(p. 27) Takuo Aoyagi, a Japanese engineer whose pioneering work in the 1970s led to the modern pulse oximeter, a lifesaving device that clips on a finger and shows the level of oxygen in the blood and that has become a critical tool in the fight against the novel coronavirus, died on April 18  in Tokyo.
. . .
Mr. Aoyagi’s contribution to medical science was built on decades of innovation and invention. In an essay about Mr. Aoyagi, John W. Severinghaus, a professor emeritus of anesthesia at the University of California, San Francisco, wrote in 2007 that Mr. Aoyagi’s “dream” had been to detect oxygen saturation levels without having to draw blood.
. . .
But he soon ran into a problem. Blood does not flow smoothly like an open tap, but pulses through the body irregularly, thus preventing an accurate recording of dye levels. The problem, however, turned out to be an opportunity. By devising a mathematical formula to correct for this “pulsatile noise,” he created a device that measured oxygen levels with greater accuracy than before.
“Greatness in science, often, as here, comes from the well-prepared mind turning a chance observation into a major discovery,” Dr. Severinghaus wrote.
For the full obituary, see:
(Note: ellipses, and bracketed year, added.)
(Note: the online version of the obituary was updated June 20, 2020, and has the title “Takuo Aoyagi, an Inventor of the Pulse Oximeter, Dies at 84.”)
The essay about Aoyagi mentioned above is: