Download ECG

Wayne f2016
EKG
Purpose: This exercise is designed to familiarize the student with taking an ECG and observing the
phenomenon known as the Mammalian Diving Reflex.
Performance Objectives: At the end of this exercise the student should be able to:
1.
Take an ECG of another person using the stand limb leads and IWORX equipment.
2.
Explain and demonstrate the Mammalian Diving Reflex.
3.
Calculate heart rate given the duration of the cardiac cycle.
4.
Identify the P, QRS, T wave forms of an ECG.
5.
Describe what each wave form of the ECG represents.
Background
Activity stimulates the heart to contract more vigorously than it does when the body is at rest. The EKG
(electrocardiogram) sensor measures cardiac electrical potential waveforms (voltages) produced by the
heart as its chambers contract. The EKG does not directly measure of heart muscle activity. A
comparison of the EKG measured during rest and the EKG measured after mild exercise show the
changes that take place in the heart cycle due to activity.
The Electrocardiogram
The part of the EKG (electrocardiogram) before any measurement is taken is called the baseline.
The first deviation from the baseline (isoelectric point) in a typical EKG is an upward pulse following by
a return to the base line. This is called the P wave and it lasts about 0.04 seconds.
After a return to the baseline there is a short delay while the heart’s AV node depolarizes and sends a
signal along the atrioventricular bundle of conducting fibers (Bundle of His) to the Purkinje fibers,
which bring depolarization to all parts of the ventricles in a wave that is almost simultaneous.
When the AV node depolarizes there is a downward pulse called the Q wave. Shortly after the Q wave
there is a rapid upswing of the line called the R wave followed by a strong downswing of the line called
the S wave and then a return to the baseline. These three waves together are called the QRS complex.
This complex is caused by the depolarization of the ventricles and is associated with the contraction of
the ventricles.
Next there is an upward wave that then returns to the base line. This upward pulse is called the T wave
and indicates repolarization of the ventricles.
The sequence from P wave to T wave represents one heart cycle. The number of such cycles in a minute
is called the heart rate and is typically 70-80 cycles (beats) per minute at rest.
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R
P Wave
T Wave
Q
S
QRS Complex
P-R interval... 120-200 milliseconds (0.120 to 0.200 seconds)
QRS interval... under 100 milliseconds (under 0.100 seconds)
Q-T interval... under 380 milliseconds (under 0.380 seconds)
A.
Activity: ECG and Finger Pulse: Baseline Recordings
You will be using the IWorx station to record individual ECG’s and finger pulses. Each student
should make a baseline recording of their own ECG and finger pulse.
Each student should only use ONE set of electrodes for ECG, do not remove
the electrodes until you are completely finished with this exercise
1.
The equipment should be set up and preprogrammed for you. The instructor will give
you the settings for the IWorx system.
2.
Prepare the subject for recording by having them remove all jewelry from wrists and
ankles. Then swab the ventral surface of each wrist and an area on the left leg just above
the ankle with an alcohol swab. You will only be using three of the leads.
4.
Convince the subject to sit quietly with their hands resting on their legs.
5.
click <Record> and, if needed, <AutoScale> in the channel two title area
6.
You should see a rhythmic ECG tracing and pulse appear on the screen if the trace is
upside down, click <Stop> and switch the positive and negative electrode leads or right
click and <invert> . If a larger or better signal is required, the electrodes should be moved
from the wrists to the skin immediately below each clavicle
6.
When you are getting a suitable trace, type the “’subjects name’ and ‘resting’” and press
Enter on the keyboard.
7.
Click <stop> to halt recording
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8.
Proceed to the data analysis section of the exercise
9.
Each student should print a copy of their resting ECG, label the major waves on their
ECG and paste one in the indicated space.
10.
To save a picture of the EKG: Go to file, export and save as Jpeg on a flash drive or
desktop. Email the picture to yourself and then print at home or on the lab printer. If the
picture is placed in a word document, it can be resized to fit the indicated space.
Place Tracings Here
B.
Determining heart rate.
1.
Determine the heart rate as follows:
Heart rate
=
(beats / minute)
60 sec./min.
time interval between successive
intervals in seconds (R-R interval)
For a more reliable estimation of heart rate take the average of 10, R-R
intervals.
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Heart Rate (EKG) using 1, R-R interval: ________________
Heart Rate (EKG) using 10, R-R intervals: ______________
2.
Let the EKG run for approximately 10 seconds and watch for a normal
rhythm (If an arrhythmia is present, call your instructor to verify). Also
observe the relationship between atrial and ventricular rhythms.
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
______________________________________________________________
3.
Record the EKG and pulse of a student lying down after resting quietly for
a few minutes. Then have the student stand quickly. Observe differences
in the heart rate. Explain.
HR (Lying Down): _____________ HR (Standing): ________________
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
4.
Describe the effect of exercise on the EKG. Make sure the electrodes are
securely placed, disconnect the leads from the at the limb electrodes and
allow the subject to engage in several minutes of vigorous exercise,
preferably by the exercise steps provide. Rapidly return the subject to the
supine position; reconnect the limb leads. Why is speed essential in reconnecting the subject to the EKG?
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_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
C.
Calculating Intervals
1.
Calculate the P-Q interval and record the time.
2.
Calculate the overall Q-T interval and record the time.
Item
P-Q interval
Q-T interval
Rest
Exercise
sec
sec
sec
sec
Compare your values for the P-Q, and Q-T intervals for the EKG at rest to the values for the P-Q,
and Q-T intervals for the EKG after mild exercise. How do the time intervals for the EKG after
mild exercise compare to the time intervals for the EKG at rest? Explain the differences.
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
PART II- The Mammalian Diving Reflex (optional)
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Using a student volunteer, the instructor will demonstrate the Mammalian Diving
Reflex
A sphygmomanometer, stethoscope, IWORX System alcohol swabs, and volunteer are needed
for the test. A pan of ice water, pan of room temperature water and towels are needed, along with all of
the previously mentioned materials, in order to simulate the diving reflex.
Initially, a three lead EKG is performed on a subject that is sitting and resting with their arms
resting on their thighs breathing normally. For the diving reflex, the subject is asked to hold their breath
and then immerse their entire face (including forehead) into the pan of ice water. They should hold their
breath as long as possible. The EKG is used to determine heart rate before and after while holding their
breath in warm water and then ice water.
Heart Rate at end of breath holding in warm water: _____________
Heart Rate at end of breath holding in cold water: ______________
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