LAB 1 SYSC4203

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Carleton University *

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4203

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Electrical Engineering

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Jan 9, 2024

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2.0 a)Discuss how the time domain signal changes as the cut off value is lowered? How about in the frequency domain? As the cutoff value is lowered the time domain tends to give a smoother signal, in which R-peaks can be more easily identified compared to a higher cutoff frequency causing chopiness and not a clear picture of the data. . This can also be identified within the frequency domain, as the cutoff frequency lowers, the signal becomes smoother. b)Using your ECG plots, label the P, Q, R, S and T segments of one beat. Select the best lead to show your signal. What is the amplitude of your QRS complexes? Are the durations of the segments of the individual heart beat signals consistent within a single subject? Figure 1 The amplitude of the QRS complexes is around 0.13 mV as seen in Figure 1. The durations of the segments are also consistent within the subject, as the shapes of the PQRST also remain similar throughout the duration. ‘

c) What is the source of the 60 Hz noise? Identify the 60 Hz noise in the frequency plot. The source of the 60 Hz noise is caused by power line interferences. Powerline interferences are common noise sources found in ECG that are recorded from the body. This can be caused due to a stray effect of the alternating current fields due to loops in the patients cables, or loose cables or dirty electrodes. The noise can be identified slightly in figure 2. Figure 2 d)Discuss the time and frequency signals of the different low pass filter cut off values. On the attached plots indicate differences. What happens to the time signal when the cut off value decreases? What happens to the frequency signal? Is there an optimal cut off value? What happens when the cut off value is too high? Too low?

Figure 3: Time Domain 40 Hz Figure 4: Time Domain 5 Hz

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Figure 5: Frequency Domain 40 Hz Figure 6: Frequency Domain 5 Hz Figure 3 and 4 show the same signal with decreasing cutoff values (40, and 5Hz) for the time domain, while Figure 5 and 6 depict the frequency domain in similar fashion. As the cutoff frequency decreases, the signals become smoother as more of the high frequency noise (such as powerline noise) is eliminated. If the cutoff value is too high, not enough noise is removed. If it were lowered to the point of being within the range of the heartbeat (eg low pass cutoff less than 1Hz) it would begin to remove significant parts of the signal.

3.0 a)Look at each lead. Does the ECG Data look different? Why? Does the Spectral Analysis look different? Why or why not? Between different leads, the general shape of the ECG data remains the same, but the Spectral Analysis looks different, due to the noise levels differing because the signals measured from different part of the body are affected by the motion artifact to different degrees, b) Did you notice motion artifact on all leads? Why did each lead have motion artifact (or not)? Yes, motion artifact was found on all leads and this was due to the fact that the cables were placed near to large muscles groups on the body. This can be due to the subject waving, therefore motion artifcats can be seen as the muscles close to the cables are in use, which may cause small tremors in the data.

4.0 c)Plot the first 5 heartbeats and the last 5 heart beats of lead I in separate figures, with Matlab. Measure the average R-R distance and calculate the heart rate for both figures. Is there a difference between your two heart rate values? Why? First 5 identifiable (left) and last 5 heartbeats (right) The first 5 clear beats after movement had an average R-R interval of 0.474, or a heart rate of 126bpm. The last 5 beats have an average R-R interval of 0.8675 or a heart rate of 69bpm. As the body recovers from exercise, it no longer needs to sustain a high heart rate. d)Compare the PQRST shape in the first and last 5 seconds. Are the shapes compressed? Is the firing rate increased? Explain why. The main difference in the shape is the decrease in the TP interval, meaning that the firing rate has increased. The qrs complex does not change as much in length, as expected in a healthy heart adapting to different levels of activity. 5.0 a)What are the sources of noise in this lab? Are they low or high frequency? How can youremove/reduce them? You may support your answer by showing some of the graphs recorded during the lab. It was observed that there is a predominant noise source due powerline interference that is at 60Hz. Either by dissipation of lighting sources, or by ground leaks, or equipment that is poorly calibrated or insulated. Other sources of noise include movement that affects the skin-electrode interface, muscle contractions, and noise from other electronic devices that couple into the input.

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b)Does your signal ECG have a DC component? What is the source of the DC component?How can you remove it? The ECG contains a DC component from the electrode-skin contact and a common-mode. This results from the potential between the electrodes and the ground. Removing DC components in ECG means the equipment must be balanced with high input impedance, and electrodes to be constructed with materials that reduce the DC components.

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