Research On Transmission Blood Oxygen Content Monitoring System Based On Near-infrared Light

Oxygen saturation refers to the proportion of oxygenated hemoglobin of the total hemoglobin in the blood, which can accurately reflect the oxygen content within the organization as well as a measure of the body’s oxygen metabolism, and it has important significance in the process of respiratory system, cardiac disease prevention, medical diagnosis and clinical nursing and so on.The mathematical relationship between the tissue blood oxygen content and the near infrared light transmission intensity is established, based on the infrared spectroscopy(600~1300nm) technology in noninvasive blood oxygen content detection theory and the absorption differences of reduced hemoglobin and oxyhemoglobin in the near-infrared spectral, combined with the Lambert Beer law. This paper designed a noninvasive and real-time response tissue blood oxygen content monitoring system, with STM32 as the development platform.The whole system is mainly divided into three parts: light source, extract the signal, the signal processing and so on. The basic working process of the system as follows: A square wave signal with a duty cycle of 75% driven by a microprocessor drive a red light and a near infrared light diode, to avoid the interference between the afterglows. The optical signal carrying blood oxygen content is converted into a voltage signal through the photosensitive sensor. According to the characteristics of the output voltage signal of the photosensitive receiving device,this paper designed a lock-in amplifier to detect the voltage signal, amplification, demodulation, phase sensitive detection, wave filtering included. The signal is fed into the STM32 microprocessor and the data acquisition channel is sampled. Using the bubble method eliminates the extreme value which could reduce the influence brought by signal mutation situation. The signal is processed by the microprocessor, and then the final monitoring results are output.At last, the performance of the system is tested and the results show that the system designed in this paper is reasonable and practical and has good stability, which achieves the design goal. This system has the advantages of real-time, continuous and noninvasive, which has great significance in the monitoring of blood oxygen content.