What is blood pressure? | Circulatory system physiology | NCLEX-RN | Khan Academy
What is blood pressure? | Circulatory system physiology | NCLEX-RN | Khan Academy
Find out what a systolic and diastolic blood pressure mean. Rishi is a pediatric infectious disease physician and works at Khan Academy. Created by Rishi Desai.
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Content
1.35 -> So recently I went into
my doctor's office,
3.97 -> and I was told that my
blood pressure was 115/75.
9.5 -> So I thought we would talk about
exactly what this means and try
12.43 -> to figure out how to think
about blood pressure in general,
15.09 -> using these numbers
and this experience
17.94 -> as kind of a launching point.
20.25 -> So the way I think
about blood pressure
22.35 -> is I always imagine
kind of a tube
26.11 -> and I imagine blood
going through that tube.
28.31 -> And this tube is
like a blood vessel.
30.43 -> So there's blood
trying to get its way
32.54 -> from one side to the other.
34.75 -> And on its way, the neat
thing that it's doing
39.54 -> is as it flows,
it's pushing out.
42.67 -> So it's forcing
against these walls,
47.85 -> and specifically what I mean
by that is there are cells
51.54 -> and there's plasma, and all
that stuff is pushing out
55 -> against the walls of
the blood vessels.
57.37 -> So you've got a
force, and that force
61.93 -> is being exerted on the surface
area of the blood vessel.
66.72 -> So it's force over
a surface area.
69.27 -> And any time you see
force over an area,
72.6 -> you know that equals a pressure.
73.985 -> And in this case,
it's a blood pressure
75.61 -> because it's the blood
that's doing that work.
79.64 -> So this is how I think of
blood pressure, specifically
82.38 -> as those little blue arrows.
84.44 -> And the two questions that kind
of pop into my mind anytime
87.7 -> I'm thinking about
blood pressure
90.58 -> are where is the blood
pressure being taken,
95.57 -> and when are you taking it?
97.15 -> So let's start with the
first question, where?
99.91 -> And by that I mean where
in the circulatory system.
104.23 -> So you've got the heart-- and
this is my Valentine's Day
107.24 -> heart-- and you've got the
aorta coming off of the heart.
111.26 -> And it's got lots
of branches, but I'm
113.06 -> going to just draw
one branch, which
115.64 -> is the artery leading
off to my arms.
118.93 -> This is called the brachial
artery going off to my arm.
123.21 -> And usually, I'd
say 90% of the time,
126.37 -> maybe even more, the
blood pressure that you're
128.44 -> getting recorded, or the number
that's being told to you,
130.919 -> is being checked at this point.
134.21 -> I marked it with a
little x because that's
135.99 -> kind of the upper arm.
137.5 -> So that's usually where they're
checking the blood pressure.
140 -> And again, they're
checking the force
142.6 -> that the blood is putting
on the vessel walls.
145.02 -> So these little blue arrows.
147.56 -> So that answers
the where question.
149.22 -> And certainly, you can
imagine if I checked
151.29 -> blood pressure let's say at some
other spot, let's say over here
155.95 -> or over here, you might get
a different blood pressure
159.52 -> reading than if I checked
it at the yellow x.
161.77 -> So really were just talking
about that one spot.
165.7 -> Now the other question is
when are you checking it?
168.17 -> So for this, let me show you
a little table or a figure,
172.4 -> rather.
172.9 -> So imagine that over
time, time is this way,
177.68 -> you have different recordings
for blood pressure.
180.04 -> So this will be blood pressure.
183.12 -> And blood pressure
is usually measured
185.18 -> in millimeters of mercury.
187.27 -> So I'll write millimeters
of mercury here.
190.36 -> And let's go from 200
all the way down to 0.
195.16 -> And I'll use my numbers
that I got from the doctor
198.8 -> the other day to illustrate
what I'm trying to say.
201.71 -> So right at that yellow
x, at the bottom,
207.06 -> let's say of my
reading I've got 75.
210.08 -> So let's start at 75,
which is about here.
212.98 -> As the heart is pumping, the
pressure starts building up.
217.39 -> And it gets up to about 115.
221.12 -> So really what is
happening is blood
223.27 -> is making its way from the heart
as it squeezes towards that x.
228.49 -> And as it gets there, the force
that it's putting on the walls
232.79 -> is going up, up, up.
234.32 -> And as it goes up, it goes
from 75 all the way to 115.
238.52 -> So that all happens
during the squeezing part
241.95 -> of the heart cycle.
243.2 -> We call that systole.
245.63 -> So this is all happening
during systole,
247.32 -> which is when the heart
is squeezing down,
249.14 -> and we know the heart is a pump.
252.51 -> Now from that point forward,
the heart begins to relax.
256.959 -> So at this point, at 115, the
heart is now relaxing slowly.
260.72 -> And as it relaxes, the
pressure begins to fall.
264.15 -> And it continues to fall
all the way out here.
268.03 -> And the pressure gets
down to about 75 again.
271.4 -> And this is diastole.
273.14 -> So this is when the
heart is actually
275.25 -> taking a break from squeezing
and is now refilling,
278.88 -> and we call that diastole.
280.05 -> So I'll call that refilling.
287.04 -> And so during systole, you
spend about 1/3 of the time.
292.79 -> And in diastole, you spend
about 2/3 of the time.
295.73 -> And I'm talking about
one heartbeat here.
297.91 -> So this would be one heartbeat.
300.83 -> So it's not 50-50.
302.82 -> And the easy way
to remember this
304.23 -> is in a given day,
24 hour day, I
307.1 -> spend about 8 hours working
and about 16 hours relaxing,
310.05 -> or not working.
311.331 -> And so I think of the
heart doing its squeezing,
313.33 -> its work, for eight out
of 24 would be about 1/3.
317.012 -> Kind of the same as me.
317.97 -> About 1/3 of the time,
the heart is squeezing.
323.12 -> So that's how the heart
is spending its time,
326.56 -> in systole and diastole.
328.14 -> And the pressure is
ranging between 115 and 75.
331.55 -> So really it's never
just 115 or just 75.
334.89 -> It's somewhere between the two.
336.74 -> And for example, if I
checked right here in time,
339.69 -> it might be let's say 85,
or here it might be 102,
342.84 -> or here it might be 87.
345.51 -> So it's somewhere
between 115 and 75.
350.05 -> So this number I wrote up
here becomes the range.
354.7 -> This is the range
of blood pressure.
358.73 -> So when I talk about
when, it really
360.23 -> depends on when in
the cycle you're at
362.18 -> and you're somewhere
in that range.
364.17 -> And when I talk
about the where, we
365.72 -> know that we're talking
about a reading that's
367.97 -> taken in the upper arm.
368.954 -> So those are the
two thoughts that
370.37 -> should cross your mind every
time you hear a blood pressure
373.13 -> recording.
373.94 -> And of course, the
top number, 115 again,
376.41 -> is the systolic blood pressure.
378.43 -> And 75 is the diastolic
blood pressure.
Source: https://www.youtube.com/watch?v=J97G6BeYW0I