Is the blood pressure on both arms different? If it exceeds this value, be alert to subclavian artery stenosis (or occlusion)!

Author: Li Qingle, Chief Physician, Peking University People's Hospital

Reviewer: Chen Zhong, Chief Physician, Beijing Anzhen Hospital, Capital Medical University

Many friends will find that the blood pressure on both sides of their arms is different when measuring blood pressure. This is because the brachial arteries on both sides of the arms have different origins and different blood flow in the blood vessels. Generally speaking, as long as the blood pressure difference between the two arms is within 20mmHg, it is normal and there is no need to worry too much.

However, if the difference in blood pressure between the two arms is too large (greater than 20 mmHg), the first thing to consider is the problem of the vascular lumen, the most common of which is the stenosis (or occlusion) of the subclavian artery. And most of the causes are atherosclerosis, because if the atherosclerotic plaques in the lumen are large enough, it can cause the lumen to shrink, the blood flow will decrease, and the pressure will be different. Most of the time, when the blood pressure difference is 20-40 mmHg, especially when it exceeds 40 mmHg, it is a positive indicator, which may be a problem with the proximal subclavian artery.

Figure 1 Original copyright image, no permission to reprint

Of course, there are many reasons for subclavian artery stenosis (or occlusion). In addition to subclavian artery atherosclerotic plaques, there are also Takayasu arteritis, etc., which can cause narrowing of the lumen.

However, the blood pressure difference between the two sides is not much, and it may also be subclavian artery stenosis.

Because chronic stenosis can form very good collateral circulation compensation, coupled with the vertebral artery blood steal (backflow), and the backflow is sufficient, the blood pressure of the two upper limbs may not be much different at this time, but in fact the impact of blood steal is very serious. Because it is the stolen intracranial blood flow, it will indirectly affect the intracranial blood supply. In this case, some imaging examinations are needed to determine whether there is stenosis.

Of course, there are some rare cases, such as aortic dissection. Dissection means that the aortic endothelium is torn, which means that there is blood flow between the aortic walls and compresses the inner cavity, affecting blood flow. After the tear, it can affect the vertebral arteries including the subclavian artery, but this type of lesion is relatively rare.

For some people, the subclavian artery is locally compressed and pressed by lymph nodes or other tumors, which can also cause a large difference in blood pressure on both sides.

But the most common cause is atherosclerotic stenosis (or occlusion) of the subclavian artery.

From an anatomical point of view, the left subclavian artery is a direct branch from the left side of the aortic arch; the innominate artery is the first branch from the right side of the aortic arch, and after the innominate artery branches out from the aortic arch, it divides into the right carotid artery and the right subclavian artery.

Of course, another important branch is the vertebral artery of the cerebellar circulation, which originates from the subclavian artery.

Therefore, the subclavian artery mainly controls or supplies blood to the upper limbs, as well as the posterior circulation of the cerebellum.

Figure 2 Original copyright image, no permission to reprint

Subclavian artery stenosis (or occlusion) is actually a manifestation of atherosclerosis in the subclavian artery. With the advent of an aging society, when the elderly, including many patients with chronic diseases, cannot control their diseases well, the endothelium of the blood vessels is damaged, which makes them prone to arteriosclerosis.

Atherosclerosis is very common. As we all know, atherosclerosis occurring in the coronary arteries is coronary heart disease. Similarly, if atherosclerotic plaques occur in the subclavian artery, the lumen of the subclavian artery will become narrower, the plaques will become larger, and the stenosis will become more severe. This disease process is called subclavian artery stenosis (or occlusion).

However, some patients with severe subclavian artery stenosis may have insufficient blood supply to the upper limbs, resulting in ischemic symptoms such as upper limb fatigue and coldness. Blood backflow from other circulations such as the cerebellar circulation and vertebral artery can cause steal syndrome.

Therefore, if the disease of subclavian artery atherosclerosis stenosis (or occlusion) continues to develop, it will cause a series of symptoms, including subsequent steal syndrome and so on.

Once steal syndrome occurs due to atherosclerotic stenosis (or occlusion) of the subclavian artery, it will cause vertebral artery reflux. The vertebral artery normally ascends from the intervertebral foramen of the cervical vertebra to the cerebellar circulation to supply blood to the cerebellum, but the blood in the vertebral artery flows back to the upper limbs, so the blood in the cerebellar circulation will be insufficient.

At this time, the vertebral-basilar artery system, that is, the blood supply to the cerebellum and brainstem will be insufficient, and the patient will experience local dizziness, including difficulties in positioning and standing.

Some people even have articulation disorders, which means they can’t speak clearly. They want to express something, but they can’t say it out loud. But if you ask them to write, they may be able to write it out. This means that ischemia in the cerebellum, including the vicinity of the brainstem, will cause some obstacles of insufficient local blood supply.