Takuo Aoyagi

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

Early life, education and career Aoyagi was born February 14, 1936, in Niigata Prefecture, Japan. His parents were Monshichi and Tatsu Aoyagi. His father was a mathematics teacher and his mother was a homemaker. He then worked for a time for the scientific instrumentation company Shimadzu Corporation, before moving to the research division of the medical equipment company Nihon Kohden in 1971.

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. The following year, Aoyagi became a laureate of the Asian Scientist 100 by the Asian Scientist.