Research On Arterial Blood Pressure Estimation Using Pulse Wave

OBJECTIVE:Arterial blood pressure is an important physiological parameter for the assessment of cardiovascular function; it is widely used in disease diagnosis, clinical application as well as in prognosis, so it is very important to measure it precisely. At present, discontinuous blood pressure measurement methods such as Korotkoff Sound Method are main methods in clinical application. However, these methods can only examine blood pressure value at a specific time and can not inspect the change of beat-to-beat blood pressure continuously. On the other side, compared with the result of invasive arterial blood pressure measurement, these methods are prone to significant errors. According to this situation, this study is proposed to describe the relationship between pulse wave transit time (PWTT) and arterial blood pressure (ABP) and discuss the reliability of continuous estimation of ABP using PWTT.METHODS:The following research work has been carried out in this study:1. Using the MIMIC database offered by Massachusetts Institute of Technology (MIT), firstly we get the electrocardiogram (ECG), Photoplethysmography (Pleth) and invasive arterial blood pressure (ABP) data from the database, and then calculate PWTT from ECG and Pleth. Meanwhile, mean blood pressure (MBP) is acquired from invasive ABP. Linear regress method is used to derive the equation of PWTT and MBP. Then the estimation of MBP is calculated through the equation and is compared with the real value for assessment.Based on the results of above research, by setting up a hardware and software platform for data acquisition, we collect patients'physiological signals in ICU of the Fourth People's Hospital of Jinan, and test the accuracy of continuous estimation of ABP using PWTT. The research work involves several aspects as follows:(1) The acquisition of multi-channel physiological signals. Establish the interface of data acquisition system by using LabWindows/CVI. One-wire linked electrocardiograph is acquired using electrocardiograph sensors designed and welded by ourselves; patients' pulse wave is obtained by HK2000B pulse wave sensor. Analog signals acquired by above sensors are converted to digital signals by National Instrument's USB-6211 data acquisition card. Patients' invasive arterial blood pressure is obtained using PowerLab data analysis recorder system.(2) Data processing. Data processing is performed largely by MATLAB7.0 software, included the peak point detection of ECG R Wave, the characteristic point detection of pulse wave, the calculation of PWTT and MBP. After that, the equation between PWTT and MBP is obtained through linear regression analysis, and then root mean square error (RMSE) is calculated.RESULTS:ABP has a typical negative linear correlation with PWTT. Within the scope of certain time, MBP can be estimated using PWTT, and RMSE is less than 5mmHg. The result of clinical sampling data analysis points to the same conclusion, the method is feasible for noninvasive continuous ABP monitoring.Estimation of ABP using PWTT is only suitable for short time, while the change of ABP is not dramatic. For long time medical care (such as more than 24 hours), the factors that affect arterial blood pressure, such as cardiac output, peripheral resistance, elasticity of blood vessels, change significantly, the fluctuant range of ABP is also large. PWTT can not synchronously track the large variations of ABP.On the other side, for different experimental subjects, the equation between ABP and PWTT is not the very same. It shows the effect of individual difference on the correlation can not be ignored.CONCLUSION:Estimation ABP using PWTT has better practicability and spread potentiality. On the base of the above research, continuous estimation of ABP has higher measurement accuracy and simple operation; also it can reduce health-care spending and the burden on society.Based on the existing research level, estimation of ABP using the same transform function for all patients is not suitable; it will lead to serious errors, so we should seriously consider the effect of patients'individual difference. In the future research, we should take full consideration of the effect of patients' emotions, conditions and physiological status on ABP, improve the precision of long time ABP monitoring, get ready for the further clinical research and application.