Blood pressure measuring devices
Hypertension, or high blood pressure--also known as the "silent killer"--affects more than 60 million Americans. Blood pressure measuring devises are theonly means through which high blood pressure can be detected. In the course of his pioneering work on blood circulation in the 1600s, William Harvey (1578-1657) noted that blood pulsated out of a severed artery as if it were underrhythmic pressure. Nearly a century later, Stephen Hales (1677-1761), an English clergyman and physiologist, devised a technique to measure the pressure exerted on the vessels as blood was pumped through them. Hales inserted a brass pipe into an animal's blood vessel and used the windpipe of a goose (for its flexibility) to connect the pipe to a long glass tube. The height to whichthe animal's blood spurted up into the tube gave a measure of the force propelling the blood. One of Hales' most dramatic experiments using this simple manometer involved a white mare, tied flat on the ground to a stable door; theglass tube in this instance was 12 ft. 9 in. (3.8 m) long, and the horse's blood rose in it to a height of 9 ft. 6 in. (2.9 m). Hales began his blood pressure measurement experimentation around 1706, continued around 1712-13, and finally reported his technique in his 1733 book Haemastaticks. Anothercentury passed before the Hales manometer was improved upon. In 1828 French physician Jean Leonard Marie Poiseuille (1797-1869) replaced the long glass tube with a U-shaped tube filled with mercury and calibrated to record pressurelevels in millimeters of mercury. The German physiologist Karl Friedrich Wilhelm Ludwig modified Poiseuille's manometer in 1847, adding a revolving cylinder and float with a revolving drum on which the blood pressure was recorded.This device was called a kymograph. It was further refined by Etienne-Jules Marey with his 1863 sphygmograph, another blood pressure recorder. The first blood pressure measuring device that required no skin penetration was the sphygmomanometer pioneered by Samuel Siegfried von Basch (1837-1905), a German physician, in 1876. This rather inaccurate device was replaced in 1896 by the sphygmomanometer of the Italian physician Scipione Riva-Rocci (1863-1937), the prototype of today's standard instrument which uses anarm band which is inflated until the blood flow through the arteries can nolonger be detected. Air is then released from the band, and blood pressure measured on a mercury manometer at the moment when the pulse reappears. While Riva-Rocci's instrument was accurate, it measured only systolic pressure--pressure within the artery when the heart is contracting. A Russian physician, Nikolai Korotkoff, added the missing element when he suggested in 1905 that a stethoscope be used to listen to the blood flow in the brachial arteryof the elbow. Heard through the stethoscope, the tapping that begins when airis released from the band is the systolic pressure; the moment the tapping sound disappears is the diastolic (between contractions) pressure.
Wide clinical use of blood pressure measurement using the sphygmomanometer was promoted by American surgeon Harvey Williams Cushing. Standard readings were soon established and became basic indicators of heart and lung health or problems. Today, virtually every visit by an adult to a doctor includes a bloodpressure test. Many types of blood pressure measuring devises are now available, even for home use, for which automated meters are preferable because of their simplicity. Automated meters are battery-operated electronic ordigital devices which measure either sound or force and eliminate the need for a stethoscope, using instead a microphone device. There is even a cufflessoscillometric meter, which reads blood pressure from a device in whichthe patient's finger is placed. Home blood pressure measuring devices offerobvious advantages, even though they provide less accurate readings than those obtained at a physician's office.
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