Design Of A Noninvasive Test Method For Human Arterial Oxygen Saturation On Adaptive Filter

The paper introduces the non-invasive detection method of Arterial Oxygen Saturation. The noninvasive testing circuit of arterial oxygen saturation is designed. And making efforts to improve the test accuracy in motion, restrain the impact of human scattering process.By study the content of absorbing substance in human tissue and its near-infrared absorption spectrum, it discuses the near-infrared light absorptive amount of oxyhemoglobin and deoxygenated hemoglobin can be changed due to pulsation, but the absorptive amount of other human tissue keeps mostly unchangeable. The paper puts forward that the photon propagation average path length in modified Lambert-Beer equation is introduced into the calculation formula derivation of oxygen saturation, and the 730nm and 940nm near-infrared led which has little influence on the human scattering process is used for testing light source, in order to reduce the test error which is caused by human scattering effect.The noninvasive test circuit of body arterial oxygen saturation is designed according to the photoplethysmography of pulse wave. The high frequency interference of the stray light is attenuated which is based on the method of frequency range. The driving circuit of testing source and anti-Rossi circuit of compound signal are controlled by DSP sequence signal, so the sending testing signal is synchronous with the separation-receiving signal. The constant and pulsating segment is extracted respectively from second-order high-pass filter and low-pass filter. According to the characteristic of the physiological signal, the reverse phase circuit and AC signal amplifying circuit is used respectively for raising the testing precision.The adaptive LMS filter is adopted to eliminate the motion artifact of which the frequency domain overlaps the useful signal, thus raising the testing precision in motion. The paper proposes using the delay signal of pulsating quantity as input reference signal of the adaptive filter, thus benefiting simplified the design of hardware structure.