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Transcript
NU – AP 2
iworx ECG & Heart Sounds
Exercise 31A (modified)
Electrocardiogram (ECG), Heart Sounds, and Exercise Activity
1. PURPOSE




To perform an ECG recording in a human subject, identify and interpret the waveforms in terms of
depolarization and repolarization.
Calculate ECG parameters such as QRS interval, PR and QT segments, and analyze their significance
Experimentally correlate heart sounds to electrical conduction in the heart and phases of cardiac
cycle.
Compare and analyze ECG recordings in rest and after exercise.
2. INTRODUCTION
The ability of the cardiac muscle to contract is intrinsic, e.g. it does not depend on the nervous
system to initiate its contraction, and it continues even if all connections are severed. Two systems
exert their effects on heart activity: one is the autonomic nervous system, and the other is the
instrinsic conduction system or nodal system of the heart. This consists of autorhytmic non-contractile
cells specialized to initiate impulses throughout the heart. This way, the heart depolarizes and
contracts in an orderly sequential manner, and beats as a coordinated unit. See Figure 31.1 of your lab
manual for the components of the intrinsic conduction system.
The electrical currents generated and transmitted through the heart spread throughout the body
and can be recorded with an electrocardiograph. A graphic record of that activity is called an
electrocardiogram (ECG). For analysis, the ECG is divided into segments and intervals (Fig.1) Review
your textbook for a detailed description of the waveforms. While ECG is a record of voltage and time, it
reflects electrical events happening in relatively large amount of muscle, so it does not reflect the
activity of nodal tissue only. We can infer that muscle contraction will follow the excitation of muscle
tissue, this is something that is not recorded in an ECG.
The main goal of this exercise is for students to become familiar with recording and interpreting
different cardiovascular parameters. Electrocardiograms (ECGs) reflect the electric activity of the heart.
Cardiac parameters involve different ECG intervals, as well as the R-wave amplitude (expressing the
force of ventricular contraction) and the heart rate. The characteristic heart sounds correspond to the
closing of the AV and semilunar valves. In the first part of the experiment students will relate phases of
the ECG profile with the heart sounds. In the second part, students will compare the ECG parameters
recorded in rest and after aerobic exercise.
In the first part of this lab activity you will record the electrocardiogram (ECG) of a group member
while listening to the characteristic “lub-dub” heart sounds at rest. The “lub” sound occurs during the
early phase of ventricular contraction and is produced by closing of the atrioventricular valves, which
prevents blood flow into the atria. When the ventricles relax, the blood pressure drops below what is
in the artery and the semilunar valves close, producing the “dub” sound. In the second part, you will
only record ECG at rest and immediately after a short aerobic exercise. Two different subjects should
be recorded for the first and the second part.
EXPERIMENTAL SET-UP
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1.
2.
3.
4.
5.
6.
See Figure 2 for the different sensors/instruments to be used in this lab.
Double-Click iWorx/LabScribe Software on Desktop to start the program
Click “Settings -> Select “AP_2 ECG Exercises”
Open “ECG_heartsound” settings
Remove all jewelry, watches, etc. from wrists.
Use alcohol swabs to clean and scrub the 3 regions on the inside of the subject’s forearms
where the electrodes will be placed.
7. Remove the plastic disk from a disposable electrode and snap lead wires onto the disposable
electrodes
8. Attach the disposable electrodes on the regions describes below.
 RED (+1) LEAD is attached to the right wrist.
 BLACK (-1) LEAD is attached to the electrode connected to the left wrist.
 GREEN (C) LEAD (the ground) is attached to the electrode on the right leg (inside ankle).
 Make sure that both stethoscope and the event marker are ready to be used (Figure 2).
Figure 1 . The normal electrocardiogram: P wave Figure 2 Sensors and instruments used in
corresponds to atrial depolarization, the QRS
exercises 31 and 33.
complex to ventricular depolarization, and the Ta) Stethoscope
wave to the ventricular depolarization. In a
b) Event Marker
normal heart, the size, deflection, and timing of
c) Pulse Plethysmograph
waves tends to be consistent.
d) ECG cable & Electrode lead wires
a
b
c
d
3. PROCEDURES
PART 1 - Recording of ECG and Heart Sounds (at rest)
1. The experimental subject (Subject) should sit quietly with both hands on their laps in supine
position.
