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Biology 220, Lab Exercise 10 & 11
LABORATORY EXERCISE 10
(BIOPAC STUDENT LAB: LESSON#5)
Introduction to the Electrocardiogram (ECG): Effects of Exercise
OBJECTIVES:
1. Describe the normal pattern of impulse production and conduction in the
tissues of the heart.
2. Describe the normal ECG and explain how it is produced.
3. Obtain an ECG prior to physical exercise, immediately postexercise and 2-minutes
post-exercise. Evaluate the cardiac rate, P-R segment, ST segment and TP segment
of each. Be able to explain the changes that occur.
4. Describe the effects of sympathetic and parasympathetic innervation upon the
heart.
5. Correlate the ECG waves and intervals with the (a) phases of the cardiac cycle, (b)
heart sounds, (c) aortic pressure, (d) position of AV valves & aortic & pulmonary valves,
(e) left ventricular volume, and (f) left ventricular pressure
INTRODUCTION
In previous lab exercises, you observed the electrical activity that was produced by
contracting skeletal muscles. The recording was called an electromyogram or EMG. In today’s
exercise you will be recording the electrical events of the heart muscle. Because the cardiac
muscle cells have such a long action potential, the electrical events create a consistent,
reproduceable sequence of waves in a recording called an ELECTROCARDIOGRAM OR ECG
(EKG). Furthermore, there are no motor units in the heart, and all cardiac muscle cells in the
atria or ventricles contract fully and simultaneously; therefore, the amplitude of the electrical
waves should not change. Before going any further, let’s review the association between the
electrical events of the heart and the mechanical events. Electrical events include depolarization
and repolarization of the cardiac muscle tissue. Remember that all atrial cells will depolarize first;
then the ventricular cells will depolarize. Answer the following 3 questions before proceeding:
(refer to Chapter 9 in your textbook if necessary)
Q1. What characteristic of cardiac muscle fibers enables the cells to depolarize
simultaneously?
____________ ________________
Q2. Why is there a delay between atrial depolarization and ventricular depolarization?
Q3. How long does an action potential last in a cardiac muscle cell? _________________
rd
Note in figure 14-27 in your textbook (Silverthorn, 3 ed.), that the electrical events of a
cardiac muscle cell precedes the contraction by a few milliseconds. This is an important point to
keep in mind when analyzing an ECG.
The electrical events of the heart are controlled by the heart’s internal cardiac conduction
system during normal heart rhythm. In vivo, the rhythmic beating of the human heart will occur at
a rate of approximately 70-80 beats/ minute in the complete absence of any nervous or hormonal
rd
influences on the SA node (pacemaker- refer to page 470, Silverthorn, 3 ed.).
The mechanical events of the heart are divided into contraction and relaxation. This is called the
cardiac cycle. One cardiac cycle consists of atrial contraction and relaxation followed by
ventricular contraction and relaxation. The contraction phase is called SYSTOLE, and the
relaxation phase is called DIASTOLE. When you take your pulse rate, you are actually
measuring the number of ventricular systoles in a given period of time. Before coming to lab,
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Biology 220, Lab Exercise 10 & 11
answer the following questions and label Figure 1 below:
•
What is your resting heart rate? ______________________bpm (beats per minute)
•
Name 2 places on your body
where the pulse is normally taken: ____________________________________________
•
Why is the SA node considered to be the pacemaker of the heart?
Most likely your heart rate was not 70-80 bpm. It was probably lower if you are resting.
Therefore, nervous and/or hormonal factors must be regulating the heart rate in vivo. As you
know, a large number of sympathetic and parasympathetic axons terminate on the SA node
rd
(refer to p.480, Silverthorn, 3 ed.). Activity in the parasympathetic (vagus) nerves which release
acetylcholine (ACh) causes the heart rate to decrease, whereas activity in the sympathetic
nerves which release the neurotransmitter norepinephrine (NE), increases the heart rate.
Furthermore, sympathetic nerve fibers also innervate the cardiac muscle and will stimulate
an increase in strength of contraction. Parasympathetic neurons (from the Vagus N.) have very
little effect on the force of contraction. In the resting state, there is considerably more
parasympathetic activity to the heart than sympathetic, and so the normal resting heart rate of
about 60-70 bpm is below the inherent rate of 70-80 bpm.
