On April 18, 2020, the father of modern blood oxygen measurement technology, Takuo Aoyagi passed away in Tokyo. The pulse oximeter, he invented, is a kind of medical equipment that non-invasively measures the arterial blood oxygen saturation or arterial hemoglobin oxygen saturation. It has now become a piece of vital equipment in hospitals all over the world.
However, it is such a tool that benefits people worldwide, but its inventor is rarely known.
1936: Gospel Year for Anesthetized Patients
In clinical, many diseases can cause a lack of oxygen supply for patients and even lead to death due to hypoxia during surgery. Therefore, real-time monitoring of arterial blood oxygen concentration is critical in clinical rescue.
The traditional spo2 measurement is to first collect blood from the human body (usually the arterial blood of the radial artery and femoral artery) and then use a blood gas analyzer to analyze and measure the blood oxygen saturation. However, the repeated blood draws can easily lead to pseudoaneurysms in the patient. And it also causes a lot of unnecessary pain. The worse is that this method usually takes at least 20-30 minutes to obtain results and cannot be monitored in real-time. This delay can be fatal because hypoxia can cause severe brain damage within 5 minutes. Therefore, many medical workers hoped to provide adequate oxygen to anesthetized patients and monitor their blood oxygen levels in real time. For them, 1936 was a landmark year.
This year, neuropathologist Cyril Courville published his landmark paper in the medical journal, Asphyxia as a Consequence of Nitrous Oxide Anesthesia, pointing out the risks of clinical anesthesia. In the same year, the New York anesthesiologist expanded into the American Society of Anesthetists. As an educational organization and academic group for anesthesiologists, ASA is committed to the safety of anesthesia, aiming to improve and maintain the medical practice standards of clinical anesthesia and strengthen the anesthesia monitoring of patients. Eighty years later, the ASA Charity Foundation supports the Lifebox project, which provides pulse oximeters to "resource-poor countries" worldwide to achieve safer anesthesia.
Also, in 1936, a legendary little boy was born in an ordinary family in Niigata Prefecture on the west coast of Japan. He is an outstanding biomedical engineer and the father of modern blood oxygen measurement technology Aoyagi Takuo. Since the advent of Takuo Aoyagi's pulse oximeter, all the problems of spo2 measurement during anesthesia operations have been solved. During the surgery, The doctors only need to put the measuring instrument(Usually the fingerclip spo2 sensor) on the patient's finger to measure the spo2 level continuously and non-invasively.
From World War II to today
During World War II, a young American physiologist named Glenn Allen Millikan developed an ear oximeter to monitor the hypoxia of military pilots. However, the monitoring results of such devices fixed on the ears are not accurate.
In 1958, 22-year-old Takuo Aoyagi graduated with a major in electrical engineering from the Faculty of Engineering at Niigata University and joined a scientific instrument company in Kyoto. In 1971, he transferred to a Japanese medical device company called Nihon Kohden and began to engage in the development of medical devices.
During his work at Nihon Kohden, there were early devices that could monitor human blood oxygen levels. But these devices were bulky, and the readings were not accurate enough. Takuo Aoyagi began to look for a lighter and more precise method to detect the blood oxygen saturation of the human body without drawing blood.
At the beginning of the research work of pulse oximeter, the ear oximeter during World War II drew his attention. He began to study the secret behind this instrument. When hemoglobin, which carries oxygen transport in the blood, is combined with oxygen, the light it absorbs is different. And this device takes advantage of this, using two different wavelengths of light (red light and infrared light) to measure the pilot's blood oxygen level.
Inspired by this method, three years later, he developed an oximeter that does not require blood collection but only needs to shine a light on the blood vessels of the fingertips to measure human blood oxygen content. At the time, he was 38 years old.
In 1972, when studying the dye dilution method to measure the amount of blood pumped by the human heart, Takuo Aoyagi discovered that the flow of human blood would produce a kind of "noise" that interferes with the dye dilution curve. This noise carries information about the oxygenation of arterial blood. He uses innovative technology to eliminate the noise so that the oxygen level can be read clearly. It leads him to discover a method for pulse oximetry using light signals of two different wavelengths.
