How does a blood pressure monitor work?

In fact, many friends do not understand the working principle of the blood pressure monitor. This is because the working steps of the blood pressure monitor are relatively many, and some more professional algorithms are also included. The working principles of general sphygmomanometers can be divided into two types, one is the auscultation method, and the other is the oscillometric method. The auscultation method requires listening to the Korotkoff sounds of the blood pressure and then calculating.

1. Auscultation

The method of measuring human blood pressure by listening to the Korotkoff sounds of blood pressure with a stethoscope is called auscultation, and the sphygmomanometer that measures blood pressure by auscultation is called an auscultation sphygmomanometer. Such as mercury sphygmomanometer, blood pressure meter, etc. For more than a hundred years, people have been exploring more reliable methods and instruments for measuring blood pressure, but all have been unsuccessful, including oscillometric electronic sphygmomanometers. Therefore, regular hospitals in my country have to continue using mercury sphygmomanometers. Developed countries in Europe and the United States have banned the use of mercury sphygmomanometers for environmental reasons, and their medical institutions use sphygmomanometers. In the face of the fact of repeated failures, some people in the international community call the auscultation method the gold standard for blood pressure measurement. Hundreds of years of historical facts have proved that the auscultation method is irreplaceable so far. The auscultation sphygmomanometer is a scientific and classic blood pressure measurement instrument.

Auscultation classification:

Auscultatory sphygmomanometers are divided into manual auscultatory sphygmomanometers, semi-automatic auscultatory sphygmomanometers and automatic auscultatory sphygmomanometers. Common manual auscultation sphygmomanometers include mercury sphygmomanometers and sphygmomanometers; semi-automatic auscultation sphygmomanometers include assisted-reading sphygmomanometers; automatic auscultation sphygmomanometers include automatic auscultation sphygmomanometers.

1. The manual auscultation sphygmomanometer uses mercury as a pressure gauge. The measurer uses the human ear to listen to the original blood pressure Korotkoff sounds (from heavy to light, and then disappears or changes) through a stethoscope, and reads the systolic and diastolic pressures based on the Korotkoff sounds heard and the pressure gauge. Although the auscultation method is currently the most accurate method for measuring blood pressure, it is affected by the following factors: (1) the level of training; (2) hearing; (3) attention; (4) eyewitness differences in judgment. The reliability of blood pressure measurement is entirely determined by the professional level, hearing, fatigue level and work attitude of the measurer. Also, since blood pressure is an instantaneous value, it cannot be repeated or reconciled, so what the measurer says is what it is. 2. The semi-automatic auscultatory sphygmomanometer uses an electronic probe similar to a stethoscope to listen to the Korotkoff sounds of the blood pressure and amplify the volume through electronic technology. People next to the sphygmomanometer can hear the rhythmic Korotkoff sounds of the blood pressure (all of which are the same heavy sound) and read the systolic and diastolic blood pressure based on the Korotkoff sounds heard and the pressure gauge. This method eliminates the influence of (1) level of training, (2) hearing, and (3) attention, but is still affected by eyewitness differences in judgment. Although it can enable more people to use it to measure blood pressure, some people still find it troublesome to use. 3. The fully automatic auscultatory sphygmomanometer uses an electronic probe similar to a stethoscope to listen to the Korotkoff sounds of blood pressure and converts them into digital signals through modern digital technology. Finally, the signals are displayed on the sphygmomanometer, thus realizing the automation of blood pressure measurement. This type of blood pressure monitor is also divided into semi-automatic and fully automatic. The one that can be inflated manually and deflated automatically is called semi-automatic; the one that can be inflated and deflated automatically is called fully automatic. This sphygmomanometer is not affected by eyewitness differences in training level, hearing, concentration and judgment, and everyone can use it to accurately measure blood pressure.

2. Oscillometric method

Oscillometric method is also called oscillation method

, it was 1990

A relatively advanced electronic measurement method developed in the modern times.

The principle is briefly described as follows:

First, tie the cuff around your arm and automatically inflate the cuff. When it reaches a certain pressure (generally 30 to 50 mmHg higher than the systolic pressure), stop pressurizing and start deflating. When the air pressure reaches a certain level, blood can flow through the blood vessels with a certain oscillation wave. The oscillation wave is transmitted through the trachea to the pressure sensor. The pressure sensor can detect the pressure and fluctuations in the measured cuff in real time. As the air is gradually released, the oscillation waves become larger and larger. As the cuff becomes more loosely in contact with the arm during deflation, the pressure and fluctuation detected by the pressure sensor become smaller and smaller. Choose the moment of the largest fluctuation as the reference point. Based on this point, look forward for the fluctuation point with a peak value of 0.45, which is the systolic pressure. Look backward for the fluctuation point with a peak value of 0.75, and the pressure corresponding to this point is the diastolic pressure. The pressure corresponding to the point with the highest fluctuation is the average pressure. It is worth mentioning the constants 0.45 and 0.75. It is different for each manufacturer and should be based on the results of clinical tests. Moreover, large manufacturers may also process different blood pressures in different segments and set different constants.

Several technologically advanced companies in the world have developed pressurized synchronous measurement technology (MWI technology), which is a technology that measures blood pressure during the pressurization process, greatly shortening the measurement time; at the same time, through linear pressurization technology, the measurement accuracy is also greatly improved.