This post is the fourth in a series based on my soon-to-be published book, The History & Future of Medical Technology. Each week I’ll present highlights from one of thirteen chapters.
Reverse Engineering the Human Body
Companies often use reverse engineering to keep pace with competitors. Instead of copying products, which would likely violate patents, engineers figure out how to imitate the competitors’ products. Reverse engineering is likewise a powerful tool for medicine, because while restoring even partial function can be immediately beneficial, it may be a long time before we understand the underlying natural processes well enough to recreate them.
Through the process of reverse engineering, biomedical engineers are learning how to alleviate pain, prevent seizures, repair the senses, restore involuntary muscle function, and re-enable voluntary muscle function.
Many great inventions were the result of reverse engineering: the battery, artificial pacemakers, and implantable cardiac defibrillators are good examples, all of which involved bioelectricity.
Reverse engineering is a two-step process. This first step is to acquire an accurate and reliable understanding of the target’s external behavior. The second step is to design and construct a device that behaves similarly. (An important exception: an implantable cardiac defibrillator does not behave like a heart’s electrical system, but restores a heart’s electrical system to its normal behavior.)
Chapter 4, “Human Electricity,” chronicles the first phase of the process, focusing on the development of electrocardiography and 3D cardiac mapping. It’s a fascinating bit of history. In essence, medical researchers discovered that the behavior of the heart’s electrical system could be monitored and analyzed based on electrical signals appearing on the surface of the skin.
The first electrocardiograph was actually a frog’s innervated gastrocnemius muscle as described
here. In 1856, Heinrich Muller and Rudolph von Kolliker used what became known as the rheoscopic frog to show that electric currents are produced during the heartbeat. The sciatic nerve of the rheoscopic frog was laid across the beating ventricle of another frog’s heart. They observed one and sometimes two contractions of the rheoscopic frog’s leg muscle with each beat. That’s right: The first electrocardiogram was displayed as a twitching frog muscle.
No one was going to lay a frog’s sciatic nerve across the beating ventricle of a human heart. Needed was a device sufficiently sensitive and fast-responding to detect the signals generated by the heart’s natural pacemaker at points on the skin. Such a device, the capillary electrometer, was invented by Gabriel Lippmann in 1872. Lippmann placed mercury and then dilute sulfuric acid in a U-shaped glass tube. Inserting wires at either end, the interface between the mercury and sulfuric acid changed shape in response to tiny, fast-changing electrical currents.
William Einthoven showed that a mathematical correction had to be applied to the capillary electrometer tracing in order to get the actual electrocardiogram. Einthoven went on to develop an instrument that directly displayed the actual electrocardiogram: the string galvanometer. Einthoven also identified the segments in a normal electrocardiogram, labeling them
PQRST, and defined the standard electrocardiograph leads. Because his laboratory was about one mile from the nearest hospital, he even developed a way to acquire electrocardiograms over a phone line.
The electrocardiogram has become a standard diagnostic tool. It also helped guide development of artificial pacemakers and implantable cardiac defibrillators, as discussed in the next chapter.
In medicine, reverse engineering may be a waypoint rather than the final destination. With 3D cardiac mapping and ablation systems it’s sometimes possible to re-engineer the heart’s electrical system. Today, ablation is a common treatment for tachycardia (very rapid heart beat). Electrophysiologist Jason Jacobson at Northwest Memorial Hospital suggests that in the future we may use tissue engineering to treat heart block (very slow heart beat).
Next time: The Rhythm of Life
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