The main principle of a sphygmomanometer is to pressurize air to compress a local artery, thereby stopping the pulsation of that artery and measuring the blood pressure during that period. The measurement principle of a sphygmomanometer can be divided into two types: the auscultatory method and the oscillometric method.
The auscultatory method, also known as the Korotkoff sound method, is further divided into the artificial Korotkoff sound method and the electronic Korotkoff sound method. The artificial Korotkoff sound method is the method we usually see doctors and nurses using a pressure gauge and stethoscope to measure blood pressure; the electronic Korotkoff sound method uses electronic technology to replace doctors and nurses in measuring Korotkoff sounds. Its principle involves a cuff wrapped around the upper arm, whose pressure acts on the brachial artery. Adjusting the gas in the cuff changes the pressure, and the sound of the pulsation is heard with a stethoscope, thus obtaining the systolic and diastolic blood pressure.
The oscillometric method, also known as the oscillation method, is a relatively advanced electronic measurement method developed in the 1990s. Its principle is to automatically adjust the inflation of the cuff wrapped around the upper arm to change the pressure. Blood flow through the blood vessels creates certain oscillation waves, which are received by the pressure sensor. As the cuff is gradually deflated, the pressure and fluctuation detected by the pressure sensor change accordingly based on the changes in the oscillation waves. The moment of maximum fluctuation is selected as the reference point. Based on this point, a fluctuation point forward is found to be the systolic pressure, and a fluctuation point backward is found to be the diastolic pressure. These values are set differently by different manufacturers.
