Research On Novel Pulse Oxygen Saturation Measurement System

Oxygen saturation is one of the most important biological parameter to evaluate human health. The scattering effect of human tissue and blood is ignored in traditional method to measure oxygen saturation. The measuring error is inevitably large and will become larger when oxygen saturation reduces. To improve the measuring accuracy, this paper presents a novel method. A new measuring system has been designed. And the feasibility of new method and the ability to improve the measuring accuracy are preliminarily proved by Monte Carlo simulation and experiment. The main research work includes:This paper reviews traditional method to measure oxygen saturation and its research situation and points out the limitation of traditional method based on Lambert-beer Law and the reason of large measuring error in the situation of low oxygen saturation and hypoperfusion. The traditional method is a process of dimensionality reduction, which loses information, introduces the system error and limits the precision of measurement when taking scattering into consideration.From the standpoint of the quantity of information, this paper presents a new method that the peak and valley values of dual-wavelength logarithmic photoplethysmography waves are used as the independent variables to develop a linear regression model to predict the arterial oxygen saturation. Two methods of extracting the characteristics(in time domain and in frequency domain) are proposed to match three ways of distinguishing different wavelength channels(time division, frequency division and grating spectroscope). And the relevant matlab programs are developed. Under the premise of considering the influence of scattering and kinds of individual difference, the paper simulates the transmitted light intensity distribution of photon through the finger tip model with Monte Carlo simulations method, and the characteristic quantity of the photoplethysmography waves are calculated meanwhile. The partial least squares fitting method is used to build the linear regression model of the relationship between oxygen saturation and characteristic quantity, and the predicted effect using the new method is compared with the one using R value method. From the perspective of simulation, the new method is verified.This paper presents the design idea of new type pulse oximeter, namely photoelectric signal is acquired by the high-precision AD, so that it can replace many hardware which is needed in analog pulse oximeter, as well as the control methods and feedback algorithm in digital pulse oximeter are simplified. Moreover, this paper elaborates the system solutions, the hardware circuit diagram and relevant software flow pattern of the new type pulse oximeter. Finally, the novel pulse oximeter is successfully developed, as well as the upper computer visual interface, which provides a platform for the effective implement of the new measuring method.The preliminary validation experiment based on the new oxygen saturation measuring platform is designed and the change of oxygen saturation during the experimenter's labored breathing is acquired, as well as the characteristic quantity of the photoplethysmography waves is extracted. The traditional R value method and the new method for oxygen saturation calculation formula are fitted by the partial least squares fitting method, and the feasibility and the ability to enhance oxygen saturation measurement accuracy of the new method are verified.