On April 26, 1974, Takuo Aoyagi reported his pulse oximetry to the Japanese Society of Medical Electronics and Biologic Logic Engineering (MBE) and created one with his collaborator and colleague Michio Kishi. The prototype of the pulse oximeter, the company filed a patent application in 1974, listing the two as inventors. Five years later, this invention was granted a patent.
In 1975, the first commercial pulse oximeter made by Takuo Aoyagi's method was launched. This oximeter consists of a probe containing a light-emitting device and two photodetectors. It can reach the photodetector from two wavelengths of light through the earlobe to measure the absorbance change of each wavelength according to the pulse of arterial blood. The device can quickly and non-invasively assess the spo2 level, enabling clinicians to find abnormalities in hemodynamics and breathing earlier, avoid patient injury, and evaluate the effect of clinical intervention in real-time.
Since then, Takuo Aoyagi has continued to promote oxygen monitoring technology development, stimulating technological innovation in oximeter equipment worldwide. The Medical device manufacturers around 1978 adopt his principles and inventions. After improvements, they produced commercial oximeters and successfully sold them on the market. In 1986, the American College of Anesthesiologists recommended that pulse oximeters be used to monitor patients undergoing anesthesia. Until today, the size of the oximeter has become smaller and smaller, the technology has become more and more mature, and more importantly, the cost has also become lower and lower, which has made it enter the wards and operating rooms all over the world.
In recent years, Takuo Aoyagi's invention has been increasingly recognized by people. The World Health Organization strongly supports this invention and is especially suitable for patients undergoing anesthesia surgery. In today's advanced medical technology, many oximeters come in various shapes and complete functions. But all pulse oximeters are based on Aoyagi Takuo's original pulse oximetry principle.
One of the vital testing indicators during surgery
For many years, body temperature, pulse, respiratory rate, and blood pressure are the four main vital signs of patients in the medical community. Till the 1980s, the real-time spo2 level measurement is spread and recognize. The spo2 becomes the fifth sign in the clinical, an indicator of whether oxygen is transported from the lungs and heart to other parts of the patient's body.
In 2007, the World Health Organization (WHO) recognized pulse oximetry as one of the most significant testing indicators during surgery. Since then, the WHO has launched the "Global Pulse Oximetry Project" to ensure that every patient undergoing surgery receives pulse oximetry monitoring.
In 2015, the Institute of Electrical and Electronics Engineers (IEEE) awarded Takuo Aoyagi the Medal for Medical Technology Innovation. And They announced that his research has resulted in a four-fold reduction in mortality from anesthesia. Every year, this honor is awarded to individuals and teams who have made outstanding contributions or innovations in the fields of medicine, biology, and healthcare technology. Takuo Aoyagi received this award for his pioneering contributions to pulse oximeters, and he was the first Japanese to receive the award.
Material
- 1.https://anesthesiology.pubs.asahq.org/article.aspx?articleid=2583677
- 2.https://journal.chestnet.org/article/S0012-3692（16）30698-5/fulltext
- 3.https://healthmanagement.org/c/icu/leadingpeople/nihon-kohden-s-dr-takuo-aoyagi-receives-2015-ieee-medal-for-innovations-in-healthcare-technology
- 4.https://www.researchgate.net/publication/5798912_Takuo_Aoyagi_Discovery_of_Pulse_Oximetry
- 5.https://www.businesswire.com/news/home/20150624005442/en/Nihon-Kohden%E2%80%99s-Dr.-Takuo-Aoyagi-Receives-2015
- 6.https://www.ieee.org/about/awards/bios/healthcare-recipients.html
- 7.https://www.amperordirect.com/pc/help-pulse-oximeter/z-pulse-oximeter-history.html
- 8.https://www.contemporarypediatrics.com/modern-medicine-feature-articles/pulse-oximetry-fifth-vital-sign
- 9.https://www.google.com/amp/s/www.washingtonpost.com/local/obituaries/takuo-aoyagi-whose-pulse-oximeter-helps-hospitals-fight-coronavirus-dies-at-84/2020/05/03/685b3ec6-8d45-11ea-a0bc-4e9ad4866d21_story.html%3FoutputType%3Damp
- 10.https://ethw.org/Takuo_Aoyagi
- https://www.legacy.com/news/celebrity-deaths/takuo-aoyagi-1936-2020-pulse-oximeter-inventor/
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