CHRIS PRIEST & MARK CLARKE / SCIENCE PHOTO LIBRARY CHRIS PRIEST & MARK CLARKE / SCIENCE PHOTO LIBRARY
A nurse taking the blood pressure of a pregnant woman. The instrument used is a sphygmomanometer. A cuff is inflated around the upper arm until it is tight enough to stop the flow of blood in the main artery. This pressure is recorded as the systolic pressure of the pumping heart. The cuff is then deflated, to give the diastolic pressure of the relaxed heart between pumps. 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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