The Development Of Medical Breath CO₂,NO₂ And O₂ Measurement System

Carbon dioxide and oxygen from the breath involved in the body's metabolism and exchanged in the lungs of the human body. Changes in concentration of the two substances directly reflects the state of the body's metabolism, breathing and pulmonary circulation.Nitrous oxide as an anesthetic gases used in clinical applications, and it is widely used in obstetrics and gynecology, dentistry and anesthesia. Monitoring the concentration of carbon dioxide, oxygen, and nitrous oxide in clinical surgery, can monitor the patient's physical conditions and the breathing machine fault, guiding doctors to operate breathing machine,effectively improve the safety of the procedure, in order to ensure the security of the patient's life provides a protective mechanism, reducing the occurrence of medical accidents, is of great significance to the development of healthcare idustry. At present, the domestic for multi-gas measurement technology research less, multi-gas module are mostly from abroad, it is expensive, based on this, this paper developed a small sidestream of carbon dioxide, nitrous oxide, oxygen measurement module.Multi-gas measuring module adopts Non-Dispersive Infra-Red(NDIR) method and digital oxygen sensor to achieve carbon dioxide, nitrous oxide and oxygen concentration detection, the major works comprise research about the key components and measurement method based on infrared spectrum, the scheme design of measurement system, and the module system of machinery, hardware, software, compensation algorithm research and engineering calibration and so on several aspects has carried on the detailed design, especially in the aspect of signal extraction and feature analysis in-depth research, synchronous extract high quality CO2 signals and N2 O signals to calculating parameters. Consider the resources of multi-gas detection software and multi-channel demand, this paper adopts STM32F4 series microcontroller and 8-way chopper structure of Synchronous signal detection scheme,provides a hardware platform and machinery platform for the multi-gas monitor study of future.In this paper, the medical devices industry standards of respiratory gas monitors as thebasis to develop a multi-gas module verification program. Through multi-gas module system testing, as well as the validation data and analysis results show that the multi-gas module designed in this paper has good stability, accuracy and validity, the precision of CO2 and N2 O :±(0.2 vol% + 2% of reading) and ±3.0 vol%, exceeded the standard requirements, and the minimum suction flow rate can reach the degree of microflow 50 ml/min. Finally, the paper summarizes the deficiency of the module at present, the current progress in the study of gas detection and the future research work of multi-gas measurement.