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Biopotentials :)
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- 1Origin's of Biopotential's and Electrophysiological Measurement.*Many organs in the human body manifest their function through electrical activity.
*The heart produces a signal called an Electro Cardiogram ECG.
*Brain- Electroencephalogram. EEG
*Eyes: Retina-Electroretinogram ERG. Eye movement-Electrooculogram. EOG
*Muscles- Electromyogram. EMG. - 2What can Electrophysiological Measurement's tell us.* Measurements (among other signals from the body) can provide vital clues, to normal pathological functions of the organs.
*ECG- Abnormal heart rhythms, arrhythmia's.
*EMG- Neuromuscular disorders. - 3Electrical Activity at a cellular level.*Origin's of the biopotential's can be traced to electrical activity at a cellular level.
*The electric potential across a cell membrane is the result of different ionic concentrations that exist inside and outside the cell. - 4The Nernst Potential*The electrochemical concentration gradient across the semipermeable membrane.
*The cell separates high concentrations of K+ inside the cell and low concentrations of Na+ outside the cell (along with other ions in less significant proportions.) - 5Resting Potential.* The difference in ionic concentration across the cell membrane.
- 6Action potentials.* Excitable cells in the body produce action potentials.
*Resulting from a rapid flux of ions across the cell membrane, in response to electric stimulation or;
*Transient change in the electric gradient of the cell.
*The electric excitation of the cells generates currents in surrounding volume conductors manifesting itself as potentials on the body. - 7Bio-potential's at a cellular level- ECG.*Each cell in the heart produces a characteristic action potential.
*The activity of the cells in the SA node of the heart produces an excitation, which propagates from the atria to the ventricles through well defined pathways, and eventually throughout the heart.
*This electric excitation produces a synchronous contraction of the heart muscle.
*The associated signal is an ECG - 8Bio-Potential's at a cellular level- EEG.*Electric excitation of a neurone produces an action potential that travels down its dendrites and axon;
*Activity of a massive number of neurones and their interactions within the cortical mantle results in the EEG signal. - 9Bio-Potential's at a cellular level-EMG.*Excitation of the neurones transmitted via a nerve to a neuromuscular junction produces stimulation of the muscle fibres. Constitutive elements of muscle fibres are the single motor units.
*Their electrical activity is a single motor unit potential.
*The electrical activity of a large number of single motor unit potentials from groups of muscle fibres, manifests on the body surface as the EMG. - 10Bio-potential's at a cellular level-EOG.*The retina of the eye is a multilayered, regularly structured organ containing cells called rods and cones which sense light and colour.
*Motion of the eyeballs inside the conductive contents of the skull allows the electric potentials.
*Placing the electrode in the vicinity of the eyes (on the sides, temples, above or below), picks up the potentials associated with eye movements-EOG - 11ECG SPEC'S* Amplitude: 1-5mV
*Bandwidth 0.05-100 (Hz).
*Sensor type: Ag/AgCl disposable.
*Error source: motion artefact, 5o Hz, power line interference.
*Applications: Diagnosis of, Ischaemia, arrhythmia, conduction effects. - 12EEG SPEC'S.*Amplitude: 0.001-0.01
*Bandwidth: 0.5-40 Hz.
*Sensor Gold plated/Ag/AgCl reusable.
*Error source: thermal (Johnson), RF NOISE, 50Hz.
*Application: Sleep studies, seizure detection, cortical mapping. - 13EMG SPEC'S*Amplitude 1-10mV.
*Bandwidth 20-2000 Hz.
*Sensor: Ag/ Carbon/stainless steel needle.
*Error: 50Hz, RF.
*Applications: Muscle function, neuromuscular disease, prosthesis. - 14EOG SPEC's*Amplitude: 0.01-0.1
*Bandwidth: dc-10.
*Sensor type: Ag/AgCl.
*Error source: Skin potential motion.
*Applications: eye position, sleep state. - 15Note worthy features of Biopotential's. And General problems with acquisition.*Small amplitudes (10uV to 10mV)
*Low frequency ranges of signals, dc- several hundred hertz.
*Presence of biological interference (skin electrodes, motion etc.)
*Noise from environmental sources (power line interference, radio frequency, electromagnetic etc. - 16Acquisition of ECG signals, lead system.*Acquired by placing electrodes directly on to torso, arms and legs.
*Activity on body surface reflects activity of heart muscle underneath and in its proximity.
*Clinically accepted 12-lead system, comprises a combination of electrodes taking measurements from different regions designated limb leads, precordial leads and chest leads. Limb leads I-III. Precordial lead's aVR/VL/VF derived by combining signals from limb leads. the remaining 6 are chest leads V1-V6.
*ECG's from leads help define nature of the activity on a specific part of the heart muscle (ischaemia/infarction- damage) on the left side may be noticeable on lead III etc. - 17Acquisition of ECG signals- amplitude, electrodes.*Signals are small in amplitude, making measurements susceptible to artefacts, generated by the relative motion of the electrode and the skin, as well as the activity of muscles.
*Electrodes must be good quality, silver coated with silver chloride or recommended.
*Electrolyte gel used to enhance conduction between skin and electrode metal.
*Artefacts from skin + electromagnetic interference must be minismised.
*ECG instruments are often used in critical care environments, they must be electrically isolated for safety and protected from high voltages generated by defibrillators. - 18Applications of ECG Biopotential amplifiers.*Used in many monitoring instruments, pacemakers, and defibrillators. ECG acquisition is also useful in many clinical applications, such as diagnosis of arrhythmias, ischaemia or heart failure.
- 19EEG Signal aquisition*characterised by extremely small amplitudes (microvolts.)
