Electromyography (EMG)

Electromyogram Electromyograph A tracing made with an 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 cells Amplitude range: 50 mV to 30 mV Frequency range: 7 to 20 Hz depending on the size of the muscle To perform EMG, a needle electrode is inserted through the skin into the muscle tissue Because 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 performing To perform EMG, a needle electrode is inserted through the skin into the muscle tissue Because 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.

Electromyogram (EMG) (cont.)

Blood Pressure

Blood Pressure Measurements Pressure is force per unit area Non-invasive measurement Palpatory Method Auscultatory Method Oscillometric Method Invasive measurement

Auscultatory Method systolic pressure diastolic pressure

Auscultatory Method 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) Also with this method, several measurements should be done.

Auscultatory Method (cont.) ADVANTAGES +) Auscultatory technique is simple and does not require much equipment DISADVANTAGES -) Auscultatory tecnique cannot be used in noisy environment -) 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 -) 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 cuff pressure is deflated either linearly or stepwise 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.

Oscillometric Method (cont.) ADVANTAGES +) In the recent years, oscillometric methods have become popular for their simplicity of use and reliability. +) MP can be measured reliably even in the case of hypotension -) Many devices use fixed algorithms leading to large variance in blood pressures DISADVANTAGE

Measurment disply

Electroencephalography (EEG)

EEG measurement EEG is a representation (writing on paper or display on CRT, PC) of the electrical activity of brain The 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 brain The technique involves the following: Biopotential pickup: cranial or cerebral surface transducer electrode EEG signal conditioning: transducer output amplification and filtering (0.1 to 100 Hz) EEG signal recording: signal displayed on graphic recorder, CRT or PC EEG 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 Alpha 8 - 13 Hz Signal is generated in the brain Voltage amplitude range is from 1 to 100 mV peak-to-peak at low frequencies (o.5 to 100 Hz) EEG frequency bands: Delta 0.5 - 4 Hz deep sleep, lucid dreaming, increased immune functions, hypnosis Theta 4 - 8 Hz deep relaxation, meditation, increased memory, focus, creativity, lucid dreaming, hyponagogic state Alpha 8 - 13 Hz light relaxation, "super learning", positive thinking Beta 13 - 22 Hz relaxed focus, improved attentive abilities Gamma 22-30 Hz and higher associated with information-rich task processing and high-level information processing

EEG electrode placement Standard electrode placement known as 10-20 system 10-20 system drives from the spacing of electrodes at intervals of 10% and 20% of the distance between particular points on the scalp An asymmetry of 1 cm can alter an EEG reading The 10-20 EEG electrode placement system

EEG recording modes Unipolar: 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