Blood oxygen level is a reflection of a person’s physical fitness. Blood oxygen saturation is an important parameter reflecting the blood circulatory system and respiratory circulatory system, and an important indicator to judge whether the human body is healthy or whether the surrounding environment is hypoxic. The normal level of the human body should be above 95% oxygen saturation. When the concentration of blood oxygen in the blood is low, it can affect the normal working of organs such as the heart and brain. Many clinical diseases will cause the lack of oxygen supply, which will directly affect the normal metabolism of cells, and even threaten human life in serious cases. Therefore, real-time monitoring of blood oxygen saturation is very important in clinical rescue.
Classification and principle of blood oxygen saturation detection
The measurement of blood oxygen saturation is usually divided into two categories: electrochemical method and optical method.
The traditional electrochemical method of blood oxygen saturation measurement requires blood collection from the human body (arterial blood is most commonly used), and then electrochemical analysis is performed using a blood gas analyzer to measure the arterial oxygen partial pressure (Pa02) within a few minutes. And calculate the arterial oxygen saturation (Sa02). Since this method requires arterial puncture or cannulation, causes pain to the patient, and cannot be continuously monitored, it is difficult for the patient to receive timely treatment when in a dangerous situation. The advantage of the electrochemical method is that the measurement results are accurate and reliable, but the disadvantage is that it is troublesome and cannot be continuously monitored.
Optical method is a new optical measurement method that overcomes the shortcomings of electrochemical method. It is a continuous non-invasive blood oxygen measurement method that can be used in emergency wards, operating rooms, recovery rooms and sleep research. At present, pulse oximetry is the most widely used method. Its principle is to monitor the change of blood absorption of light, measure the percentage of oxyhemoglobin (Hb02) in total hemoglobin (Hb), and directly obtain Sp02.
The non-invasive oximeter mainly consists of a microprocessor, memory (EPROM and RAM), two digital-to-analog converters that control the LEDs, a sensor that filters and amplifies the signal received by the photodiode, and digitizes the received signal. It consists of an analog-to-digital converter provided to the microprocessor.
▲ Principle diagram of blood oxygen saturation meter
The advantage of this method is that it can continuously measure the human body without damage, and the instrument is simple and convenient to use, so it has been paid more and more attention. The disadvantage is that the measurement accuracy is lower than that of the electrochemical method, and the error is larger when the blood oxygen value is low. Using the principle of optical method, ear oximeters, multi-wavelength oximeters and the newly developed pulse oximeters have appeared successively. Require. Although they are less than satisfactory in some respects, the clinical benefits they produce are widely recognized.
Photoelectric sensor for non-invasive blood oxygen saturation monitoring
The sensor is a key component that can sense the partial pressure of oxygen in the blood and convert it into a usable output signal. Its damage will directly lead to inaccurate detection or failure of the whole machine to work. The blood oxygen sensor can be mainly divided into finger type, earlobe type, wrapping type and adhesive type according to the shape. No matter what the shape is, the principle and composition of blood oxygen sensors are the same, and they are composed of light-emitting devices and receiving devices. The light-emitting device is composed of red light with a wavelength of 660nm (650nm) and an infrared light-emitting tube with a wavelength of 940nm (910nm). Most of the photosensitive receiving devices use PIN-type photodiodes with large receiving area, high sensitivity, small dark current and low noise, which convert the received incident light signal into electrical signal.
Most of the newly developed pulse oximeters use a finger-sleeve sensor probe, which is placed on the fingertip when in use. Two light-emitting diodes placed side by side are fixed on the upper wall of the finger sleeve, and the light-emitting wavelengths are respectively 660nm red light and 940nm infrared light. The lower wall is a photosensitive receiving device, which converts the red and infrared light transmitted through the finger into electrical signals. When the oximeter is running, the time-sharing driving circuit makes the two light-emitting diodes emit light at a certain time interval and with a relatively low duty cycle. Calculate the whole blood absorption rate a660 and a940, and then combine the experimental calibration coefficients A and B, and substitute them into a special formula to calculate the value of blood oxygen saturation.
▲ Finger oximeter
Centaurus blood oxygen optical sensor
The SpO2 blood oxygen optical sensor developed by FATRI is a sensor that provides blood oxygen saturation measurement using a new optical measurement method, which can perform high-precision blood oxygen level detection and has the best flexibility to accommodate multiple wavelength options. The KGXV01 series of sensors are specially developed and designed for medical applications with the critical requirement of peak wavelength selection. The source material is GaAIAs combined with GaAIP with a clear epoxy lens. Due to FATRI’s ability to provide components and complete sensor packages, this sensor is characterized by high precision, durability and high performance.
▲Related parameters of FATRI KGXV01 series sensor
FATRI Health and Medical Division focuses on the research and development, production and sales of health and medical high-tech products. In the future, FATRI will be committed to using modern advanced materials science, sensing technology, molecular biology and artificial intelligence technology to develop new products for treatment, surgical assistance, detection and postoperative detection. Combining detection technology, Internet technology and the medical industry, we deeply explore the meaning behind various health data, and strive to use disruptive technology to solve the pain points of human health and improve human health.