Parasympathetic stimulation of the SA node causes the pacemaker cells to take longer to reach
threshold while sympathetic stimulation causes the cells to reach threshold at a faster rate
(reference: Fig. 9-24, textbook). Today we will see how resting and exercising have an effect on
the autonomic nervous system, in turn, influencing the heart rate. The electrocardiogram (ECG
or EKG) is primarily a tool for evaluating the electrical events within the heart. The action
potentials of cardiac muscle cells can be viewed as batteries that cause electrical charge to move
throughout the body fluids. These fluctuations of electrical charges or currents can be detected
by electrodes at the surface of the skin. Before proceeding any further, READ pp.471474"The Electrocardiogram", IN YOUR TEXTBOOK (by Silverthorn, 3rd ed.).
Figure 1. Label the waves in the simulation of the normal ECG above (2 cardiac cycles).
The ECG line looks a little like an action potential but actually each wave represents a
different part of the action potentials that are generated in different regions of the myocardium. In
the ECG, the P wave represents depolarization of the atria; the QRS complex reflects the
depolarization of the ventricles. The T wave represents repolarization of the ventricles at the
beginning of diastole. There are 3 times when no current is flowing in the heart musculature and
the ECG remains at baseline:
1.
2.
3.
during AV nodal delay (from end of P to beginning of QRS complex), and known as the PR
segment (because sometimes the Q wave is too small to detect), resting value= 0.16 seconds
th
(Guyton, Medical Physiology 10 ed.) ;
during the plateau phase of ventricular depolarization prior to repolarization, visible as the ST
segment (end of S to beginning of T wave) resting value=0.12 seconds; and
during isovolumetric ventricular relaxation and initial filling of the ventricles prior to atrial
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Biology 220, Lab Exercise 10 & 11
depolarization - TP segment (end of T to beginning of P wave) .
During periods of strenuous exercise it is these 3 phases of the cardiac cycle that exhibit the most
change in duration. We will be examining this in today’s lab experiment.
·
Now label the PR, ST, and TP segments in Figure 1 on the previous page. You should
learn the significance of each segment as described above (refer to Fig 14-21 in your text
book if you need assistance).
Although atrial depolarization is represented by the P wave of the ECG, atrial contraction
(atrial systole) is delayed (about 10 msec) as a result of the latent period during which time
calcium ions enter the cytosol from the ECF. Maximal atrial contraction actually occurs between
the P & Q waves of the ECG. And although the QRS complex represents ventricular
depolarization, maximal ventricular systole actually occurs between the S & T waves, for the
same reasons. Ventricular diastole begins at the middle of the T wave and ends at the R peak of
the next QRS complex on the ECG.
• Label atrial & ventricular systole in Figure 1 on the preceeding page.
In this experiment, you will be using the Biopac Student Lab to visualize your ECG,
electrocardiogram. You should understand how to calculate heart rate, determine interval times
and wave lengths by hand from a paper copy. You will also calculate these values on the
Computerized Biopac Lab using the tools from the tool bar. Your instructor will show you how to
calculate the heart rate by hand on paper and from the Biopac.
Figure 2 . Set up for the ECG, Biopac Lesson 5.
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Biology 220, Lab Exercise 10 & 11
PROCEDURE:
to be tested on each person, time permitting. Note that we will NOT be following the
directions on the computer screen after the calibration step is completed.
·
·
·
·
·
1. Set up the electrodes as shown in figure 2. Open Lesson 5 (L05-ECG.1)using
your test subject’s first name or i.d. number for the folder title. Click OK.
2. Make sure that the electrodes adhere securely to the skin. If they are being pulled
up, you will not get a good ECG signal. Plug the SS2L lead into Channel 2 on the
acquisition unit. Perform the calibration step.
3. After the reading stops, obtain a resting ECG by clicking on Record. The subject
must be sitting and not moving or talking!! Record the resting ECG for about 20
seconds, then click on Suspend. Take your pulse rate and record in table 10.1 (to
verify the accuracy of the Biopac recording). The ECG recording should look typical
of that in Figure 1 with discernable waves. If it looks abnormal, check the placement
of the electrodes and repeat the recording.
