The story I was told was that president Lyndon Johnson was having heart trouble. Coming right out of the Apollo age, the powers that be said "we can send a person to the moon, why can't we build an artificial heart". They thought it would be a relatively simple problem to solve. At that time the battery technology wasn't there, so the only way to make something work was nuclear power. They came up with an implanted sterling engine, powered by a nuclear thermopile with the cold side of the heat flow being the human body. In that case, the limiting factor for how much power could be generated was how much heat could we dump into the human body without causing things like internal burns and necrosis. They actually built several prototypes, tested them in animals, but never in humans. These devices were enormous, they typically had a large thermopile/sterling engine portion connected by a shaft or hydraulic connection to the pumping portion of the device. Both needed to be implanted in the body, and the devices were entirely mechanical, no electronics needed. The thermopile drove the sterling cycle engine, which then either acted on hydraulic working fluid to actuate the blood pump, or used a shaft or similar to actuate the blood pump from the sterling engine.
a few links: https://physicstoday.scitation.org/doi/full/10.1063/PT.3.316... https://ota.fas.org/reports/8232.pdf https://www.nytimes.com/1972/03/21/archives/nuclear-heart-pu... https://www.theatlantic.com/technology/archive/2013/03/the-t...
Even if you _can_ package it, still needs batteries for redundancy and clearly those don’t fit inside either. Patients with batteries carry around massive backpacks.
Brings a new meaning to ‘having a meltdown’ though. Overheating nuclear heart would literally boil your blood.
That may be because of the difference between output power and input power needed to produce it. One citation there says the mechanical efficiency of the heart is about 20%.
Typically these devices use between 10-30 watts of power for each side of the heart (in the LVAD case). For an artificial heart (which is two LVADs, basically a LVAD and a RVAD) it's more like 30-60 watts of continuous power.
The human heart is amazing.
Unfortunately we moved away from the Jetson's future.
It's interesting, one of the major development challenges for these devices was making them safe so that if the patient were to be cremated they didn't create a small dirty bomb.