 60% of the body mass without fat also called lean body mass is composed of water 2/3 of which is intracellular.

Ø most of the remaining water is found in extracellular compartments in the form of interstitial fluids.

Ø Only 5% of the body water is present in the blood plasma.

Ø the extravascular fluid can also accumulate in the pleural cavity called hydrothorax, in the pericardial cavity called hydropericardium, or in the peritoneal cavity called hydroperitoneum or ascites.

Ø Anasarca is severe generalized edema marked majorly by the swelling of the subcutaneous tissues and accumulation of fluid in the body cavities.

CAUSES OF EDEMA;

Ø  There are two major causes of edema one is the inflammatory edema and the second is noninflammatory edema

Inflammatory edema causes:

This includes the following

·      Acute inflammation

·      Chronic inflammation &

·      Angiogenesis

Ø Acute inflammation isn't that much involved. As in acute inflammation edema does occur by the release of histamine and TNF (tumor necrotic factor) from stromal cells but with less extent, as it is not for a long time as compared to chronic inflammation.

Ø For chronic and acute inflammation click here

Noninflammatory causes of edema:

Before we discuss the noninflammatory causes of the edema we should know about two fluid pressures

·      The hydrostatic pressure

·      Oncotic pressure/colloidal osmotic

Ø Blood movement in vessels is mainly maintained by the above  two pressures working in an opposing manner

Ø Medically Hydrostatic pressure is mainly the pressure that maintains the outflow of the blood from the arteriolar end and from the microcirculation or capillary bed by the inflow of the blood.

Ø Oncotic pressure is created by the plasma proteins mainly the albumin, normally this pressure is slightly increased so that the fluid flow is maintained and less amount of fluid outflow occurs to the interstitial space.

Ø Now fluctuation (increase or decrease in either of the pressure) in these two pressures due to some pathology will lead to edema which can be more and less depending on the type, nature, and severity of the disease.

Ø Excess of the edema is removed by the lymphatic system through thoracic ducts.

Ø Let's differentiate briefly the transudate and exudate.

 Difference between exudate and transudate

Transudate	Exudate
Due to increased hydrostatic pressure or decreased osmotic	Because of increased vascular permeability i.e inflammation
Protein poor	Protein-rich
Specific gravity < 1.012	Specific gravity >1.02
Noninflammatory	Inflammatory edema

 

  Ø  From the following diagram we can clearly see how the hydrostatic pressure and osmotic pressure balance the blood movement in the vessel and how it moves little fluid to the interstitium by increasing little amount of the intravenous osmotic pressure

 

                          

          

  Ø Now let's discuss the noninflammatory causes of the edema one by one. 

      will continue from here in the next part of this article