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***If you group member moves, the ECG trace will move off the top or bottom of the screen. If he
or she moves any muscles in the arms or upper body, electromyograms (EMGs) from the muscles
will appear on the ECG recording as noise. ***
2. A second person (Recorder) in your group should begin listening the heart sounds placing the
stethoscope on the left region of the subject chest (Figure 3). When the person can clearly hear
the “lub” and “dub” sound pattern, he or she should be ready for recording with “event
marker.”
***Heart sounds can also be heard by placing the stethoscope over the arteries in the neck.***
3. A third person (Operator) will use the computer. Operator will click on Record button on the
top right side of the Main window of Labsribe software. Operator will also click on Autoscale
button on the upper margin of each channel whenever the recording shifts out of the screen.
4. When the Subject and Recorder are ready, Operator will start the recording by clicking on the
Record button.
5. During the recording, Recorder will press and hold the event marker button when he or she
hears the “lub” (first) sound and releases the button when hears the “dub” (second) sound.
 Pressing the button will result in vertical line (from baseline to peak) in Heart Sound
channel
 Holding the button will result in a horizontal line in Heart Sound channel
 Releasing the button will result in a vertical line (from peak to baseline) in Heart Sound
channel
6. The Operator should record for 1 minute, and the recording should have a good, noise free,
portion for at least 15 seconds in length so that an easier data analysis can be performed
(Figure 4).
7. While recording, the Operator should pay attention and perform the followings if necessary;
 When any of the recordings shifts out of screen, click on the Autoscale button on its
channel.
 When any of the recordings looks inverted, right click on and select Invert on its
channel.
 When the recording moves fast and the time scale (on X axis) is too short, click on
double display time (may require couple of clicks) icon on the upper toolbar (Figure 5).
 Note the average resting heart rate (V2 –V1 = ….bpm) on Heat Rate channel
8. When the recording is completed Operator will;
 click on Stop to halt the recording.
 Save the file as “GroupName_ecgHeartSound” on the Desktop of your computer. Make
sure to designate the file type as *.iwxdata.
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Figure 3. Experimental student with electrodes
properly attached, while another student listens
to the heart sounds using the stethoscope and
recording with the event marker.
iworx ECG & Heart Sounds
Figure 4 ECG and event marker recordings displayed
in the Analysis window. Lines and labels were added
to figure to indicate the locations where cursors
should be placed to measure the time intervals
between the R wave and the “lub” and the T wave
and the “dub”.
PART 2 - Recording of ECG at Rest.
1. The Subject of this part should be a different student. Note that some aerobic exercise is
required.
2. The recording will be as described in Part 1, from #1 through #7, but excluding the heart
sounds. The heart sounds channel may be minimized.
3. Operator will continue recording for 3 min.
4. Operator will also type and enter the followings next to the Mark box to the right of Mark
button;
 Type 0 second and press Enter key on keyboard when begin to record.
 Type 60 seconds and press Enter key on keyboard when 1 minute is passed while
recording.
 Type 120 seconds and press Enter key on keyboard when 2 minutes is passed while
recording.
5. When the recording is completed Operator will;
 click on Stop to halt the recording.
 Save the file as “GroupName_ecgRest” on the Desktop of your computer. Make sure to
designate the file type as *.iwxdata.

PART 3 - Recording of ECG after short aerobic exercise
1. First, the ECG wires will be unplugged from the electrodes, but electrodes will be left intact on
Subject’s skin.
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2. Then, the subject will perform some aerobic exercises such as running/jogging in the hallway
outside the classroom or around the parking lot for 3 to 5 minutes, or jumping for a couple of
minutes. For optimal results, try to get the heart rate elevated (over 100 bpm).
3. Recording will be performed as described in Part 1, from #1 through #7, but excluding the heart
sounds.
4. When the Subject comes back from exercise, the wires will be attached, and the Operator
immediately will begin recording.
5. Operator will continue recording for 3 minutes or until the Subject’s heart rate returns to
normal, as it was recorded during the resting period.
