Blood pressure represents the force exerted by circulating blood against the walls of the body’s arteries. It is measured in millimeters of mercury (mmHg) and expressed as two numbers: systolic (pressure during heartbeats) and diastolic (pressure between heartbeats). While blood pressure is expected to be similar in both arms, slight differences can occur, prompting measurement in both arms during initial assessments.
Normal Fluctuations
Small variations in blood pressure readings between the two arms are common and typically do not indicate a health concern. The mean systolic difference is around 1.1 mmHg (normal range -9 mmHg to 11 mmHg), and the mean diastolic difference is approximately 0 mmHg (normal range -10 mmHg to 10 mmHg). These minor differences can arise from physiological factors, such as subtle variations in muscle contraction or blood vessel anatomy, or even from measurement technique. For instance, the dominant arm might exhibit slightly higher readings due to increased activity. These fluctuations are within the expected range and generally do not warrant further investigation.
Underlying Causes
A significant and consistent difference in systolic blood pressure between arms, defined as 10-15 mmHg or more, can signal an underlying medical condition. One cause is peripheral artery disease (PAD), where plaque buildup (atherosclerosis) narrows arteries and restricts blood flow, often more severely in one limb. This reduced flow leads to a lower pressure reading in the affected arm.
Other conditions can also contribute. Subclavian artery stenosis, a narrowing of the subclavian artery, can cause a notable difference. Aortic dissection, a serious condition involving a tear in the aorta, can lead to a substantial pressure difference, sometimes exceeding 40 mmHg. Coarctation of the aorta, a congenital narrowing, or atypical connections like fistulas or a persistent patent ductus arteriosus, can also result in varying readings.
Health Risks
A persistent, significant difference in blood pressure between arms is an important diagnostic sign. A systolic inter-arm difference of 10 mmHg or more is associated with an increased risk of future cardiovascular events, including heart attack and stroke. This difference indicates a higher likelihood of underlying vascular disease.
Research shows that for every 1 mmHg difference in systolic pressure between the arms, there is approximately a one percent increase in the predicted 10-year risk of developing new angina, a heart attack, or a stroke. Detecting such a disparity can be an early indicator of systemic arterial issues, such as stiffening or narrowing of arteries, which can affect blood flow throughout the body.
Medical Evaluation and Management
If a healthcare professional detects a significant blood pressure difference between your arms, they will begin with repeated measurements to confirm the finding. The arm with the higher reading will often be used for all subsequent measurements. A thorough physical examination will follow, focusing on signs of vascular disease or other contributing conditions.
To identify the underlying cause, further diagnostic tests may be recommended. These could include an ultrasound to visualize blood flow and detect blockages, or advanced imaging like CT angiography or MRI for detailed images of blood vessels and the aorta. Once a diagnosis is established, management strategies vary depending on the specific condition. This might involve lifestyle modifications, medications to manage blood pressure or cholesterol, or in some cases, surgical interventions to correct abnormalities or address blockages.