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As early as 1876 Marey began to study the oscillometric method of blood pressure measurement of blood pressure, but it was not until 1976 that Ramsey invented an instrument to determine mean arterial pressure using the oscillometric method. This was followed by the development of methods for estimating systolic and diastolic blood pressure. As the estimation methods were further refined, the more established oscillometric sphygmomanometer became available in 1991.

Unlike the benchtop mercury sphygmomanometer, which determines systolic and diastolic pressures by identifying the appearance and disappearance of the Koch sound. The oscillometric method of electronic sphygmomanometers senses pulse wave information during deflation or inflation and obtains systolic and diastolic pressure data through a complex series of conversions and calculations. During deflation, the blood flow in the arm artery goes from completely blocked to gradually returning to normal, and the pulse signal in the brachial artery goes from absent to present, and tends to increase and then decrease. The amplitude of this pulse signal is weak, but can be sensed, amplified by the pressure transducer of the sphygmomanometer and results in an envelope based on the change in cuff pressure and the change in pulse amplitude (figure below). Different manufacturers have their own specific procedures for calculating systolic and diastolic pressures, with the systolic-to-apical ratio ranging from 45% to 57% and the diastolic-to-apical ratio ranging from 74% to 82%.

1,The manual auscultation method sphygmomanometer is the use of mercury, etc., as a manometer, and the measurer uses the human ear to listen to the original blood pressure Koch sound (from heavy to light and then disappearing or changing) through a stethoscope and reads the systolic and diastolic pressure according to the Koch sound heard in conjunction with the manometer; although the auscultation method method is currently an accurate method of measuring blood pressure, the manual auscultation method is influenced by several factors, including.

(1) The level of training received;

(2) Hearing;

(3) Attention;

(4) Poor visualization in judgment. The reliability of blood pressure measurement is entirely determined by the level of expertise, hearing, fatigue and work attitude of the measurer, and because blood pressure is an instantaneous value, not repeatable and not compoundable, how much the measurer says is how much.

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