I am a theoretical physicist and currently Director of 
July 08, 2011
Heart with no heartbeat
NPR had an interesting story on a new type of artificial heart. Older models had tried to replicate the human heart with its pumping mechanism but have been unable to create models that work without problems for a long time.
This new heart is radically different in that it foregoes the pumping action and has motors that continuously drive blood through the body. This makes for a much simpler design with less chance of breakdown. It seems as if the pumping action is not essential for the working of the body, though it is still early days and we do not have long-term data on the effects.
If the results hold up and a heart that beats is not really necessary, it means that the beating heart is a product of evolution that is functional but not optimal. This would illustrate once again that the processes of evolution do not necessarily produce the best design but merely a design that works. This will not be the first time that thinking that nature's design is the best and trying to copy it has sent us in the wrong direction. Early experiments with flight tried to emulate the flapping wing action of birds with little luck.
What is kind of weird is that with this new artificial heart, there will be no heartbeat, no pulse, and the EKG signal will be a flat line. So the most common markers we currently use to see if someone is dead or alive would indicate that the person is dead.
Comments
I've always wondered why somebody didn't think of this. I don't know of too many human-designed pumps that work with anything like the rhythmic squeezing of the heart- that always seemed to me like an evolutionary kludge that came about simply because hearts are made of muscle and that's what muscle is able to do. The analogy to powered flight is a suggestive one.
If it works there are going to be a lot of bad jokes about the recipients eating brains, though. ;)
The artificial heart may pump better. But it likely (I can't tell from article) doesn't respond to blood factors which regulate the natural heart based on changing environmental circumstances. It also likely doesn't secrete substances, like heart cells do (atriopeptin).
And so, it's hard to objectively conclude what is optimal.
Mano,
Optimality of the heart design is constrained by the need to supply blood to every part. As an engineer, I can tell you that routing hydraulic or even electrical lines across a fully rotating interface is a mess. The only biological examples I can think of are bacterial flagellum, which obviously don't have a circulatory system. Rotational pumps are necessarily assembled from separate pieces and are thus simply unfeasible for a human-scale biological process to produce and maintain. Hate to nit-pick, but this is not an example of sub-optimality.
Robert