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## Blood pressure

# Blood pressure changes over time

## Video transcript

Let's imagine that I'm here. And this is me at
the age-- actually, I'll do this right now-- so
let's say at the age of 31. And then I go into the future. So this is a line
for the present. And then I go into the future. And this is me again. And this is now
at the age of 71. So I've got 40 extra years. I've even picked up a cane
to help me walk around. And finally, I go even
further in the future, and I'm being very optimistic. And I'm going to go ahead and
say this is at the age of 101. I live to be a centennial. And I'm sitting in a
wheelchair, and I'm going to wave out at you. So that's me in a wheelchair
at the age of 101. And we're going to
apply that formula we've been talking about so much,
delta P equals Q times R. So I said Q is cardiac output. And we've got R is resistance. So we've got this formula. And let's say I go to
the doctor's office. And I go today, and
I go in 40 years, and I go again when I'm 101. And today, they tell me my
blood pressure is 120 over 80. And actually, I went
not too long ago, and that's pretty much
what they told me it was. And I go in the future,
and in 40 years, they tell me it's
actually gone up. My blood pressure
is now 150 over 90. And in fact, I go
again, when I'm 101, and they say it's 180
over, let's say, 105. So the blood pressure is
rising, and that's basically what I'm told. And they say, well, you've
got to make sure you eat well and exercise, and that should
help your blood pressure. And I'm left wondering what the
connection is between the two. So let's figure out what
that connection is exactly. So my blood pressure, I
just said, is 120 over 80. And if I want to figure out my
mean arterial pressure, meaning the average pressure
in my arteries, I can actually use
my blood pressure to give me a good guess as
to what it's going to be. So I know that I
spend about 1/3-- my mean arterial
pressure is going to equal 1/3 times my
systolic, because I know I spend about 1/3 of the
time-- my heart does anyway-- spends 1/3 of its time beating. And it spends 2/3 of
its time relaxing. And the relaxing pressure is the
diastolic pressure, that's 80. And so that works
out to about 95. And so that's how I came
up with that 95 number. And that's also why it's
not exactly 100, which is what you'd think an average
would be between two numbers. But it's because we don't spend
the exact same amount of time in systole as diastole. So then if I wanted to figure
out here, it would be 1/3 times 150 plus 2/3 times 90. And that works out to 110. And if I wanted to do
it at the age of 101, my mean arterial pressure would
be 1/3 times 180 plus 2/3 times 105. And that works out to 130. So I figured out my
mean arterial pressure. Let me write that with a line. I also need my mean
venous pressure, because we know
we're going to have to subtract the two
from one another to get the delta P, delta
meaning the difference. So mean venous pressure
right now is about 5. And let's assume-- this is
one of a few assumptions we're going to make-- let's assume
that it doesn't change, that over a few years, it
really stays around the same. It's about 5. Well, then if I know that, my
delta P is easy to figure out, right. I can just take 95 minus
5, and that'll get me 90. And I can take 110
minus 5, and that's 105. And I can take 130
minus 5, and that's 125. So I figured out my delta
P, which is basically my mean arterial pressure
minus my mean venous pressure, and that equals my delta
P. OK, so far so good. Now let me change colors to
figure out my Q, my flow. And right now, I
have, let's say, a stroke volume-- I'll
write it up here-- stroke volume, meaning
each time my heart beats, about 70 milliliters
of blood go out. So each time my heart
beats, it sends out to the rest of the
body 70 ml of blood. And that's based on the fact
that I'm about 70 kilos. And my heart rate is about
70, very relaxed heart rate. And let's assume, just as we did
with the mean venous pressure, that that doesn't change. So this is not going
to change over time. So this works out to
about 5 liters a minute because Q is simply-- let me
write that here-- Q is simply SV times HR. And so I'm just multiplying
those two numbers together, and you get about
5 liters a minute, and it doesn't change over time. So 5 liters a minute here,
5 liters a minute here. And I should probably mention
all of my pressure units should be millimeters
of mercury. I didn't write that, just
to not clutter up the board. But let's just assume that--
well, it's not assuming. It is millimeters of mercury. So now using my
equation, I can now say, well, delta P-- and
actually maybe up here I should even change this. It should be blue so
