Electromyography,,Electrooculography,Electroretinography, PhonoCardioGraph,,Heart Sounds

1. UEEG002
MEDICAL
INSTRUMENTATION
ERG,EOG,PCG
D.Poornima, AP(Sr.Gr)/EEE
Sri Ramakrishna Institute of Technology,
Coimbatore

2. Electromyography (EMG)
• Measures muscle response or electrical activity in response to a nerve's stimulation
of the muscle.
• The activity is similar to that observed in the cardiac muscle, but in the skeletal
muscle, repolarization takes place much more rapidly, the action potential lasting
only a few milliseconds.
• The test is used to help detect neuromuscular abnormalities.
• During the test, one or more small needles (also called electrodes) are inserted
through the skin into the muscle.
• The EMG pattern is a summation of the individual action potentials from the fibres
constituting the muscle or muscles being studied.
• The muscle potentials range from 50 mV to 5 mV and the duration from 2 to 15 ms.
• The values vary with the anatomic position of the muscle and the size and location
of the electrode.
• In a relaxed muscle, there are normally no action potentials

3. Electrodes For EMG
• Electrodes for electromyographic work are usually of the needle type
• Needle electrodes are used in clinical electromyography, neurography and other
electrophysiological investigations of the muscle tissues underneath the skin and
in the deeper tissues.
• The material of the needle electrode is generally stainless steel.
• Stainless steel electrode material creates a lot of noise.
• But preferred in EMG work due to its mechanical solidity and low price.
• Needle electrodes are designed to be fully autoclavable and in any case they
should be thoroughly sterilized before use.

4. • A concentric (coaxial) core needle electrode contains both the active
and reference electrode within the same structure.
• It consists of an insulated wire contained within a hypodermic needle.
• The inner wire is exposed at the tip and this forms one electrode.
• The concentric needle is very convenient to use and has very stable
electrical characteristics.
• Care should be taken to maintain the surface electrode in good
condition in order to avoid artefacts.
• Concentric needle electrodes are made by moulding a fine platinum
wire into a hypodermic needle having an outside diameter less than
0.6 mm.
• One end of the needle is bevelled to expose the end of the wire and to
provide easy penetration when the needle is inserted.
• The surface area of the exposed tip of the wire may be less than
0.0005 mm2

5. • The ground electrode for EMG studies usually consists of a conducting strip which is inserted into a salin
e soaked strap and wrapped around the patient’s limb.
• The ground electrode is usually positioned over bony structures rather than over large muscle masses

6. EMG Machine
• EMG measurements are important for the myoelectric control of prosthetic devices (artificial limbs)
• Involves picking up EMG signals from the muscles at the terminated nerve endings of the remaining limb and
using the signals to activate a mechanical arm.
• This is the most demanding requirement from an EMG
• EMG is recorded by using surface electrodes or more often by using needle electrodes
• Electrodes pick up the potentials produced by the contracting muscle fibres.
• The signal is amplified and displayed on the screen of a CRO.
• Also applied to an audio amplifier connected to a loudspeaker.
• A trained EMG interpreter can diagnose various muscular disorders by
listening to the sounds produced when the muscle potentials are fed to the
loudspeaker.
• Tape recorder is included to playback and study of the EMG sound waveforms at a later convenient time.
• Waveform can also be photographed from the CRT screen by using a synchronized camera.

7. • A typical EMG signal ranges from 0.1 to 0.5 mV
• They may contain frequency components extending up to 10 kHz.
• Such high frequency signals cannot be recorded on the conventional pen recorders
and therefore, they are usually displayed on the CRT screen.
• Modern EMG machines are PC based available both in console as well as laptop
models
• Provide full colour waveform display, automatic cursors for marking and making measurements
• Keyboard available to access important test controls.
• Has facilities for recording of the EMG and evoked potentials.
• The stimulators are software controlled.
• For report generation in the hard copy form, popular laser printers can be used

8. Electrooculography (EOG)
• Recording of the bio-potentials generated by the movement of the eye ball.
• Potentials are picked up by small surface electrodes placed on the skin near
the eye.
• One pair of electrodes is placed above and below the eye to pick up voltages
corresponding to vertical movements of the eye ball.
• Another pair of electrodes is positioned to the left and right of the eye to
measure horizontal movement.
• The recording pen is centred on the recording paper, corresponding to the
voltage changes accompanying it.
• EOG has applications mostly for research and is not widely used for
clinical purposes

9. Electroretinography (ERG)
• Electrical potential exists between the cornea and the back of the eye and it changes
when the eye is illuminated.
• The process of recording the change in potential when light falls on the eye is called
electroretinography.
• ERG potentials can be recorded with a pair of electrodes.
• One of the electrodes is mounted on a contact lens and is in direct contact with the
cornea.
• The other electrode is placed on the skin adjacent to the outer corner of the eye.
• A reference electrode may be placed on the forehead
• A general purpose direct writing recorder may be used for recording electroretinogra
ms.
• The magnitude of the ERG voltage depends upon the intensity and duration of the
light falling on the eye, it may be typically about 500 mV.

10. PhonoCardioGraph (PCG)
• The phonocardiograph is an instrument used for recording the sounds
connected with the pumping action of the heart.
• Phonocardiography is the recording of all the sounds made by the heart
during a cardiac cycle.
• Sounds produced by healthy hearts are remarkably identical
• These sounds provide an indication of
 the heart rate and its rhythmicity.
 gives useful information regarding effectiveness of blood pumping
and valve action.
 Abnormal sounds can be corelated to specific physical abnormalities
• Instrument used for the clinical detection of heart sounds is acoustical
stethoscope which has been improved to electronic stethoscope due to it
s high fidelity.
• Electronic stethoscope consisting of a microphone, an amplifier and a
head set.
 Can detect heart sounds which are too low in intensity or too high in
frequency to be heard in a purely acoustal instrument.

11. Origin of Heart Sounds
• The sounds are produced by the mechanical events that occur during the heart
cycle
• These sounds can be from the movement of the heart wall, closure of walls and
turbulence and leakage of blood flow.
• The first sound
 corresponds to the R wave of the ECG
 longer in duration, lower in frequency, and greater in intensity than the sec
ond sound.
 the sound is produced by closure
of the mitral valves between the
upper and lower chambers of the
heart (it occurs at the termination
of the atrial contraction and at the
onset of the ventricular contraction)

12. The frequencies of these sounds are generally in the range of 30 to 100 Hz and the duration is between
50 to 100 ms.
The second sound is higher in pitch than the first, with frequencies above 100 Hz and the duration betw
een 25 to 50 ms.
This sound is produced by the slight back flow of blood into the heart before the valves close and then
by the closure of the valves in the arteries leading out of the ventricles.
This means that it occurs at the closure of aortic valves.
The heart also produces third and fourth sounds but they are much lower in intensity and are normally i
naudible.
The third sound is produced by the inflow of blood to the ventricles and the fourth sound is produced b
y the contraction of the atria.
These sounds are called diastolic sounds and are generally inaudible in the normal adult but are comm
only heard among children

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