Research On Wrist-wearing Blood Pressure Measurement Device Based On Tonometry

Cardiovascular disease has posed a great threat to human health.In China,cardiovascular disease is the most common cause of death for urban and rural residents.And for cardiovascular disease,hypertension is a significant risk factor.Strengthening blood pressure monitoring can effectively reduce the mortality rate of hypertension.People's blood pressure varies with the physiological rhythm.The current commonly used intermittent blood pressure measurements can only provide the blood pressure at the time of measurement,which will cause that individual measurement results are quite different.However,continuous blood pressure monitoring can provide richer and more comprehensive records of information.A comfortable,portable,safe and reliable real-time blood pressure monitoring device will be a solution to manage blood pressure.Arterial tonometry(AT),one of the non-invasive continuous blood pressure monitoring methods,has high accuracy,but it requires professional operation to make the sensors at the optimal measurement spot,which seriously affects its promotion and application.In this paper,a noval alignment-free blood pressure sensor with flexible membranes encapsulating the fluid(bp-SFMEF)is proposed,which is based on the physiological structure of finger and PASCAL's principle.The elastic membranes of sensor are made of PDMS flexible material,which ensures the safety and comfort when it contact with skin.And the pressure transmission of the sealed liquid can overcome the disadvantage of uneven stress distribution in elastomer.Based on this,the hardware and software of a wearable tonometer for blood pressure measurement are developed.The system communicates with the host computer through bluetooth with low power consumption.Meanwhile,the pulse wave signal processing and feature extraction are further studied.The experimental results show that the measurement results meet the AAMI standard.The main research work of this paper is summarized as follows:(1)The finite element model of skin and radial artery was established to analyze the distribution of arterial pressure on skin surface.According to the actual measurement by AT,the requirements of flexibility and position fault tolerance are put forward.Inspired by the physiological structure of finger and PASCAL's principle,we propose the bp-SFMEF.By establishing a one-dimensional spring-mass-damp mechanical model,the influence of stiffness and damp parameters of the sensor is analyzed during measurement.Based on the principle of solid-liquid coupling,the finite element simulation model is further established to analyze its position fault tolerance.Subsequently,through the process of film forming,gold wire bonding and vacuum liquid sealing,the bp-SFMEF is fabricated.The test results show that the bp-SFMEF has great linearity and position fault tolerance.(2)In order to meet the requirements of miniaturization,low power consumption and portable convenience,the prototype of wrist-wearing blood pressure measuring device based on AT is developed both in hardware and software.In hardware,chip selection and circuit design of the signal conditioning,BLE system on-chip,accelerometer and power management are completed.In the software,the design of hardware driver,the setting of BLE parameters,blood pressure measurement,and the development of Android application software are realized based on hardware design.(3)A new cascaded framework of pulse signal pre-processing and feature extraction is proposed.Smoothed by dual-density wavelet transform filtering,the raw signals of pulse wave then remove baseline drift by mathematical morphology or cubic spline interpolation.Finally,a modified slope sum function can dectect wave peaks robustly.Quality evaluation is carried out to remove bad signals.The experimental results show that the algorithm can effectively improve the signal-to-noise ratio of pulse wave,reduce the mean square error and improve the accuracy of feature extraction.