Most physical exams include a blood pressure reading. 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 for many years was used to fill the central column in standard sphygmomanometers. (Modern devices do not use mercury.)
- 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 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.
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
Falsely high pressure can result from:
- An arm cuff that is too small
- Recently consuming foods or beverages (such as coffee) that raise blood pressure
- Recent tobacco exposure
- Recent exercise
Review Date: 04/06/2010
Reviewed By: Harvey Simon, MD, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.