Download Goal: To understand bioelectrical signals To understand ECG

Goal:
To understand bioelectrical signals
To understand ECG acquisition
To understand time domain analysis of the ECG
To understand frequency domain analysis of the ECG
To become acquainted with data storage and recovery
Materials:
Electrodes
PC
ADC
LabVIEW
Isolated differential amplifiers
Oscilloscope
Connectors
Volunteer Student
Labview
Build a LabVIEW VI to acquire the ECG signal. The
program should include some signal processing. The
bandpass of the signal should be 0.05 to 100 Hz. Also,
you want to remove 60 Hz noise from the signal
(bandstop). You will also need an FFT for part 3. You
can perform the signal processing in the same VI.
(Alternatively, you could acquire the signal and process it
later using LabVIEW, Excel or Matlab.)
Filtering can occur either before acquisition (in hardware)
or after (in software).
1.
Measurement of the ECG waveform
1.1 Use the electrodes supplied in the lab to measure the
standard Lead I ECG (left arm +, right arm -).
1.2Amplify the signal using the differential isolated
amplifiers (SCXI or Grass amplifier).
1.3 Use the computer to record the ECG waveform over
three heart beats. Store the data.
1.4 Place the electrodes to measure standard Lead II
ECG (keep all the other connections).
1.5 Repeat 1.3. Be sure to store the data under a different
name.
1.6 Place electrodes to measure standard Lead III ECG
1.7 Repeat 1.3. Be sure to store the data under a different
name.
1.8 For your best Lead, collect 10 beats for later signal
averaging (Section 5)
2. Time Analysis
2.1 For data from Lead I do:
2.1.1 Measure the duration of each portion of the wave.
2.1.2 Measure the beat frequency
2.1.3 Create a file containing one beat (P-QRS-T complex)
2.1.4 Import the data into a spreadsheet
2.1.5 Consider the PQ segment as baseline and
measure the maximum amplitude and peak to
peak values for each portion of the wave.
2.2 Repeat steps 2.1.3 to 2.1.6 for Lead II
2.3 Repeat steps 2.1.3. to 2.1.6. for Lead III
2.4 Discuss the values obtained. Compare to nominal values.
3. Find the electrical axis of the heart
3.1 Calculate the area under the QRS complex for Leads I and II.
3.2 The ‘mean QRS vector’ lies in the frontal plane of the chest. Its component
in the Lead I direction equals the area under the QRS complex for that lead.
The same is true for the other leads. Calculate the orientation of the mean
QRS vector using your data from part 3.1
3.3 The mean QRS vector roughly corresponds to the anatomical longitudinal
axis of the heart. Is the orientation you found in part 3.2 reasonable? Why
don’t you need to use the Lead III data?
4. Signal Averaging
Here we will examine two averaging techniques for
computing an average ECG wave: mean and median. In
order to average, the signals have to be aligned. Use a
fiducial point in the heart beat, such as the R wave in
order to divide and align the signals.
4.1 For the 10 beat data you collected in Section 1.8,
divide it into ten beats, each starting at the R wave.
Obtain the MEAN composite signal as:
N
Cmean(n) = (1/N) *
xk (n)
k=1
for 0 =< n <= L-1, where xk, k=1,...,N are noisy epochs of
length L
4.2
Obtain the MEDIAN composite signal as:
Cmedian(n) = median {x1 (n), x2 (n),...xn(n)}
for 0 <= n <= L-1, where xk, k=1,...,N are noisy epochs of
length L.
4.3
Compare the results.
4.4
Make an artifact (glitch) in one of the signals (or use a noisy signal that you
acquired) and repeat 5.1 and 5.2. Compare the effect of the artifact on the
results.
5. Illustrate the use of the ECG as a diagnostic tool. How does the electrical activity
of the heart reflect its mechanical properties?