The feeling of tightness during blood pressure measurement is caused by the gradual inflation of the cuff of the sphygmomanometer, which closes the brachial artery. There are two ways to measure blood pressure: ① direct measurement requires percutaneous puncture to send the catheter from the peripheral artery to the aorta, which is invasive and only applicable to critical and difficult cases. Indirect measurement is the cuff pressurization method, which is non-invasive, more convenient and commonly used. Indirect measurement of blood pressure by inflating the cuff of the sphygmomanometer, the brachial artery will be closed, so the arm will feel particularly tight in the process, followed by the gradual deflation of the cuff to the airbag pressure is equal to the systolic pressure, the brachial artery blood began to be able to flow, which corresponds to the systolic blood pressure. As the cuff continues to deflate, the blood flow becomes smoother and smoother, and the feeling of tightness in the arm disappears; when the blood is able to flow completely, the corresponding pressure is the diastolic pressure. Blood pressure should be measured after resting and emptying the bladder. Only with proper preparation can an accurate blood pressure be measured.