Here, we see a diagram of the pressures within
the heart. First, we will look at diastole
and then we will look at systole. So, what
you see here is... this is at the top, you see
the aortic pressure, superimposed on that
is the left ventricular pressure and the hatched
areas are diastole. During diastole, you can
see that left ventricular pressure falls low,
that it falls below right and left atrial
pressure and blood flows into the left and
right ventricles and you can see that on the
right hand side. The little arrow is showing
that during diastole, the mitral and tricuspid
valves are open, blood is flowing in, pressure
in the right and left ventricle is low, slightly
lower than in the right atrium and the left
atrium so that blood passes from the two atria
into the ventricle. During ventricular systole,
the ventricles both contract, the pressure
rises that pushes the mitral and tricuspid
valves closed and when the pressure rises
to a high enough degree that is above aortic
or pulmonary artery pressure, the pulmonary
and the aortic valves open and blood is ejected
into the pulmonary circuit on the right side and into the systemic circuit, that is the
aorta on the left side. And the pressures
are, of course, quite different as we will see.
The average normal pressure in the lung, peak systolic pressure- that is during the
maximum time of blood flow, from the right
ventricle into the pulmonary artery, is generally
somewhere around 20 to 25 mmHg. During peak
systole on the left side, however, the pressure
is often 120 mmHg or more, so you can see
considerably higher on the left side.
No surprise, the right ventricle just has to pump to
the lungs, a nice low pressure system.
The left ventricle has to pump to the entire
body, a high pressure system.
Here we see, in the hatch lines, ventricular
systole. You can see aortic pressure.
This is the left side, of course, but it would
be similar on the right side, but at a much
lower pressure, as we just talked about. And
you can see the little diagram on the right
hand side showing you the right ventricle
and the left ventricle contracting.
When the pressure in the right ventricle exceeds the
pressure in the pulmonary artery during diastole,
the pulmonic valve opens and blood is ejected.
On the left side, when the pressure on the
left ventricle exceeds the aortic pressure
in diastole, the aortic valve opens and blood
flows into the aorta. Following contraction,
the pressure falls in the right ventricle
and the left ventricle, the pulmonic and aortic
valves close and then when the pressure falls
low enough, the mitral and tricuspid valves
open and blood flows into the ventricle in
diastole, which we just looked at a moment
ago. Let’s look at the pressures in each
of the chambers and take our way through.
In these little cartoons that you see, we
are going to be using a little balloon catheter.
Later, I’ll show you an actual picture of
this catheter. It’s used very, very commonly
to do right heart catheterizations, that is
catheterizations that involve right atrium,
right ventricle, the pulmonary artery.
The left side, of course, has a separate catheter
that goes in through the arterial system.
So, we are going to follow this little balloon
catheter through. Why do we have the balloon
on it? It’s like the sail on a sailboat.
It flows and is pulled along by the blood
that’s flowing through the heart. So, you
see here, the tip of the catheter is in the
right atrium. You can see in the little tracings
there, you can see the electrocardiogram above,
the big deflection is the QRS, that’s the
ventricular depolarization, that’s… that’s
going to set off ventricular systole and you
will notice a number of little waves in the
right atrium. We are going to look at those
little waves in greater detail.
Here they are in greater detail. There is an A wave,
a C wave and a V wave and two descents after
the waves, the X descent and the Y descent.
The A wave is right atrial and, by the way,
you can sees the similar waves in the pulmonary
capillary wedge or left atrial tracing.
So, during atrial systole, you create the A wave,
the pressure rises in the atrium as it contracts
and then as the valve starts to close, there
is a decrease in the pressure that’s the
X descent. You then see a C wave, which is
actually as the valve is shut and systole
starts and the atrium fills, there is a little
rise in pressure there. That’s followed then
by relaxation of the atrium with a fall
in the pressure, so called X descent.
Then you see the V wave,
which is due to the rise
in atrial pressure as it fills
from the inferior and superior vena cava
before the tricuspid valve opens.
And then we start with the AC and wave.
The wave is due to atrial contraction
and then there is a small
C wave relating
to closure of the tricuspid valve.
In the next two slides, you
will see the description
of what I just told you - what the events
are that are leading to the A, C and V waves?
Now, you can imagine in a patient that doesn’t
have atrial systole. Let’s say there is
a period where the atrium becomes paralyzed,
the A wave would disappear, you wouldn’t
see it in the tracing. So, these slides should
be read over a little bit carefully so that
you have a full understanding of what causes
the A, C and V waves. Now, here we see the
A, C and V waves in the right atrial pressure
tracing against the electrocardiogram.
We are going to talk much more about the electrocardiogram
later, but just to give you a little introduction,
the electrocardiogram has a small wave that
starts in a very small deflection, that starts
before the big deflection. The small deflection
is called the P wave that is atrial systole.
Then there is the large deflection that’s
QRS, that’s the ventricular depolarization
and then finally, following the QRS, there
is a T wave which is repolarization.
In other words, getting ready for another electrical
wave to pass through the heart. You’re going
to ask - how come it’s P QRS and T, what
happened to A B C and D? In the very beginning
of electrocardiography, there were a number
of waves that turned out to be artifacts, and
they were A and B and C. So, all of those
waves disappeared and the really the ones
that remained where the real ones the P, the
QRS and the T. And you can see the timing
of the electrocardiogram on the top against
the right atrial pressure tracing below.
Here it is magnified once more for you. You can
see the A wave, the C wave and the V wave.
