Airplanes don’t flap their wings

Airplanes don't flap their wingsRecently, engineers have come up with a new take on the artificial heart. Instead of a mechanical device that pumps blood through the body using rhythmic pulses (like the way our biological heart does it), the new device uses a rotating corkscrew to provide a continuous flow of blood through the body.

A heart with no pulse!? When designing an artificial organ, wouldn’t it make sense to try to replicate as close as possible the mechanism of the real deal?

Here’s an excerpt from an article talking about the new device:

“Building a heart that mimics nature’s lub-dub may be as comically shortsighted as Leonardo da Vinci designing a flying machine with flapping wings. Nature is not always the best designer, at least when it comes to things that humans must build and maintain. So the newest artificial heart doesn’t imitate the cardiac muscle at all. Instead, it whirs like a little propeller, pushing blood through the body at a steady rate. After 500 million years of evolution accustoming the human body to blood moving through us in spurts, a pulse may not be necessary.”

I think it makes an important point about how to approach biological systems. The reason the heart pulses is probably because it’s more efficient than providing constant pressure, and because it’s hard for evolution to come up with things that spin like the mechanisms in man-made pumps. This combination of energy efficiency and the limitations of design through evolution is probably behind flapping wings and spiking neurons as well.

So when approaching natural systems, the best thing to do might be to start at a purely functional level and ignore the implementation. We might ask:

-What is it that the system is trying to do? Move liquid through pipes (heart); keep a body in the air (flight); connect together sensors and muscles (brain).

-What are the principles behind it? Bernoulli’s principle; Bernoulli again; information theory and computer science.

And then we can figure out how we might address these issues with the tools at our disposal. Our solution will likely be better than what evolution came up with in some ways, and worse in others.

Getting caught up in the details (the pulsing, the flapping, the spiking) can hold us back from our goals. Perhaps the field of artificial neural networks would not be where it is today if people hadn’t figured out that we can generalize spiking activity as a rate of spikes, and easily represent that value in our computers. Neurons probably spike because it’s energy efficient, and you can more reliably get a digital (opposed to analog) signal down a communication channel. But we don’t have to worry about those things so much with modern computers. We can make things easier and better by doing it our way.

We have a lot to learn from the designs that evolution has provided us. But we should realize (and be grateful!) that we don’t have the design constraints that she had. In our short time on this planet, we have already designed birds that can fly faster than the speed of sound. Someday soon we’ll design hearts and livers and lungs that have no expiration dates. And within the next century (the blink of an eye in the timeline of the earth), we’ll design brains that will put to shame the efforts of hundreds of millions of years of evolution.


3 thoughts on “Airplanes don’t flap their wings

  1. Yes! TRF knows what he's talking about. Already there are ways you can see this applying to Kidneys and Livers. I think the heart is the most interesting because it is mainly a fluid dynamics problem which is easily solvable by engineering. I think these principles apply to biosynthetic engineering as well. Maybe we can replicate a human liver, or maybe we can take what we know about human livers and make ones that are more efficient, and filter more toxins, and prevent overdose, etc. At the same time the human body is a complex beast, and no minor change will go without consequences. It isn't exactly the best field to test out experimental technology, but we have animals for that. Evolution did a great job, but she was working within specific constraints with specific goals (reproduce then die). She never really cared about heart disease, cancer, diabetes, or alzheimers. There will soon be a future where biomedical engineering will offer us a proactive approach to chronic disease, and organ replacement is definitely a component of that reality.

  2. In a way, we have wasted years of R & D on the development heart drugs, in trying to tackle heart problems at the cellular level.The heart is a pump – just build a new pump.

  3. Yeah, that's an interesting take @eeo361; could be a major shift in how we practice medicine. The cell might be a hopelessly complex place; maybe we should try to do our work at a different level (when possible).Having said that, I think Hewl makes a good point too: "the human body is a complex beast, and no minor change will go without consequences."When our designs need to work within a biological system, we have to work with what we are given. It might turn out that the body really does need a pulsing heart for whatever reason (maybe blood vessels will stiffen up over time if they aren't rapidly blasted with fluid once in a while). I guess we have to respect the designs of evolution, but we shouldn't be afraid to challenge them either.

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