Normal adult systolic blood pressure is 12-18.67 kPa, diastolic blood pressure is 8-12 kPa, and pulse pressure is 4-5.33 kPa. In healthy people, the blood pressure of the two upper limbs may not be equal, and the difference between the left and right sides can be 1.33-2.67 kPa, and the blood pressure of the lower limbs can be higher than that of the upper limbs by about 2.67-5.33 kPa. Normal human blood pressure is not constant, measured at different times blood pressure often reads differently, and sometimes the difference is quite large, the reason for this is the natural variability of the subject’s own internal blood pressure and the influence of external environmental factors, or caused by measurement errors. 1, diurnal variation: human and most biological life phenomena have the characteristics of periodic changes during the day, such as the secretion of hormones, generally in the morning in a state of inhibition, from noon onwards gradually increase, reaching a peak in the afternoon. Human blood pressure, on the other hand, falls during sleep at night and starts to rise in the morning after waking up, i.e. there is a circadian rhythm. Generally, blood pressure is highest at 9-10 o’clock in the morning, then gradually decreases, and drops to the lowest point during nighttime sleep, with a difference of up to 5.33 kPa (40 mmHg), and rises by about 2.67 kPa (20 mmHg) when waking up, and further rises after getting up and walking, when it is most likely to induce sudden death from coronary heart disease. This 24-hour blood pressure fluctuations around the clock, mainly related to the changes in human plasma norepinephrine levels and the sensitivity of pressure receptors. 2, posture and movement: when standing, blood pressure rises slightly to ensure that the head maintains an adequate blood supply. (Therefore, the diastolic blood pressure is higher when standing than when sitting, generally no greater than 2.0 kPa). During exercise, arterial blood pressure, especially systolic blood pressure, can increase significantly; when engaged in strenuous exercise, systolic blood pressure can be as high as 24.0-26.67 kPa, and diastolic blood pressure can also be as high as 13.33 kPa. This is due to the fact that during exercise, the whole body muscle blood demand increases sharply, the heart blood discharge increases, and adrenaline secretion is strong, which makes the blood pressure rise and ensures the blood supply to the organs. After the exercise stops, the elevated blood pressure soon returns to normal. 3, emotion: when a person is in anxiety, excitement, fear, due to increased sympathetic nerve activity, adrenaline secretion increased, so that the increase in cardiac output, small artery contraction, blood pressure, especially systolic blood pressure increased significantly. And long-term, repeated mental tension and mood swings can make the cerebral cortex and subcortical centers of inhibition and excitation process dysregulation, thus affecting the vasomotor center, causing a significant increase in blood pressure. 4, eating: blood pressure usually has to be mildly increased when eating, and lasts about 1 hour, diastolic blood pressure is generally unaffected or slightly decreased, which is due to the expansion of blood vessels distributed in the abdominal cavity during digestion. 5, temperature: when the ambient temperature decreases, the peripheral blood vessels contract and blood pressure increases; when the ambient temperature increases, the skin vessels dilate and blood pressure decreases. In the warm bath also has the same change, but the diastolic blood pressure is more obvious to reduce. In addition, smoking, drinking coffee and alcohol can also cause a transient change in blood pressure.