that I'm consistent. So delta P equals Q times R.
So if delta P is 90 and Q is 5, my resistance equals 18. Right? It's just a bit of math
that I did very quickly. But 18 times 5 is 90. And here I could figure it out. 105 divided by 5 would
give me a resistance of 21. And here, I would figure out
that it's going to be 25. So one thing that I've
been told by my doctor is my blood pressure is rising. And two things that
I've assumed are that my mean venous
pressure is the same, and that my cardiac
output is the same. And if I assume that,
and that's definitely not true for everybody, but
if I assume that for me, then that means that my
resistance has gone up. Over time, my
resistance has gone up. And let's now change
screens and figure out how that could possibly happen. So let me draw myself out again. So I've got three
versions of me. I've got the present
me at the age of 31. I've got the future me with
a cane at the age of 71. And I've got the
really old version of myself living at a ripe, old
age of 101, waving, in fact. So three versions of myself. And if I was to draw
my arterial tree, let's say, a simplified
version of my arterial tree. Let's say here's a vessel
coming through, and I've got, let's say, another vessel,
and this branches here. And I've got a third vessel,
and this branches here. Right now my arterial tree
looks pretty good, pretty clean. And that's why my
resistance was 18. Blood is flowing
through very smoothly. It's going out this way to feed
the kidney and maybe to my ears and my eyes and my foot. And it's basically making
its way through, no trouble. Now at the age of 71,
something happens. Actually, let me just draw
a little divider line. At the age of 71,
something happens. I have, let's say, the
same arterial tree. I'll try to draw
it the same way. Except now, I've been
eating, for 40 years, foods that are not the best. And I certainly
haven't exercised a whole heck of a lot. I haven't gone to
the gym very often. And now I've got
buildup of plaque. So let's say I've got
a plaque right there. And I've got a plaque, let's
say, another one right there. And let's say I have
a plaque right there. So I've got three
little plaques. And we'll get into
plaque and what it's made of exactly
in a future video. But for the moment,
just think of it as something that's
blocking up that vessel. And it's usually made
of fatty substances and macrophages and
cells that have died and all sorts of basically
crud that fills up the vessels. And so, because it's
filled up the vessels, now here, my radius got smaller. My vessel radius in
here got smaller. And over here, it got smaller. So blood, as it's
flowing through, is having a tougher
time getting through because the radius is
smaller in these spots. And, as you know, if you
calculate total resistance-- and that's what, actually,
this is, total resistance-- the total resistance will
start to slowly climb up. And in this case, maybe
it climbs up to 21. And now years go by, let's
say 30 more years go by. I'm now in a wheelchair. And I continue to
not eat so well. I eat the same sort of fast
food that isn't healthy for me, but I can't possibly stop
because I find it tasty. And at the end of the day,
my vessels look like this. I have that same one
as before, let's say. And let's say this one
actually grew longer. So instead of just being
part of the vessel, let's say it's huge now. This one got very big. And let's say this one up here
actually continued and grew a little bit as well. But I also picked up another
one right here, let's say. And I also got one right here. So I have a few more
blocks in the road. And so now my blood is
having a real hard time getting through because it's
got more obstruction to flow. All my paths have
a smaller radius. And we know, and I've
mentioned a number of times now, about the relationship
between a radius and resistance. And that as the radius
everywhere gets smaller, the resistance is
going to get bigger. And so my total resistance
here, let's say, is about 25. So now you can see how eating a
certain way and not exercising is going to lead to potentially
developing these plaques that act as roadblocks and get
in the way of blood flow. And the reason that that's a
problem is that, as we see now, the radius gets smaller,
the resistance goes up. And in the previous
slide here, we actually can see now that as
the resistance goes up, assuming that the other
things kind of stay the same, your blood pressure can go up. And so when you hear,
in the doctor's office, that you have a blood
pressure of a certain number over a certain number, that's
one thing that we can measure. And what it tells
you is a little bit of information about some of
the things that we can't easily measure, such as resistance. So let's stop there,
and we'll pick up.