In recent years, due to the rapid development of our society and economy and the change of people’s lifestyle, cardiovascular disease incidence rate and related risk factors are increasing. People are paying more and more attention to their physical and mental health. In the past, blood pressure measurement had to go to the hospital and be detected by doctors with mercury sphygmomanometer. However, with the development of science and technology, sphygmomanometer is ushering in a new era of electronic sphygmomanometer. As long as you have a home electronic sphygmomanometer, people can sit at home and monitor the changes of blood pressure at any time. If you find abnormal blood pressure, you can go to the hospital in time.
Intermittent ejection of the heart produces pulse waves that travel from the aortic root along the arterial system. The mechanical parameters (such as flow rate, pressure, blood flow velocity, cross-sectional area of blood vessel, etc.) will change when the pulse wave arrives. In each cardiac cycle, the intermittent relaxation and contraction of the heart will cause the vibration of the aortic wall and the change of the aortic blood pressure from high to low. This vibration of the arterial wall is called arterial pulse.
When the pulse wave is formed in the proximal end of the aorta, it immediately spreads the blood pressure, blood flow and periodic vibration of the vascular wall along the arterial tree to the whole arterial system in a fluctuating way, thus forming the fluctuation of blood pressure from low to high, blood flow from slow to fast, and vascular wall from contraction to extension in the whole arterial system, So it can be called arterial pulse wave.
The multifunctional electronic sphygmomanometer adopts the optical capacitance product method for measurement. The principle is: the light beam is transmitted to the photoelectric receiver through transmission, and the signal is different. Hemoglobin (HB) in human red blood cells is reversibly combined with oxygen molecules, and the combined Hb is called oxyhemoglobin (HBO2). They have different absorption curves: HB absorbs less light in the red spectral region of 600nm ~ 700nm, while HBO2 absorbs more light; in the infrared spectral region of 800nm ~ 1000nm, HB absorbs more light Hemoglobin HB absorbs more light, while HBO2 absorbs less light.
In the light path, besides arterial hemoglobin, there are many other absorbers, which will seriously affect the measurement accuracy. Therefore, red light and infrared light LED are as close to each other as possible, transmitting light through a single tissue position in the human body, and transmitting light through time multiplexing processing. At the same time, at the detection end, the transmitted light intensity through the finger is converted into a voltage signal, so the photocapacitive pulse wave signal is obtained. Finally, based on the detection principle of photoelectric sensor and Lambert Beer law, the transmitted light intensity can be correlated with the output voltage of photoelectric sensor, the calculation method of systolic and diastolic blood pressure of cardiovascular system parameters can be established, and the testing equipment of noninvasive continuous blood pressure measurement method can be designed. Its advantages are: easy to use, high measurement accuracy, easy to record the measured value, lightweight and easy to carry.