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MEDICINE 101

HEART SOUNDS

The stethoscope was first invented in the early 1800's by a Parisian physician Rena Laennec, who's first stethoscope was simply a hollow wooden tube that he put up to one ear. Laennec called his invention the stethoscope after the Greek word stetho for chest and scopein for examination.

It's a simple tool really - a plastic disc on this end moves with the sound waves, which are then transmitted by hollow tubing to both ears. No need for electronics or other gadgetry.

But what do we physicians hear in the stethoscope?

The lungs make sounds as air enters and leaves. In pneumonia the small air sacks are filled with fluid and infection. They open with a crackling sound like this. In asthma you can hear a distinct honking sound.

But the stethoscope is used to the most advantage when listening to heart sounds. Lub Dub, Lub Dub - every medical student learns that the sounds of the heart are caused by the rhythmic opening and closing of the four valves of the heart. Here is what it sounds like in the stethoscope. (pause)

These valves are amazing things - they function to allow blood to flow only in one direction with the pumping of the heart. This is a cow's heart, and here are the tough but pliant parts or cusp of the aortic valve, the valve at the exit of the heart. In simple terms, the valves are much like the pockets in your pants - when the heart contracts, the flow of blood out of the heart forces the pocket of the valve to lie flat against the wall of the artery like this. When the contraction is over the pocket balloons back out, closing off the artery.

As the blood is pumped past the valve, cusps are pushed flat against the side of the vessel. As the contraction ceases the valve cusps balloon out like this.

Diseased valves produce sounds that are not normal, including murmurs. A murmur is a rumbling or whooshing sound caused by turbulent blood flow or by flow through a faulty valve. For example, if a valve leaks, some blood flows back into the heart producing an extra sound. Similarly, if a valve doesn't open properly (that is it's narrowed) a murmur is also produced. Here is what murmur's sound like.

That's why the stethoscope is so useful, so much a part of the image of a physician. By studying the sounds produced by your body, both in health and disease - this instrument allows us to understand the music inside of you!