Takuo Aoyagi and the pulse oximeter

Nearly 50 years ago, it was Mr. Takuo Aoyagi, our engineer, who invented the principle of the pulse oximeter.
We would like to introduce Mr. Aoyagi's life story and the history of pulse oximeters.

Takuo Aoyagi
The pulse oximeter is a device that continuously measures the oxygen saturation in arterial blood (how much hemoglobin is bound to oxygen) without blood sampling.
Hemoglobin turns bright red when bound to oxygen, and dark red when unbound. The oxygen saturation of arterial blood is calculated by utilizing the fact that the ease of absorbing light differs depending on the color. Two types of light with different wavelengths are emitted from one of the small devices attached to the fingertips of the hand, and the sensor on the other side measures the light that passes through the finger without being absorbed and analyzes it.
It can be fatal if there is not enough oxygen in the blood. Blood sampling does not always provide accurate, real-time information about the patient's condition, which changes over time, but using a pulse oximeter does not hurt the patient, and allows the surgeon to understand in real time, how much oxygen the patient has in their bloodstream.
Ear oximeter OLV-5100
After graduating from the Faculty of Engineering, Niigata University, Mr. Aoyagi joined the company in 1971 after working for Shimadzu Corporation (Kyoto). One of Mr. Aoyagi's beliefs at the time when he began searching for specific research themes in the development department was, "The ultimate form of patient monitoring is the automation of treatment. To get closer to that ideal, development of non-invasive continuous monitoring technology is important. "
In 1972, while improving the equipment for measuring arterial blood pumped from the heart, we discovered that the oxygen saturation of arterial blood can be measured by using the pulse of the heart.
Mr. Aoyagi later commented on this finding, "It was hard to believe that such a good discovery was waiting for us in such a convenient place."
Mr. Aoyagi, who continued his research, working on the development of prototype devices, presented this principle at a conference in 1974. There were some opinions that "I think it was an interesting study," but there were some negative opinions, so this presentation did not receive much attention.
The following year, in 1975, we launched the "Oximeter OLV-5100", which uses this principle. It was a truly unique and world class product, but there was still room for improvement in terms of performance and usability, such as the light source being a miniature bulb and the fact that the sensitivity of the sensor was poor, and demand for the product never really materialized. For these and other reasons development of the pulse oximeter was eventually suspended.
Pulse oximeter OLV-1100
The 10 years after we stopped developing the pulse oximeter, saw a great deal of movement in the medical world. With the frequent occurrence of medical accidents in the United States where patients under anesthesia for surgery lose their lives due to lack of oxygen, the usefulness of pulse oximeters came to the forefront of global attention. With many companies competing to launch smaller devices incorporating new technologies such as LEDs, photodiodes, and microcomputers, pulse oximeters became very popular. This movement spread to the domestic market in the latter half of the 1980s, and we also resumed the research and development of the pulse oximeter utilizing the know-how gained during development of the OLV-5100 and released a new product in 1988.
Pulse oximeter OLV-1200
At the time of the development of this product, there was debate over whether to manufacture it in-house, but Mr. Aoyagi said, "Currently, a single device is the mainstream, but in the future it will be essential to incorporate it into a biological information monitoring device. You should make your own products so that there are no restrictions on what you can do with them. 
As expected by Aoyagi, the arterial oxygen saturation (SpO2) is a standard parameter for most of today's biological information monitoring devices.
Mr. Aoyagi did not announce the principle of the pulse oximeter in English, but Dr. Severinghaus, a world authority on respiratory physiology who knew Mr. Aoyagi's existence, visited Japan in 1987 and met Mr. Aoyagi. After that, after being introduced in the paper, Aoyagi became known worldwide as the inventor of the pulse oximeter.

January 1987 with Dr. Severinghaus

Fall 1992, IEEE-EMBS Annual Scientific Meeting
With Chairman Rolf

February 1994, at our laboratory

The pioneering invention of the pulse oximeter was recognized for its significant contribution to improving the quality of medical care. It received the Medal with Purple Ribbon in 2002, and the Institute of Electrical and Electronics Engineers (IEEE) confirmed the technology in the medical field in 2015. He was the first Japanese to receive the “IEEE Medal for Innovations in Healthcare Technology”.
2015 IEEE Honors Ceremony at the venue
Pocket SpO2 monitor with WEC-7201 (top)
Finger probe TL-201T (bottom)
Even after the pulse oximeter had spread all over the world, Aoyagi was determined to improve the pulse oximeter technology and to apply the principles to other medical measurements. For these purposes, he continued to pursue theoretical research until his later years. Mr. Aoyagi, who seemed to be a very research-oriented person but was actually a friendly person, said, "If the pulse oximeter doesn’t have a solid theoretical grounding, it will be useless." He was also focused on the guidance of young engineers.
In April 2020, Mr. Aoyagi died at the age of 84 due to old age, while the importance of pulse oximeters is being recognized again with the spread of the COVID-19 virus.
Half a century after the principle of the pulse oximeter was first discovered, its technology has spread to medical sites around the world, dramatically improving the safety of general anesthesia surgery, and the saving lives of many patients around the world. Indeed, it can be said that the invention of the pulse oximeter was a great achievement in the history of the world.

Work Experience

• Nihon Kohden Corporation, February 1971 – Present
Chief Manager of Aoyagi Research Laboratory: Apr. 1991 – Present
General Manager of Development Department: Aug. 1985 – Mar. 1991
Deputy General Manager of Engineering Department: Aug. 1983 – Jul. 1985
Deputy Senior Manager of Development Department: Aug. 1979 – Jul. 1983
Deputy Senior Manager of Engineering Department: Sep. 1975 – Jul. 1979
Manager of Development Department: Feb. 1971 – Aug. 1975

• Shimadzu Corporation, April 1958 – January 1971

Academic Degree

Doctor of Engineering (The University of Tokyo)
Title of thesis: Non-invasive measurement of light absorption in blood based on pulsatile variation of light transmitted through body tissue (July 1993)
Supervisor: Prof. Masao Saito, Faculty of Medicine, The University of Tokyo

Principal Honors

• June 2015
IEEE Medal for Innovations in Healthcare Technology from Institute of Electrical and Electronics Engineers
• January 2013
Gravenstein Lifetime Achievement Award from the Society for Technology in Anesthesia
• June 2012
Harvey W. Wiley Lifetime Achievement Award from Innovations and Applications of Monitoring Perfusion, Oxygenation and Ventilation
• April 2002
Medal with Purple Ribbon from Japanese government
• April 2002
Social Award from Japanese Society of Anesthesiologists
• April 2000
Science and Technology Achievement Award from Japanese Science and Technology Agency
• March 1997
Okusyu Memorial Award from Japan Association for Clinical Monitoring
• June 1995
Achievement Award from Japanese Society of Medical Instrumentation