* Gold plated electrodes, placed securely on scalp to make very low resistance contact.
*10-20 lead system, clinically accepted, comprehensive allowing localisation of diagnosable features, such as seizure spikes in the vicinity of electrodes. - 20EEG- signal interpretation.* difficult to interpret, represent the comprehensive activity of billions of neurones transmitted in the brain tissues, fuilds and scalp.
* in the wave form it is possible to see inter orbital seizure spikes/full seizures such as grand/petit mal epilepsy. - 21Analysis of the frequency spectrum*Analysis of the frequency spectrum can reveal changes in signal power at different frequencies being produced at various stages of sleep as a result of anesthetic effects, and sometimes as a result of brain injury
- 22Problems/challenges associated with EEG, signal recordings* environmental/physiological (motion artefact, muscle noise, eye movement, blink artefact and sometimes heart beat signals) and electronic noise sources (50Hz, power lines, RF, electrically/magnetically induced interference).
*Good design and measuring techniques can mitigate the effects of such noise and interferences. - 23EMG signal acquisition*Muscle fibres generate electric activity whenever muscles are active, they are recorded by placing electrodes close to the muscle group.
* A pair of electrodes placed on biceps and triceps can capture EMG signals generated when muscles contract.
*Give rough indication to the force generated by muscle group.
*Electrodes are small and securedly attatched, should provide recordings free of artefacts, silver/silver chloride/gold plated/stainless steel needle electrodes.
*Because the freq range, and amplitude (is comparable or,) larger than ECG, EEG, motion artefact and interference is a problem, e;g. a bandwidth above 20Hz, can greatly reduce skin potential and induce artefacts. - 24Applications of EMG signal acquisition.* research of activity directly from muscle fibres can be clinically valuable in identifying neuromuscular disorders so invasive electrodes are needed to access fibres or neuromuscular junction, fine needle electrodes/ thin stainless steel needles are inserted/implanted to obtain local recording from muscles or fibres.
- 25EOG Signal acquisition.*Potential's generated due to movement of eyeballs, blinking can produce changes in EOG.
*Often used to study eye diseases/position and balance, a reflex called vestubulo-ocular reflex which effects the nystagmus.
*V small signal, 10-100microV. low freq, amplifier with high gain and stability desired.
*Electrode gel used, potential motion artefacts and drift in dc signal are sources of error.
*Electrodes in vicinity of eyes makes it impractical for long term use.
*Can be useful clinically in acute studies of human disorders, careful acquisition followed by appropriate analysis to interpret potential.
*Good electrode placement and selective filtering at amplifier, can obtain a relatively noise free recording. - 26Principles of biopotential recordings.*Good electrode design and attachment suited for application.
*Amplifier circuit design for suitable amplification of signal and rejection of noise and interference.
*Good measurement practices to mitigate artefacts noise and interference. - 27Electrode requirements.* Design pragmatic to reduce cost and allow for good manufacturing and reliable long term use.
- 28Silver- silver chloride.*Classic, high quality.
*Highly conductive metal Ag interfaced to its salt AgCl. Connected via electrolyte gel Na/KCl of 0.1 M, good conductivity and low junction potential without irritating.
*Produces lowest and most stable junction potentials (result of dissimilar electrolytic interfaces, a serious source of electrode based motion artefacts). - 29Reusable silver-silver chloride.*Ag disks coated electrolytically with AgCl/ particles of Ag/AgCl sutured together forming electronic structure of electrode.
*Gel soaked into foam pad/applied directly in a pocket produced by electrode casing.
*Secured to skin by non allergenic adhesive tape, connected to external instrumentation by external connector.
*Good for acute studies/basic research. - 30Disposable Silver.*Made similarly to normal silver, but minimise use of silver.
*To allow secure attachment, large foam pads attach electrode body with adhesive coating, useful for ambulatory or long term use. - 31Gold Electrodes.*High conductivity, inertness- desirable in reusable electrodes which are commonly used in EEG.
*Small reusable electrodes designed to be securely attached to scalp and shaped to make a recessed space for electrolyte gel applied through a whole in body.
* Attached in hair free area with strong adhesive e.g. colloidal/wire mesh.
*More expensive than Ag, higher junction potential, greater susceptibility to motion artefact.
*Maintain low input impedance and reusable.
*Good for short term readings. - 32Conduction Polymer Electrodes.* Simultaneously conductive and adhesive. conductive due to monovalent metal ions, backing Ag/ or Aluminium foil, allowing electric contact to external instrumentation.
*No need for gel, so can be immediately and conveniently used.
*performs adequately so long as relatively high resistivity over metallic electrodes.
*High resistivity= unsuitable for low noise measurements.
*Doesn't attach as well as conventional adhesive. So potentials at skin electrode interface.
*Signal level high and restriction of movement minimises artefact.
*Relatively inexpensive. - 33Metal Carbon electrodes.*Sturdy construction, reusable, flexible inexpensive.
Gel applied to metal electrode fastened to body by rubber band.
*Can produces high levels of artefact, bulky and awkward. High resistivity-artefacts.
*Electric impedance plethysmography- use. - 34Needle Electrodes.*Invasive, used when absolute necessary to record directly from organ/ muscle/muscle fibre.
*Metallic steel wire delivered via needle inserted at site of fibre, wire hooked and fastens to fibre even as needle removed.
*Small signal such as moor unit potential can be recorded this way.
*Limited to highly specialised/supervised clinical or research applications.
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- Fichas sobre Biopotentials :), creado por Kemi Biye-Malcolm el 20/05/2015.
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- Kemi Biye-Malcolm
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