Design Of Continuous Non-invasive Blood Pressure Monitoring Device Based On Constant Volume Method

As a basic feature of the blood circulation system,the information of blood pressure can provide a basis for doctors to diagnose the disease as soon as possible.Nowadays,with the rapid development of economy,the tempo of people’s life is speeding up and people with cardiovascular diseases is increasingly growing.Through the measurement of blood pressure,can help to understand the changes in blood pressure fluctuationsin the human body,which is conducive to the doctors’grasp of the patient’s condition.However,human blood pressure is by no means constant,which will subject to human’s emotions,physical movement and the external environment and so on.In emergency surgery,the blood pressure of the patients is more unstable,so continuous monitoring of blood pressure is of vital importance.Therefore,continuous development of non-invasive blood pressure monitoring equipment is urgently needed to meet the clinical needs.The constant volume method used in this paper is a kind of continuous non-invasive blood pressure monitoring method.Firstly,according to the photoelectric volume recording method（PPG）,the volume target value V₀ is found out when the blood vessel is in unloading state by the principle of oscillometric principle.To maintain the volume of the vessel always in the unloading state,that is to say,the pressure difference between inside and outside of the vessel will always be zero by continuously adding pressure or reducing pressure to the finger sleeve.At the moment,the external pressure measured by the pressure sensor is the internal pressure of the blood vessel,so that the blood pressure can be monitored accurately for a long time.In this paper,continuous non-invasive blood pressure monitoring device based on constant volume method will be presented,which is divided into signal acquisition and feedback control system of lower computer,data processing,display and management software of upper computer.The main works of the lower machine are to design the ring device,which is capable of collecting real-time finger arterial volume signals;continuously compare the finger artery volume V with the target value V₀;and use the STM32 single chip microcomputer to call the PID algorithm.After the output PWM wave is combined with the driving circuit to control the rotational speed of the air pump and the opening of the proportional valve,the compression and pressure relief of the finger sleeve can be realized.What’s more,the information that needs further processing will be transmitted to the uppercomputer data processing and display software hrough the serial port.The uppercomputer data processing and display software is completed by QTcreator.The main functions of the software include digital filtering,calculating systolic and diastolic blood pressure according to dynamic differential threshold method,calibrating finger artery blood pressure,real-time display of blood pressure waveform,storage and viewing of continuous blood pressure data per bout,etc.In this paper,Various parts of the function and overall performance of the continuous non-invasive blood pressure monitoring device has been tested and the function of each part of it has been verified so as to meet the design requirements.And through the comparison of the designed experiment and the analysis of the experimental results,it is shown that the device can achieve consecutive and accurate monitoring of blood pressure.Finally,this paper will give a brief summary of the whole contents,point out the deficiencies that need to be improved and show the author’s prospects for future research in this field.