Measuring Blood Pressure

To measure blood pressure, the health care provider places a blood pressure cuff around the upper arm and inflates the cuff with air. As the cuff becomes filled with air, the pressure in the cuff increases, eventually cutting off the flow of blood through the arteries in the arm.

The health care provider slowly lets air leak out of the blood pressure cuff, causing the pressure in the cuff to gradually decrease. When the pressure in the cuff falls below the systolic blood pressure in the arteries, the provider begins to hear a characteristic thumping sound as blood starts to flow again in the arm. The blood pressure cuff continues to deflate, and when the pressure in the cuff falls below the diastolic blood pressure in the arteries, the characteristic thumping sound disappears.

By listening for the beginning and termination of this sound and simultaneously watching the pressure gauge in the cuff when these events occur, the health care provider determines the systolic and diastolic blood pressure.

If the blood pressure is not measured correctly, the readings obtained may be artificially high. Several steps ensure that the measured blood pressure truly represents the patient's blood pressure:

  1. Patients should sit with their arms supported at heart level.
  2. Patients should not smoke or ingest caffeine for 30 minutes prior to blood pressure measurement.
  3. Patients should sit down for at least 5 minutes before blood pressure is measured.
  4. The bladder (inflatable part) of the blood pressure cuff should encircle at least 80 percent of the arm. A large cuff should be used for patients with thick arms.
  5. Two or more readings should be taken at least 2 minutes apart.

High blood pressure (hypertension) is a major risk factor for heart disease, congestive heart failure, stroke, impaired vision, and kidney disease. The National Heart, Lung, and Blood Institutes classifies blood pressure as normal, prehypertension, hypertension stage 1, and hypertension stage 2.

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 24 Nov 2004

Last Modified: 18 Sep 2015