What is Oximeter ? How does it work ?

What is Oximeter ?

Today (during Covid-19 Pandemic) Pulse Oximeter is a common term. It is an essential medical instrument like thermometer or sphignomanometer (blood pressure measuring instrument). It is a non-invasive diagonastic device to measure Oxygen saturation in patient’s arterial blood (SpO2) . It is fixed on the finger tip or earlobe.

Who invented it ?

Japanese Biomedical Engineer Takuo Aayogi was the inventor of Pulse Oximeter. He was a scientist in Japan’s Nihon Kohden Corporation. In 1975 Nihon Kohden launched first Pulse Oximeter OLV-5100 and in 1977 Japanese Company, Minolta produced first finger Oximeter Oximet-1471.

How does it work ?

The photo sensor of Oximeter consists of two LEDs (light emitting diode) that emit two wavelengths of light passing through the body part to the photodetector. One photo emitter is a red (R) LED, which emits light at 600–750 nm wavelength light band, and the other is infrared( IR) LED, which emits light at 850–1000 nm wavelength light band. The oxygenated blood of artery absorbs more IR light than the R LED, so the photodetector at the receiving end receives less IR light and more R light. But deoxygenated blood absorbes more R light than the IR LED, thus the photodetector receives less R light and more IR light. These LEDS are operated in sequence, for example, first R LED, then IR LED, and then both LEDS are off for sometime. At the receiving end the electrical signal corresponding to each wavelength is recorded and displayed with respect to time. The ratio of the output signal due to R and IR light is calculated. This ratio is then compared with lookup table stored in the memory of the microchip that converts the ratio into SpO2 value. This lookup table is formed based on the light absorption given by Beer–Lambart Law.
Today, Pulse Oximeter is an essential medical instrument which saves lives of many patients around the World. The invention of Pulse Oximeter was a great achievement in the medical history of the World.

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