Nowadays, many elderly people have their own blood pressure monitors at home to monitor their blood pressure regularly. However, some patients have heard that blood pressure should be measured on the left arm for men and on the right arm for women. Is there any scientific basis for this?
1. Principles of Blood Pressure Measurement
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 vessel wall. Blood pressure varies in different parts of the blood vessels (arteries, veins, capillaries) due to different pressures. The blood pressure commonly referred to is the arterial blood pressure measured externally, more specifically, the pressure in the brachial artery of the left (or right) arm. This blood pressure is mostly measured indirectly. Currently, the commonly used blood pressure monitors on the market can be divided into mercury sphygmomanometers and electronic sphygmomanometers.
The measurement principle of the mercury sphygmomanometer is to inflate the cuff to completely block the artery, and then gradually release the pressure in the cuff. When the pressure inside the artery just exceeds the pressure applied by the cuff, the blocked artery is opened and blood flows through. The highest pressure that can open the cuff is called the systolic pressure, and the lowest pressure that can open the cuff is called the diastolic pressure.
The electronic sphygmomanometer uses the oscillography method to measure blood pressure. The oscillography method can determine blood pressure by detecting the vibrations produced when blood collides with the blood vessel wall. It can automatically record the blood flow status in the arteries and convert it into digital form.
2. Factors Affecting Blood Pressure
Regardless of which type of blood pressure monitor is used to measure blood pressure, the factors that can affect blood pressure are mainly ventricular contractility, stroke volume, circulating blood volume, arterial wall elasticity, and peripheral vascular resistance. In addition, blood pressure is also influenced by nerves, body fluids, and certain endocrine diseases.
In normal individuals, the right brachial artery originates from the first branch of the aortic arch, which is the innominate artery, while the left brachial artery originates from the third branch, which is the left subclavian artery. Therefore, due to anatomical and hemodynamic factors, the blood pressure in the right arm may be about 10 mmHg higher than that in the left arm. Some patients wonder which blood pressure measurement is more reliable when there is a difference between the blood pressure in the left and right arms.
3. Normal and Special Situations
Based on the working principles of the two common types of blood pressure monitors mentioned above, it can be seen that in fact, both the left and right arms can be used for blood pressure measurement. However, the blood pressure measurement that is relatively "higher" is closer to the true blood pressure value inside the body. Dr. Liang Donghui reminds that blood pressure should generally be measured on the right arm, or the blood pressure of one side should be measured consistently, instead of following the practice of measuring on the left arm for men and on the right arm for women.
However, there is a special situation: when a patient has an aortic aneurysm or stenosis between the innominate artery and the left subclavian artery, the difference in blood pressure between the left and right arms may be even greater. In clinical practice, for patients suspected of having an aortic aneurysm or stenosis, blood pressure should be measured on both arms for comparison, but this situation does not follow the principle of measuring on the left arm for men and on the right arm for women.
