Download Week 10--Cardiovascular Physiology

Cardiac Physiology: Electrocardiogram (ECG), Pulse, Blood
Pressure, and Blood Typing
Electrocardiogram (ECG)
Useful in many clinical applications, ECGs work on the same principle as EMGs. To
fully understand an ECG, review the cardiac cycle in your textbook. Briefly, to
pump blood efficiently, the atria contract during late diastole, completely filling the
ventricles with blood. The ventricles then contract during systole, pushing blood
into the pulmonary and systemic circulations. From this we can visualize a series of
events: the atria contract, and while they are relaxing, the ventricles contract, and
after that, the ventricles relax. This is one cardiac cycle.
Like skeletal muscle, cardiac muscle contraction is initiated by ion flow across the
cell membrane. Thus, we can visualize the electrical events of the cardiac cycle using
an ECG. The basic components of an ECG are shown below, in Figure 1.
Figure 1. Basic components of an ECG trace, showing the P Wave, QRS Complex, and T wave.
With the cardiac cycle in mind, let’s take a look at the components of the ECG trace
in Figure 1. Remember that the first event of the cardiac cycle is atrial contraction.
What must happen before the atria contract? They must be depolarized by ion flow
across the membranes of atrial cells. The P Wave represents the depolarization of
the atria.
The next three parts you see in Figure 1—the Q, R, and S waves—are grouped
together in something we collectively call the QRS Complex. The QRS complex
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reflects the depolarization of the ventricles, which leads to the next major event of
the cardiac cycle: ventricular systole.
Finally the T wave reflects ventricular repolarization, which occurs during
relaxation. Why do you think we don’t see atrial repolarization in the ECG trace
shown above?
A typical ECG trace is shown in Figure 2. From this, heart rate can easily be
calculated, but a trace like this can also be used to help diagnose heart abnormalities,
from mild to severe. It’s also important to remember that ECG abnormalities may
not be indicative of any clinical condition, and may not be a cause of concern.
Figure 2. A typical ECG trace.
Remember that interpretation of the ECG is much easier if you understand the
cardiac cycle. However, remember too that the waves on the ECG trace are
electrical events, not muscular events. So, the P Wave (for instance) does not
represent atrial contraction, it represents atrial depolarization.
Pulse
Now that we have reviewed the cardiac cycle and have a visual idea of the electrical
events associated with it, it’s time to think about what is happening in the blood
vessels.
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There is always blood flowing through your major blood vessels, but you can
imagine that during ventricular systole—that component of the cardiac cycle when
the ventricles contract—that a “wave” of pressure would travel through your
arteries, moving arterial walls. Indeed, this is exactly what happens. When your
ventricles contract, they send out a given volume of blood (i.e. the stroke volume)
quickly and forcefully to your arteries. The rate at which these pressure waves
travel through your arteries should be similar to your heart rate.
We refer to this pressure wave simply as your pulse, and it can be felt at several
places in your body, where arteries are near the surface of your skin. Our bodies
have several of these so-called pulse points, such as the axillary pulse, brachial
pulse, femoral pulse, popliteal pulse, facial pulse, and carotid pulse (see figure 11.18
in your textbook).
In the questions listed below, , one question asks whether or not a pulse can be
found in veins. In answering that question, you should be thinking about why it can
or cannot be. With that in mind, your job today is to work with your lab partner and
measure his/her pulse at multiple pulse points. Is it the same at each pulse point?
Why or why not?
Blood Pressure (BP)
Blood is always moving through our blood vessels, so it always has a forwardmoving, kinetic component. But, like any fluid, it is also exerting a pressure on the
walls of our blood vessels; we call this the hydrostatic pressure. We are able to feel
the pulse wave on our arterial walls because the hydrostatic pressure is increasing
briefly. We very often refer to this pressure as our blood pressure.
It is important to understand blood pressure because our arterial walls must be
strong enough to withstand it. If they fail, and blood breaks through, this causes
aneurysm, stroke, and can very often cause death.
When measuring blood pressure, we are interested in two numbers. First, we are
interested in the pressure blood exerts on arterial walls during systole; we call this
the systolic blood pressure. Second, we are interested in the pressure blood
exerts on arterial walls during diastole; we call this the diastolic blood pressure.
Blood pressure is measured in units called millimeters of Mercury (mmHg), and it is
given as two numbers, expressed as a fraction:
Systolic pressure (mmHg) / Diastolic pressure (mmHg)
The American Heart Association recommends a blood pressure around 110/80;
significantly less than that is indicative of hypotension, but a higher blood pressure
can be indicative of prehypertension or hypertension; both hypo- and hypertension
can be cause for clinical concern, especially in the presence of other factors. Table 1
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illustrates classifications of different blood pressure ranges, as presented by the
American Heart Association.
Table 1. Different classifications of blood pressure ranges, and their corresponding systolic and
diastolic pressures.
