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  • So recently I went into my doctor's office,

  • and I was told that my blood pressure was 115/75.

  • So I thought we would talk about exactly what this means and try

  • to figure out how to think about blood pressure in general,

  • using these numbers and this experience

  • as kind of a launching point.

  • So the way I think about blood pressure

  • is I always imagine kind of a tube

  • and I imagine blood going through that tube.

  • And this tube is like a blood vessel.

  • So there's blood trying to get its way

  • from one side to the other.

  • And on its way, the neat thing that it's doing

  • is as it flows, it's pushing out.

  • So it's forcing against these walls,

  • and specifically what I mean by that is there are cells

  • and there's plasma, and all that stuff is pushing out

  • against the walls of the blood vessels.

  • So you've got a force, and that force

  • is being exerted on the surface area of the blood vessel.

  • So it's force over a surface area.

  • And any time you see force over an area,

  • you know that equals a pressure.

  • And in this case, it's a blood pressure

  • because it's the blood that's doing that work.

  • So this is how I think of blood pressure, specifically

  • as those little blue arrows.

  • And the two questions that kind of pop into my mind anytime

  • I'm thinking about blood pressure

  • are where is the blood pressure being taken,

  • and when are you taking it?

  • So let's start with the first question, where?

  • And by that I mean where in the circulatory system.

  • So you've got the heart-- and this is my Valentine's Day

  • heart-- and you've got the aorta coming off of the heart.

  • And it's got lots of branches, but I'm

  • going to just draw one branch, which

  • is the artery leading off to my arms.

  • This is called the brachial artery going off to my arm.

  • And usually, I'd say 90% of the time,

  • maybe even more, the blood pressure that you're

  • getting recorded, or the number that's being told to you,

  • is being checked at this point.

  • I marked it with a little x because that's

  • kind of the upper arm.

  • So that's usually where they're checking the blood pressure.

  • And again, they're checking the force

  • that the blood is putting on the vessel walls.

  • So these little blue arrows.

  • So that answers the where question.

  • And certainly, you can imagine if I checked

  • blood pressure let's say at some other spot, let's say over here

  • or over here, you might get a different blood pressure

  • reading than if I checked it at the yellow x.

  • So really were just talking about that one spot.

  • Now the other question is when are you checking it?

  • So for this, let me show you a little table or a figure,

  • rather.

  • So imagine that over time, time is this way,

  • you have different recordings for blood pressure.

  • So this will be blood pressure.

  • And blood pressure is usually measured

  • in millimeters of mercury.

  • So I'll write millimeters of mercury here.

  • And let's go from 200 all the way down to 0.

  • And I'll use my numbers that I got from the doctor

  • the other day to illustrate what I'm trying to say.

  • So right at that yellow x, at the bottom,

  • let's say of my reading I've got 75.

  • So let's start at 75, which is about here.

  • As the heart is pumping, the pressure starts building up.

  • And it gets up to about 115.

  • So really what is happening is blood

  • is making its way from the heart as it squeezes towards that x.

  • And as it gets there, the force that it's putting on the walls

  • is going up, up, up.

  • And as it goes up, it goes from 75 all the way to 115.

  • So that all happens during the squeezing part

  • of the heart cycle.

  • We call that systole.

  • So this is all happening during systole,

  • which is when the heart is squeezing down,

  • and we know the heart is a pump.

  • Now from that point forward, the heart begins to relax.

  • So at this point, at 115, the heart is now relaxing slowly.

  • And as it relaxes, the pressure begins to fall.

  • And it continues to fall all the way out here.

  • And the pressure gets down to about 75 again.

  • And this is diastole.

  • So this is when the heart is actually

  • taking a break from squeezing and is now refilling,

  • and we call that diastole.

  • So I'll call that refilling.

  • And so during systole, you spend about 1/3 of the time.

  • And in diastole, you spend about 2/3 of the time.

  • And I'm talking about one heartbeat here.

  • So this would be one heartbeat.

  • So it's not 50-50.

  • And the easy way to remember this

  • is in a given day, 24 hour day, I

  • spend about 8 hours working and about 16 hours relaxing,

  • or not working.

  • And so I think of the heart doing its squeezing,

  • its work, for eight out of 24 would be about 1/3.

  • Kind of the same as me.

  • About 1/3 of the time, the heart is squeezing.

  • So that's how the heart is spending its time,

  • in systole and diastole.

  • And the pressure is ranging between 115 and 75.

  • So really it's never just 115 or just 75.

  • It's somewhere between the two.

  • And for example, if I checked right here in time,

  • it might be let's say 85, or here it might be 102,

  • or here it might be 87.

  • So it's somewhere between 115 and 75.

  • So this number I wrote up here becomes the range.

  • This is the range of blood pressure.

  • So when I talk about when, it really

  • depends on when in the cycle you're at

  • and you're somewhere in that range.

  • And when I talk about the where, we

  • know that we're talking about a reading that's

  • taken in the upper arm.

  • So those are the two thoughts that

  • should cross your mind every time you hear a blood pressure

  • recording.

  • And of course, the top number, 115 again,

  • is the systolic blood pressure.

  • And 75 is the diastolic blood pressure.

So recently I went into my doctor's office,

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