was a Japanese engineer, known for his work leading to the modern

pulse oximeter Pulse oximetry is a noninvasive method for monitoring a person's oxygen saturation. Peripheral oxygen saturation (SpO2) readings are typically within 2% accuracy (within 4% accuracy in 95% of cases) of the more accurate (and invasive) reading of ...

Early life, education and career

Aoyagi was born February 14, 1936, in

Niigata Prefecture is a Prefectures of Japan, prefecture in the Chūbu region of Honshu of Japan. Niigata Prefecture has a population of 2,227,496 (1 July 2019) and is the List of Japanese prefectures by area, fifth-largest prefecture of Japan by geographic area ...

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

. His parents were Monshichi and Tatsu Aoyagi. His father was a mathematics teacher and his mother was a homemaker. Aoyagi received an undergraduate degree in

electrical engineering Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems which use electricity, electronics, and electromagnetism. It emerged as an identifiable occupation in the l ...

from

Niigata University is a national university in Niigata, Niigata Prefecture, Japan. It was established in 1949 and has its major origins in Niigata Medical College (established in 1922) and in Niigata Higher School (established in 1919). It is one of the largest Jap ...

in 1958. He then worked for a time for the scientific instrumentation company

Shimadzu Corporation is a Japanese public KK company, manufacturing precision instruments, measuring instruments and medical equipment, based in Kyoto, Japan. It was established in 1875. The American arm of the company, Shimadzu Scientific Instruments, was founde ...

, before moving to the research division of the medical equipment company

Nihon Kohden is a Tokyo-based leading manufacturer, developer and distributor of medical electronic equipment, which include EEGs, EMG measuring systems, ECGs, patient monitors and clinical information systems, with subsidiaries in the U.S., Europe and A ...

in 1971.

Pulse oximetry

An earlier oximeter had been invented by Glen Millikan, building on work by

Karl von Vierordt Karl von Vierordt (July 1, 1818 – November 22, 1884) was a German physiologist. Vierordt was born in Lahr, Baden. He studied at the universities of Berlin, Göttingen, Vienna, and Heidelberg, and began a practice in Karlsruhe in 1842. In ...

, Karl Matthes, and others. Earl Wood and his PhD student J. E. Geraci made some improvements. These early devices were inaccurate and difficult to use. The main idea was to measure the difference in how blood absorbed red light versus infrared light. An obstacle was that the

pulse In medicine, a pulse represents the tactile arterial palpation of the cardiac cycle (heartbeat) by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed near the surface of the body, such as at the nec ...

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 was a Japanese manufacturer of cameras, camera accessories, photocopiers, fax machines, and laser printers. Minolta Co., Ltd., which is also known simply as Minolta, was founded in Osaka, Japan, in 1928 as . It made the first integrated autofocu ...

. Nihon Kohden submitted an application for a

patent A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an enabling disclosure of the invention."A p ...

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. In 2007,

World Health Organization The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...

listed pulse oximeter as an essential device for Surgical Safety Checklist for Patient.

Later career

Nihon Kohden moved Aoyagi to a desk job in 1975, and only brought him back into their research group ten years later. 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.

Death

Aoyagi died in Tokyo on April 18, 2020.

Awards and honors

The

University of Tokyo , abbreviated as or UTokyo, is a public research university located in Bunkyō, Tokyo, Japan. Established in 1877, the university was the first Imperial University and is currently a Top Type university of the Top Global University Project by ...

gave Aoyagi a doctorate in engineering in 1993. Aoyagi received the

Medal with Purple Ribbon are medals awarded by the Government of Japan. They are awarded to individuals who have done meritorious deeds and also to those who have achieved excellence in their field of work. The Medals of Honor were established on December 7, 1881, and we ...

from the

Emperor of Japan The Emperor of Japan is the monarch and the head of the Imperial House of Japan, Imperial Family of Japan. Under the Constitution of Japan, he is defined as the symbol of the Japanese state and the unity of the Japanese people, and his positio ...

in 2002. Aoyagi was the 2015 recipient of the

IEEE Medal for Innovations in Healthcare Technology Through its awards program, the Institute of Electrical and Electronics Engineers recognizes contributions that advance the fields of interest to the IEEE. For nearly a century, the IEEE Awards Program has paid tribute to technical professionals ...

Early life, education and career

Pulse oximetry

Later career

Death

Awards and honors

References

Further reading