Tuesday, February 05, 2008

Hemodynamics - Edema

Above figure from Heartzine.Go there to learn about circulatory system.

To review your anatomy of the circulatory system go to this great website at the Texas Heart Institute.

60% of the human body is water. So an average person of 155 lbs is made up of 93 lbs of water and 62 lbs of solids. The 42 liters of water can be broken down this way:

Interstitial (space outside the blood vessels and in between cells) 8 liters
Plasma 3 liters
Cerebrospinal fluid and other 6 liters
For a total of 17 liters

A total of 25 liters (including Red Blood Cells)

Blood pressure is the force of blood pushing against the walls of arteries. It's expressed as the number of millimeters it can force a column of mercury upwards.

Normal blood pressure is a reading of 120/80 or lower. High blood pressure is a reading of 140/90 or greater.

Another type of pressure is osmotic pressure. Osmotic pressure is the amount of hemodynamic pressure that must be applied on the side with low water concentration to prevent water from passing into the saltier side.

Go to this Colorado State osmotic pressure simulator site and you can see the effects of increasing or decreasing solute on either side of a permeable membrane.

You can learn about osmotic pressure here (interactive) and here (physics).

Edema is a shift of water from the vascular space into another compartment, usually the interstitial compartment. Here is one website that discusses edema in general.

Low protein edema also called a transudate, occurs when there is excess venous pressure (hydrostatic edema) or low plasma osmotic pressure. Each of these conditions allows water to leave the vascular spaces and enter the tissue spaces.

One example of low protein edema is varicose veins due to excess venous pressure. Read more about varicose veins here.

Osmotic edema is another type of low protein edema. It occurs when plasma albumin levels are abnormally low allowing water to escape from the vascular space to the interstitial space. Osmotic edema is often associated with liver disease because the liver is the primary producer of albumin.

Generalized edema (anasarca) is another example of low protein edema.

High Protein Edema is the fluid accumulation seen in inflammation. Inflammatory edema would be seen in a sprained joint.

Lymphedema is due to obstucted lymphatics. See more here.

Cerebral and pulmonary edema can be fatal. Swelling of the brain results in increased pressure on the brain. Pulmonary edema can impair gas transport and exchange or encourage bacterial growth.

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