4. Unclip the lead wires from the electrodes. Have the test subject jog on the
treadmill or perform jumping jacks for two minutes at a pace that will significantly
raise the heart rate. DO NOT ALLOW THE SUBJECT’S HEART RATE TO
INCREASE >80% ABOVE NORMAL RESTING VALUES. NOTE: If you are in poor
physical shape or sick, you should not perform this exercise as the test subject- have
someone else in your group do it.
5. After exercising, re-attach the lead wires to the electrodes and immediately click
on Resume. Record the post-exercise ECG for about 20 seconds and click on
Suspend. Take your pulse rate and record in Table 10.1.
6. Wait 2 minutes and click on Resume to get the 2-minute postexercise ECG.
Record for 20 seconds. Click Suspend and take your pulse rate (record in table
10.1). Now click on Done to exit the ECG reading for this student. Note: Biopac
data is not automatically saved. After each student is done, click on "copy to floppy
or network". Save in \biology on al\Student Data\ student data storage Bio 220
7. Re-open Lesson L05 from the lessons menu and hook the next person up to the
Biopac unit. Repeat steps 1-7 for 2 people in your group. If time allows you can
test all members or your group.
DATA ANALYSIS:
1. Enter the Review Saved Data mode.
2. Magnify 4-6 cardiac cycles in the resting segment and print in landscape format. Save
printout for future reference.
3. Analyze your data:
Set up the measurement boxes at the top of the screen as follows:
CH 2 delta T (delta time / change in time; this is an ‘x’ axis measurement)
CH 2 BPM (beats per min)
CH 2 delta [difference in AMPLITUDE (y-axis) between the first point and last point
that is highlighted]
The delta time measurement is the difference in time between the end and beginning of an area highlighted by the I-beam
tool on the graph in seconds or milliseconds (ms).
The BPM measurement first calculates the difference in time between the end and beginning of the area selected by the Ibeam tool, and then divides this value by 60 seconds/minute, which gives you beats per minute.
Delta tool will measure the difference in amplitude (millivolts – mv) between the first point and last point that is
highlighted..
4. Using the I-beam cursor, select the area between two successive RESTING R waves. Read
the BPM measurement and record it: ________. Record the BPM for the next 2 heartbeats and
record: ________, _______. Now determine the mean of the 3 BPMs and record in Table 10.1.
5. Determine the amplitude (milliVolts) of the P wave and R wave. To do this, use the I-beam
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Biology 220, Lab Exercise 10 & 11
cursor to highlight 3 different P waves from beginning to the highest point in the P wave, in each
segment of the experiment. The amplitude of the wave (mV) will appear in the “delta”
measurement window. Write these values down and calculate the mean (___________,
__________, __________mV). Record the MEAN in Table 1. To find the max amplitude of the R
wave, highlight from the end of the P wave to the top of the R wave. Do this in 3 consecutive
cardiac cycles and calculate the mean. (You may need to magnify the area to get an accurate
measurement. Use the delta value to record the amplitude of 3 consecutive R waves
(___________, __________, __________mV), determine the mean and record the MEAN for
each segment of the experiment in Table 10.1.
6. Determine the duration of a PR segment (highlight from the peak of the "P" wave to the top of
the R wave), an ST segment (bottom of "S" to top of "T" wave), and the TP segment (top of "T" to
peak of "P" wave of next cardiac cycle). To do this, MAGNIFY A SMALL SECTION IN EACH
SEGMENT OF THE EXPERIMENT. Then highlight each interval with the I-beam cursor and read
the Delta T measurement window. Record your data in Table 1.
7. Repeat steps #1-6 on the other 2 segments of the lesson (immediately post-exercise and 2
minutes later).
Table 1. ECG data*** of test subject:____________________________________
Mean
Mean
(top of P to
(bottom of S
(top of T to top
Mean
amplitude of amplitude of top of R)
to top of T)
of P)
heart rate
P wave
R wave P-R interval* ST interval*
T-P interval*
Pulse
ECG
(bpm)
(mv) @
(mv)@
(seconds)_____(seconds)_____(seconds)_______rate**__
Resting
(1st segment)
________________________________________________________________________________________________
Immediately
post-exercise
(2nd segment)
% change
between 1st
& 2nd segment
________________________________________________________________________________________________
2 min
post-exercise
(3rd segment)
% change
between 2nd
& 3rd segment
_____________________________________________________________________________
@use the delta tool to determine these values
* use the "delta T" tool to determine these values.
