23.13: Heart Sounds
Heart sounds are generated by the turbulence in blood flow due to the closing of heart valves. These sounds are best perceived slightly away from the valves, where the blood flow disseminates the sound.
Auscultation is the process of listening to these internal body sounds using a stethoscope. The heart produces four types of sounds, but only two—S1 and S2—can usually be heard with a stethoscope.
S1, also known as the "lub" sound, is caused by the closure of atrioventricular (A-V) valves at the start of ventricular systole. It is characteristically louder and longer. S2, the "dub" sound, occurs due to the closure of semilunar valves at the beginning of ventricular diastole.
The other two sounds, S3 and S4, are usually inaudible and result from blood turbulence during ventricular filling and atrial systole.
Heart sounds offer insights into the heart's mechanical functioning. A heart murmur is an abnormal sound heard before, between, or after normal heart sounds, or it may mask them. In children, particularly between 2 and 4 years old, murmurs are common and usually harmless, often disappearing with growth. These are known as innocent or physiologic murmurs. However, in adults, murmurs typically signify a valve disorder. Stenosis is when the heart valve doesn't fully open or is too narrow, disrupting normal blood flow. Incompetence, on the other hand, occurs when the valve doesn't fully close, leading to a backflow or regurgitation of blood. Both conditions can cause distinctive murmurs, aiding in their diagnosis.
