SAMUEL ASHFIELD / SCIENCE PHOTO LIBRARY SAMUEL ASHFIELD / SCIENCE PHOTO LIBRARY
Blood pressure measurement. Doctor taking the blood pressure with a sphygmomanometer and listening to the heartbeat with a stethoscope of a patient (not seen). A cuff is inflated around the patient's upper arm until it is tight enough to stop the flow of blood in the main artery. As the cuff is deflated, the systolic pressure of the pumping heart is taken, then the diastolic pressure of the relaxed heart (between pumps) is taken. Blood pressure is expressed as a difference between these two measurements, in millimetres of mercury (mm Hg). Although blood pressure varies over the day, it is an important measure of bodily health.
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