The X descent follows the C wave and the Y
descent follows the V wave.
Now, our catheter has moved across the tricuspid
valve and into the right ventricle and instead
of low level pulsations, low level changes
in the A, C and V waves, we see large fluctuations
in the diagram below corresponding to the
generation of pressure during systole and
then relaxation during diastole. Again, remember
that the pressure in the right ventricle is
much lower than in the left ventricle because
it’s pumping to a low pressure system- the
pulmonary artery, in a normal person, of course.
When there is disease, sometimes the right
ventricle pumps to higher pressures because
the resistance in the lung goes up and we
are going to talk about what determines pressure
in the cardiovascular system at a later point.
As we move the catheter through the pulmonic
valve and into the pulmonary artery, you again
see the fluctuations as the pressure rises
during ventricular systole and then falls
during diastole. We don’t get down as low
as we do in the right ventricle because when
the pulmonic valve closes, pressure doesn’t
go any further down. In the right ventricle,
of course, pressure continues to fall with
the pulmonic valve closed and that, of course,
initiates the opening of the tricuspid valve
and blood flows in to the right ventricle
during diastole. If we move the catheter out
and wedge it in a small blood vessel in the
lung, the… the opening of the catheter points
downstream and actually records the pressure
in the pulmonary capillaries. The pressure
in the pulmonary capillaries is approximately
the same as the pressure in the left atrium
and the pulmonary veins. So, what we are really
seeing is, we are seeing a measure of the diastolic
pressure in the left ventricle when we measure
the pulmonary capillary wedge pressure. So,
with the right heart catheterization, we get
right atrial pressure, we get right ventricular
pressure, we get pulmonary artery pressure
and we get a pulmonary capillary wedge pressure
which is a reflection of pulmonary vein and
left atrial pressure which is reflection of
left ventricular pressure during diastole.
And this measure, pulmonary capillary wedge
pressure is frequently used as a measure of
how well the left ventricle is functioning.
Is it functioning with a nice filling pressure
or is the filling pressure very high because
the left ventricle is functioning abnormally?
Here we see the four pressure tracings, four
chambers that we just talked about.
In the upper left hand corner, you see the A, C and
V waves of the right atrium. Right next to
it, you see the right ventricle with a high
systolic pressure and a low diastolic pressure.
In the right... in the left lower quadrant,
you see the pulmonary artery pressure which
during systole has the same pressure as peak
pressure in the right ventricle, but in diastole,
doesn’t fall as far, and then in the final
right hand lower quadrant, you see the pulmonary
capillary wedge pressure. Again, showing some
of the A, C and V waves that you see in the
right atrium. They are a little muted because
you are seeing A, C and V waves at a distance
from the left atrium, but nevertheless, very
similar to what you see in the right atrium.
And here we see the catheter being advanced
from the right atrium all the way on your
left hand side into… into the right ventricle
with the high pressure and then followed by
a low pressure that’s approximately the
same as right atrial pressure followed by
pulmonary artery pressure just as high as
right ventricular systolic pressure, but never
gets as low and then finally, pulmonary capillary
wedge pressure which is approximately the
same as pulmonary artery diastolic pressure.
And again, as we said before, is a reflection
of filling pressures on the left side of the
heart. In fact, during the cardiac cycle,
there are other things that affect the pressures
in the heart besides the squeezing or relaxing
of the ventricles and the atria. What is that?
That is, in fact, respiration. When you take
a deep breath, you are actually creating negative
pressure inside your chest that allows the
lungs to expand. When you exhale, you are
actually creating a small amount of positive
pressure that causes the lungs to collapse.
That pressure is transmitted to the heart.
So, during inspiration, pressures are slightly
lower and during expiration, pressures are
slightly higher. And you can see that wave
form here as the patient breaths in and out.
Now normally, this is inconsequential. It's 1
or 2 mmHg. However, when patients have lung
disease and they make great efforts to breathe,
the negative intrathoracic pressure and positive
intrathoracic pressure may be significant
and actually cause significant changes in
the intracardiac pressures of the atria and
a little bit about ventricular systole.
What happens during ventricular systole
is that the ventricles push blood
out into the pulmonary artery
and into the aorta.
How much blood do they push out?
What's pumped out with each
beat is called the stroke volume.
It's a little bit
like the piston in the car, right?
Each time the piston moves up,
it pushes out a certain amount of of gas
out of the the piston chamber.
And that is a certain volume and that is
the each stroke has a certain volume.
So that the cardiac output has
stroke volume and heart rate.
We're going to talk a little bit
more about that in just a moment.
But it's important to understand
each squeeze pushes out a certain
amount of blood.
Normally in most people,
it's about 80 cubic centimeters of blood.
With each squeeze, obviously,
we can measure that.
And if it's lower, that means the heart's
not functioning as well as it ought to.
And there's a number of reasons for that,
which we will also discuss in a moment.
If it's more than that, it's
because the heart is being stimulated
by something, for example,
being stimulated by adrenaline
or by an overactive thyroid
or a whole bunch of different reasons.
During the filling phase, of course,
the ventricle has to fill
with the same amount of blood
that it squeezes out.
So 80 cc's of blood
has to go into the two ventricles
so that during the next Systole
they can push out 80 cc's
and they have to be balanced, right?
If one ventricle pumps
more than the other, you're soon
going to have all the blood end up on
one side of the circulation or the other.
So the two have to be balanced, of course.