Unformatted text preview: e heart rate is (60s/min)/0.81s = 74 beats/min. This is a fairly typical resting
heart rate, based on the values in Table 1.
We can also calculate the interval times and compare those to the typical values in Table 1. We will
compare using percent error:
|actual value − theoretical value|
Since the P − R interval gives a range, use the average, 0.16 s, as the theoretical value.
percent error = 5 (5) Time
(s) Peak Time (s) Peak 1 0.50 Peak 2 1.25 0.75 Peak 3 2.07 0.82 Peak 4 2.92 0.85 Peak 5
Table 2: Time difference between R peaks in Fig. 3. Interval length (s) percent error P−R 1.20 − 1.07 = 0.13 19% QRS 1.38 − 1.20 = 0.18 80% Q−T 1.52 − 1.20 = 0.32 16% Table 3: Comparison of interval values in Fig. 3 to the typical values in Table 1. 2.6 EMG An electromyogram (EMG) measures the electrical activity of muscles. As with the heart, other muscles in the body are also activated by ion ﬂow across the cell membranes. In a clinical setting, this can
be done to test for damage to the muscle or muscle-nerve connections, or to ﬁnd the cause of a muscle
weakness, paralysis, or twitching. As with the EKG test, electrodes are placed on the patient’s skin.
The amplitude of the electrical activity correlates to the strength of the muscle contraction. It is also
dependent on the quantity of nerve impulses that are sent to the muscle. For this reason, it is easy to
observe large muscles like the biceps in the arm or the quadriceps in the leg. Smaller, less visible muscles
can also be measured with an EMG. We will measure the electrical activity in the masseter muscle in the
jaw. 3 Equipment The EKG sensor we will use today is very similar compared to those found in a medical setting, but
somewhat simpliﬁed with the reduced number of leads. Since the EKG sensor looks at the potential
difference between the various electrodes, we will start the lab with a brief experiment looking at known
potentials using a simple voltmeter.
The equipment we will use today includes:
• Extech DC power supply
• Meterman 15XP digital multimeter 6 • Pasco Scientiﬁc PK-9025 conductive paper with point electrodes
• Vernier EKG Sensor
• Vernier Go!Link
• Vernier’s Logger Lite 1.6.1 software
• alcohol wipes
• adhesive electrodes 3.1 Extech DC power supply The power supply produces a ﬁxed potential difference between two points. The power supply has
two terminals, each of which should be attached to an electrode. Once they are attached, turn on both the
power strip and the power supply itself, and set the "Output Voltage" to 10 V. 3.2 Meterman 15XP digital multimeter, functioning as a voltmeter A voltmeter is a device that can measure the potential difference (in volts) between one point and
another. In this course you will frequently use a digital multimeter, which can function as a voltmeter, an
ohmmeter or an ammeter. In order to set up the multimeter for use as a voltmeter, you should ﬁrst turn
the knob on the multimeter to V, so that the meter reads DC volts. Next, plug one lead into the ground or
"COM" terminal and one into the terminal marked "V". (The third terminal, labeled "A mA µ A", is used
for measuring currents.) If you hear your meter beep and turn off, that is a power saving feature. You can
simply turn it back on by moving the selector switch over one setting and moving it back. Be sure to turn
the meter off...
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