Seeking detailed development process and principle of electronic sphygmomanometer

The principle of electronic sphygmomanometer and verification At present, more and more digital electronic sphygmomanometer into the medical and health supplies market, there are a large number of non-invasive blood pressure monitor used for clinical purposes in the health care system and multi-parameter monitor and other equipment, which *** with the same characteristics of the dynamic non-invasive measurement of the human body's blood pressure (systolic and diastolic blood pressure). The accuracy of blood pressure measurement is related to the lives and health of the general public. The state listed the sphygmomanometer as the national compulsory verification of measuring instruments. At present, most of the non-invasive electronic sphygmomanometer using oscillometric method of blood pressure measurement. Measurement department of these blood pressure measuring instruments can only check its static indicators, for its measurement of blood pressure (systolic diastolic blood pressure) accuracy of the test, there is no really feasible methods and means. Therefore, it is necessary to oscillometric method of electronic sphygmomanometers to measure the accuracy of blood pressure calibration method to explore. I. Principle of oscillometric electronic sphygmomanometer Blood pressure is the lateral pressure of the blood in the blood vessel for the unit area of the vessel wall, that is, the pressure. In other words, the static pressure of blood in a blood vessel is blood pressure. The blood pressure in the human body varies in a time cycle, with systolic blood pressure being the maximum value of blood pressure and diastolic blood pressure being the minimum value of blood pressure, as shown in Fig. 1. Fig. 1 The quantities that a sphygmomanometer measures are systolic blood pressure and diastolic blood pressure. The oscillometric method of measuring blood pressure, on the other hand, is when the pressure of the cuff strapped to the arm is about 60 mmHg above the systolic pressure of the blood vessels, which are blocked. As the cuff pressure drops, the blood vessel is turned from blocked to open, and this process generates a series of small pulses in the cuff, see Figure 2. pick up the small pulses and connect their peaks to form a curve, resulting in an envelope, see Figure 3. according to the shape of the envelope, find the corresponding characteristic points to identify systolic and diastolic blood pressures. Fig. 2 Fig. 3 The shape of the envelope is mainly influenced by systolic and diastolic blood pressure, blood vessels and mechanical properties of the arm. Among them, systolic and diastolic blood pressure are the main influencing parameters. The oscillometric method of blood pressure measurement does not have a sound theoretical derivation, so that the determination of the characteristic points can only rely on the statistical generalization of the collected samples, and thus it can be said that the oscillometric method of blood pressure measurement is a statistically based method with a certain degree of discrete nature. II. CALIBRATION METHOD The calibration of the electronic sphygmomanometer by the oscillometric method is divided into two parts: static and dynamic. The static calibration refers to the calibration of the accuracy of the sphygmomanometer sensor pressure measurement. This is a routine calibration and is not discussed here. Dynamic calibration refers to the calibration of the accuracy of the sphygmomanometer in measuring systolic and diastolic blood pressure. At present, there is no really feasible method of dynamic calibration of sphygmomanometers at home and abroad. This article focuses on the discussion. 1. It can be seen from the measurement of sphygmomanometer, the most effective method of dynamic calibration is to produce a standard systolic and diastolic blood pressure, to the sphygmomanometer measurement. The difference between the sphygmomanometer's measurement and the standard value is the basic error in the sphygmomanometer's measurement of systolic and diastolic blood pressure. △Pd=Pdj-Pdb; △Ps=Psj-Psb; where: △Pd: the basic error of diastolic pressure of sphygmomanometer; △Ps: the basic error of systolic pressure of sphygmomanometer; Pdj: diastolic blood pressure measurement of sphygmomanometer; Pdb: the standard value of diastolic blood pressure; Psj: systolic blood pressure measurement of sphygmomanometer; Psb: the standard value of systolic blood pressure. There are two main parts to this method: generating a standard systolic and diastolic blood pressure; and making that standard value measurable by the sphygmomanometer. (l) Generate standard systolic and diastolic blood pressure From the definition of systolic and diastolic blood pressure, it can be seen that the generation of standard systolic and diastolic blood pressure is actually to produce a standard analog blood pressure