The Human Body


Pulse (physiology), rhythmic expansion of the arteries resulting from passage of successive surges of blood, produced by continuing contractions of the heart. The arteries resemble elastic tubes, and at each contraction of the heart, 30 to 60 g (2 to 4 oz) of blood are forced into the already-filled vessels. The consequent distension passes along the arterial system at a rate of about 7 m (about 23 ft) a second until it reaches the capillaries, in which it is lost because of peripheral resistance to blood flow and lack of elasticity in the vessel walls.

The pulse may be felt wherever an artery passes over a solid structure, such as a bone or cartilage. The crest of the pulse wave represents the systolic pressure; the trough, the diastolic (see Blood Pressure). The rate of the pulse varies from 150 beats per minute in the embryo, to about 60 in the aged. Autosuggestion and certain training programs may alter the rate substantially (see Biofeedback; Consciousness, States of; Sports Medicine). In disease, the pulse rate usually varies in direct ratio to the body temperature; this correspondence is so regular that an experienced physician can approximate the temperature of a patient from observation of the rate of the pulse. The pulse is commonly taken at the wrist, and changes in its rate, rhythm, and strength alert the specialist to existing or impending disease. A pulse may sometimes be observed in the large veins; it is usually twice as fast as the arterial pulse, and is caused by variations in pressure in the left auricle by variations in pressure in the left atrium. See Heart.