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Old 05-07-2012
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Heart Polycythemia and cardiac output

Hi,

I've read in FA that increases in blood viscosity would increase the resistance. My question is would this result in a decreased cardiac output since the TPR is increased? I've searched, but have only found conflicting statements. Thanks!
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Old 05-07-2012
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cardiac output = mean arterial pressure - right atrial pressure
------------------------------------------
TPR


Hope i helped .. for more detail go to page 64-66 in Board review series (Physiology)
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Old 05-07-2012
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Yes, viscosity is proportional to resistance. So if viscosity increase's so will the resistance. But Resistance is inverse to flow so if resistance increases, then flow decreases. So hyperviscosity slows flow through vessels as there is increased peripheral resistance. Due to sluggish movement the amount of blood returning to the heart is reduced. At the same time, cardiac output is increased, due to the viscosity of the blood b/e polycythemia is increased blood volume that leads to hypertension and stagnation of blood flow. So I guess its increased cardiac output?
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Old 05-08-2012
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If resistance is increased for any reason, then venous return would be decreased as less blood would get from the arteries to the veins. This would mean less blood reaching the heart and there for less blood pumped out (decreased C.O).

On top of that increased resistance increases afterload and therefore also further decreases cardiac output.
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Old 05-08-2012
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In relation to "polycythemia vera", as both the red cell mass and plasma volume increase, the total blood volume expands, This results in an increase in cardiac output, vasodilation(why the blood reaching back to the heart decreases), and a reduction* in peripheral vascular resistance.
Check out the the link I send you, on the same page is "Management of polycythemia vera". Read the highlighted cardiac output part.
http://books.google.ca/books?id=H85d...20vera&f=false
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Old 05-08-2012
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I guess earlier on there's increased C.O due to vasodilation and increased blood volume. But later continued increase in viscosity plays the greater role and causes decresed C.O?
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