Polycythemia

Polycythemia is the rise in hematocrit ratio from 45% to 70%


   Normal hematocrit ratio is around 45%.  This ratio provides information about the percentage of red blood cells to plasma.  Dehydration causes the hematocrit to rise which causes the viscosity of the blood to rise due to a greater percentage of the blood makeup provided by red blood cells.  A rise in viscosity decreases the flow rate of the blood and forces the heart to work harder to circulate the blood through the periphery.  Anemia, the opposite of polycythemia, is a low RBC count which drops blood viscosity and increases flow rate while putting less stress on the heart.
   The increase of relative viscosity by more than twofold has a porportionate effect on the resistance to blood flow.  The effect of such a change in hamatocrit ratio may be appreciated when it is recognized that even in the most severe cases of essential hypertension, total peripheral resistance rarely increases by more than a factor of two.  In hypertension, the increase in peripheral resistance is achieved by arteriolar vasoconstriction.

Sample Problems:

Define polycythemia

Answers:

An increase in hematocrit ration from 45% to 70%

For more information on this topic, please refer to Berne & Levy , 127

Also, check out the following links that may be helpful:

• Alphabetical listing - including polycythemia vera and polycythemia secondary
• Myeloproliferative Disorders
• And, as always, if you have questions, or if you can suggest a helpful link, please e-mail me.

No!
Please don't make me go to any of those pages!
I want to go somewhere completely different!

This page was written by Ammon Fager , a student in this course.

BME 403 Pages maintained by the T.A., Douglas Miles.