| |
heart sounds
sounds heard on the surface of the chest in the heart region, which can be amplified by a stethoscope in order to be heard more distinctly. They are caused by vibrations generated during the normal cardiac cycle and may be produced by muscular action, valvular actions, motion of the heart, or blood passing through the heart. The first heart sound (S1) is heard as a firm but dull “lubb” sound. It consists of four components: a low-frequency, indistinct vibration caused by
ventricular contraction; a louder sound of higher frequency caused by closure of the mitral and tricuspid valves; a vibration caused by opening of the semilunar valves and early ejection of blood from the ventricles; and a low-pitched vibration produced by rapid ejection. The second heart sound (S2) is shorter and higher pitched than the first, is heard as a “dupp” and is produced by closure of the aortic and pulmonary valves. The third heart sound (S3) is faint and is caused by blood rushing into the ventricles. It can be heard in most normal persons between the ages of 10 and 20 years. The fourth heart sound (S4) is rarely audible in a normal heart but can be demonstrated on graphic records. It is short and of low frequency and intensity,
and is caused by atrial contraction. The vibrations arise from atrial muscle and from blood flow into, and distention of,
the ventricles.
Copyright 2007. An Elsevier publication. All rights reserved.
Click here for important legal information about Dorland's Medical Dictionary.
|
