An instrument used for measuring blood pressure. A cuff attached to the device is wrapped around the person’s arm and inflated until it compresses the main artery in the arm. The cuff is deflated while the doctor listens to the blood flow through a stethoscope. The sphygmomanometer records the pressure on a mercury-filled glass column or a digital display.
The traditional device for measuring blood pressure in clinical practice, devised by Riva-Rocci and Korotko? about a century ago. Measurement depends on accurate transmission and interpretation of the pulse wave to an artery. The sphygmomanometer is of two types, mercury and aneroid. The former is more accurate. Both have some features in common – an in?ation-de?ation system, an occluding bladder encased in a cu?, and the use of AUSCULTATION with a STETHOSCOPE. The mercury sphygmomanometer consists of a pneumatic armlet which is connected via a rubber tube with an air-pressure pump and a measuring gauge comprising a glass column containing mercury. The armlet is bound around the upper arm and pumped up su?ciently to obliterate the pulse felt at the wrist or heard by auscultation of the artery at the bend of the elbow. The pressure, measured in millimetres of mercury (mm Hg), registered at this point on the gauge is regarded as the pressure of the blood at each heartbeat (ventricular contraction). This is called the systolic pressure. The cu? is then slowly de?ated by releasing the valve on the air pump and the pressure at which the sound heard in the artery suddenly changes its character marks the diastolic pressure. Aneroid sphygmomanometers register pressure through an intricate bellows and lever system which is more susceptible than the mercury type to the bumps and jolts of everyday use which reduce its inaccuracy.
While mercury sphygmomanometers are simple, accurate and easily serviced, there is concern about possible mercury toxicity for users, those servicing the devices and the environment. Use of them has already been banned in some European hospitals. Although it may be a few years before they are widely replaced, automated blood-pressure-measuring devices will increasingly be in routine use. A wide variety of ambulatory blood-pressuremeasuring devices are already available and may be ?tted in general practice or hospital settings, where the patient is advised on the technique. Blood-pressure readings can be taken half-hourly – or more often, if required – with little disturbance of the patient’s daily activities or sleep. (See also BLOOD PRESSURE; HYPERTENSION.)
n. an instrument for measuring *blood pressure in the arteries. It consists of an inflatable cuff connected to a graduated scale gauge calibrated in millimetres of mercury (mmHg). The cuff is applied to a limb (usually the arm) and inflated to exert pressure on a large artery until the blood flow stops. The pressure is then slowly released and, with the aid of a stethoscope to listen to the pulse, it is possible to determine both the systolic and diastolic pressures (which can be read on the scale). Automated electronic devices are increasingly used.
If the tip of one ?nger is laid on the front of the forearm, about 2·5 cm (one inch) above the wrist, and about 1 cm (half an inch) from the outer edge, the pulsations of the radial artery can be felt. This is known as the pulse, but a pulse can be felt wherever an artery of large or medium size lies near the surface.
The cause of the pulsation lies in the fact that, at each heartbeat, 80–90 millilitres of blood are driven into the AORTA, and a ?uid wave, distending the vessels as it passes, is transmitted along the ARTERIES all over the body. This pulsation falls away as the arteries grow smaller, and is ?nally lost in the minute capillaries, where a steady pressure is maintained. For this reason, the blood in the veins ?ows steadily on without any pulsation. Immediately after the wave has passed, the artery, by virtue of its great elasticity, regains its former size. The nature of this wave helps the doctor to assess the state of the artery and the action of the heart.
The pulse rate is usually about 70 per minute, but it may vary in health from 50 to 100, and is quicker in childhood and slower in old age than in middle life; it is low (at rest) in physically ?t athletes or other sports people. Fever causes the rate to rise, sometimes to 120 beats a minute or more.
In childhood and youth the vessel wall is so thin that, when su?cient pressure is made to expel the blood from it, the artery can no longer be felt. In old age, however, and in some degenerative diseases, the vessel wall becomes so thick that it may be felt like a piece of whipcord rolling beneath the ?nger.
Di?erent types of heart disease have special features of the pulse associated with them. In atrial FIBRILLATION the great character is irregularity. In patients with an incompetent AORTIC VALVE the pulse is characterised by a sharp rise and sudden collapse. (See HEART, DISEASES OF.)
An instrument known as the SPHYGMOGRAPH registers the arterial waves and a polygraph (an instrument that obtains simultaneous tracings from several di?erent sources such as radial and jugular pulse, apex beat of the heart and ELECTROCARDIOGRAM (ECG)) enables tracings to be taken from the pulse at the wrist and from the veins in the neck and simultaneous events in the two compared.
The pressure of the blood in various arteries is estimated by a SPHYGMOMANOMETER. (See BLOOD PRESSURE.)... pulse
n. a device for measuring pressure in a liquid or gas. A manometer often consists of a U-tube containing mercury, water, or other liquid, open at one end and exposed to the fluid under pressure at the other end. The pressure can be read directly from a graduated scale. See also sphygmomanometer.... manometer
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