Unformatted text preview: d trace, choose Run 1. Change the name to "Lead I" then click OK.
. When you are satisﬁed with
Switch the location of the EKG leads to conﬁguration II. Click
Lead II’s trace, store it and change the name. Do the same for Lead III. Insert a legend on the graph by
clicking Analyze then Legend. Copy this graph into your worksheet.
We can use these three traces to determine the orientation of the patient’s heart by thinking about the
location of the red and green clips relative to the heart. The relative amplitude of the R peaks in the three
traces will be our guide .
• Lead I, with the red and green clips on the arms, is essentially looking in a direction horizontal to
the heart. If the maximum R amplitude is in the Lead I trace, the heart’s dipole is mostly in the
• Lead II looks at the right arm and the left leg, so if the maximum R amplitude is in the Lead II trace,
the heart’s dipole is at approximately 60◦ from horizontal.
• Lead III uses the left arm and left leg. A maximum R amplitude on the Lead III trace indicates an
12 Figure 7: Angle of the dipole orientation.
orientation of 120◦ from horizontal.
• If two of the R peaks have approximately the same amplitude, the heart’s dipole is halfway between
This is illustrated in Fig. 7. The dipole orientation tends to vary with body shape. More elongated people tend to have more vertically-oriented hearts, and people with stockier body types often have more
horizontally- oriented hearts. 6 Experiment: EMG In this experiment, we will measure the potential of the masseter (jaw) muscle. This is a good opportunity for the other partner to be the "patient", if they want to. Students with TMD or any other jaw disorder should not be the patient in this experiment.
(At this time, we have no idea how the electrodes interact with makeup. It may be best for students
wearing makeup to not be the patient in this experiment, since it is possible that the makeup would hinder
the electrical connection of the electrode to the skin.)
Scrub the left cheek with an alcohol wipe to remove excess oil from the skin. Attach two of the
electrodes to the left side of the face, as shown in Fig. 8, angling the top electrode sideways. This allows
the lead to hook over the ear, giving stress relief to the electrode. The third electrode attaches to the right
arm. If the same patient is doing the EMG as the EKG, the electrode is already in place. Otherwise, attach
the electrode to the right arm as shown in Fig. 5(b). Alternatively, the patient can attach the electrode to
the back of the right hand. This placement introduces a little more noise, but not enough to change the
relative measurements we will be making.
Connect the black lead to the electrode on the right arm. The red and green leads connect to the jaw
electrodes. It does not matter which one is connected to which electrode.
The EMG measurement needs a different sampling rate and duration than we used in the EKG measurement. In Logger Lite, click Experiment then Data Collection... (or use the key command Ctrl+D).
Change the duration to 30 s. Set the sampling rate to 100 samples/s.
13 Figure 8: Placement of the three electrodes for the EMG measurement. The reference electrode is placed
on the right arm, either above the elbow as in the EKG measurement or on the back of the right hand.
The patient should sit comfortably at a location w...
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