Development Of Oxygen Saturation Monitor With ZigBee Communication

Oxygen is an important element to keep human body alive, and oxygen saturation isan important vital sign to reflect oxygen ying situation of human body. It is closely linke d to the body's cardio-pulmonary system, respiratory system and circulatory system. Once the oxygen is unable to be delivered to the brain and heart, ultimately it will lead to the death of human body. Therefore, monitoring the oxygen saturation has important practical value and significance.The dissertation originated from the project of "the Research of Wearable Non-invasive Continuous Monitoring of Human Body Parameters", funded by the Science and Technology Agency of Jilin Province, to complete the task of oxygen saturation and pulse rate measurement. In the dissertation, the two-wavelength transmission-type non-invasive measurement was adopted, using the technology of photoelectric detection, MCU, ZigBee wireless communication and data processing, to design an oxygen saturation monitor with ZigBee communication.On the basis of analyzing and understanding the oxygen saturation monitor at home and abroad, the dissertation studied the theory of oxygen saturation measurement and the optical model of human tissue, and deduced the theory calculation formula of measuring arterial oxygen saturation, using Lambert-Beer law and Photo PlethysmoGraphy. It completed overall plan design of oxygen saturation monitor with ZigBee communication, and analyzed the three key technical problems that likely to be encountered, according to the main characteristics of the monitor.The design of the monitor's hardware platform took MSP430 MCU (Micro Controller Unit) as the core, coordinating and controlling other functional modules, to extract the analog signal of human pulse wave. In all, five functional modules have been completed: the oxygen saturation probe module with the optical modulation function of pulse signal on finger tip; the signal conditioning module with the function of signal amplification, separation and filtering; the human-computer interaction module with the function of operation setting and data display; the power module with the function of power supplying to other modules. In the dissertation, the schematic circuits and device parameters of the designed modules have been given in detail. After the tests, it shows that the hardware platform developed works normally and can extract the complete human pulse wave.MSP430 MCU is a microprocessor with online-programming function. With modular design method, using the IAR Embedded Workbench (V3.42A) software, the dissertation completed the programs corresponding to those functional modules of the monitor, such as the pulse wave signal acquisition subprogram, the DAC control subprogram of light intensity, the digital filtering subprogram, the pulse wave extraction subprogr am, thereal-time control subprogram, the and data display subprogram, the alculation subroutine of R, pulse and oxygen saturation, etc. In order to construct the monitoring system with other physiological parameters monitors, the dissertation wrote the data communication protocol, and gave a detailed description about its format and content.In order to get credible test results, the dissertation directly obtained the experimental data from the human body to plot the calibration curve, and completed the calibration experiments of the monitor under certain conditions. Ultimately, through the data analysis, it worked out the empirical formula of the SpO2:SpO2=-108.8207R2+130.2099.R+59.1806Contrasting the oxygen saturation monitor developed with the PM-9000 (Expresse) portable multi-parameter monitor that the First Hospital of Jilin University used for clinical application in respiratory medicine, the technical specifications of the oxygen saturation monitor were concluded. The measuring range of SpO2 is 0 to 100%, itsaccurac10y is±3% (80% ~ 100%), and its display resolution is 1%. The measuring range of pulse is 0 to 300 beats/min, its accuracy is±3%, and its display resolution is 1 beat/min.It is thus clear that, the oxygen saturation monitor with ZigBee communication developed obtained credible results, achieved the desired design specifications, and provided the foundation for the research group of the project to commercialize the instrument later.