Microsoft LPF-00004 Manuel de l'opérateur télécharger pdf (Page 64)

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380, COPYRIGHT MARCH 2002, AXON INSTRUMENTS, INC.

EMG, EEG, ECG Recording

1) EMG

An electromyogram (EMG) can be recorded in many ways, each with its own special requirements.

Surface EMG electrodes have the advantage of being non-invasive but suffer from artifacts or even

total loss of signal during movements. They are also not as selective as implanted EMG electrodes.

Implanted electrodes must be capable of remaining in the same location and must be of an appropriate

size and separation. EMG electrodes available from Semcos Associates are constructed from gold

plated dental probes that have barbs that hold the electrode in place in the muscle. To record a

maximal signal, bipolar electrodes should be placed in parallel with the muscle fibres. An electrode

spacing of 2-10 mm is appropriate for most mammalian muscles. Close spacing of electrodes reduces

cross-talk from other muscle sites and is therefore appropriate for selective recording from local areas.

Low frequency components of muscle activity propagate for longer distances than do high frequency

components. The bipolar electrode configuration acts as a high-pass filter whose cut-off frequency is

determined by electrode spacing. Close spacing results in a high cut-off frequency, thus filtering out

some of the remaining low frequency components from distant muscle activity. However, close

electrode spacing also reduces, in a non-linear fashion, the amplitude of the signal. Larger electrodes

reduce the impedance (see section on source impedance and noise) but are less selective of the site of

muscle activity.

The frequency range of the EMG is between 50-3000 Hz, although the electrode configuration and

separation will have considerable influence on what frequencies are recorded. The signal size ranges

from 10-1000 µV for surface recording, and 50-3000 µV for invasive recording.

Several SmartProbes are available for recording EMGs with the CyberAmp. These include the

AI 401, 402, and 405 active amplifiers and the AI 417 passive adapter. Electrode leads can also be

directly connected to the differential inputs of the CyberAmp. Before selecting an adapter, please see

the section on Common-Mode Rejection Ratio on page 39.

2) ECG

Electrocardiogram (ECG) signals are usually of a large amplitude and easily recorded. As electrode

spacing is reduced there is an increasing possibility of recording unwanted EMG signals from

neighboring muscles and the traditional electrode placement sites minimize these artifacts. The

AI 417 Passive 2 mm Adapter or any of the active amplifier probes are suitable for ECG recording.

The normal frequency range of the mammalian ECG is 0.2-100 Hz. Amplitudes range up to 2-3 mV.

3) EEG

The electroencephalogram (EEG) signals range from 10-300 µV in amplitude and have a frequency

range of 0.2-50 Hz. A single differential EEG channel is best recorded with the assistance of one of

the low-noise, AI 400 series active probes.

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Microsoft LPF-00004 Manuel de l'opérateur Page 64