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February 15, 2013 7:58 pm
Most bodily sounds are familiar because we can hear them. We know what breathing sounds like, and sneezing, and the whispering noise you get when you rub your ear lobe between your finger and your thumb. But we also know what a heartbeat sounds like, although our own is usually inaudible, and we can sometimes hear other people’s. As a child, you can stick a pretend stethoscope on to an adult’s chest to hear them say, “Bu-dum bu-dum bu-dum”. We get used to hearts beating in the cinema and on television: a film will trap its heroine in a dark car park, underlining the scariness with a soundtrack of amplified BA-BOOM! BA-BOOM!
As a doctor, you have to be able to describe a “normal” heartbeat before you can appreciate anything abnormal. Medicine uses the phrase “lub-dub” or “lub-dup” to describe the noise the heart makes: this is what you can hear through your stethoscope. The term aims to capture the slight distinction in quality between the first and the second heart sounds.
The first heart sound, or “lub”, is generated by the atrioventricular valves closing. Once the top two chambers of the heart – the atria – have finished emptying blood into the bigger bottom chambers, or ventricles, the valves between the atria and the ventricles clamp shut in order to prevent blood leaking in the wrong direction. The second heart sound, “dub” or “dup”, occurs after the ventricles have pumped the blood out of the heart into the big blood vessels – oxygenated blood into the aorta, to be delivered to the body, and deoxygenated blood into the pulmonary artery, to be returned to the lungs. The flaps of the aortic and pulmonary valves are more rigid than those of the atrioventricular valves, so the sound they make when they close is slightly shorter and crisper.
Changes in rhythm can signal an abnormality. You may hear a gallop, where an extra heart sound causes a “lub-dub-dub, lub-dub-dub” noise, like a horse’s hooves coming towards you. This isn’t necessarily pathological, though it can signal heart failure. Or the rhythm may have broken down completely, into the “irregularly irregular” chaos of atrial fibrillation (“lub … dup-lub … dup … lub-dup-lu … b-dup”), which is caused by the atria fibrillating, or quivering, and so filling and emptying in a chaotic fashion.
Other sounds are due to various heart conditions. Clicking and snapping noises are usually generated by abnormally stiff valves opening or shutting (or you may hear the mechanical clunk of a prosthetic valve). Then there are the sloshing and rumbling sounds we call “heart murmurs”, caused by changes in the velocity and turbulence of the blood as it flows through the heart. Changes in the valves’ function can allow blood to leak in the wrong direction, causing audible eddies; or blood may whoosh through a resistant valve with abnormal force.
Learning to identify murmurs gives medical students nightmares. The first step is learning to hear the subtle distinction between “lub” and “dub” – if you don’t you will struggle to know where you are in the heart’s cycle, and so won’t be able to work out when the extra sounds are taking place.
I did my revision in Starbucks. There are lots of websites that allow you to listen to recordings of the heart; when I went to get a coffee I’d leave my laptop on the table making unusually human noises. Once my friend played a respiratory soundtrack at the same time. One of our computers was wheezing, the other had tachycardia. “The famous medical sense of humour!” said the woman sitting next to us, kindly.
Sophie Harrison is a hospital doctor in South Yorkshire
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