Pulse oximetry

An earlier oximeter had been invented by Glen Millikan, building on work by Karl von Vierordt, Karl Matthes, and others. Earl Wood and his PhD student J. E. Geraci made some improvements.^[2] These early devices were inaccurate and difficult to use.^[1] The main idea was to measure the difference in how blood absorbed red light versus infrared light.

An obstacle was that the pulse of blood created a great deal of noise. Early devices tried to work around this by limiting measurement to the ear, and with other methods. Shortly after starting at Nihon Kohden in 1971, Aoyagi showed how to remove the noise from the measurement, leading to a practical and accurate measurement of oxygen in the blood. Similar ideas were developed slightly later by Masaichiro Konishi and Akio Yamanishi of Minolta.^[2]

Nihon Kohden submitted an application for a patent on the resulting device in 1974, which named Aoyagi and his colleague Michio Kishi (who helped create a pilot model) as co-inventors. The patent was granted in 1979.^[2]

In 2007, World Health Organization listed pulse oximeter as an essential device for Surgical Safety Checklist for Patient.^[3][4]

Later career

Nihon Kohden moved Aoyagi to a desk job in 1975, and only brought him back into their research group ten years later.^[5][6] After returning to research, Aoyagi came back to ideas similar to those of the pulse oximeter. He developed a device, which he called a "pulse spectrophotometer", and which used these ideas to measure the diffusion of a dye injection in the bloodstream. This gave a relatively non-invasive way to measure liver blood flow and plasma volume.^[5]