POST LAB PHYSIOLOGY QUESTIONS 1. Explain how you calculated the highest frequenc

Question

POST LAB PHYSIOLOGY QUESTIONS

1. Explain how you calculated the highest frequency component of your subject’s ECG. What was the frequency and, using this information, what sampling rate would you use to adequately capture a good representation of the ECG when recording?

2. The ECG waveform is not symmetrical unlike the differential recording example provided in lecture (with a bipolar waveform - equal deflections in positive and negative directions). What reasons can you think of for this observation?

3. When you switched to recording the EMG signals you still have two electrodes and a ground just as you did with the ECG. Explain why you think you do not see an ECG signal.

4. The position of electrodes often influences the appearance of the recorded signal (it does not change the actual signal). In the EMG experiment, explain why the signals are different when the electrodes are positioned along the muscle versus across the muscle.

5. If a signal that you were interested in recording had a frequency of 60Hz and background noise was at a similar frequency (50-60Hz) would it be possible to eliminate the noise by using filters? Explain your answer.

Explanation / Answer

1) Frequency band of standard ECG components is typically 0.05-100Hz. High frequency components, resulting from the fragmented waveform of electrical activation of the myocardium, can be filtered from high resolution ECG signals in the 150 to 250 Hz frequency band. Since these components are very low in amplitude (measured in µV), sophisticated computer analysis is required to reliably extract them.

High Frequency refers to the analysis of the high frequency spectral components of the QRS complex in an electrocardiogram (ECG).

Sampling Rate can be chose according to Nyquist's Sampling theorem. To accurately represent the shape of the signal, or to determine peak maximum and peak locations, a higher sampling rate is required – Typically a sample rate of 10 times the bandwidth of the signal is required.

2)Assymetric ECG wave form may be due to presence of cardiac diseases. It can also be caused by patient movement, loose or defective electrodes, improper grounding, or faulty ECG equipment.

3)ECG and EMG signal capturing sites are different in our body.

4)The ability of surface electrodes to accurately detect the activity of a particular muscle relies not only on their being placed over the muscle but also on their position in relation to muscle fibre orientation.

5)An ideal notch filter can supress the 60Hz noises from the given ECG frequency

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