6. Operator will also type and enter the followings next to the Mark box to the right of Mark
button;
 Type 0 second and press Enter key on keyboard when begin to record.
 Type 60 seconds and press Enter key on keyboard when 1 minute is passed while
recording.
 Type 120 seconds and press Enter key on keyboard when 2 minutes is passed while
recording.
2. When the recording is completed Operator will;
 click on Stop to halt the recording.
 Save the file as “GroupName_ecgExercise” on the Desktop of your computer. Make
sure to designate the file type as *.iwxdata.
Figure 5 – Shortcut buttons on LabScribe software
4. DATA ANALYSIS
Use Table 1 for calculations
Table 1 – Guide to Measurements of EKG Components
Component
(Value to be
How to Measure
Measured)
Place one cursor on the peak of R wave on ECG channel.
R wave to
Place the second cursor on the onset (top of first vertical
“lub” interval line) of event marker on Heart Sounds channel.
T wave to
“dub” interval
P wave
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Value to be Recorded
T2 - T1 on either ECG or
Heart Sounds channel
Place one cursor on the peak of T wave on ECG channel.
Place the second cursor on the offset (top of second vertical
line) of event marker on Heart Sounds channel.
T2 - T1 on either ECG or
Heart Sounds channel
Place one cursor at the beginning of P wave and the second
cursor at the end of the P wave on ECG channel.
T2 - T1 on ECG channel
only
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R wave
Amplitude
Place one cursor at the beginning of QRS complex and the
second cursor at the end of the QRS complex on ECG
channel.
Place one cursor on the peak of Q wave before R wave and
the second cursor on the peak of the R wave on ECG
channel.
P – R Interval
Place one cursor at the beginning of P wave and the second
cursor at the beginning of QRS complex on ECG channel.
P-R Segment
Place one cursor at the end of P wave and the second
cursor at the beginning of QRS complex on ECG channel.
QRS Complex
S-T Segment
Q - T Interval
T - P Interval
Beat Period
(R – R
Interval)
Place one cursor at the end of the QRS Complex and place
the second cursor at the beginning of the following T wave
on ECG channel.
Place one cursor at the beginning of QRS complex and the
second cursor at the end T wave on ECG channel.
T2 - T1 on ECG channel
only
V2 - V1 on ECG channel
only
T2 - T1 on ECG channel
only
T2 - T1 on ECG channel
only
T2 - T1 on ECG channel
only
T2 - T1 on ECG channel
only
Place one cursor at the end of the T wave and place the
second cursor at the beginning of the following P wave on
ECG channel.
T2 - T1 on ECG channel
only
Place one cursor on the peak of R wave and the second
cursor on the peak of adjacent R wave to its right on the
ECG channel.
T2 - T1 on ECG channel
only
PART 1 – Analysis of Recorded Data of ECG and Heart Sounds (at rest)
1. Scroll through the recording and find a section of data with four to six good ECG cycles in
succession.
2. Four complete ECG cycles can be selected by;
i. Placing the cursors on either side of a group of four complete ECG cycles
ii. Clicking the Zoom between Cursors button (Figure 5) on the toolbar to expand that
segment to the width of Main window.
3. Click on the Analysis window icon in the toolbar (Figure 5). You will see the mathematical
functions above the uppermost channel. Values for V2-V1 (y-axis, vertical), T2-T1 (x-axis, time),
and Mean (average between two cursors) from each channel can be seen across the top margin
of each channel.
4. For this Part, calculate the average R-lub and T-dub interval ONLY. Use Table 1 as a guide; place
the two cursors on specified positions to determine the values on data tables. When the
cursors are in correct positions, the data can be obtained from the numbers below V2-V1, T2T1, and the Mean functions for the channel desired.
*** Data can be input on Excel file, AP2_HeartSounds_ECG_Tables_v1.xls or can be written down
on the printed data tables. ***
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5. Analyze the data of 3 different cycles.
