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I have a species that is a descendant of modern humans, but containing superior bioengineered organs. One of these organs would be a small heart-like organ inside the head. This heart connects with the lungs, and would keep the brain alive for a period of time after the main heart failed.

My question is: would a heart located much closer to the brain keep the organism conscious for longer than without in situations where many Gs are being exerted on the organism, such as when performing maneuvers in a fighter jets?

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    $\begingroup$ Is it the only heart, or this organism will have two hearts? $\endgroup$
    – Alexander
    Jul 24, 2018 at 8:01
  • $\begingroup$ There is a clue in the OP's question "after the main heart failed". Yes, the enhanced human will have 2 hearts $\endgroup$
    – kiltannen
    Jul 24, 2018 at 8:05
  • $\begingroup$ I was considering even three hearts. $\endgroup$
    – Starpilot
    Jul 24, 2018 at 8:15
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    $\begingroup$ A possible downside of your idea is that a stroke will happen to these people much more frequently, possibly becoming the leading cause of death, as it will cause death much more quickly than for 'normal' humans. An aneurism in the brain would lead to extremely quick bleeding out and plaques which developed in your 'brain heart' would be pushed into the vessels in your brain immediately and with additional force causing complete closure of the vessels much more easily. $\endgroup$
    – Alex2006
    Jul 24, 2018 at 9:42
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    $\begingroup$ Brains really , really, do not like varying blood pressures in them. Having a heart inside the braincase will inevitably induce massive pressure fluctuations as the heart expands and contracts. Even if it is a very fancy constant-volume slinky type pump. Unless you can also redesign the fundamental architecture of the brain tissue, you would expose your victim to extreme risk of strokes and aneurisms. $\endgroup$
    – PcMan
    Feb 28, 2021 at 19:19

6 Answers 6

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The issue with the brain during high g-force maneuvers is that less or no blood reaching the brain means less or no oxygen supplying the neurons, leading to loss of consciousness.

While it is true that the heart pumps the blood, it's the lungs that replenish it with oxygen.

During a high g-force maneuver pulling the blood downwards and away from the head, the heart of your species would have to suck it even more against the gravity gradient.

When you study pumps at University you are always told that while pumping liquid pushing is way better than sucking it: beyond a certain sucking pressure, you induce cavitation, which severely damages the pipes and/or the pump. In this case cavitation in the bloodstream would be dangerous for the veins and/or the heart, with also the possible formation of thrombosis.

All in all, I think this is a worse implementation than our present model.

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    $\begingroup$ "less or no blood" - too much is even worse. Pilots can sustain lower levels of negative G before "red-out" than they can positive before they "black-out" $\endgroup$
    – Baldrickk
    Jul 24, 2018 at 13:28
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    $\begingroup$ So, you're almost after a diffusion surface at the back of the nasal passage - minature heart connected to minature lungs, over a tiny distance so that the Gs applied have minimal affect? $\endgroup$
    – Chronocidal
    Jul 24, 2018 at 13:31
  • $\begingroup$ @Chronocidal That would mean a complete second circulatory system to avoid backflow, wouldn't it? $\endgroup$
    – Orphevs
    Jul 24, 2018 at 13:41
  • $\begingroup$ @Orphevs I feel like a set of valves should do just fine to prevent backflow $\endgroup$
    – John Dvorak
    Jul 24, 2018 at 14:57
  • $\begingroup$ @John Dvorak backflow might be the wrong word, sorry. If high gees are trying to move blood away from the head, having one connected circulatory system might defeat the purpose of the secondary heart, if the blood can just be pressed away. With a separate bloodflow for the brain, it couldn't be moved far. $\endgroup$
    – Orphevs
    Jul 24, 2018 at 16:29
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The tendency to want to faint when being subjected to high Gs results in lack of oxygen to the brain caused by increased difficulty for the body to pump the blood to the brain.

So if there were a tiny heart in the brain, it would pull blood and your normal heart would push blood, adding a little bit extra force in situations where pumping up blood is more difficult such as when being subjected to high Gs. So yes, such a person would be able to withstand higher Gs.

How many more Gs depends entirely on the force of the tiny heart in the brain, but the amount of Gs which can be withstood is likely going to be proportional to the amount of extra force the tiny heart can provide.

Consider also that the pump of the heart and of the heart in the brain is likely going to be synchronous, or otherwise you'd stress the arteries leading to the brain too much. Also in a somewhat unrelated note, the arteries leading to the brain would still likely have to be much thicker than what they are now, so you should keep that in mind (otherwise something as simple as a heart murmur would risk serious pressure on the artery leading to the brain, which over time could be fatal should it weaken and break).

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Cool Idea,

I'd have to go with a definately yes - but it's going to be hellishly complicated getting the blood in and out. You're going to have to either go with a completely separate redundant circulatory system connecting this heart with the brain, or figure out some other method of stopping the 2 hearts from competing.

Mind you, if the Doctor can do it then I guess so can your metahumans...

However you do achieve it - I definately think it will help your people handle high Gforces better.

The other problem I suspect you'd run into is the heart has a lot of movement (all that pumping! Ker-thump ker-thump ker-thump...) - and the brain isn't too happy with being bashed about...

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A possible solution, given that we're talking about pretty advanced bioengineering here. Why not just go whole hog and get rid of the heart entirely?

Basically, the heart is a kind of invagination of the great vessels with powerful musculature and some electric stimulation to keep it ticking regular.

Rather than a single, central pump with a sub-station pump in the head, engineer a system where all the vessels (from the aorta ~ vena cava on down to the main branches and lesser vessels) pump peristaltically? Combined with a system of back-flow reflux valves (such as already exist in the veins) you should be able to achieve a continuous & active flow of blood throughout the system.

I imagine that the check valves, especially those in the head and neck will help reduce or eliminate the effects of gravity 'sucking' the blood away from the brain. Also, the peristalsis will keep the blood flowing continuously and thus perfuse the brain.

Obviously the bioengineers would be using a type of cardiac muscle that, like the muscles of the heart, do not tire the way skeletal muscle does. Just like a heart, it won't do for the system to rest or shut down untimely!

The long and short of this system is that you have "lots of little tiny hearts" in the brain (and everywhere else)!

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Move the brain to the heart instead.

Strong G-forces push blood to the extremeties of the body. That means the head or the feet depending on whether you're swooping upwards or downwards. Both are bad for the brain. The brain would be safer if located in the middle of the body.

This also means an injured heart sends blood to the brain before everything else. If the heart has completely failed the chest brain will not save you. But if it is flagging the chest brain will last longer then the head brain.

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Loss of consciousness from high G-forces is an issue of blood being pushed out of the brain, into blood vessels lower into the body. This is possible because blood vessels and their surrounding tissues are flexible and do, to some extend, expand and contract depending on pressure inside.

If you experience high G-forces, a rather large pressure difference builds along your body. G-force roughly translates to +x pressure/length, so the longer blood can flow more or less freely along the direction of said force, the greater the effect.

A second miniature heart inside the brain won't have any effect on this, the blood will still drain according to G-forces.

A more realistic solution, I think, would be a system of blood vessels designed to work against pressure differentials, for example by a) blood vessel walls being able to stiffen/relax dynamically in reaction to G-forces or b) muscular "valves" that can temporarily restrict blood flow while high G-forces are acting. The former solution would allow for resistance against permanent high G-forces but is more complex biomechanically, the second will prolong the time you could spend at high G (but you might eventually still pass out due to restricted blood flow).

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