Blood Pressure Measurement Standards: How to Obtain an Accurate Value

Accurate blood pressure measurement is the foundation for obtaining accurate values, and the measurement process must be standardized. A mercury sphygmomanometer that meets metrological standards should be selected for measurement. The value is expressed by the height of the mercury column. However, this type of sphygmomanometer must be calibrated regularly by a metrological monitoring unit to accurately reflect the human body's blood pressure value. The operating steps of the most commonly used mercury sphygmomanometer are as follows: (1) Before measuring blood pressure, the person being measured should rest quietly for 5 minutes to eliminate the influence of factors such as fatigue or tension on blood pressure; tea, alcohol and coffee should not be consumed within 30 minutes before measurement. (2) The person being measured can be seated or lying down, but it is best to be seated. Sit on a chair with your back against the chair back, expose your right upper arm, and place your elbow at the same level as your heart. Regardless of the person's position, the zero point of the sphygmomanometer should be placed at the level of the heart. (3) Use an appropriately sized cuff. Generally, ordinary adults can choose an air cuff with a width of 13-15cm and a length of 30-35cm. Obese people or those with large arm circumferences should use a larger size cuff, and children should use a smaller cuff. (4) Position the cuff with the middle of the brachial artery, wrapping it tightly around the patient's upper arm. The lower edge of the cuff should be 2-4 cm above the elbow crease. The cuff should not be too tight or too loose, so that the patient does not experience pain due to excessive tightness, nor should it be too loose to allow the cuff to rotate. (5) Place the chest piece of the stethoscope on the brachial artery in the elbow crease, and then inflate the cuff with the small bulb. Inflate quickly, adding 30 mmHg after the pulsation sound is no longer audible. Then slowly release the knob of the small bulb to allow the mercury column to descend slowly (ideally at 2-6 mmHg/s) for accurate reading of the result. (6) When the first sound is heard during deflation, the pressure value indicated by the mercury column height is the systolic pressure. This sound gradually intensifies and then becomes a softer murmur. After the pressure decreases again, a sound without murmurs appears, gradually weakens, and quickly disappears. Generally, the pressure value indicated by the mercury column height when the arterial sound disappears is the diastolic pressure. For children, pregnant women, those with severe anemia, those with aortic valve insufficiency or those whose arterial sounds are not absent, the diastolic pressure is the pressure indicated by the height of the mercury column when the arterial sound suddenly becomes low before it disappears. (7) Blood pressure must be measured twice consecutively each time. When measuring repeatedly, the air in the cuff should be completely emptied, and after the mercury column drops to the 0 mark, rest for 30 seconds before re-inflating and measuring. The average of the two measurements should be recorded. If the difference between the systolic or diastolic pressure readings of the two measurements is >2 mmHg, the measurement should be repeated after 2 minutes, and the average of the three readings should be taken. (8) It is recommended to use the blood pressure of the right upper arm as the standard, but it should be noted that the comparison should be made on the same side each time. Blood pressure in a normal person is not constant throughout their life, and the blood pressure value of the same person will not be exactly the same on different days or at different times of the same day. Such fluctuations and differences in blood pressure are a normal physiological phenomenon, as long as they are within the normal range. (1) Age: Blood pressure in children and adolescents increases with age, with a significant increase in systolic pressure. After age 40, men and women experience a significant increase in arterial blood pressure, with systolic blood pressure rising more significantly than diastolic blood pressure. Men's blood pressure is slightly higher than women's, but women experience a more significant increase after menopause. (2) Day and night: Blood pressure is generally higher during the day and drops to its lowest level during sleep at night. Blood pressure begins to rise after waking up, peaking between 8:00 and 10:00 AM, and then gradually decreases. Blood pressure begins to rise again about 1 hour after lunch, with a small peak between 6:00 and 8:00 PM, but slightly lower than in the morning, and then gradually decreases again. It can be seen that there are two peak periods and two troughs in blood pressure during the day, with the difference between the highest and lowest blood pressure reaching 40 mmHg. (3) Season: Generally, blood pressure tends to rise in winter and slightly decreases in summer. However, if it is too hot and the body sweats profusely, the loss of body water increases the viscosity of the blood, which in turn increases the pressure on blood vessels. These factors can cause a slight increase in blood pressure. (4) Body position: Generally, blood pressure is higher when sitting than when standing. In addition, the blood pressure in the four limbs of a normal person may not be exactly the same, with the blood pressure in the right upper limb being about 10 mmHg higher than that in the left upper limb. Also, because the femoral artery in the lower limb is thicker and has a larger blood flow, the blood pressure in the lower limb is 20-40 mmHg higher than that in the upper limb when lying flat under normal circumstances, while there is no difference in blood pressure between the left and right lower limbs. Due to this difference in blood pressure between the left and right upper limbs, it is stipulated that the blood pressure in the right upper limb should be used as the standard when measuring blood pressure. (5) Others: Physical activity, mental stress, anger, excitement, insomnia, anxiety, tension, fullness, or straining during defecation can all cause a temporary increase in blood pressure. The degree of increase in blood pressure caused by these situations is 10-30 mmHg or greater. For normal people, they do not feel anything obvious and can recover with rest. However, for patients with hypertension, acute cardiovascular and cerebrovascular events are likely to occur under these conditions.