The document discusses bio-potentials and their significance in biomedical instrumentation, highlighting their origin, measurement, and related biological signals such as ECG, EEG, and EMG. It explains the mechanisms behind action potentials, including ionic concentration differences and their implications for nerve conduction rates. Additionally, it emphasizes the importance of good electrode design and placement for accurate bio-potential recording.

1. UECE104 – Bio medical instrumentation
Electro-Physiology and Bio-Potential Recording
Dr.S.MARY PRAVEENA
ASSOCIATE PROFESSOR
ECE DEPARTMENT
SRI RAMAKRISHNA INSTITUTE OF TECHNOLOGY
COIMBATORE-10

2. Electro-Physiology and Bio-Potential Recording
• The origin of Bio-potentials
• Bio-potential electrodes
• Biological amplifiers
• ECG
• EEG
• EMG
• PCG
• Lead systems and Recording methods
• Typical waveforms and Signal characteristics.
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3. What are bio potentials?
Bio-potential:
• An electric potential that is
measured between points in
living cells, tissues, and
organisms, and which
accompanies all biochemical
processes.
• Also describes the transfer of
information between and
within cells.
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4. • Certain Systems of the body generate their own monitoring signals, which
convey useful information about the functions.
• These signals are the bioelectric potentials associated with nerve
conduction, brain activity, heart beat, muscle activity and so on.
• Bioelectric potentials are actually ionic voltages produced as a result of the
electrochemical activity of certain special types of cells.
• Through the use of transducers which are capable of converting ionic
potentials into electrical voltages, these natural signals that are monitored
can be measured and the results can be displayed in a meaningful way to
aid the physician in his diagnosis and treatment of various diseases.
The Origin of Bio-Potentials:
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5. • Surrounding the cells of the body are the body fluids. These fluids are conductive solutions
containing charged atoms known as ions.
• The principle ions are sodium (Na+), Potassium (K+), and Chloride (Cl-).
• The membrane of cells, such as nerve and muscle cells, permits the entry of potassium
and chloride ions but effectively blocks the entry of sodium ions.
• For example the permeability of sodium ions is about 2x10^(-8) cm/s and for potassium
and chloride ions it is 2x10^(-6)cm/s and 4x10^(-6) cm/s respectively.
• Due to the difference in permeability values of different ions, the concentration of sodium
ions inside the cell becomes much lower than the outside the cell.
Resting and Action Potentials:
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6. • When a cell is excited and generates an action potential ionic currents begin to flow.
• The rate at which an action potential moves down a fiber or is propagated from cell to cell
is called the propagation rate.
• In nerve fibers, the propagation rate is also called the nerve conduction rate (or)
conduction velocity.
• The velocity varies widely, depending on the type and diameter of the nerve fiber.
• The usual velocity range in nerves is from 20 to 140 meters per second (m/sec).
• Propagation through heart muscle is slower, with an average rate from 0.2 to 0.4 m/sec.
• Special time-delay fibers between the atria and ventricles of the heart cause action potentials
to propagate at an even slower rate, 0.03 to 0.05 m/sec.
Propagation of Action Potentials:
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7. Propagation of Action Potentials:
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8. Mechanism behind biopotentials
• Concentration of potassium (K+) ions is 30-50 times higher
inside as compared to outside
• Sodium ion (Na+) concentration is 10 times higher outside
the membrane than inside
• In resting state the membrane is permeable only for
potassium ions
Potassium flows outwards leaving an
equal number of negative ions inside
Electrostatic attraction pulls potassium
and chloride ions close to the membrane
Electric field directed inward forms
Electrostatic force vs. diffusional force
mV
Vm 100
...
70 



9. Mechanism behind biopotentials
• When membrane stimulation exceeds a threshold
level of about 20 mV, so called action potential
occurs:
 Sodium and potassium ionic permeabilities of the
membrane change
 Sodium ion permeability increases very rapidly at first,
allowing sodium ions to flow from outside to inside, making
the inside more positive.
 The more slowly increasing potassium ion permeability
allows potassium ions to flow from inside to outside,
thus returning membrane potential to its resting value.
 While at rest, the Na-K pump restores the ion
concentrations to their original values
• The number of ions flowing through an open channel
>106/sec
• Body is an inhomogeneous volume conductor and
these ion fluxes create measurable potentials on
body surface
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10. • To measure bioelectric potentials, a transducer capable of converting ionic potentials into
electric potentials is required.
• A transducer consists of two electrodes, which measure the ionic potential difference
between their respective points of application.
• Measurement of individual action potentials can be made in some types of cells, such
measurements are difficult because they require precise placement of an electrode inside a
cell.
• The common form of measured bio potentials is the combined effect of a large number of
action potentials as they appear at the surface of the body (or) at one or more electrodes
inserted into a muscle, nerve or some part of the brain.
The Bioelectric Potentials Measurement Fundamentals
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11. • Electro-Physiology and Bio-Potential Recording
• The origin of Bio-potentials
• Bio-potential electrodes
• Biological amplifiers
• ECG
• EEG
• EMG
• PCG
• Lead systems and Recording methods
• Typical waveforms and Signal characteristics.
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12. Bioelectric Signals Sensed by Biopotential Electrodes
and Their Sources
Bioelectric Signal Abbreviation Biologic Source
Electrocardiogram ECG
Heart—as seen from body
surface
Cardiac Electrogram — Heart—as seen from within
Electromyogram EMG Muscle
Electroencephalogram EEG Brain
Electrooptigram EOG Eye dipole field
Electroretinogram ERG Eye retina
Action potential — Nerve or muscle
Electrogastrogram EGG Stomach
Galvanic skin reflex GSR Skin
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13. Electrodes – Basics
• High-quality bio-potential measurements require,
• Good amplifier design
• Use of good electrodes and their proper placement on the
patient
• Good laboratory and clinical practices
• Electrodes should be chosen according to the application
• Basic electrode structure includes:
• The body and casing
• Electrode made of high-conductivity material
• Wire connector
• Cavity or similar for electrolytic gel
• Adhesive rim
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