09/07/17 MACHINES-V-NATURE: SERVICE LONGEVITY
All of us are awed by the resilience of human organs, indeed of life in general. And I, for one, am also amazed by the wizardry of modern doctors who push our resilience and bodily efficiency to ever-higher levels. In particular, having survived a “catastrophic heart failure” seven years ago—as cardiologists amazingly reeled me back from the rim of the eternal abyss—I marvel at the human heart, an organ that trudges on relentlessly throughout a person’s life. But as a zealous apostle of science & technology I often reflect on man-made machines as a counterpoint to biological organs.
Your heart beats an average of 60 times a minute in adulthood (faster in childhood), and that adds up to some 2-3 billion cycles in the course of a seventy-year lifetime. Awesome! So I wondered how man-made machines stack up against that and was surprised to realize that engineering is catching up to nature. Corresponding statistics for the cyclical performance of your latest automobile engine, for instance, are as impressive as those for the human heart.
Every car has a tachometer, which registers the revolutions of the engine. Most cars run at around 2,000 revolutions per minute (zooming beyond 2,000 when you gun the pedal and descending to 1,000 or so when you crawl). On a typical highway drive you average about one mile/minute and so you put your engine through 2,000 revs each mile (or minute). Thus, through a 150,000-mile life of your engine (now easily exceeded by most cars), your car engine goes through some 3 billion revs!
Now, consider what constitutes a rev in a typical (4-stroke) car engine. A revolution is a complete turn of the crank and the synchronized cam shafts on their axes. During one revolution the pistons ascend and descend through the cylinder bore while the cams rocks between two extreme positions to open or shut the valves. (The ingenuity of the internal combustion engine lies in the convoluted crank and the pear shape of the cam.) Whereas a heart has no moving parts that can fail by fatigue or friction or overheating, and operates by static contractions (really, regulated spasms), a car engine comprises many moving parts. Each of the cylinders deployed in tandem has rotating shafts, rocking cams, piston rods, plunging piston heads, intake valves, exhaust valves, etc. Furthermore, your car engine goes through more than fifty revolutions for each beat cycle of your heart (2000 versus 30).
Of course a car engine gets service during which it is “tuned up” (to ensure the moving parts are in synchrony) and lubrication is applied, etc. But so do human hearts, through special stimulation by hormones and by pharmacological boosts applied when needed to struggling hearts (like mine). So, cycle for cycle the common automobile engine seems to trump the human heart!
But will engineering ever exceed or even match nature’s reliability? At present there are artificial and fully implantable human hearts available that are available, at least as a stopgap measure pending transplant of donor hearts. So, there’s hope. And with humanity poised on the threshold of mass automation and robotics, who knows?