Innovating On Dynamic Respirometry Based On Bio-impedance Method

Respiration is one of the most basic physical activities, which is necessary to maintain human life. Through respiration, human intake oxygen from the external environment constantly in order to oxidize nutrients in vivo. At the same time, carbon dioxide is eliminated from the body, which is produced on oxidation, so as not to disturb the body functions of an excess of carbon dioxide. Therefore, respiration is an important physiological process of human body, and the guardian of human respiratory care is an important part of technology of modern medicine.With the improvement of people's living standards and health concern for themselves, the emphasis is moving from hospital to communities and families. Therefore, portable monitoring equipment which can realize real-time, dynamic and continuous monitoring of human physiological indexes is the first choice for the future health care. But the existing breathing monitor only serves as the bed guardianship in the hospital, which made it difficult to move toward the community and the family. Therefore, the development of a portable breathing monitor becomes a trend. Modern guardianship technology requires continuous monitoring of various physiological parameters, making it non-invasive, accurate and stability, minimize discomfort, without any allergies, which has many problems to be resolved. At present, it is difficult to realize real-time monitoring equipment with continuous monitoring of respiratory parameters. Respiratory frequency is an important parameter of respiratory behavior, through which we can obtain much internal physiological information, and its detection is also easier to achieve, so the respiratory frequency is the main monitor object of the existing breath guardianship equipment.At present, the most commonly used respiratory detection method is bio-impedance method. It is non-invasive, safe, simple and cheap. However, because respiratory signals are low-frequency signals, it is vulnerable to the effects of interference, such as heartbeat, blood stream, motion artifact and so on, and the influence of motion artifact is especially significant. Therefore, it is difficult to identify respiratory waveform. Over the years many scholars at home and abroad have been discussing how to reduce interference in respiratory detection, especially motion artifact, but it has not been resolved, some explorative research was mentioned in order to solve the problem, the main point of the paper is how to reduce the interference to obtain smooth respiration signal, and improve its dynamic adoptability.This paper based on bio-impedance method which is used in the detection of respiratory signal. In view of the shortcoming of traditional two-electrode method and four-electrode method, the author mentions some explorative research on how to reduce noise. Since respiratory signal has the characteristics of cyclical, and the interference signal has a characteristic of randomness, a new method of combining time-domain filtering with spatial filtering has been presented. By increasing electrodes in space, that is combining the multiple respiratory signals to reduce the effects of interference, such as heartbeat, blood stream, motion artifact and so on, and verified by the experiments on the chest at different location of the electrodes of the waveform. On that basis, we has carried on the observation and comparison to the following 6 kind of situations: (1) traditional two-electrode method; (2) traditional four-electrode method; (3) two-way respiratory signal (four electrodes) in the airspace and the time-domain filtering; (4) two-way respiratory signal (eight electrodes) in the airspace and time domain filtering; (5)three-way respiratory signals (six electrodes) for airspace and time-domain filtering; (6) four respiratory signal (eight electrodes) in the airspace and time domain filtering. Finally, method (4) was chosen because of its high stability and good result.To test the method, a low consumption and portable type instrument has been designed based on MSP430 Micro Controller Unit (MCU) with this method. In the hardware design, the improved envelope detection circuit has been used to enhance the breath signal demodulation effect; and the using of second-order Butterworth low-pass filter has effectively reduced the effects of interference, after that, signal attenuation is small and denoising effect is nice; In the software design, we applied the moving average artithmetic and median value average method to reduce the noise of signal, which make respiratory signal steady and smoothness. In order to test the anti-jamming ability of the prototype, human experiments have been conducted, and human experiments proved that the instrument can reduce interference on the effects of respiration, and obtain the smoother breath waveform for the respiratory rate calculability.