It is the same age and other conditions of the same healthy people, compared to the level of blood pressure is also different. Medical research confirms that the level of blood pressure is mainly related to cardiac output, heart rate, peripheral vascular resistance, aortic elasticity, and the ratio of effective blood volume to circulatory system vascular volume. The specific mechanisms are as follows. (1) Cardiac output per beat: when the heart ejects more blood during contraction, i.e., when the cardiac output per beat increases while other regulating factors remain unchanged, the systolic blood pressure increases while the diastolic blood pressure does not increase significantly. Conversely, when the blood ejected during cardiac contraction decreases, systolic blood pressure decreases and diastolic blood pressure remains unchanged. The level of systolic blood pressure and the heart’s ability to contract, that is, the strength of the heart’s “pump” function. (2) Heart rate: the number of heartbeats per minute. When the heart rate increases, the diastolic blood pressure rises and the systolic blood pressure does not rise significantly. When the heart rate slows down, the diastolic blood pressure decreases and the systolic blood pressure does not change significantly. (3) Peripheral vascular resistance: the resistance of blood to forward flow. It is mainly regulated by changes in the caliber of resistance vessels and the viscosity of blood. When peripheral vascular resistance increases, diastolic blood pressure rises and systolic blood pressure rises insignificantly; conversely, when peripheral vascular resistance decreases, diastolic blood pressure decreases more than systolic blood pressure. Therefore, the level of diastolic blood pressure mainly reflects the size of peripheral vascular resistance. (4) The role of the aorta and other large blood vessels as “elastic reservoirs”: this role is unlikely to change significantly in adolescents. Only in middle age, the elastic fiber of the arterial wall changes (such as sclerosis, calcification), to the aorta and other large blood vessels, the elastic retraction force decreased, the lumen caliber becomes larger, and can be dilatable to reduce the role of “elastic receptacle” weakened. Therefore, the systolic blood pressure will increase in middle age and old age, which is a pathological phenomenon. (5) Ratio of circulating blood volume to vascular system volume: a decrease in arterial blood pressure is caused when there is a large amount of blood loss, fluid loss (vomiting, diarrhea) and/or an increase in the volume of the vascular system. Clinically, the application of diuretics or sodium restriction therapy (low-salt diet) to reduce circulating blood volume and achieve antihypertensive therapy is the reason for this.