Between Issues

Commemoration of Dr. Takuo Aoyagi’s Impact: A Tree that was Heard to Fall

June 10, 2021

Robert J. Kopotic, MSN, RRT, PhDh
Adapted from Special Feature on Pulse Oximeters: The invention that changed the paradigm of patient safety around the world. (LiSA (1340-8836) vol28 No3 Page237-308, 2021.03 (in Japanese)

View more articles from this special collection hosted by the APSF on Pulse Oximetry and the Legacy of Dr. Takuo Aoyagi.

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Takuo’s sojourn into mortality came on February 14, 1936, when he arrived to his parents Monshichi and Tatsu Aoyagi. In 1958, he graduated from Niigata University with a degree in electrical engineering and started work in the medical device industry with the Shimadzu Corporation. In 1971, he joined the Nihon Kohden Corporation, where he completed his life’s work over the next almost 50 years. He received a PhD in engineering from the University of Tokyo with his thesis: “Non-invasive measurement of light absorption in blood based on pulsatile variation of light transmitted through body tissue.”

Dr. Aoyagi has received many accolades and honors but, in my opinion, the finest came from Professor John Severinghaus, who in 1987 met Takuo and then recognized him in the worldwide medical literature for invention of the pulse oximeter. In the attached photo, Takuo is standing next to me and Dr. Severinghaus is to his side, while they both received Lifetime Achievement recognition during the 2012 Innovations and Applications of Monitoring Perfusion, Oxygenation and Ventilation (IAMPOV) symposium on the campus of Yale University. The following IAMPOV was held at St. Luke’s International University in Tokyo in 2015. The next meeting will be held in London in 2021.

In the proceedings of the 2007 IAMPOV symposium, John Severinghaus walked the attendees through several decades of advancements in optical spectroscopy of the ear, a method that allowed the calculation of blood’s saturation with oxygen but required complex calibration. This work was mainly focused on assessing pilots in flight. Then came Takuo that “was interested in measuring cardiac output noninvasively by the dye dilution method using a commercially available ear oximeter. He found through computation that dividing the absorptions of the red (805) and infrared (930) signals by each other cancelled the pulse noise which prevented measuring the dye washout accurately. He then realized that these pulsatile changes could be used to compute saturation from the ratio of ratios of pulse changes in the red and infrared. His ideas and equations were shared, adapted, and improved by Minolta into the first practical finger type device in 1977, stimulating other firms to further improve and market pulse oximeters worldwide in the mid-1980s.” Severinghaus summarized, “Greatness in science often, as here, comes from the well-prepared mind turning a chance observation into a major discovery.” Severinghaus JW. Takuo Aoyagi: discovery of pulse oximetry. Anesth Analg. 2007;105(6 Suppl):S1-4.

I received the news of Dr. Aoyagi’s passing from Dr Katsuyuki Miyasaka (“Kats”), who as a physician researcher, worked closely with Takuo for over 30 years. During that same period, I became associated with Kats as we were co-investigators in the NIH-NHLBI, Collaborative Clinical Trial on High Frequency Ventilation in Premature Infants.” Contract #NO1-HR-46005 (RFP-NHLBI-84-4; HIFI-Trial). In that study, pulse oximetry data were part of the collected parameters. Kats and I grieved about the loss of a brilliant mind, kind friend, and noble man that had blessed our lives. I then reminisced with Kats about Takuo and his wife (Yoshiko) telling me about meeting someone else of my faith (i.e., the Church of Jesus Christ of Latter-Day Saints). Takuo had a valued relationship with the renowned Dr. Homer Richards Warner from the University of Utah. A cardiologist by training, Homer was the first to develop an electronic medical record system in the United States, but he had some experience with the dye dilution method. The two couples stayed at each other’s homes on multiple occasions. I remember Takuo speaking highly of Warner’s contributions to medicine and Warner reciprocating. Takuo reminded me and my son, that he knew another Christian missionary, i.e., “Elder Homer Warner* that came to Japan as a young man.” Takuo and Yoshiko mentioned their cherished visits to Homer and Kay Warner in Salt Lake City.

John Severinghaus credited the development of the CO2 electrode to Richard Stow (John refined Stow’s design to include a more stable electrolyte, which then became the Stow-Severinghaus electrode used for measuring CO2 in blood gas analyzers). Similarly, Takuo gave credit to others for refining pulse oximetry, “I appreciate Minolta. Without their recognition of idea of pulse oximeter, the idea might be buried.” Anesth Analg. 2007;105 (6 Suppl):S3.

While his intimate family of survivors include his wife (Yoshiko), and three children (Kaori, Midori and Yasutoshi), so many others have been and continue to be blessed by Takuo’s creation of pulse oximetry and his never-ending curiosity of the interrelationship of engineering concepts related to human physiology, particularly with interactions between heart, lung and vascular function. Sense Takuo’s vision, when with Kats 20 years ago he wrote, “Opening of the first door of pulse photometry gave us pulse oximetry. The next door of pulse photometry opens to multi-wavelength pulse photometry. Dyshemoglobins (e.g., COHb and MetHb) can be measured with a multi-wavelength system. The elimination of artifacts caused by body movement is possible without sacrificing response time. It may also become possible to measure hemoglobin concentration.” Aoyagi T, Miyasaka K. Pulse oximetry: its invention, contribution to medicine, and future tasks. Anesth Analg. 2002;94(1 Suppl):S1-3.

“Dr. Aoyagi hoped to use the oximeter to develop a noninvasive way of measuring cardiac output (the amount of blood pumped by the heart) through a method known as dye dilution, in which dye is injected into a patient. Rather than aid fighter pilots in dogfights, he hoped that his invention would signal a hospital patient’s need for artificial ventilation.” See “Takuo Aoyagi, whose pulse oximeter helps hospitals fight coronavirus, dies at 84,” › local › obituaries › 2020/05/03:

I wish to take minor liberty with a quote from Sir Isaac Newton, “If WE have seen further, it is by standing upon the shoulders of giants.” For me that is certainly the case for my apprentice association with Takuo Aoyagi. His engineering efforts raised awareness that ischemia is a precursor of major organ failure and that patients are benefitted through its early detection by monitoring oxygen carrying capacity and perfusion. Dr. Aoyagi was small in height but mighty tall in deed and in humility. I treasure his impact upon my life, many kind words, and thoughtful critiques of ways I could be better personally and professionally.


Robert J. Kopotic, MSN, RRT, PhDh

Bob Kopotic is a Critical Care Manager of Clinical and Medical Affairs for Edwards Lifesciences. In his pre-medical device industry efforts, he completed graduate and bachelor’s degrees in bioengineering, clinical care & physiology and then, worked in critical care as a Registered Nurse & Respiratory Therapist. Bob is an experienced lecturer, industry spokesperson, and symposium organizer. At the Emory University and UC San Diego, he conducted animal, bench and clinical studies of circulation, oxygenation, and ventilation, while also developing advanced life support and monitoring systems. Bob’s direct association with Takuo Aoyagi began over 20 years ago.

Another Elder Homer Warner

Dr. Hormer Warner (1922-2012), with whom Dr. Aoyagi had close contact, was a Mormon missionary when he was young and engaged in missionary work in Japan when he was young. He was said to be fluent in Japanese. Dr. Warner was a cardiologist, known not to obtain patents and was a pioneer in cardiac decision-making programs. His use of the dye dilution method was known but is not clear whether the two discussed this. Dr. Warner is in fact the Elder Warner that Dr. Aoyagi was telling Dr. Kopotic about.

Read more articles from this special collection hosted by the APSF on Pulse Oximetry and the Legacy of Dr. Takuo Aoyagi.