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Measuring Blood Pressure

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Updated February 20, 2007

Measuring Blood Pressure

The Sphygmomanometer:

Blood pressure is measured using a sphygmomanometer. Most people call it a blood pressure gauge (or cuff). Manual versions of the blood pressure gauge have three components: an arm cuff, a pressure gauge and a stethoscope. Electronic blood pressure gauges do not need a stethoscope.

The Numbers:

Blood pressure is measured in two numbers, the systolic (top) and the diastolic (bottom). The systolic number represents the pressure when the heart is pumping blood. The diastolic is the pressure on the arteries between pumps.

How to Get the Top Number:

The blood pressure cuff is wrapped around the arm and inflated to well above your systolic blood pressure. This cuts off circulation to the arm. The air is gradually reduced and the gauge measures the dropping pressure in the cuff. Meanwhile, you or someone else is listening through the stethoscope for the pulse. When the pulse can be heard again, the pressure in the cuff is equal to the force of the heart pumping (systolic pressure).

How to Get the Bottom Number:

To get the second reading, the diastolic blood pressure, air is continued to be released from the blood pressure cuff. This is the pressure when the heart is not pumping (think of it as the resting pressure). When the pressure of the cuff is less than the diastolic (resting) pressure of the artery, the pulse can no longer be heard.

What is a normal, healthy blood pressure?:

  • Systolic: 119 or lower
  • Diastolic: 79 or lower

What is a pre-hypertension reading?:

  • Systolic: 120 to 139
  • Diastolic: 80 to 89

What is a high blood pressure reading?:

Stage 1

  • Systolic: 140 to 159
  • Diastolic: 90 to 99

Stage 2

  • Systolic: 160 or higher
  • Diastolic: 100 or higher

source: National Institutes of Health
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