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
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