The principle of electronic blood pressure monitor

Apr 07, 2021
The electronic blood pressure monitor uses the principle of the oscillometric method, also called the oscillation method. It is a relatively advanced electronic measurement method developed in the 1990s. The principle is briefly described as follows: First, tie the cuff to the arm and inflate the cuff automatically. After reaching a certain pressure (generally 30~50mmHg higher than the systolic pressure), the pressure will be stopped and the air will start to deflate. When the air pressure reaches a certain level, The blood flow can pass through the blood vessel, and there is a certain oscillating wave, which propagates to the pressure sensor through the trachea, and the pressure sensor can detect the pressure and fluctuation in the measured cuff in real time. Gradually deflate, the oscillating wave gets bigger and bigger. Re-deflation As the contact between the cuff and the arm becomes looser, the pressure and fluctuations detected by the pressure sensor become smaller and smaller. Choose the moment with the largest fluctuation as the reference point. Based on this point, look forward to the peak value of 0.45 fluctuation point, which is the systolic blood pressure, and look backward for the peak value of 0.75 fluctuation point, which corresponds to this point. The pressure is the diastolic pressure, and the pressure corresponding to the point with the highest fluctuation is the average pressure. The oscillometric sphygmomanometer is a very popular sphygmomanometer, and 80% of households with a sphygmomanometer use the oscillometric sphygmomanometer.
Because the value measured by the oscillometric method fluctuates, there is no regularity, and there may be several maximum values, so the calculated data cannot truly reflect the value of blood pressure. Therefore, the oscillometric method of measuring blood pressure is also based on assumptions. First, the test subject’s waveform is standardized; second, the formulas and coefficients (0.45 and 0.75) used to calculate the blood pressure value are the same as those of the test subject. In general, healthy people can roughly conform to this coefficient. Unhealthy People often do not meet, but only unhealthy people need a blood pressure monitor more. The judgment basis of the oscillometric method is given by statistical methods through a large number of population experiments, so this measurement method will inevitably cause measurement errors for some populations, and sometimes the error can reach tens of millimeters of mercury. According to statistics, the oscillometric method is only suitable for 70% of the population, and for the other 30%, the error is large. For the same person, the oscillometric method is sometimes accurate, sometimes the error is large.
Verification method of inaccurate measurement by oscillometric method:
Method 1: Use a shaking water bottle instead of your arm to observe the readings of the oscillometric sphygmomanometer
Use a mineral water bottle to fill 3/4 of the water, fix the cuff of the oscillometric sphygmomanometer to the outside of the mineral water bottle, shake the mineral water bottle rhythmically, the oscilloscope sphygmomanometer will give corresponding readings to prove the oscillometric method The reading of the sphygmomanometer is unreliable under certain conditions. Using the same method, it is absolutely impossible for a pulse wave sphygmomanometer to give a reading.
Method 2: Measurement of blood pressure after exercise
The oscillometric sphygmomanometer uses empirical data to determine blood pressure readings, but it is only suitable for blood pressure measurement in a calm state, and cannot be used for post-exercise blood pressure measurement. When performing exercise blood pressure measurement, the pulse wave sphygmomanometer and the oscilloscope sphygmomanometer are used to measure the blood pressure of both arms at the same time, and the blood pressure value is recorded.