CATEGORY
SYSTOLIC (mmHg)
DIASTOLIC (mmHg)
Hypotension
Desired
Prehypertension
Stage 1 Hypertension
< 90
90-119
120-139
140-159
< 60
60-79
80-89
90-99
Stage 2 Hypertension
Hypertensive Crisis
160-179
≥ 180
100-109
≥ 110
Today you will have the opportunity to practice measuring blood pressure on your
lab partner. If you have not done it before, you will realize it takes a little practice,
so if you do not get it today it’s all right—just keep practicing (see figure 11.20 in
your textbook). Your lab instructor will go over the steps to measure blood
pressure with you, but you’ll need a blood pressure cuff, or sphygmomanometer,
as well as a stethoscope.
Excellent instructions on how to measure blood pressure can also be found at this
link:
http://homepage.smc.edu/wissmann_paul/anatomy1/1bloodpressure.html
After you’ve practiced measuring blood pressure, have your lab partner do several
minutes of exercise (jumping jacks or a running lap around the building); measure
his/her blood pressure again. Has it changed?
Blood Typing
Tranfusion of whole blood is clinically indicated when a substantial blood loss
occurs. However, the donor blood must be tolerated by the recipient’s immune
system, or an attack will be mounted and the transfused red blood cells will
agglutinate (or clump). The agglutinated blood will then clog small blood vessels,
and the donor red blood cells will eventually rupture.
Ultimately, surface proteins on red blood cells (RBCs) determine whether or not
blood may be safely transfused. Any substance that the immune system can
recognize as foreign is called an antigen. Specific plasma membrane proteins may
trigger an immune response (attack) if they occur on the donor’s RBCs, but do not
occur on the recipient’s RBCs. Blood is typed based on the presence or absence of
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groups of these antigenic RBC surface proteins. There are two different blood
groupings that are used to type blood for transfusion purposes, ABO and Rh. Two
RBC antigens determine ABO blood groups, the A antigen and the B antigen. Only
one RBC antigen of concern occurs in Rh blood groups, the Rh factor (also known as
the D antigen).
Antibodies are glycoproteins made by special types of lymphocytes in response to
foreign antigens. Antibodies will form a complex (i.e. bind) with RBC antigens,
causing the RBCs to clump together. In blood typing, antibodies that are known to
bind to specific RBC antigens are used to test for the presence of those antigens on
blood of unknown type. Today we will be using anti-A antibodies (Anti-A serum) to
test for the presence of A antigens, anti-B antibodies to test for B antigens, and antiRh antibodies to test for the Rh factor on synthetic blood. Any agglutination
(clumping) that results indicates the presence of that antigen. The results will then
be used to determine the ABO and Rh type of the synthetic blood.
Antigen Presence Based on Agglutination Results
Antibody Added to Blood
Agglutination?
Anti-A
Yes
No
Anti-B
Yes
No
Anti-Rh
Yes
No
Blood Typing based on Antigen Presence
A Antigen Present? B Antigen Present?
yes
yes
yes
yes
yes
no
yes
no
no
yes
no
yes
no
no
no
no
Antigen on RBC?
A antigen present
A antigen not present
B antigen present
B antigen not present
Rh factor present
Rh factor not present
Rh Factor Present?
yes
no
yes
no
yes
no
yes
no
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Blood Type
AB+
ABA+
AB+
BO+
O-
Questions
1. Why does the QRS Complex have higher amplitude than the P Wave?
2. Which component of the cardiac cycle is not visible in the ECG trace? Why?
3. Is an abnormal ECG always cause for immediate medical concern?
4. Why can heart rate be detected as a pulse?
5. Which artery is felt when taking pulse at the neck?
6. Which artery is felt when taking pulse at the wrist?
7. You measured your lab partner’s pulse at various points. Was it the same
everywhere? Explain why or why not.
8. What factors affect blood pressure? (hint: use your textbook to answer this
question). Would a nervous patient at the doctor’s office have a higher blood
pressure than a patient who is calm, all other things being equal?
9. After exercise, did your partner’s blood pressure change? How?
10. How would the body benefit from a change in blood pressure during
exercise?
Updated 4/8/14
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Bio 221 - Lab 10
Cardiovascular & Lymphatic Systems – (Part 2)
Identify all assigned organs and structures on all lab specimens in which they
appear.
I. Cardiovascular System:
A. Hepatic Portal Circulation
 Hepatic Portal V.
 Splenic V.
 Inferior mesenteric V
 Superior mesenteric V.
B. Fetal Circulation – Note: Certain fetal structures undergo a name change
when they close at birth; the postnatal name is given in parenthesis ( )
 Placenta
 Umbilical cord
 Umbilical/placental vein (round ligament of the liver/ligamentum
teres hepatis)
 Umbilical/placental arteries (medial umbilical ligaments)
 Ductus venosus (ligamentum venosum)
 Ductus arteriosus (ligamentum arteriosum)
 Foramen ovale (fossa ovalis)
C. Circle of Willis/Cerebral Arterial Circle
 Common carotid A.
 External carotid A.
 Internal Carotid A.
 Vertebral A.
 Basilar A.
 Posterior cerebral A.
 Posterior communicating A.
 Middle cerebral A.
 Anterior cerebral A.
 Anterior communicating A.
II. Lymphatic System:
A. Lymph nodes
 Cervical nodes
 Axillary nodes
 Inguinal nodes
B. Spleen
C. Lymphatic vessels
D. Lymphatic trunks & ducts
 Thoracic duct/left lymphatic duct
 Right lymphatic duct
 Cisterna chyli
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