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Current time:0:00Total duration:5:27

Learn how a stethoscope can help determine blood pressure

Video transcript

so this is a picture of dr. korotkov dr. krupov is a very famous russian doctor lived about a hundred years ago and something he came up with something very clever still affects all of us or most of us today so new have in the early 1900s and around 1905 he started thinking he was thinking about blood vessels and he was trying to figure out how to use his stethoscope let's draw the skin here over the blood vessel had to use his stethoscope to listen and figure out the blood pressure so he was thinking how can I get about to do that so first thing he decided to do was inflate a cuff like a blood-pressure cuff and it would put a lot of pressure on the outside of the skin on that blood vessel so he thought wallets for example let's do something like 200 millimeters of mercury and for this example let's just assume that he's working with me let's assume that he's working with my blood vessel and my blood pressure is about 115 systolic over 75 diastolic so if you put 200 millimeters of pressure on the outside what's going to happen the first thing is that that vessel is definitely not going to stay open right it's going to collapse down so it's going to do this as it gets all that pressure and the blood is going to turn right around and say well we can't go through this way so if he listens with this stethoscope here if he's listening he would really hear silence he or he would hear nothing at all and be very quiet let me put silence because there's no blood flowing at this point because the vessels collapsed okay so dr. korotkov thought about this and said okay well what if what if I go ahead and do something slightly different let's let's open this up a little bit because what he's going to do next is instead of putting 200 millimeters of pressure as he did the first time he's going to put exactly 115 exactly the systolic pressure in my blood vessels and he's still going to listen with his stethoscope so here's the status hope as before he's going to listen and now the pressure on the inside of the blood vessel actually does reach 115 for just a moment right so it gets there for just a moment and a little spurt of blood gets through so I'll say a little pulse or spurt of blood makes it through and here's the interesting bit as that blood is going through because that vessel just barely opens up it actually has to squeeze its way through and it creates a lot of turbulence meaning that that blood is not flowing smoothly it's actually bouncing off of the walls creating lots of movement and that actually translates into sound waves because all the little air molecules get shaken up and you can actually hear that so when you hear that pulse when you get a pulse you actually hear some sound so for the first time you actually get a little bit of noise so I'll put that down to noise and the reason for this noise is that you have turbulent flow which is actually really really important and it's interesting that he observed that or figure that out so when you go from silence as to noise n dr. Krotz cough realized that that's the moment when you've actually figured out someone's systolic blood pressure really kind of a neat way to deduce this right it's a stall like blood pressure and so then he said okay what if I take it one step further what if I relaxed that pressure on the outside even more so instead of 115 now let's say that pressure is I'm going to say 75 75 millimeters of mercury and he's of course using a stethoscope to listen he's still listening and he realizes that now blood is actually going to flow really smoothly very smooth flow through this vessel and we actually call that laminar flow so now you get laminar flow laminar flow as opposed to the true vielen flow you had before and now that you have laminar flow you don't have all that bouncing off of the walls that I was talking about earlier and so because of that it's actually quite quite quiet it's very silent again so again you go back to silence but for a very different reason the first time there was no blood flowing that was when there was 200 millimeters of mercury but now there's 75 millimeters of mercury which is a lot less and you still get silence but for a different reason now there is blood flowing but it's flowing so smoothly called laminar flow that you really don't hear anything with your stethoscope and he realized that now when you go from a noisy situation back to a silent situation now you figured out someone's diastolic blood pressure so every single time we go to the you know physician's office or to see the nurse practitioner to get our blood pressure taken we owe it to dr. crock often his observations about a hundred years ago