Mercury sphygmomanometers. There are two types: tabletop and standing. Tabletop mercury sphygmomanometers are structurally sound and reliable; standing sphygmomanometers are height-adjustable and are the most commonly used due to their reliable results. However, the latter is slightly larger and less portable, and both pose a risk of mercury leakage. Their blood pressure measurement principle is based on auscultation, and they mainly consist of three parts: a balloon, a cuff, and a manometer. The rubber bladder of the cuff is connected to the balloon and the manometer respectively, forming a closed tubing system. Manometers come in two types: mercury column and spring.
Electronic sphygmomanometers. Depending on the measurement site, they can be further subdivided into upper arm, wrist, finger, manual, and automatic types. Their advantages are ease of operation and intuitive readings; simply turning on the switch automatically takes measurements, making them suitable for home use. However, electronic sphygmomanometers also have the disadvantage of large errors and require frequent calibration with a standard mercury sphygmomanometer. Its operating principles include auscultation (also known as Korotkoff sound method) or oscillometric method (also known as oscillation method). It mainly consists of a gas pressure sensor, a pressurized miniature air pump, an electronically controlled exhaust valve, related software, a mechanical slow exhaust valve, and a solenoid fast exhaust valve.
The pneumatic sphygmomanometer, also known clinically as anhydrous sphygmomanometer or spring-loaded sphygmomanometer, uses an air pump to measure pressure. It is small and portable, but with repeated use, the spring's properties can change, affecting the accuracy of the results. Therefore, it requires periodic calibration against a standard mercury sphygmomanometer. It is rarely used clinically now.
