Sunday, 10 May 2009

Sounds of Korotkoff

Earlier this year I was telling D and Lola II about how we’d been taking blood pressure measurements the old-fashioned way with a stethoscope and a cuff on the upper arm attached to a squeezy ball. You pump up the pressure until there are no pulse sounds, then you let the pressure down until you start to hear a pulse at the elbow (this is the upper number = systolic pressure, equivalent to the force that the heart can pump), then you let the pressure down further until the sounds disappear (lower number = diastolic pressure, equivalent to the resistance in the arteries, capillaries and veins). It all seemed very straightforward until D asked what the sounds actually were, and I had no idea.

Yesterday I was revising cardiovascular medicine, and came across a paragraph in a textbook that explains it perfectly.

“At the systolic pressure, a faint tapping sound is heard as blood first begins to pass the cuff. With further lowering of the pressure, the sound becomes louder, then dull and muffled before finally disappearing. These are the sounds of Korotkoff, which are produced by turbulent flow in the brachial artery. The change from staccato to muffled sound occurs when blood first passes under the cuff continuously, even though the artery is still partially constricted. Continuous flow has a different auditory quality than interrupted flow.”

[It’s an American textbook; ‘different... than’ always makes me wince. I can tolerate 'different... to' and 'different... from' but not 'different... than'.]

I’m back with cardiovascular disease again today: atherosclerosis, dyslipidaemia, reverse cholesterol transport. They think that women have a lower rate of heart disease because of a protective effect from oestrogen – after menopause the risk seems to become comparable to men. There’s something to look forward to.

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