The human heart is one of nature’s engineering masterpieces. This modest size organ, a little larger than its owner’s fist, is actually two pumps; one for circulating blood through the lungs where it picks up oxygen and the other for supplying the oxygenated blood to the body. The heart pumps a huge volume of blood during a lifetime, roughly 200 million liters in 75 years, beating two to three billion times without downtime. The heart is also amazingly efficient, feeding itself enough oxygenated blood to meet its own energy requirements. But it all depends on a precision pacing system. When its electric clockwork goes bad, the heart can beat too slowly, too rapidly, or too irregularly.
The implantable pacemaker is one of mankind’s engineering masterpieces. This small device, much smaller than its owner’s fist, is a kind of metronome for the heart, helping it keep proper rhythm. As the pioneer implantable device, the cardiac pacemaker has taught researchers invaluable lessons about designing enclosures, power sources, electrodes, and wires for the body’s internal environment. These lessons have been exploited by subsequent devices such as cochlear implants, diaphragm pacemakers and deep brain neurostimulators.
The path that led to today’s pacemakers and implantable cardiac defibrillators presents crucial lessons. For starters, great technology is often the product of incremental advances made in the face of extreme skepticism, indifference, and even opposition. Second, nature offers shortcuts to those who possess the optimism and determination to look for them. Third, there are often simple solutions to seemingly intractable problems.
We take pacemakers for granted today, but not that long ago people died from heart block—the heart’s inability to reliably deliver the electrical signals from its natural pacemaker to its main pumping chambers, the ventricles.
The first solution to this problem was for many patients worse than the disease. External pacemakers paced the heart by delivering nasty shocks to the chest. Patients jumped with each beat; suffered burns where the electrodes touched the skin; and were tethered most of the time to standard power outlets. Some patients turned their external pacemakers off, preferring death.
The second solution was to attach the electrodes directly to the heart. This was major surgery with its long recovery time, discomfort, and risks. Surgeons found that the voltages required to pace the heart with implanted electrodes rose over time. Several advances were necessary to bring that problem under control. Making sure the electrodes were ultra-clean was one of them.
Finally, researcher Seymour Furman discovered how to use catheters to deploy the electrodes, making pacemaker implantation a relatively minor procedure. Here was nature’s shortcut.
But it’s the convergence of biological and artificial solutions that could make cyborgs of most of us in the future. A technology called cell encapsulation promises to augment or replace failing organs. Transplanted cells are placed inside a capsule with a semi-permeable membrane. The cells could, for example, produce insulin while being protected against immune rejection. Such a device could be combined with a continuous glucose monitor.
As such devices proliferate, it may become hard to tell where the machine ends and the human begins.
Next time: Wireless Chemistry
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