There's nothing really newBMJ 1999; 318 doi: https://doi.org/10.1136/bmj.318.7183.580 (Published 27 February 1999) Cite this as: BMJ 1999;318:580
Once upon a time a King had a little daughter for whom he would do anything. She wanted an apple made of pure gold, and because he was rich he had one made for her. The princess wanted a pony with a coat of the purest white and because he was powerful, he had the land searched and the best one sent to the palace for her. One night she looked into the dark sky from her bed chamber and asked for the moon.
The King sent for the court astronomer and said, “Tell me about the moon.” “The moon, sire,” he said, “is three miles above the earth and made of green cheese.” The King sent for his engineer, and said, “My daughter wants the moon. Please get it down for her.” “Sire,” he said, “what the astronomer did not tell you is that the moon is in fact very large and heavy and suspended on thick chains. Even with my longest cranes I could not reach it, and even with my best tower of pine tree scaffolding, it would be impossible to free it and bring it to earth.” The King, exasperated, shared the dilemma with the court jester. “Let me talk with her, Sire,” he said.
He told the Princess her bedtime story and looking out of the window together he asked, “What is the moon like?” “The moon is the size of my thumb nail.” “How do you know?” asked the jester. “Look,” she replied, “I can just cover it with the end of my thumb, and it is made of beautiful silver.” The court jeweller made a moon to the Princess's specifications and she was content.
To complete the story I would have to explain how they coped with the reappearance of the silver moon in the sky at the same time as the Princess had the moon hanging around her neck on a little chain, but that is enough of the fairy story for now.
I was reminded of the tale by the recent reports of the successful use of a tiny impeller pump as a replacement heart. Since the 1960s surgeons have told engineers that the heart is a pumping chamber, of such and such a capacity and pressure characteristics, with inflow and outflow valves. Like the court engineer, they have tried to please the King. They have been largely defeated by the combined difficulties of the mechanics of the pumping chamber, pistons and pusher plates, the procoagulant nature of the materials, and the need for two valves which will neither fail nor clot. The brilliance of the little pump implanted with such success by Steve Westaby in Oxford is that it does what the heart does, but in a way achievable by engineers. Someone, somewhere managed to get beyond a description of the heart as we know it and asked the question, in bare essentials, what do you want the heart to do? The engineered device does not work on intermittent volume displacement, which is the solution reached by evolutionary biology, but by a continuous stream of blood driven by an electromagnetically coupled impeller spinning in the blood stream, creating continuous unidirectional flow.
The point that the story brings to mind is that when surgeons talk to scientists, bioengineers, or computer programmers, they are very ready to tell them what they want but it may be not what they really need.
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