Takuo Aoyagi, the inventor of the pulse oximeter, died of old age on April 18. He was 84 years old.
The pulse oximeter is a device that measures blood oxygen levels noninvasively, for example, by clamping it on a finger. This important medical device is now being used around the world in treatments for the new coronavirus to detect signs of severe illness. Despite its decades of widespread use, few know who invented the pulse oximeter.
Aoyagi was born in Niigata Prefecture. Influenced by his father, who was a math teacher, Aoyagi had dreamed of becoming an inventor since he was a young boy. After graduating from the Faculty of Engineering at Niigata University in 1958, he joined Shimadzu Corp. In 1971, Aoyagi moved to Nihon Kohden Corp.
He started to develop the pulse oximeter after he was dispatched by Nihon Kohden to the Anesthesiology and Pain Relief Center at the University of Tokyo Hospital, for research.
When surgery is performed using a general anesthetic, there is a risk of the patient's breathing stopping due to the anesthetics. In those days, surgery staff monitored patients for hypoxia only by direct observation, and accidents often occurred.
An oximeter had already been invented that measured oxygen levels by irradiating blood, but the procedure included venous blood.
"We need a device to continuously measure oxygen levels in arterial blood that delivers oxygen from the heart to the rest of the body," Aoyagi was told by an anesthesiologist at the university.
Eventually, Aoyagi successfully retrieved information from pulsing arterial blood by measuring beams passed through the skin, establishing the principle of pulse oximetry.
He acquired a patent in 1974 and another company launched a finger measurement device in 1977. The trend of securing the safety of anesthesia picked up in the United States and Europe since the 1980s and the device came to be used globally.
Nobuaki Shime, 56, the vice chairman of the executive board of the Japanese Society of Intensive Care Medicine and professor at the Emergency and Critical Care Medicine at Hiroshima University, said: "Today, the device is widely used by medical institutions for both inpatients and outpatients. The arrival of a medical device that enabled easy measurements of blood oxygen levels without collecting blood was revolutionary."
Even after the device's use became widespread, Aoyagi was never satisfied and continued research to improve its accuracy until his later years. Katsuyuki Miyasaka, 76, professor emeritus of St. Luke's International University, has known Aoyagi for about 40 years, and had helped his research several times. Aoyagi had no problem being an experimental test subject. To reduce his blood oxygen level, he would desperately hold his breath even after he turned 70 years old.
"I was just overwhelmed by him doing that," Miyasaka recalled.
On the other hand, Masayoshi Fuse, 73, a former section chief in charge of the Nihon Kohden Aoyagi laboratory, said, "It might look like Aoyagi was just committed to research, but he was very friendly."
Not only did he work on his own research, he also invited young researchers from outside and enthusiastically instructed them, according to Fuse.
Aoyagi was especially well versed in paintings. In 1987, Aoyagi and Miyasaka together participated in an international academic gathering held in the former Soviet Union. Miyasaka still remembers Aoyagi standing still before an overwhelming number of paintings at the Hermitage Museum.
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