About Bio-electric Potentials

1. Bioelectric potentials
Mrs.V.SrirengaNachiyar, AP/ECE
Ramco Institute of Technology
Academic Year: 2017-2018 (Even)

2. Bioelectric potentials
• To measure bioelectric potentials, a transducer
capable of converting ionic potentials and
currents into electric potentials and currents is
required.
• Such a transducer consists of two electrodes
which measure the ionic potential difference
between their respective points of application.

3. Electrocardiogram (ECG)
• Bio potentials generated by the muscles of the
heart results In Electrocardiogram.
• ECG bio-signal typical specifications:
• low differential voltage from 0.4 to 3 mV
• high common-mode rejection ratio level
• low frequency range
• high noise

4. Heart internal structure

5. DESCRIPTION
• Heart is divided into four chambers
• Two upper chambers- left & right atria
• Two lower chambers-left & right ventricles
• Right atrium receives blood from the veins of the
body & pumps into right ventricle
• Oxygen enriched blood then enters the left atrium
from which it is pumped into the left ventricle
• Electrodes: A conductor through which
electricity enters or leaves an object, substance,
or region

7. Cont…
• Each action potential in the heart originates
near the top of the right atrium at a point called
the pacemaker or Sinoatrial node (SA)
• Pacemaker- A group of specialized cells that
spontaneously generate action potentials at a
regular rate.
• To initiate the heart beat, the action potentials
generated by the pacemaker propagate in all
directions along the surface of both atria

8. Cont…
• The wave terminates at a point near the center of
the heart are called the Atrioventricular (AV)
node.
• At this point, some special fibers act as a delay
line to provide proper timing between the action
of atria & ventricles.
• Once the electrical excitation has passed through
the delay line, it is rapidly spread to all parts of
both ventricle by the bundle of hiss called
purkinje fibers, used to initiate action potentials.

9. Typical ECG waveform

10. Cont….
• P-wave: represents the depolarization of the
atrial musculature
• QRS Complex: combined result of
repolarization of the atria and depolarization of
ventricles
• T-wave: wave of ventricular repolarization
• U-wave: the result of after potentials in the
ventricular muscles.

11. Electroencephalogram (EEG)
• Measures neuronal activity of the brain
• Waveform varies according to the location of
measuring electrodes on the surface of the
scalp
• For wide-awake person- unsynchronized high
frequency EEG
• For drowsy person-produces large amount of
rhythmic activity in the range 8-13Hz
• For asleep person-amplitude & frequency of
waveform decreases.

12. Cont….
• Light sleep-large amount of amplitude & low
frequency waveform
• Deeper sleep- even slower and higher
amplitude waves
EEG Frequency bands:
Below 3 ½ Hz – Delta
From 3 ½ to 8Hz - Theta
From 8 to 13Hz - Alpha
Above 13Hz - Beta

13. EMG- Electromyogram
• Bioelectric potentials associated with muscle
activity
• It may measured at the surface of the body
near a muscle of interest or directly from the
muscle by penetrating the skin with needle
electrodes
• EMG electrodes pickup potentials from all
muscles
• EMG waveforms appears very much like a
random-noise waveform

14. Cont…
• The amplitude of measured EMG waveform is
the instantaneous sum of all the action
potentials generated at any given time.
• Because these action potentials occur in both
positive & negative polarities at a given pair
of electrodes

15. Other Bioelectric potentials
• ERG (Electroretinogram) – A record of
complex pattern of bioelectric potentials
obtained from the retina of eye
• EOG (Electro-Oculogram) – a measure of
variations in the corneal retinal potential as
affected by the position of the eye
• EGG (Electrogastrogram) – associated with
the peristaltic movements of the gastroretinal
tract

16. References
• Leslie Cromwell, “Biomedical
Instrumentation and Measurement”, Prentice
Hall of India, New Delhi, 2007.
• John G.Webster, “Medical Instrumentation
Application and Design”, 3rd Edition, Wiley
India Edition, 2007
• Khandpur, R.S., “Handbook of Biomedical
Instrumentation”, TATA Mc Graw-Hill,
New Delhi, 2003.
• M. Arumugam,” Biomedical
Instrumentation”, Second Edition.