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How fingertip pulse oximeter works

Non-invasive measurement infrared technology is used to measure fingers, toes, and ears. This is the most common place for oxygen measurement in pulse oximeters. It is more accurately called blood oxygen saturation, or SpO2 for short.

It will show the results of the test in digital form, which mainly shows the ratio of total oxygen saturation under actual oxygen content, generally expressed as a percentage. The typical blood oxygen saturation of the human body is 90-100%, but the minimum is also It can go up to 60%. The blood oxygen saturation of the human body depends on many factors, the most important of which is the poor blood supply capacity of the patient's body, and the reading of HbO2 will decrease.

Working Principle

By driving a red light LED (660nm) and an infrared light LED (910nm) in sequence, the blue line indicates the degree of induction curve of the receiving tube to reduced hemoglobin when the hemoglobin has no oxygen molecules, and the reduced hemoglobin pair can be seen from the graph The absorption of red light at 660 nm is relatively strong, while the absorption length of infrared light at 910 nm is relatively weak. The red line represents the induction curve of oxyhemoglobin when the hemoglobin with red blood cells with oxygen molecules, the absorption channel of 660nm red light is relatively weak, and the absorption of 910nm infrared light is relatively strong.

In blood oxygen measurement, reducing hemoglobin and aerobic hemoglobin, by detecting the difference between the two types of light absorption at different wavelengths, the measured data difference is the most basic data for measuring blood oxygen saturation. In the blood oxygen test, the two most common wavelengths of 660nm and 910nm are actually required to achieve higher accuracy. In addition to the two wavelengths, they must be increased, and even up to 8 wavelengths. The main reason is that the human hemoglobin is reduced In addition to hemoglobin and oxyhemoglobin, there are other hemoglobins. We often see carbon-weight oxyhemoglobin. More wavelengths are beneficial for better accuracy.

 

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