61 - 65 Physiology SBAs for the Primary FRCA
Question 61
You've noticed QRS complexes in your patient's BIS trace and have deduced that there must be interference from the ECG.
Which of the following is false regarding biological signals?
- EEG signals are measured in mV
- Beta waves have a frequency of 12 - 30 Hz
- The ECG measures frequencies between 0.05 and 150 Hz
- EMG can interfere with ECG
- The amplitude of the ECG is classically around 1 - 2 mV
Answer
- EEG signals are measured in mV
EEG signals are measured in microvolts.
In terms of signal amplitude, it goes muscle, then ECG then EEG.
Amplitudes:
- EMG - 100 microvolts up to 30 mV
- ECG - 1 - 2 mV
- EEG - 10 - 100 microvolts
The significant overlap in voltage between EMG and ECG means that they can interfere with one another.
Frequencies:
- Alpha - 8 - 13 Hz
- Beta - 12 - 30 Hz
- Delta - 1 - 4 Hz
- Theta - 4 - 8 Hz
- ECG - 0.05 to 150 Hz
- EMG - 5 - 450 Hz