6. Record your data in the following table:
Table 2. Heart Sound parameters
Interval (msec)
Cycle 1
Cycle 2
R-lub
T-dub
Cycle 3
Average
PART 2 – Analysis of Recorded Data of ECG at rest
1. Perform the analysis as described above in Part 1. Refer to Table 1, but do not analyze R wave
to “lub” and R wave to “dub” intervals.
2. Analyze the data of three different cycles.
3. For each component record and fill out the data Table 3, “ECG Measurements at rest.” Analyze
3 cycles, record the values, and then write down the average
PART 3 – Analysis of ECG data after aerobic exercise
1. Perform the analysis as described above in Part 1. Refer to Table 1, but do not analyze R wave
to “lub” and R wave to “dub” intervals.
2. Analyze the data at 0 sec, 60 sec, and 120 sec. at the marked portions of your recording.
3. For each component record and fill out the data Table 4, “ECG Measurements after Exercise”
for for three different ECG cycles.
4. Compare the average values of the different parameters at rest and after exercise in Table 5.
5. QUESTIONS
Table 3. Parameters calculated for ECG recording at Rest
Measured at Rest
Mean Values
Cycle 1
Cycle 2
Cycle 3
Average
R wave Amp
P wave
P – R Interval
P- R Segment
QRS wave
Q – T Interval
S -T segment
T – P Interval
T-wave
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Beat Period
(T to T
Interval)
Table 4. ECG parameters after exercise.
ECG parameters after Exercise
Mean
Values
0 min
(3 values)
0 min
Average
After 60 min
(3 values)
After 60 min
Average
After 120 min
(3 values)
After 120 min
Average
R wave
Amp
P wave
P–R
Interval
P- R
Segment
QRS wave
Q–T
Interval
S -T
segment
T–P
Interval
T-wave
Beat Period
(T to T
Interval)
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Table 5. Comparison of ECG parameters at Rest and after Exercise
Mean
Values
R wave
Amp
P wave
P–R
Interval
P- R
Segment
QRS wave
Q–T
Interval
S -T
segment
T–P
Interval
T-wave
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Normal
values
(sec)
Measured at
Rest
At 0 sec
Measured After Exercise
At 0 sec
After 60 sec
After 120 sec
0.060.11
0.12-0.2
0.08
0.12<
0.310.41
0.12
varies
0.16
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QUESTIONS
1. (consult your textbook if necessary)
Heart
What
Electrical event in the
Sound
provokes it
atria/ventricle
“Lub”
sound
Phase of cardiac cycle
“Dub”
sound
2. Using the formula below, calculate the average heart rate of the subject and write down on
the table below.
Heart Rate (beats/min) =
60 𝑠𝑒𝑐𝑜𝑛𝑑𝑠 𝑝𝑒𝑟 𝑚𝑖𝑛𝑢𝑡𝑒
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑠𝑒𝑐𝑜𝑛𝑑𝑠 𝑝𝑒𝑟 𝑏𝑒𝑎𝑡 (𝑀𝑒𝑎𝑛 𝐵𝑒𝑎𝑡 𝑃𝑒𝑟𝑖𝑜𝑑)
At Rest
At 0 sec.
Measured After Exercise
At 0 sec
At 60 sec. At 120 sec
Mean Heart
Rate
When was the subject’s HR the most elevated?
2. In relationship with Table 5: which parameters changed the most during exercise and why?
Discuss your results in relationship to the events of the cardiac cycle.
3. Recovery Heart Rate refers to the heart’s ability to return to normal values after physical (aerobic)
activity. It is measured two minutes after exercise and is the most common measurement in
determining cardiovascular fitness. It is calculated by subtracting the two min (120 sec) HR from
the HR at 0 sec. The bigger the value (quicker the HR returns the resting value) indicates a
healthier heart and the smaller the value indicates a less healthy heart.
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Assume that two healthy subjects with similar physical conditions (age, gender, height, weight, etc)
performed Leg Exercises (under same conditions and time frame) and their mean HRs are
determined from EKG recordings on the table below;
Subject A
Subject B
HR (at
Rest)
72
80
HR (0 sec after Exercise)
HR (120 sec after Exercise)
115
125
80
115
a) Which subject has the highest recovery HR and a healthier heart?
b) Give some possible explanations as to why one may have a “healthier” heart.
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