** pulse rate is taken by hand after each segment of the test
*** use a maximum of 2 numbers to the right of the decimal point in each of your data recordings, if applicable
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Biology 220, Lab Exercise 10 & 11
10 pt assignment (turn these 2 pages in before leaving lab today)
Name: _____________________________
·
DATA ANALYSIS QUESTIONS:
·
Where did you see the greatest change in the duration of each segment of the cardiac cycle
(PR, ST or TP) immediately post-exercise compared to the resting ECG? Why did these
changes occur?
·
Did the 2 minute post exercise heart rate (bpm) return to resting values? If not, why ?
Should you expect to see significant changes in the duration of the P wave, QRS complex or
T wave when comparing resting to immediate-post-exercise ECG’s? Why or why not?
• Was there a large difference between the amplitude of the P waves when comparing the first
and second segments of the test? The R waves? If so, what is the reason for the big difference?
REVIEW QUESTIONS
1. Think of the placement of the electrodes in an EMG vs. an ECG. Why don’t the electrodes
have to be placed directly over the heart for an ECG recording to be made?
2. Why do the mechanical events of the cardiac cycle occur a fraction of a second later than the
electrical events?
3. Explain how and why the heart rhythm would change if the cells of the SA node stopped
functioning.
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Biology 220, Lab Exercise 10 & 11
4. What things would you look for, in an ECG, to determine abnormal rhythms (arrhythmias) in the
heart? (refer to your textbook)
5. What is the calculation for cardiac output?
6. Describe how venous return, parasympathetic stimulus, and sympathetic stimuli affect cardiac
output.
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Biology 220, Lab Exercise 10 & 11
LABORATORY EXERCISE 11
VIRTUAL PHYSIOLOGY - EFFECTS OF DRUGS ON THE FROG HEART
We have already learned that the organ systems that coordinate all of the bodily
functions are the nervous and endocrine systems. They do this by secreting chemicals,
endogenous secretions, which act upon target cells that exhibit specific receptors for the
chemicals. The chemicals reach their target by traveling in the blood and ISF. The endogenous
secretions are so named because they are produced by the body and act internally. However,
we can also regulate many of the bodily functions by taking drugs into our body. Many drugs
simulate the actions of endogenous secretions while others act uniquely. A drug is therefore,
considered to be exogenous and exhibits pharmacological effects upon the body. The
exogenous, pharmacological effects of drugs may be the same as the endogenous physiological
effects of natural secretions. We will see examples of this in the Virtual Physiology Frog lab
today.
Open the Virtual Physiology Frog CD to the lab that deals with Frog Heart. You will be
instructed to dispense various drugs onto an exposed frog heart in this virtual lab. After the
application of each drug, the heart rate will be displayed and a myogram of the atrial and
ventricular contractions will be shown to you on an oscilloscope screen.
Ventricular contraction
Atrial contraction
You should read through the information in the virtual exercise after running the lab experiment in
order to help you answer the questions.
Record the Frog heart rate and amplitude (force) of contraction in the table below :
Drug
Heart Rate
(bpm)
NORMAL
CALCIUM
DIGITALIS
PILOCARPINE
ATROPINE
POTASSIUM
EPINEPHRINE
CAFFEINE
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Ventricular
Amplitude
(# of squares)
Other Observations:
e.g. atrial fluctuations, etc.
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Biology 220, Lab Exercise 10 & 11
NICOTINE
(topical)
(systemic)
Data Review:
You should be able to explain and describe the effects of the following drugs on heart rate and
strength of contraction: 1) pilocarpine, 2) epinephrine, 3) atropine, 4) caffeine, 5) potassium and
6) nicotine.
Questions for further Review:
1. Which of the drugs exhibited sympathomimetic activity and what does this term mean?
2.
Which of the drugs exhibited parasympathomimetic activity and what does this term mean?
3. What are the molecular mechanisms that cause K+ (potassium) to affect the heart rhythm?
Why would excessive K+ in the blood stream cause death?
4. Describe the molecular effects of Atropine on the nervous system.
5. Ground troops in the Iraqi war were issued injectable atropine. Can you explain why this may
be useful?
6. Why do the effects of nicotine that is delivered topically or systemically differ?
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