2nd practiceMedical Informatics

Biomedical Signal ProcessingTAMUS, Zoltán Ádám

zoltanadam_tamus@yahoo.com

Action potential Electroneurogram (ENG) Electromyogram (EMG) Electrocardiogram (ECG) Electroencephalogram (EEG) Electrogastrogram (EGG) Phonocardiogram (PCG) Carotid Pulse (CP) Vibromyogram (VMG) Vibroarthogram (VAG)

Basic component of bioelectrical signals

Caused by the flow of Na+, K+ and Cl- ions across the cell membrane

Resting potential:• In their resting state, the membrane readily

permit the entry of K+ and Cl- ions, but effectively block the entry of Na+ ions.

• The permeability of membrane for K+ is 50-100 times that for Na+ ions.

• A cell in resting state is said to be polarized.• The resting potential is in order of -60 to -

100 mV

Depolarization:• When a cell is excited the membrane

changes its characteristics and begins to allow Na+ ions to enter the cell.

• This movement of Na+ ions constitutes an ionic current, which further reduces the membrane barrier to Na+ ions.

• This leads to an avalanche effect: Na+ ions rush into the cell.

• The inside of the cell becomes positive.• The peak value of action potential is about

20 mV

Repolarization:• Membrane depolarization also increases the

permeability of membrane for K+ ions via a voltage-dependent K+ channels.

• The permeability of membrane for Na+ ions decrease near the peak of depolarization.

• The efflux of K+ ions from the cell makes the inside more negative thereby effecting repolarization back to the resting potential.

• Duration in nerve and muscle cells ~1 ms, in heart muscle cells 150-300 ms

All-or-none phenomenon

Absolute refractory period: 1 ms in nerve cells

Relative refractory period: several ms in nerve cells

The ENG is an electrical signal observed as a stimulus and the associated nerve action potential propagate over the length of nerve.

ENGs may be recorded using concentric needle electrodes or Ag-AgCl electrodes at the surface of the body.

In order to minimize muscle contraction strong but short stimulus is applied (100 V amplitude, 100-300 μs).

ENGs have amplitudes of the order of 10 μV.

Wrist BElbow - below

the elbow AElbow – above

the elbow

Typical values of propagation rate or nerve conduction velocity are:• 45-70 m/s in nerve fibres• 0.2-0.4 m/s in heart muscle• 0.03-0.05 m/s in time delay fibres between

the atria and ventricles. Neural diseases may cause a

decrease in conduction velocity.

Motor units Single Motor Unit

Action Potential (SMUAP)

Normal SMUAPs are usually biphasic or triphasic

3-15 ms in duration, 100-300 μV in amplitude, 6-30 Hz in frequency range

The 10-20 system of electrode placement for EEG recording.

The commonly used terms for EEG frequency range:• Delta (0.5-4 Hz): deep sleep• Theta (4-8 Hz): beginning stages of sleep• Alpha (8-13 Hz): principal resting rhythm• Beta (>13 Hz): background activity in tense

and anxious subjects

a: delta, b: theta, c: alpha, d: beta, e: blocking of alpha rhythm by eye opening, f: marker 50 μV, 1 sec

The electrical activity of the stomach consists of rhythmic waves of depolarization and repolarization of its constituent smooth muscle cells.

The activity originates in the mid-corpus of the stomach, with intervals of about 20 s in human.

Recorded by abdomen electrodes e.g. three electrodes along the antral axis of stomach and the common reference electrode

The CP is a pressure signal recorded over the carotid artery.

Parts of CP:• P (percussion wave): ejection of blood from the left

ventricle• T (tidal wave): reflected pulse from the upper body• D (dicrotic notch): closure of the aortic valve• DW (dicrotic wave): reflected pulse from the lower body

Direct mechanical manifestation of contraction of a skeletal muscle.

Accompanies the EMG Recorded by contact microphones or

accelerometers placed on the muscle surface.

The VAG is the vibration signal recorded from a joint during movement (articulation) of the joint.

Normal joint surfaces are smooth and produce little or no sound.

Joint affected by osteoarthiritis and other degenerative diseases may have suffered cartilage loss and produce grinding sounds.

The VAG is complex signal and difficult to analyze.