Electromyography (EMG)

Electromyogram

A tracing made with an electromyograph

Electromyograph

Electromyography (EMG) is a medical technique for measuring muscle response to

nervous stimulation. An electromyograph detects the electrical potential generated by muscle cells

when these cells contract.

EMG Signal Characteristics Signal is generated in the muscle cellsAmplitude range: 50 V to 30 mVFrequency range: 7 to 20 Hz depending on the size

of the muscleTo perform EMG, a needle electrode is inserted

through the skin into the muscle tissueBecause of the needle electrodes, EMG may be

somewhat painful or extremely painful to the patient, and the muscle may feel tender for a few

days, surface electrodes are used→That gives much less accurate results with a higher level

of disturbance from the surrounding environment.

EMG Signal performingTo perform EMG, a needle electrode is inserted through

the skin into the muscle tissueBecause of the needle

electrodes, EMG may be somewhat painful or extremely

painful to the patient, and the muscle may feel tender for a few days, surface electrodes

are usedThat gives much less accurate

results with a higher level of disturbance from the

surrounding environment.

Electromyogram (EMG) (cont.)

Blood Pressure

Blood Pressure Measurements

Auscultatory Method

1.Non-invasive measurement

2. Invasive measurement

Palpatory Method

Oscillometric Method

Pressure is force per unit area

Auscultatory Methodsystolic pressure

diastolic pressure

systolic pressure

diastolic pressure

Auscultatory Method

Also with this method, several measurements should be done.

Pulse waves that propagate through the

brachial artery, generate Korotkoff sounds.

There are 5 distinct phases in the Korotkoff

sounds, which define SP and DP

The Korotkoff sounds are ausculted with a

stethoscope or microphone (automatic

measurement)The frequency range is

20-300 Hz and the accuracy is +/- 2mmHg

(SP) and +/- 4mmHg (DP)

Auscultatory Method (cont.)

-) The observations differ from observer to another

-) A mechanical error might be introduced into the system e.g. Mercury leakage, air leakage, obstruction in the cuff etc.

-) The observations do not always correspond with intra-arterial pressure

-) Auscultatory tecnique cannot be used in noisy environment

+) Auscultatory technique is simple and does not require much equipment

ADVANTAGES

DISADVANTAGES

-) The technique does not give accurate results for infants and hypotensive patients

Oscillometric Method

The intra-arterial pulsation is transmitted via cuff to transducer (e.g. piezo-electric)

The arterial pressure oscillations (which can be detected throughout the measurement i.e. when Pcuff > SP and Pcuff< DP) are superimposed on the cuff pressure

SP and DP are estimated from the amplitudes of the oscillation by using a (proprietary) empirical algorithm.

The cuff pressure is deflated either linearly or stepwise

Oscillometric Method (cont.)

DISADVANTAGE -) Many devices use fixed algorithms leading to large variance in blood pressures

+) In the recent years, oscillometric methods have become popular for their simplicity of use and reliability.

ADVANTAGES

+) MP can be measured reliably even in the case of hypotension

Measurment disply

Electroencephalography (EEG)

EEG measurementEEG is a representation (writing on paper or display on

CRT, PC) of the electrical activity of brainThe electroencephalograph is an apparatus uses electrodes

placed on a patient’s scalp to measure (detect), amplify, display in graphic form, and record the weak electrical

signals generated by the brainThe technique involves the following:

Biopotential pickup: cranial or cerebral surface transducer electrodeEEG signal conditioning: transducer output amplification and filtering

(0.1 to 100 Hz)EEG signal recording: signal displayed on graphic recorder, CRT or

PCEEG signal analysis: visual or computer interpretation of resulting

EEG

EEG measurement

Current due to voltage drops along the path of the axon

lead to scalp potentials (EEG).

EEG characteristic Signal is generated in the brainVoltage amplitude range is from 1 to 100 V peak-to-peak at low

frequencies (o.5 to 100 Hz)EEG frequency bands:

Delta0.5 - 4

Hzdeep sleep, lucid dreaming, increased immune

functions, hypnosis

Theta4 - 8 Hzdeep relaxation, meditation, increased memory,

focus, creativity, lucid dreaming, hyponagogic state

Alpha8 - 13

Hzlight relaxation, "super learning", positive

thinking

Beta13 - 22

Hzrelaxed focus, improved attentive abilities

Gamma22-30 Hz and

higher

associated with information-rich task processing and high-level information processing

EEG electrode placement Standard electrode placement known as 10-20 system10-20 system drives from the spacing of electrodes at intervals of 10%

and 20% of the distance between particular points on the scalpAn asymmetry of 1 cm can alter an EEG reading

The 10-20 EEG electrode placement system

EEG recording modesUnipolar: Composed of a number of scalp leads connected

to a common indifference point (one electrode is common to all channels such as an earlobe )

Unipolar

EEG recording modes (cont.)Unipolar average: Composed of a number of scalp leads

connected to a common indifference point (summation of scalp electrodes is common to all channels)

Unipolar average

EEG recording modes (cont.) Bipolar: Achieved by the interconnection of scalp electrodes

Bipolar