Why is the blood pressure in the upper limbs different and I feel dizzy when I shake my arms?

Author: Guo Baolei, Associate Researcher, Zhongshan Hospital, Fudan University

Xu Tiantong, School of Clinical Medicine, Fudan University

Reviewer: Fu Weiguo, Professor of Zhongshan Hospital, Fudan University

Have you ever seen the siphon phenomenon in your life? When you put one end of a water pipe into the water and the other end is below the water surface, the water will flow along the pipe until the water levels on both sides are balanced. This phenomenon caused by pressure difference is widely used in nature and human society. However, in our blood vessels, there is also a similar "siphon" phenomenon, which is the "blood stealing" of the subclavian artery. The blood pressure on both sides of the upper limbs is different, and you feel dizzy when you swing your arms. These manifestations may be the manifestations of subclavian artery steal syndrome caused by the "blood stealing" of the subclavian artery.

1. What is subclavian artery “blood steal”?

The subclavian artery is the main artery of the upper limbs, responsible for transporting blood to the upper limbs. At the same time, one of its branches, the vertebral artery, is responsible for supplying blood to the posterior 1/3 of the brain, including the cerebellum and brainstem, and is essential for maintaining body balance. Subclavian artery stenosis or occlusion is a peripheral arterial disease caused by blockage of one or both blood vessels, which leads to poor blood flow, insufficient blood supply to the upper limbs and brain, and a series of ischemic symptoms.

Figure 1 Copyright image, no permission to reprint

The most common cause of subclavian artery stenosis or occlusion is atherosclerosis. Atherosclerosis is a disease closely related to age, which is usually more common in the middle-aged and elderly population. Therefore, subclavian artery stenosis or occlusion is common in the middle-aged and elderly. In this process, the plaques formed by hardening cause vascular stenosis. When the stenosis reaches a certain degree, the blood flow will be affected, forming a pressure difference, resulting in inconsistent blood pressure in the upper limbs on both sides. Since the subclavian arteries on both sides and the parts extending into the skull form a circular arterial circuit (the professional name is the Willis circle), blood flows back from the other side of the Willis circle through siphoning, causing retrograde blood flow in the vertebral artery, causing ischemic symptoms. It looks like the subclavian artery "stole" the blood from the contralateral vertebral basilar artery or internal carotid artery system, so a series of symptoms of posterior circulation ischemia appear. The subclavian artery originates directly from the aorta and is at the bifurcation. The blood flow there is prone to form vortices. The continuous impact of the pulsating blood flow can cause damage to the vascular endothelial cells, induce thrombosis or atherosclerotic plaque formation, and cause arterial stenosis. Therefore, the opening of the subclavian artery is prone to stenosis, and it is more common on the left side. Other pathogenic factors include multiple arteritis, congenital arterial malformations, congenital heart disease, trauma or surgery, aortic dissection, thrombosis, autoimmune diseases, etc., and their basic principles are the same.

2. What are the symptoms of subclavian steal syndrome?

There are generally no symptoms in the early stages of subclavian artery stenosis or occlusion. As the disease progresses, symptoms of upper limb ischemia or posterior circulation cerebral ischemia will appear.

Symptoms of upper limbs include pain, weakness, numbness, and coldness in the arms. In severe cases, ulcers and tissue necrosis may occur at the ends of the fingers. Symptoms of cerebral ischemia include dizziness, diplopia, blurred vision, slurred speech, dysphagia, tinnitus, hemiplegia, etc., especially when the upper limbs are active. Some patients feel dizzy when they swing their arms because of insufficient blood supply to the limbs, which aggravates the "blood stealing" during activities, and the brain is also ischemic. When the important balance center of the brain is not supplied with enough blood, the patient will feel dizzy or even faint. These symptoms of transient cerebral ischemia are commonly known as "mini-strokes." Therefore, if you often fall suddenly or experience other symptoms mentioned above, they may be arterial health alarms issued by the body. You should seek medical attention in time and have regular physical examinations. It is worth noting that if the patient has a history of coronary artery bypass grafting, when symptoms of myocardial ischemia such as angina pectoris occur, you should also be alert to whether the ischemia is caused by stenosis or occlusion of the subclavian artery opening.

During the examination, if the pulse on one side is weak or even absent, and the blood pressure on both sides is asymmetric, with the blood pressure on one side significantly lower than the other side, and the difference is more than 10 mmHg, this is likely a sign of subclavian artery stenosis or occlusion. Further diagnosis of subclavian artery stenosis or occlusion requires vascular ultrasound or angiography, among which ultrasound Doppler vascular examination has a very high accuracy rate for diagnosing subclavian artery "blood steal" and can preliminarily determine the abnormality and scope of the lesion. In addition, CT angiography is also an important means of making a clear diagnosis, which can clearly determine the location of the lesion and the degree of stenosis.

Figure 2 Copyright image, no permission to reprint

3. How to treat subclavian steal syndrome?

For patients with asymptomatic mild subclavian artery stenosis, conservative treatment can be used, and medication can be taken according to the cause. For example, if the stenosis is caused by atherosclerosis, statins are usually used to control blood lipids to slow down the progression of plaques; if necessary, antiplatelet aggregation drugs are needed to prevent arterial restenosis and plaque formation.

As the degree of stenosis increases, patients may experience the various ischemic symptoms mentioned above, and surgical treatment should be actively performed at this time. Minimally invasive interventional surgery can be used, and the specific methods include balloon dilatation and stent implantation. First, select a suitable blood vessel as the surgical approach according to the degree of occlusion, with the femoral artery as the first choice, and then use a balloon catheter to dilate the blood vessel, and then implant a stent at the lesion. The stent is like a bridge in the blood flow. When our own blood vessels cannot provide a smooth passage for blood, the stent plays a supporting and unblocking role. If the balloon dilatation is good and the degree of vascular stenosis is low, the stent may not be placed.

If the interventional procedure fails or the patient is not suitable for interventional treatment, a surgical procedure, also known as open vascular bypass reconstruction, is required. Open surgery is usually performed under general anesthesia. The doctor will make an incision in the neck or chest to expose the narrowed blood vessels, and then use the patient's own blood vessels or artificial blood vessels to bypass the narrowed part and create a new blood flow channel. However, compared with minimally invasive interventional surgery, open vascular bypass surgery is more traumatic and has a higher risk of infection.

In addition, patients with subclavian artery stenosis should avoid consuming high-salt, high-sugar, and high-fat foods in daily life, and quit smoking, drinking, and exercise appropriately, which will help control the disease.

IV. Summary

Subclavian artery stenosis or occlusion is a common vascular disease, but it is often ignored because its symptoms are not obvious. When measuring blood pressure, it is advisable to observe whether there is a difference in blood pressure between the two upper limbs to promptly detect asymptomatic subclavian artery "blood steal" phenomenon. For symptomatic patients, minimally invasive interventional treatment has become the main treatment method, and its safety and effectiveness have been recognized. At the same time, for patients with complex conditions such as coexisting other diseases, comprehensive evaluation and treatment are required to select the most appropriate treatment plan.