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So this is a picture of Dr. Korotkoff.

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Dr. Korotkoff is a very famous Russian doctor who lived about a 100 years ago and something he came up with, something very clever, and that still affects all of us or most of us today.

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So he lived in the early 1900s and around 1905, he started thinking.

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He was thinking about blood vessels, and he was trying to figure (let's just draw the skin here over the blood vessel)

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"How to use the stethoscope to listen and figure out the blood pressure?"

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So he was thinking "How can I get about to do that?"

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So, first thing he decided to do was inflate a cuff like a blood pressure cuff

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and he would put a lot of pressure on the outside of the skin on that blood vessel,

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so he thought, "well for example, let's do something like 200 mmHg

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and for this example let's just assume that he is working with me,

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let's assume that he is working with my blood vessel

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and my blood pressure is about 115 systolic over 75 diastolic.

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So, if you put 200 mm of pressure on the outside,

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what's going to happen? The first thing is that that vessel is definitely not going to stay open, right?

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It's going to collapse down, so it is going to do this.

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As he gets all that pressure in the blood, it is going to turn right around

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and say, "well we can't go through this way."

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So, if he listens with his stethoscope here, if he is listening, he would really hear silence here,

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he would hear a nothing at all, it would be very quiet.

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So we put "silence"

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because there is no blood flowing

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at this point, because the vessel is collapsed.

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Okay, so Dr. Korotkoff thought about this and said "okay well, what if I go ahead and

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do something slightly different?" Let's open this up a little

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bit, because what he is going to do next is instead of putting 200 mm of pressure

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as he did the first time, he is going to put exactly 115,

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exactly the systolic pressure