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Unformatted text preview: (a) Placement of the leg electrode. (b) Placement of the arm electrodes.
One student from each lab group will act as the "patient" for today’s experiment. (If time remains at
the end of the lab, the other partner is welcome and encouraged to also record an EKG trace of their own.)
Oil that builds up on the skin will decrease the effectiveness of the electrical connection, so using alcohol
wipes clean off the skin where the electrodes will be attached. The electrodes will only stick once, so try
to place them properly the ﬁrst time and press them ﬁrmly in place.
For the EKG portion of the lab, one electrode will be placed on the inside of each ankle, slightly above
the ankle bone, as shown in Fig. 5(a). Place one electrode 1 − 2 inches above the elbow on the inside of
the arm, as shown in Fig. 5(b).
Switch the leads on the DMM from the point probes used above to the banana cables with an alligator
clip on the end. Using the DMM, measure the potential difference between your right ankle and left arm,
right ankle and right arm, and right and left arms by attaching the DMM to the electrodes with the alligator
clip. Record these values on your worksheet.
The black alligator clip on the EKG sensor records a reference voltage, which shows up in the trace as
the isoelectric line. The red and green alligator clips together form a "lead", which is a term for how the
pair together is oriented. Each lead reveals unique information based on the lead’s orientation relative to
the axis of the heart. (This information is often condensed in a construct called Einthoven’s Triangle after
the inventor of the modern EKG, Willem Einthoven. For a great video that explains Einthoven’s Trinagle
and other related EKG topics, see .) We will examine three different leads in today’s experiment:
(Note: For now, I’m going to write this assuming we will have computers.)
Log on to the computer (Note: I’ll want to include instructions for how to do so.) Connect the Go!Link
cable to the EKG Sensor and the computer.
Open the Logger Lite software from the icon on the desktop. To set up the details of the data collection,
click Experiment then Data Collection... (or use the key command Ctrl+D). Make sure that the mode is
time based, the duration is 3 s, and that the "Sample at Time Zero" box is checked. Change the sampling
10 Conﬁguration Black Green Red Lead I
Lead III right ankle
right ankle right arm
left arm left arm
left ankle Table 4: EKG lead conﬁgurations. rate to 60 samples/second. Click Done.
Connect the three leads of the EKG sensor to the patient’s electrodes in the Lead I conﬁguration. The
patient should stand comfortably. As we will see in the EMG experiment, muscle movement produces
electrical activity, so the patient needs to try to remain still throughout the data collection process. The
other student should operate the computer while the patient is connected to the EKG Sensor to minimize
the patient’s movements.
. The EKG trace will show up on the screen
To collect the EKG data, click the Collect button
over the next three seconds, and the vertical axis should autoscale when the collection is complete. Look
at the trace. Does it look relatively smooth? Does there seem to be a somewhat ﬂat baseline? Do the
PQRST peaks (the ones you can see; not everyone will have all ﬁve...
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This document was uploaded on 02/15/2014.
- Spring '14