Many elderly people nowadays have their own blood pressure monitors at home to regularly monitor their blood pressure. However, some patients have heard that blood pressure measurement should be done on the left arm for men and the right arm for women. Is there any scientific basis for this?
1. Principle of Blood Pressure Monitors
Dr. Liang Donghui explains that blood pressure refers to the pressure exerted by the blood in the blood vessels on the unit area of the blood vessel wall. Blood pressure varies in different parts of the blood vessels (arteries, veins, capillaries) due to different pressures. Usually, blood pressure refers to the measurement of arterial blood pressure obtained externally, specifically the pressure in the brachial artery of the left (or right) arm. This type of blood pressure measurement is mostly indirect. The commonly used blood pressure monitors on the market can be divided into mercury sphygmomanometers and electronic blood pressure monitors.
The measurement principle of mercury sphygmomanometers involves inflating the cuff to completely occlude the artery. Then, the cuff is gradually deflated, and when the pressure inside the artery exceeds the pressure applied by the cuff, the occluded artery is opened to allow blood flow. The pressure at which the cuff is just opened is taken as the systolic pressure, and the pressure at which the cuff is fully deflated is taken as the diastolic pressure.
On the other hand, electronic blood pressure monitors use oscillometric methods to measure blood pressure. This method detects the vibrations produced by the blood flow colliding with the blood vessel wall and converts them into digital form to record the blood flow status in the artery.
2. Factors Affecting Blood Pressure
Whether using a mercury sphygmomanometer or an electronic blood pressure monitor, the factors that can affect blood pressure are mainly ventricular contractility, stroke volume, circulatory blood volume, arterial wall elasticity, and peripheral vascular resistance. In addition, blood pressure is also influenced by the nervous system, body fluids, and certain endocrine disorders.
The right brachial artery in normal individuals originates from the first major branch of the aortic arch, called the innominate artery, while the left brachial artery originates from the third branch, called the left subclavian artery. Therefore, due to anatomical and hemodynamic factors, the blood pressure in the right arm can be around 10 mmHg higher than that in the left arm. Some patients may wonder which arm's blood pressure measurement should be believed since there is a difference between the left and right arm measurements.
3. Normal and Special Situations
Based on the working principles of the two common types of blood pressure monitors mentioned above, in practice, blood pressure can be measured on either the left or right arm. However, the blood pressure that is "higher" is closer to the true blood pressure inside the body. Dr. Liang Donghui suggests that blood pressure measurement should generally be done on the right arm or by consistently measuring on one side rather than following the "left for men, right for women" rule.
However, there is a special case where the difference in blood pressure between the left and right arm may be greater. This occurs when a patient has an aortic aneurysm or aortic stenosis located between the innominate artery and the left subclavian artery. In such cases, blood pressure should be measured on both arms for patients suspected of having an aortic aneurysm or aortic stenosis, but this situation does not follow the "left for men, right for women" principle.
