Biopotential.pptx

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.

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. 21-04-2023 UNIT -I Biomedical Instrumentation - SEM 5 ECE 2

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 . 21-04-2023 UNIT -I Biomedical Instrumentation - SEM 5 ECE 3

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 : 21-04-2023 UNIT -I Biomedical Instrumentation - SEM 5 ECE 4

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: 21-04-2023 UNIT -I Biomedical Instrumentation - SEM 5 ECE 5

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 : 21-04-2023 UNIT -I Biomedical Instrumentation - SEM 5 ECE 6

7. Propagation of Action Potentials : 21-04-2023 UNIT -I Biomedical Instrumentation - SEM 5 ECE 7

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

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 21-04-2023 UNIT -I Biomedical Instrumentation - SEM 5 ECE 9

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 21-04-2023 UNIT -I Biomedical Instrumentation - SEM 5 ECE 10

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. 21-04-2023 UNIT -I Biomedical Instrumentation - SEM 5 ECE 11

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 21-04-2023 UNIT -I Biomedical Instrumentation - SEM 5 ECE 12

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 21-04-2023 UNIT -I Biomedical Instrumentation - SEM 5 ECE 13