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Theory of Blood Pressure Measurement

According to the American Heart Association, hypertension (high blood pressure) claimed 56,561 lives in the United States in 2006. Blood pressure is an important indicator of heart function that is easily measured and usually manageable.

  1. History

    • The Rev. Stephen Hales, a British veterinarian, first recorded blood pressures in 1733 by inserting brass pipes into the arteries of animals. By the early 1800s, non-invasive blood pressure measurement methods existed. In 1896, Italian physician Scipione Riva-Rocci developed the traditional blood pressure apparatus known as a sphygmomanometer.

    Types

    • Blood pressure measurements generally reflect arterial pressure. Invasive methods involve inserting an instrument into the body, while non-invasive methods do not. Additionally, blood pressure measurements may be continuous or intermittent. In the hospital, continuous invasive monitors are the ultimate standard of blood pressure measurement, because they give more accurate, long-term information.

    Common Instruments

    • There are many devices for measuring blood pressure. However, blood pressure is usually measured with a stethoscope coupled with an aneroid or mercury sphygmomanometer. Digital sphygmomanometers do not require the use of a stethoscope. A sphygmomanometer is made up of a cuff with an inflatable bladder; a manometer, or pressure gauge; and a rubber hand bulb with a pressure-control valve.

    Units of Measurement

    • Blood pressure is expressed in "millimeters of mercury" (mm Hg) and typically includes two numbers. The top (first) number indicates the systolic pressure, or pressure of blood flow during the heartbeat. The bottom (second) number reflects the diastolic pressure, which is the blood pressure in the resting heart (between heartbeats).

    Measurement Process

    • In order to measure blood pressure, the examiner typically wraps a rubber cuff around the patient's upper arm and inflates it. This squeezes the brachial artery in the arm, temporarily interrupting blood flow. The examiner then releases the air in the cuff while listening with a stethoscope. The first sound occurs when the blood starts pulsing through the artery. The corresponding measurement is the systolic pressure. As the cuff continues to deflate, the last sound corresponds to the measurement of diastolic pressure.

    Normal Results

    • Age and health are among factors that affect blood pressure values. Ideally, for adults ages 18 or older, a normal blood pressure should not exceed 120/80 mm Hg. However, repeated measurements are important to determine whether a person truly has hypertension.

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