Doubled up circulatory system issue

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Doubled up circulatory system issue

Postby caters on August 26th, 2017, 9:35 pm 

My Kepler Bb humanoids have a doubled up circulatory system. Literally, they have 2 hearts, and every blood vessel doubled up because of that. The right heart is in normal anatomical position and the left heart is inverted so as to have the 2 aortas right next to each other and thus the center of mass being as close to dead center as possible.

However this poses a problem. This problem has to do with arterial blood pressure and more specifically systolic blood pressure. If you look at any pair of arteries where 1 artery is right next to another artery of the same size, the blood pressure being the same and in sync in both arteries causes the force on the walls to be asymmetric which in turn causes blood pressure to be asymmetric initially.

In a few arteries such as the aorta, this extra force is no problem. But in most arteries, this extra force from the systolic blood pressure in a pair of arteries causes there to be an asymmetric dilation throughout all except a few arteries. Vasodilation in general lowers blood pressure. Lower blood pressure means less force which means less dilation. However, it also means that arterial pressure is closer to venous pressure. This will lead to decreased venous return and so the 2 hearts will pump a higher volume of blood per beat at a higher heart rate to compensate. This raises blood pressure which causes a vicious cycle.

If this vicious cycle is not stopped, the arteries will start to tear, causing pain and anemia. With a tear in an artery, it can tear further down until it branches, tear back into the lumen(which is the best scenario) or tear through the other layers and cause internal bleeding. With normal collagen and other supportive proteins, a tear in an artery would pretty much always mean internal bleeding. Because this would be happening in all but a few arteries, the humanoid would bleed to death very quickly.

But lowering the blood pressure is of no use because the 2 hearts will just compensate by pumping harder and faster. Not only that but there is 1 reason that I have kept this doubled up circulatory system and that is that if something goes wrong with 1 heart, the other can compensate and so the humanoid will only have heart problems affect circulation if both hearts are affected.

So if lowering the blood pressure is of no use, 1 heart can compensate for a damaged heart, and getting the 2 arteries in a pair of arteries further apart is not possible, then how could I prevent this vicious cycle of extra force -> asymmetric blood pressure -> dilation -> lowered blood pressure -> raised stroke volume and heart rate -> raised blood pressure -> dilation

from occuring in the first place without getting rid of the doubled up circulatory system and using a single circulatory system with a single heart?
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Re: Doubled up circulatory system issue

Postby neuro on August 27th, 2017, 10:10 am 

caters » August 27th, 2017, 2:35 am wrote: then how could I prevent this vicious cycle of ....

Tell you what you should do: get a physiology textbook.
Most of what you are claiming here is nonsense.
And blood pressure is acutely controlled by baroceptors - which sense pressure and not dilation - and over the long term by the regulatory systems in the kidney (renin-angiotensin-aldosterone), the existence of which you do not seem to be aware of.
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Re: Doubled up circulatory system issue

Postby TheVat on August 27th, 2017, 11:07 am 

Don't most science fiction writers just say something like "The Denebians have two hearts," and leave it at that?
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