Your body may look symmetric, but if you look a little closer, you may notice that one eye may be a bit lower than the other, or maybe one hand or foot is a little larger. Inside your body, most of your organs, including blood vessels, are arranged asymmetrically, so what does this mean for your blood pressure?
Blood pressure can vary between your right and left arms and the reason for this could simply be caused by a muscle pressing on a blood vessel, causing turbulence in the body. However, it could be much more serious and a sign of cardiovascular disease, which can lead to strokes, heart attacks, or blood vessel damage. Continue reading to find out why it’s important to check your blood pressure in both arms and what to do if they’re not the same.
What is blood pressure?
Blood pressure is the force of blood against the walls of your blood vessel. When the heart contracts, blood pressure rises to a maximum, and the recorded pressure is called the systolic blood pressure. When your heart relaxes, the pressure recorded is diastolic pressure.
Blood pressure is measured in millimeters of mercury (mmHg) and recorded as a ratio, with the top number being the systolic pressure and the bottom number being the diastolic pressure.
A normal adult blood pressure is defined as a systolic BP of 120 mmHg or less and a diastolic BP of 80 mmHg or less. Hypertension (high blood pressure) is defined as having a systolic BP greater than or equal to 130 mmHg and/or diastolic BP greater than or equal to 80 mmHg.
High blood pressure is diagnosed after taking repeated BP measurements, over an extended period of time, and getting consistent results. Blood pressure is affected by stress, position, hydration, hormone levels, salt in the diet, medications, and other variables. Since it can fluctuate from minute to minute it is important to measure blood pressure repeatedly, rather than just a single measurement.
Why might your blood pressure be different between your two arms?
Your heart sits just to the left of the midline in your chest cavity. The largest blood vessel in the body, the aorta, leaves through the left side of the heart and transports blood to a network of branching blood vessels that supply the body with oxygen and nutrients.
The arteries that branch off the aorta and go towards the left and right sides of the body are different. On the right side, the brachiocephalic trunk comes off the aorta and splits into the right common carotid artery and right subclavian artery. The left common carotid and left subclavian arteries to come directly off the aorta. These differences mean that the risk for increased turbulence leading to arterial thrombosis is not the same for the right and left subclavian arteries. Arterial thrombosis causes blood vessel stiffening and obstruction over time and is four times more likely in the left subclavian than in the right. The difference in arterial branching affects the blood pressure measured on the left and right arms.
Blood vessels are surrounded by muscle, fat, and connective tissue. When muscles put pressure on the blood vessels around the heart, it can cause transient turbulence, which may affect blood pressure. However, this effect on blood pressure should be temporary and minor, which is why it’s important to understand your blood pressure on both sides of the body.
How should you have your blood pressure checked?
Whether measuring at home or at a doctor’s office, your blood pressure should be taken in both arms simultaneously, if possible. A blood pressure difference of less than 5 mmHg between the left and right arm is considered normal. This minor difference is usually due to the asymmetry in how the blood vessels come off the aorta, the main vessel leaving the heart.
When measured in both arms, a consistent significant difference in blood pressure greater than 5 mmHg could indicate that the artery with the higher pressure is narrower or stiffer than in the opposite arm. This information is important for understanding your potential health risks such as stroke, peripheral artery disease, or other cardiovascular conditions.
Blood vessels can narrow over time due to cholesterol deposits which can increase the resistance to blood flow. Think of this as similar to the way that mineral deposits on the inner surface of a hose can reduce water flow. When blood vessels are narrowed, the heart must contract more forcefully to overcome the resistance and maintain blood flow, creating an increase in blood pressure.
A significant and persistent difference in blood pressure between the left and right arm can also be a sign of aortic dissection. This serious condition is due to a tear in the wall of the aorta. Symptoms of an aortic dissection may vary but could include severe chest or back pain, severe abdominal pain, loss of consciousness, weakness in the arms and legs, among others.
If there is a consistent difference of more than 10 mmHg in blood pressure readings between your arms, your blood pressure should be taken in the arm with the higher pressure. If there is more than a 20-mmHg difference between the blood pressure readings in your arms, your doctor may request further testing.
High blood pressure, left untreated, can lead to peripheral artery disease (PAD), which can cause complications such as heart disease, strokes, and blood vessel damage that may harm the kidneys and the eyes.
What is peripheral artery disease?
Peripheral artery disease is a narrowing of the arteries that carry blood away from the heart to other parts of the body. Here are Some important statistics to know about PAD:
- The risk of PAD increases with age.
- Over half of affected people with PAD do not have symptoms.
- Approximately one-fourth of individuals with PAD have diabetes mellitus.
- Smokers have a 2.5 times higher risk of developing PAD.
- Twice as many African Americans are affected than non-Hispanic whites, regardless of age.
This is why it’s important to be proactive in monitoring your blood pressure.
The research behind these recommendations
An analysis of 24 previous blood pressure studies involving 57,000 participants revealed that people with a difference in systolic blood pressure of more than 5mmHg between their arms had a higher mortality rate than those with a difference of less than 5 mmHg. Furthermore, over ten years, each 1-point difference in intra-arm blood pressure was associated with a 1% increase in death from any cause and a 1% to 2% increase in the risk of cardiovascular death.
Differences in blood pressure between arms are fairly common, with 3.6% of healthy adults having a difference in blood pressure. The prevalence of blood pressure differences between the left and right arm rises to 7% in people with diabetes and 11.2% in individuals diagnosed with hypertension.
Individuals with increased blood pressure differences between the left and right arms are associated with an increased risk of cardiovascular disease. Researchers discovered that those with high blood pressure, diabetes, and pre-existing cardiovascular disease, as well as those without a diagnosis of cardiovascular disease, are at a higher risk.
In people with diabetes, a significant difference in intra-arm blood pressure can also signal chronic kidney disease. These high-risk individuals should monitor their blood pressure on both arms often.
While it is important to be aware of factors that can increase your risk of heart disease, it is also important to be mindful of factors that can decrease your risk, especially modifiable ones such as diet, physical activity, excessive alcohol consumption, or smoking.
Which arm should I use to take my blood pressure?
Systolic and diastolic blood pressure measurements are used to make treatment decisions for high blood pressure. For this reason, after checking your blood pressure in both arms, record and track your blood pressure in the arm with a higher reading. The blood vessels that are subjected to the most trauma over time are the ones most likely to sustain damage that can have a negative impact on your health.
It is a good idea to periodically check your blood pressure in the arm that had a lower reading, just to verify that nothing has changed. Of course, if you have an arm injury or other serious reason to avoid checking your blood pressure in one of your arms, then you should check your blood pressure in the uninjured arm.
Taking the time to check your blood pressure at home can help you pick up on patterns early. It is also never too early to start proactively protecting your blood vessels through a healthy diet, minimizing high stress, and plenty of physical activity!
Leann Poston, MD, is a licensed physician in Ohio who holds an MBA and an M.Ed. She is a full-time medical communications writer and educator who researches and writes about medicine, education, and healthcare administration.