The so-called high pressure is the pressure of blood on the blood vessel wall when the left ventricle contracts to squeeze blood into the aorta; The so-called low pressure is the pressure of blood on the blood vessel wall at the end of left ventricle diastole; When the left ventricle contracts, the pressure of intravascular blood pressure is the highest, so it is commonly called high pressure, while at the end of left ventricle diastole, the pressure of intravascular blood pressure is the lowest, so it is commonly called low pressure.

The blood circulation state of human body is determined by systolic blood pressure (high pressure) and diastolic blood pressure (low pressure), so it is necessary to measure high pressure and low pressure when measuring blood pressure.