Portable Non-invasive Digital Pulse Oximeter Designed Study

Oxygen Saturation monitoring offers perfusion information of organization. It can help understanding the oxygen carrying capacity of the blood of patients, which has been widely used in various health care situations. Health care system has been changed from traditional concentration diagnosis and treatment in large hospital to community and home health care. It is now necessary to develop portable medical machine with low-cost and low-power to improve the health conditions of patients. Though traditional invasive blood oxygen test was accurate, it always brought patients the pain. Besides, it could not perform continuous monitoring. Non-invasive Oxygen Saturation monitors used in domestic routine monitoring today have disadvantages of high import cost, high power consumption, poor interference immunization, and small detection range.In this article, we first depicted the principle and method of non-invasive blood oxygen monitoring. Then, we analyzed the traditional discrete component design based on analog probe, modified Single Chip Module (SCM) design based on analog probe, and widely used design based on digital probe. Next, we compared the advantages and disadvantages of various designs based on the characteristics of blood oxygen signal. After that, we design a new low-cost low-power digital pulse blood oxygen monitor. In the design, a high resolution digital detector based on light-frequency converter was adopted to improve precision and detecting range, A DC tracking filter was planted to remove baseline-drift to improve anti-interference capacity, and a pulse rate detection algorithm using rising and falling edge was applied to improve detection accuracy. By this design, stable pulse waveform and pulse rate could still be captured when body moved gently and fingers trembled slightly. After repeating the experiment under different conditions of Fluck Index2 oximeter simulator, we found that the accuracy was 1% when oxygen saturation at 35% to 100 %, the accuracy was 4% when low perfusion at value of≤0.2%, and the pulse rate error is less than 1. It indicates that the design had been improved the precision, detecting range, repetitiveness and anti-jitter to a certain extent. It is suitable for the application of families, communities and other medical care occasions.