| With the development of economy and technology,sedentary lifestyle is becoming more and more common.Maintaining a long sitting position without physical activity is potentially harmful.Sitting for a long time can lead to the decline of heart function,easily cause chest tightness and even cause cardiovascular disease such as myocardial weakness,arteriosclerosis and coronary heart disease.With the urgent need for people to understand their health,conventional monitoring methods such as electrocardiograms and polysomnography have been unable to meet the needs of people in daily life to prevent diseases,the main reason is that the current monitoring equipment has constraints,complicated operations and high costs,so it is impossible to carry out personal daily monitoring.At the same time,as important information reflecting the physical condition of the human body,the changes of heart rate and respiration rate are important contents of daily monitoring.However,although devices such as smart bracelets on the market are less restrictive,they cannot obtain successive heartbeats and respiration intervals,so their clinical value is not high.In response to the above needs and problems,this paper has launched research on unrestrained monitoring of heart rate and respiration rate in a sitting postion.(1)Detection Systems: By introducing the characteristics and principle of generation of ballistocardiogram(BCG)signal and respiration signal,a method based on the collection of body vibration signal is proposed,it uses PVDF piezoelectric film sensor to collect BCG signal and respiration signal in human sitting position,the charge amplifier and host computer are combined,a heart rate and respiratory rate monitoring system for a sitting posture is set up.(2)Heart rate and cardiac cycle extraction method: for the shortcomings in the current cardiac cycle extraction method based on BCG signal,an extraction algorithm of cardiac cycle based on the maximum J peak of BCG signal is proposed.First,the original BCG signal is preprocessed,which mainly include baseline drift and removal of high-frequency interference signals.Then the short-term autocorrelation and the short-term average amplitude difference function are used to construct the heartbeat cycle function.And windows are divided according to the estimated value to find the maximum J peak of BCG signal.Finally,the heartbeat template of the current BCG signal is constructed according to the J peak,and the template is used to locate the successive heartbeat position to obtain the heart rate and cardiac cycle.(3)Respiration rate and respiration interval extraction method: the original respiration signal is preprocessed including baseline drift and high frequency interference signal removal,then the threshold empirical formula is established by combining the period and amplitude characteristics of the respiration signal.Finally,the respiratory peak position is adaptively located by dynamically updating the threshold value to extract the respiration rate and respiration interval.(4)Medical contrast experiment: the extraction method in this paper is compared with the results from polysomnography.The results extracted by two methods in different sitting postions are compared by the mean error and period mean difference: the average error of heart rate does not exceed 2.41%,the accuracy rate is not less than 97.59%,the average difference of cardiac cycle does not exceed 30ms;the average error of the respiration rate does not exceed 3.92%,the accuracy rate is not less than 96.08% and the average error of the respiration interval does not exceed 144.48 ms,the results show that the extraction method of cardiac cycle and respiration interval in this paper has high accuracy and stability and can meet the daily unbound monitoring of individuals physiological information. |
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