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Lecture 13

PHGY 210 Lecture Notes - Lecture 13: Needle Valve, Korotkoff Sounds, Wiggers Diagram

Course Code
PHGY 210
Michael Guevara

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Lecture 13 - Cardiovascular Physiology (Part 7 of 9)
(1) Right Heart
Wiggers diagram was all for left side of heart. The exact same thing is happening on
right side of heart. Whatʼs the difference? First of all everything is on the right and
second, instead of seeing big pressures going up 120mmHg it goes up to maybe about
20mmHg because pressures on right are less than pressures on left. Everything is
happening a the same time though. You have the same four cycles of the cardiac cycle.
(2) Starlingʼs Law of the Heart (Frank-Starling Mechanism)
Whatʼs a typical end diastolic volume? About 120 -140. Stroke volume is about 70. This
is what youʼre at now. If we could increase this more, when you stretch cardiac muscle it
contracts more forcefully so if you increase the EDV, youʼll get a more forceful
contraction and youʼll eject more blood (higher stroke volume). You get this curve by
doing a bunch of EDV. You get this in exercise. Your cardiac output goes up, your
venous return goes up and the atria and ventricles filling goes up and that increase in
EDV will generate more force therefore more stroke volume so your cardiac output will
go up because of this.
Thereʼs a concept called pre-load and this is the state of load on the muscle just before it
contract. So if the EDV is bigger, the amount of stretch in the muscle is bigger, prior to
contraction the pre-load is bigger. We talked about measurement of pressure in the right
atrium before remember? Well one of the reasons we do this is to assess this pre-load.
You can make a measurement of volume in ventricle using x-rays or echocardiography
or you can just make a measurement of the pressure in the right atrium. If the volume of
blood in right atrium is bigger, the pressure is going to be bigger as well and the amount
of blood in the ventricle will also be bigger. So you see thereʼs a direct correlation
between the pressure in the atrium and the volume of blood in the ventricle. Thatʼs why
the pressure in right atrium is measured it to get a measurement of the index of the
degree of filling in the ventricle.
(3) Valvular Murmurs
On Wiggers diagram we had two heart sounds. On some people you hear 3 or 4 heart
sounds. Other people have these softer heart sounds called murmurs. You can hear this
with stethoscope. Not all murmurs are pathological or physiological. Not always a sign
something is wrong with heart.
(4) Normal Valves
Normal flow of blood through valves: When the valve (any one of the four) is fully open
thereʼs a big hole and the blood flows through adn the flow is smooth or laminar so you
donʼt hear anything. When the valve closes as it should, if it closes completely, thereʼs
no flow - you hear nothing. You have a normal situation. When the valve closes
completely, thereʼs no flow. You hear nothing. This is the normal situation.
(5) Abnormal valves
If you have a valve that is a stenosed valve (it doesnʼt open properly due to calcification
or whatever) the blood is going to squirt through this smaller opening at high speed and
itʼs going to see that expanse ahead of it so the flow moving through the valve is going to
expand because now you have the full size of the atrium or the ventricle or whtever and
that creates turbulent flow. That flow will shake the leaflets of the valve or the heart itself
and youʼll get a sound.
An insufficient valve doesnʼt close properly so you have a small opening there and there
will be flow of blood through the valve (in this case, backflow) and youʼll hear a murmur.
Sarah Margareta Ibrahim
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This is not a physiologic sound itʼs a pathologic sound because something is wrong with
the valve.
(6) Systemic Arterial Blood Pressure.
Youʼre measuring the blood pressure in the arteries! And youʼre measuring it on the left
heart (the systemic side of circulation).
(7) Arterial Blood Pressure
The aortic pressure stays high throughout the resting period in the heart when the
ventricular pressure is almost zero. During the ejection phase, you eject a volume of
blood (the stroke volume) into the aorta. The aorta is an elastic organ. As you pump
blood into the aorta it will stretch. This blood has to go to the arterioles and such where
there is a high resistance so it takes time for that blood to flow through that whole
system so the pressure there will stay high for some time.
There are four different pressures to calculate. The peak pressure is the systolic
pressure (usually around 120 mmHg). The minimum pressure is diastolic pressure
(usually around 80 mmHg). If you subtract the diastolic pressure from the systolic
pressure you get the pulse pressure (usually around 40 -> 120-80). The fourth pressure
is the mean arterial pressure this is the pressure that you would give a steady pressure
to have the same cardiac output. This is the diastolic pressure + of the pulse pressure.
A typical mean arterial pressure is around 100mmHg.
(8) Measurement of Blood Pressure
"Direct method or indirect methods (palpitation, auscultation, oscillometry).
(9) Direct Method
Done. You make an arterial puncture and you take a tube with something that can make
a measurement of pressure (manometer) you can put a small plastic tube into artery of
patient that will translate pressure into voltage and voltage goes off to a monitor. Thatʼs a
direct method.
(10) Aneroid Sphygmomanometer
Makes a measurement of the pressure of the pulse (the arterial bp). This uses an
aneroid gauge (meaning no fluid involved). Thereʼs a cuff, an inflating bulb and an
aneroid gauge. The purpose of the bulb is to pump air into the cuff and to decrease the
pressure you turn the valve the other way (remember the lab).
(11) Aneroid Gauge
If you look in aneroid gauge there is a vacuum chamber. The air thatʼs coming in from
the cuff is filling that dark space. If thereʼs air up there at a pressure and thereʼs no
pressure at the bottom - it will push the bottom down and cause the pointer to move).
(12) Mercury Sphygmomanometer
Why is bp measured in mmHg? Historical. Instead a vacuum we had a column of
mercury at the bottom and we would use the height of the column to make a measure of
mercury at that point (you see a gauge in centimeters and mm) and this is the same way
that Hales measured his stuff).
(13) Method of Palpitation
Palpate means to touch. You pump the cuff, increase the pressure. When the pressure
in the cuff is higher than the systolic arterial bp, the artery will close. No pulse. Then you
turn the needle valve to let the air out of the cuff.
(14) Palpitation Graph
The pressure in the cuff will fall and fall and fall and at some point, youʼll begin to feel
the pulse. This is the systolic BP (that pressure). As the pressure in the cuff falls the
pressure in the cuff will become zero. You can only measure the systolic this way. You
have to use something else to get diastolic.
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