"The heart produces around 1 or 1.5 watts of hydraulic power, and we want to take maybe one milliwatt," Pfenniger explains. "A pacemaker only needs around 10 microwatts." At the Microtechnologies in Medicine and Biology conference in Lucerne, Switzerland, earlier this month, Pfenniger presented results from a trial in which a tube is designed to mimic the internal thoracic artery, a millimeters-wide vessel that doctors sometimes cannibalize for surgery because it is redundant. The most efficient of the three off-the-shelf turbines he tested produced around 800 microwatts, which could run devices much more power hungry than today’s pacemakers.
But attendees at the meeting raised a heart-stopping possibility: Could the turbine’s turbulence provoke a blood clot? When blood gets trapped in eddies, it starts to coagulate. Pfenniger’s research showed that all three turbines produced some turbulence, though in differing amounts, and he and his colleagues acknowledge that they’ll have to address turbulence to avoid blood clots.
A competing design by electrophysiologist Paul Roberts of Southampton University Hospitals NHS Trust avoids that problem because it does not have a rotating part in the path of the blood flow. Instead, it’s attached to a pacemaker lead, and it works by using the blood pressure changes of a heart beating to move a magnet back and forth. But a prototype tested in a pig produced only about one-fifth of the energy a pacemaker needs -- much less than Pfenniger’s turbine.
Similarly, Dan Gelvan, CEO of Sirius Implantable Systems, acquired a patent for extracting energy from the circulatory system in 2005. But Gelvan’s device, which was also tested in animals, uses a piezoelectric transducer located alongside moving organs instead of inside an artery.