wave, so that the accuracy of its peaks and valleys should meet the requirements of the calibration. From the definition of blood pressure can be determined: since blood pressure refers to the static pressure, so regardless of the simulated blood pressure wave pressure medium is liquid or gas will not produce additional uncertainty on the calibration. (2) To enable standard systolic and diastolic pressures to be measured by the sphygmomanometer. Oscillometric method of electronic sphygmomanometer (hereinafter referred to as sphygmomanometer) is by wrapping around the arm in the cuff in the pressure from high to the bottom of the change process, the arm brachial artery from blocking to conduction, so that the cuff in the cuff superimposed on a series of small pulses of pressure. The sphygmomanometer senses these signals and, after certain operations, finds the systolic and diastolic pressures of the human brachial artery. (Wrist-type oscillometric electronic sphygmomanometer principle and arm-type equivalent, will not be discussed here.) It can be seen that the sphygmomanometer calibration in the generation of standard blood pressure wave signal, there must be a mechanism responsible for the blood pressure wave signal transmission to the sphygmomanometer. This transfer mechanism is equivalent to the human arm transferring blood pressure to the sphygmomanometer and is called the analog arm. The mechanical properties of the analog arm are equivalent to those of the human arm. The advantages of this method of calibration are: ① It meets the requirements of value transmission. The above calibration method is based on the basic definition of blood pressure and produces standardized values from the measurement of the sphygmomanometer. These values are easily traceable. ② The method is reliable. The process of calibrating a sphygmomanometer using this method is exactly the same as the working process of a sphygmomanometer measuring blood pressure. Therefore, it can be said that there is no additional error in the method. ②Complete verification of sphygmomanometers. This method considers the cuff of the sphygmomanometer as a sensing part of the sphygmomanometer. Therefore, it is said to be able to test the sphygmomanometer completely. It is technically very difficult to realize this calibration method, and it is very difficult to generate the standard blood pressure wave and to make the analog arm. There is no means to realize the calibration method at home and abroad. By the Guangdong Provincial Institute of Metrology and Guangdong Provincial Institute of Medical Devices *** with the development of the oscillometric method of electronic sphygmomanometer calibration device to realize the calibration method. The uncertainty of its standard systolic and diastolic blood pressure is 0.3kPa (2mmHg). It makes this calibration method from the idea to reality. 2. From the working principle of the sphygmomanometer can also be derived from another method of verification. (Strictly speaking, this method can not be completed to transfer the value of the test.) The basic idea of this method is to restore the envelope. It first collects a certain amount of crowd envelope, after statistical induction to determine a typical envelope. This envelope implicitly contains the systolic and diastolic measurements, i.e., it is nominalized to the values of systolic and diastolic blood pressure. This typical envelope is returned to the sphygmomanometer during the calibration process by a device connected via a pipeline. The sphygmomanometer sensor senses the pressure change, picks up the envelope, and determines the blood pressure value. The difference between the value measured by the sphygmomanometer and the nominal value of blood pressure for the typical envelope is the fundamental error of the sphygmomanometer in measuring blood pressure. The biggest problem with this method is that the nominal systolic and diastolic blood pressure values of the envelope cannot be verified by conventional experimental methods. That is to say, it is not traceable. Currently there are some foreign devices based on this method. These devices can be used for the development of sphygmomanometers and auxiliary calibration in the production process, but it is not appropriate to use them in the daily calibration. III. CONCLUSION The above mainly introduces two methods of calibrating the oscillometric electronic sphygmomanometer, in which the first method should be more in line with the requirements of the value transfer calibration. However, there are some problems, mainly because the basic theoretical support of the oscillometric method is still lacking, which makes the establishment of the analog arm mechanics model quite difficult, and can only rely on the method of statistical induction for processing. With the continuous improvement of the oscillometric method, we believe that its verification methods and means will also continue to improve.