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What is hypertension? | Circulatory system diseases | Health & Medicine | Khan Academy

January 21, 2020

Let’s talk about hypertension. And I’ll write that
here, hypertension. And hypertension basically
means high blood pressure. And we actually categorize
it in different groups. So let’s use my blood pressure,
115 over 75 as an example. And I had drawn a
small figure for you where I had blood
pressure on this side and I had time on this side. And I said at my blood
pressure does something like that, where
the peak is 115. This is the systolic
blood pressure. And I said that the lowest point
is going to be, for me, 75. And that was my
diastolic blood pressure. And we know everyone has a
different blood pressure. So let’s organize blood
pressures into groups. Let’s say, let’s figure
out what group goes where. And so, to do that, I’m going
to draw a couple number lines. So let’s imagine that I
have, here in brown, I’ll do my systolic blood
pressure on this side. And I’ll do the diastolic
on the other side. I’ll do diastolic over here. And we’re going to actually
put them next to each other. And I’ll try to make about
the same size, like that. So let’s say this is
really high pressure. This would be like 200. And this is all in
millimeters of mercury. 200 millimeters of mercury. And at the very
bottom would be 0. So let’s make them
kind of the same. And that means that up
here would be about 100. And this would be about–
let’s say this is 120. This would be about
140, let’s say. Maybe this is 160. And this is 180. And I’m going to do
the same thing here. Let’s say this is about
100, except this time I’m going to go the other side. Let’s say this is about
80, and this is 60, 40, 20. Maybe I didn’t draw it as well,
but I think you get the idea. So this is my number line. And the reason I drew the
systolic numbers higher than the diastolics
is because we know that generally speaking–
or not generally speaking– always the systolic
pressure is going to be higher than the
diastolic pressure. So that’s why I
separated it out. But you can imagine
that these numbers go up and these go down. I’m just being lazy
not drawing it all out. So let’s say that
my pressure is 115. This in my systolic pressure. Now let’s do that one first. Where does that fit? Well, on this number line,
115 would be about right here. And actually anything
below 120 is actually kind of in the green zone. And this goes all
the way down, to 0. So let’s say my
systolic was 97, or 103. That would all be
in the green zone. And what I mean by
that is, I would say I do not have hypertension. I have no hypertension. So that’s kind of
a nice, safe, area to have your blood pressure
in, in terms of hypertension. Now for diastolic pressures, we
know that diastolic pressures are the low range
of a blood pressure. And so those numbers
are going to be lower. Here, anything below
80 is considered in that safe green zone. So below 80 is where
you want to be. And I want to be
very specific, I don’t mean to say that a blood
pressure of 5 would be good. What I mean is that you
don’t have hypertension. So you don’t have
high blood pressure. And that’s where it’s different
from having low blood pressure. So just for right now, the green
zone in terms of high blood pressure. Now, let’s say my
systolic blood pressure was a little bit higher. Let’s say it’s between 120
and 140, somewhere in here. Then I’m in the yellow zone. And that yellow zone means
that I don’t have hypertension, but I’m getting there. So I’m getting closer, and
this would be prehypertension. And on the other side,
on the diastolic side, we use 90 as a cut off. So I’ll write in 90. And anything between
80 and 90 would be kind of in that yellow zone. And that’s your
prehypertension zone. It’s prehypertension. So you’re still not there yet. Now in terms of high
blood pressures– again, you don’t want
high blood pressures– but in terms of getting
there, if you’re above 140, you have hypertension. So this zone in here,
140 to 160 in particular, is considered stage
one hypertension. And between 90 and 100 for
diastolics, that would be stage one. And now if you have
something above 160 for your systolic
blood pressure– so I’ll just say
above 160, and that means even higher than
200, so if let’s say you have 201– that
would be stage two. So you can see that
the higher you go, the higher your stage number. And the same is
true on this side. So let’s say you have a
really high diastolic blood pressure, well above 100. You’d have stage
two hypertension. All the way down there,
this is stage two. So I’m just going to do a
couple quick examples for you. So let’s say– I’ll do them
in yellow, different color– let’s say that you
have 145 as a systolic. And your diastolic
is, let’s say, 87. Well, 145 is right here, right? And 87– actually, let me
do it the same color just to be consistent. So 145 is right here. And 87 is in here. So your systolic pressure
is stage one hypertension, and your diastolic pressure
is in prehypertension. So when you’re in different
stages for the diastolic and the systolic what
you do, the rule, is that you go with
the higher stage. So in this case,
stage one is higher. So this person would
be considered stage one hypertension. Now we can do one more example,
just to make sure you get it. So let’s do a different color. Let’s say I’ll do
the next one in red. So you have, let’s say
126 over, let’s say 101. Well, this person, 126
is actually right here. And 101 is right above
the 100 mark, right there. So this person is
actually prehypertensive if you’re looking at just
their systolic value. But they’re actually in
stage two hypertension if you’re looking at
the diastolic value. So overall, they’re
going to be in stage two, because the rule, again, is that
you go with the higher stage. So that’s how you
figure out what stage of hypertension
someone’s in.


  • Reply maryam17123 November 9, 2012 at 8:59 am


  • Reply HERS FitWell November 18, 2012 at 3:35 pm

    Thank you for the playlist….

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    Absolutely, check out all of the playlists if you have time and let me know if there are videos you'd like to see me make.

  • Reply Bartosz Jagielski March 15, 2013 at 10:49 pm

    i can't understand 120/80 is pre hipertansion?

  • Reply Bartosz Jagielski March 15, 2013 at 10:50 pm

    for example 60/40 is normal?

  • Reply khanacademymedicine March 16, 2013 at 6:14 am

    Very low values like 60/40 are not normal for an adult, but for the purposes of this video we would say that this person does not have hypertension (albeit they may have a different problem – abnormally low blood pressure).

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    Thanks very much for the video … but the quality is low

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  • Reply yea it's reall ! February 25, 2016 at 10:20 am

    nice video (120/80 is normal) (contraction) systolic take num (120) if you go over it then u have hypertension* ( relaxation ) diastolic (80) if you go over it then you gat hypertension … a second point is prehypertension which is (120-139)systolic —-(80-89)diastolic Stage 1 (140-159 ) systolic (80 -89 )diastolic Stage 2 -greater than 160 and 100 — correct if wrong thnks

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  • Reply Kathy Colley June 3, 2017 at 10:05 pm

    Great video!

  • Reply kae samoro January 21, 2018 at 4:21 pm

    FOr the benefit of those watching, now that it's 2018… there are new guidelines for Hypertension… and pre hypertension is now 120-129 / <80… and 130-139/80-89 is now stage 1 hypertension and stage 2 is >= 140/ >=90…

  • Reply Lilly Miss February 13, 2018 at 12:52 am

    This is a great video ! but can there be one remade with the new hypertension guidelines.It would be very helpful 🙂

  • Reply Pike Nike July 25, 2018 at 7:30 am

    Thanks sir nice presentation. Simple and clear

  • Reply John R August 18, 2018 at 11:26 pm

    115 – 75 Nice – Yeah, once in a while I get systolic down to 115 (always in the evening), but in the morning, it's up 10 – 15 point and this is with 300 mg labetalol which I take religiously every 8 hours. If you have 115 without medications, consider yourself very lucky!

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