Instruments to measure blood pressure

Most physical exams include a blood pressure measurement. Patients should not smoke, exercise, or drink caffeinated beverages within 30 minutes before their blood pressure measurement.

Measuring Blood Pressure

• The standard instrument used to measure blood pressure is called a sphygmomanometer. Measurements are given as units of mercury, which has filled the central column in standard sphygmomanometers for years. (Modern devices are designed to prevent mercury spillage.)
• An inflatable cuff with a meter attached is placed around the patient's arm over the artery while the patient is seated, their back is supported, and the arm being used is around the level of the heart. The inflated cuff briefly interrupts the flow of blood in the artery, which then resumes as the cuff is slowly deflated.
• The person taking the blood pressure listens through a stethoscope.
• The first pumping sound your health care provider hears is recorded as the systolic pressure, and the last sound is the diastolic pressure.
• If a first blood pressure reading is above normal, the health professional may take two or more measurements separated by 2 minutes with the patient sitting or lying down. Another measurement may be taken after the patient has been standing for 2 minutes. If the measurements are still elevated, your health care provider should take blood pressure readings from both arms.

To measure blood pressure, your doctor uses an instrument called a "sphygmomanometer, " more often referred to as a blood pressure cuff. The cuff is wrapped around your upper arm and inflated to stop the flow of blood in your artery. As the cuff is slowly deflated, your doctor uses a stethoscope to listen to the blood pumping through the artery. These pumping sounds register on a gauge attached to the cuff. The first pumping sound your doctor hears is recorded as the systolic pressure, and the last sound is the diastolic pressure.

Although this test has been used for more than 90 years, it is not completely accurate or sensitive. The following factors can cause a falsely low pressure reading:

• An arm cuff that is too wide
• Dehydration

Falsely high pressure can result from:

• An arm cuff that is too small
• Stress
• Recently consuming foods or beverages (such as coffee) that raise blood pressure
• Recent tobacco exposure
• Recent exercise

Office blood pressure readings taken by a doctor are more likely to be higher than readings measured at home. This can be caused by "white coat hypertension, " which is blood pressure that is only elevated during a doctor's office visit. It is defined as a daytime blood pressure away from the doctor's office of less than 135/85 mg Hg and no evidence of complications of blood pressure elsewhere in the body. Patients with white-coat hypertension may require additional blood pressure readings.