Pulse Oximetry Based On Dynamic Spectroscopy

Pulse oximetry is a reliable, arterial, noninvasive easy continuously determining oxygen saturation to use means in virtually of any setting. Because there are still several drawbacks in the design of the pulse oximetry system and its signal processing, the system needs improving in accuracy, repetition and stability. Most of the conventional pulse oximeters use analog techniques to accomplish a series of tasks such as the modulation, the demodulation, the separation of two wavelengths of lights, the separation of AC and DC, the filtering, the extraction of photoplethysmography characteristics and so on. These processing approaches not only increase the complexity of the system but also greatly decrease its reliability and stability. To avoid all these defects we proposed methods of designing a digitized pulse oximetry system. In this system, we used a high speed A/D converter oversampling the analog signal, to improve resolution. Then the digital signal processing methods were used to replace the conventional analog circuits to complete a series of work so as to improve the performance character of the pulse oximeter. We mainly performed the following research work to achieve this goal.Firstly, a digital pulse oximetry system was designed. Oversampling methods for ADC are based on sampling an analog signal at a much higher rate. That higher sampling rate makes it possible to increases signal-to-noise ratio and the effective resolution of the conversion. We used this method to increase the effective resolution of the ADC in signal measurement,especially for the tiny signal measurement. With this method, a series of conventional analog circuits were omitted.Secondly, the measuring principle of the pulse oximeter is based on traditional test method. Its accuracy is not gratifying due to various factors influencing the measurement result, such as the principle, measuring condition and individual discrepancy. In this system a new pulse oximetry based on dynamic spectroscopy (DS) is introduced, it can promote the accuracy of the pulse oximeter evidently. The dynamic spectroscopy method is able to eliminate the interference of the individual discrepancy and measuring condition in principle. This new method can eliminate the measurement error of pulse oximetry theoretically.Finally, the method of extracting the photoplethysmography is frequency division multiplex light modulation. And we use digital demodulation method to recover the sampling signal to analog signal.