Well, you've spent some time in the SIM lab this
week where you measured blood pressures in each other.
And you were thinking a little bit more intensely about systolic blood
pressure and diastolic blood pressure during that experience.
Blood pressures do vary throughout the day in humans,
but we do have a standard that we consider as being the normal cutoff for
normal blood pressures in adults that are resting.
And we would say that systolic pressure should be less than 120 millimeters
of mercury.
Diastolic pressure should be less than 80 millimeters of mercury, right?
And if we think about blood pressure in general we would say,
wow, is it possible for somebody's blood pressure to fall too low?
And the answer is yes, it is possible.
A sustained, slightly low blood pressure
could end up being not a problem at all.
And we would consider low blood pressure only to be a problem only when
it actually interferes with the ability to carry blood to tissues, right?
If we, for example, could not get blood adequately to the brain,
that would be a bad thing.
We would pass out and we would hope that cardiovascular regulation
would prevent us from experiencing a drop in blood pressure
that would cause our brain not to get an adequate blood flow.
So the whole point of regulating blood pressure is to keep
our systemic blood pressure in a range that allows tissues to be perfused,
but also in a range that ensures that the cardiovascular
system can continue to work normally for a very long time.
So if we experience chronic hypertension,
there are a couple of reasons that that could be a problem for
the cardiovascular system and the body as a whole.
Can you think of what they might be?
Why would it be a problem to have chronic, continuous hypertension?
Steph.
>> Maybe it can damage your vessels?
>> It can damage the blood vessels.
That's absolutely correct.
So, if you have elevated blood pressure, you will start to first see some damage
in the, the endothelium that lines the blood vessels.
That can, over time, cause blood vessels to narrow and restrict blood flow.
What else is a problem?
>> There can be a problem with the heart because it's
working harder to pump the blood.
>> Exactly, strain on the heart can be a major problem.
When the heart has to pump more forcefully with every beat
to eject blood because of chronic hypertension,
the heart will begin to undergo structural changes.
Its wall will get thicker, and we actually will start
to see the heart go into this long progression that we call heart failure.
Yes.
>> I wonder if I can share a nursing fact?
>> Absolutely, yeah.
>> And that's that many patients don't feel the symptoms of hypertension for
the first 10 or 20 years.
So if you have high blood pressure, you might not feel like anything's wrong but
your body is experiencing this slow damage to your vessels and organs.
And that's why it's important that we measure blood pressure all the time in
patients.
>> It's is really true, I mean, and if you are just your normal,
everyday person walking around enjoying life,
you should have your blood pressure checked at least annually.
Just to ensure that you're staying in that normal,
healthy range, blood pressure-wise.
Cool, so how does the body regulate blood pressure?
Remember that we're thinking about, when we talk about systemic blood pressure,
what we're thinking about is that we want to keep mean arterial pressure
regulated at a level that will allow
the tissues to receive the blood flow that they need.
But that will not be so high that the blood vessels and the heart are damaged.
So what is going to influence mean arterial pressure?
Andre.
>> Is cardiac output one of the factors?
>> Absolutely.
How might that be important?
>> Well, if you have more blood being pumped by the heart,
then there would be more pressure in the vessels.
>> Right, because the more blood you pump into the vessels,
the more force is being exerted against the walls.
Absolutely right.
So you've already studied the heart, and
you have some idea about how we regulate cardiac output.
And what we know is that if cardiac output goes up and nothing else changes,
mean arterial pressure will go up, right?
Is there anything else that would influence mean arterial pressure?
>> Resistance.
>> Resistance, so that's the thing that we came
to a little bit of understanding about this week.
What's resistance going to do to mean arterial pressure?
>> It could increase it, because the more resistance on the vessels and
the blood has to flow through that, it can increase your pressure.
>> Exactly, so the greater the resistance, if we increase the vascular resistance and
nothing else changes, then mean arterial pressure will go up dramatically, right?
And which vessels are the ones that create the most vascular resistance?
>> Is it the arterioles?
>> Exactly, the arterioles, yes.
Okay, so we actually, in a region of the brain called the brain stem,
we have centers that help to integrate cardio vascular function,
help us maintain a normal cardiac output, and
help us regulate systemic blood pressure.
So we think of those as the cardiovascular regulatory centers.
And in terms of regulating blood pressure,
those centers receive input from sensory receptors that are called baroreceptors.
Baroreceptors are just receptors that are present in the walls of the blood vessels,
and they detect how much the blood vessels are stretching.
And when the blood vessels stretch more, like they would if blood pressure goes up,
then signals are sent to the cardiovascular centers.
And the cardiovascular centers will cause vasodilation to occur, or they'll
slow the cardiac output so that blood pressure can return to its normal level.
And so we expect to see that kind of regulation going on throughout the day.
So that even though we may change our activity level, or may go to sleep and
rest for a while, our blood pressure will be able to be adjusted so
that we can maintain it within that normal, healthy range.
And then blood volume, usually we don't expect blood volume to change too much.
But if blood volume changed dramatically,
that would also have an impact on our blood pressure.
And so we have long-term mechanisms that involve hormonal regulation and
the action of the kidney, that can actually cause changes in blood volume.
That can then cause corresponding changes in blood pressure.