The lateral pressure of intravascular blood on the blood vessel wall is referred to as blood pressure for short. Normal adults have systolic blood pressure of 90 ~ 140mm Hg, diastolic blood pressure of 60 ~ 90mm Hg, and pulse pressure difference of 30 ~ 40mm Hg. The upper limb blood pressure of healthy people is not equal, the difference between the left and right sides can reach 10 ~ 20mm Hg, and the lower limb blood pressure is about 20 ~ 40mm Hg higher than that of the upper limb.