As your heart pumps, it sends blood throughout your body, putting pressure on the walls of your blood vessels, especially your arteries. Your blood pressure is the measurement of the force of blood through your vessels. If you are healthy, your heart pumps blood to all the body's cells without causing undue stress on the vessels. Blood pressure is usually measured in either the right upper or left upper arm. A normal blood pressure is typically less than 120/80 mmHg (millimeters of mercury).
Understanding the Numbers
Systolic blood pressure measures the pressure when your heart contracts, propelling blood through your circulatory system. This is the top, higher number in the blood pressure measurement. Diastolic blood pressure measures the pressure as your heart relaxes, represented by the bottom, lower number. Blood pressure fluctuates every day for a variety of reasons: time of day, activity level, stress, age and physical condition, among others, but consistently high blood pressure (hypertension) requires lifestyle changes and/or medication to lower pressure and stop blood vessels from being damaged.
Pressure Difference Between Arms
There is a normal variation in inter-arm blood pressure, or the pressure between right and left arms. Usually it is less than 10 mmHg and, according to the American Heart Association, you should talk to your doctor if the difference is consistently greater. This could be an indicator of an underlying condition such as coronary artery disease (CAD), the narrowing of arteries supplying blood to the heart, or peripheral vascular disease (PVD), narrowing of other blood vessels that do not carry blood directly to the heart.
Which Arm to Measure?
Because there is a pressure difference between arms, measuring both arms initially is important to prevent a misdiagnosis of hypertension. Then, according to the American Heart Association, the arm with the higher blood pressure should be used to determine if you have hypertension. When monitoring hypertension, your doctor will likely also use the arm with the higher blood pressure to guide management decisions. When monitoring blood pressure at home, you should also use the arm with the higher reading.
PVD and CAD
In a 2007 Japanese study of 386 patients with suspected CAD, 63 percent of those with inter-arm blood pressure differences were found to have the disease. A 1991 study by Johns Hopkins Medical Institutions found that a significant difference in inter-arm blood pressures is more often symptomatic of PVD. The study found a greater "incidence and magnitude" of difference in right and left arm blood pressures with PVD than with CAD. Interestingly, the study found that neither arm consistently had the higher pressure.
While inter-arm blood pressure can be an indicator of an underlying circulatory condition, there are other risk factors that can indicate either PAD and CAD. These include smoking, high cholesterol, obesity, diabetes, hypertension and a sedentary lifestyle. Stopping smoking, controlling diabetes and high blood pressure, eating a healthy diet and exercising help prevention the diseases.