Study On Impedance Cardiogram Detection And Analysis Method

Cardiovascular diseases threatened human physical and mental health seriously,and the morbidity and mortality remained high.Impedance cardiogram and electrocardiosignal can objectively reflect the physiological condition of human heart,therefore,synchronous detect impedance cardiogram and electrocardiogram can better know the health status of heart,meanwhile,hemodynamic parameters such as stroke volume and cardiac output can also be calculated according to impedance cardiogram,the detection effect is more comprehensive than measuring ECG signals alone.Firstly,a non-invasive impedance cardiogram detection system is designed based on impedance method.The system consists of hardware and software,hardware is mainly composed of incentive source module,impedance cardiogram detection circuit and electrocardiogram measurement system.In order to obtain sinusoidal voltage signal with adjustable frequency and stable waveform,Choosing DDS technology design incentive source,the constant current source for the impedance cardiogram detection system must meet special requirements such as higher output impedance and current accuracy,designed a voltage-controlled current source with low power consumption and high precision combine the second generation current mirror;after the constant current from excitation source injected into thoracic cavity,the thoracic impedance signals collected by the detection electrodes have denoised,envelope detected,differentiated and amplified can obtain DC impedance,AC impedanceand its differential signals respectively;the ECG measurement system mainly consists of amplification,notch filter,right-leg-drive and level elevation.In software part,the signals detected synchronously are filtered twice,selecting Equiripple Band-Stop filter to eliminate power frequency interference;using Butterworth filter and High-Pass filter to filter high-frequency noise and baseline drift,and locate the relevant feature points in the denoised signal.Then,using impedance method calculate cardiac hemodynamic parameters,the left ventricular ejection time can be estimated in the differential impedance cardiogram,but it has some inaccuracy.Because of the system adopts synchronous detection mode,for the purpose of reduce calculation errors,based on the periodicity corresponding relationship between electrocardiogram and impedance cardiogram in time domain,the characteristic points of ECG and ICG signals are marked respectively,calibrate left ventricular ejection time by QT interval,QRS interval and RR interval in electrocardiogram,an improved method for calculating stroke output is proposed.Finally,the cardiac function parameters of 12 healthy subjects were measured under four experimental conditions by using impedance cardiogram detection system combined with improved calculation method.The results show that in actual measurement the system can detect the ICG and ECG signals in human thoracic cavity completely and clearly,the relationship between cardiac impedance and ECG signals is right;When measuring state change,the improved method calculated the left ventricular ejection time more stable,and the difference of stroke output is more obvious,the cardiac hemodynamic parameters of 12 subjects were within the normal range.Therefore,the hardware system and improved method can be used to measure human cardiac function parameters.