p.10
Overpotential Mechanisms in Electrodes
What is overpotential?
The difference between the observed half cell potential and the equilibrium zero-current half-cell potential.
p.8
Half-Cell Potential and Its Measurement
What does the standard reduction potential table indicate?
It indicates the standard reduction potentials of various half-reactions at 25°C, 101 kPa, and 1M concentration.
p.17
Biopotential Electrodes: Function and Design
What is the purpose of biopotential electrodes?
To serve as an interface between the body and machine.
p.12
Polarizable vs Non-Polarizable Electrodes
What characterizes a perfectly non-polarizable electrode?
It responds to current as a perfect conductor would, allowing current to pass freely across the electrode/electrolyte interface with low voltage development.
p.16
Half-Cell Potential and Its Measurement
What is the formula for the half-cell potential of the Ag/AgCl electrode?
E = E_Ag^0 + (KT/q) ln(a_Ag+) = E_Ag^0 + (KT/q) ln(Ks/a_Cl-).
p.12
Electrode-Electrolyte Interface Dynamics
What is the equivalent circuit of an electrode?
It includes components such as half-cell potential (Ehc), electrode capacitance (Cd), leakage resistance (Rd), and series electrolyte and skin resistance (Rs).
p.22
Recording Bioelectric Signals: ECG, EMG, EEG
What does an Electrocardiogram (ECG) measure?
It measures the electrical activity of the heart.
p.3
Recording Bioelectric Signals: ECG, EMG, EEG
What was the first table-model electrocardiograph and who manufactured it?
The first table-model Enithoven electrocardiograph was manufactured by the Cambridge Scientific Instrument Company of London in 1911.
p.4
Recording Bioelectric Signals: ECG, EMG, EEG
How has the ECG machine evolved over time?
It has evolved into compact electronic systems that often include computerized interpretation of the electrocardiogram.
p.13
Biopotential Electrodes: Function and Design
Why is the ideal case of electrically identical electrodes rare in practice?
Because the half-cell potentials depend on factors like electrode corrosion, change of ion concentration over time and location, temperature fluctuation, skin contact, and current.
p.5
Biopotential Electrodes: Function and Design
Why is the function of biopotential electrodes not as straightforward as it seems?
Because the electrode carries out a transducing function, converting ionic currents in the body to electronic currents in the electrode and lead wire.
p.7
Half-Cell Potential and Its Measurement
On what factors does the half-cell potential depend?
The metal involved and the concentration of its ion in the electrolyte.
p.11
Polarizable vs Non-Polarizable Electrodes
What type of current is associated with a perfectly polarizable electrode?
Displacement current only.
p.9
Electrode-Electrolyte Interface Dynamics
What is the relationship between ionic activity and ion concentration for low ion concentration?
For low ion concentration, ionic activity (a) is approximately equal to the concentration of the ion.
p.15
Silver/Silver Chloride Electrode Characteristics
What are the characteristics of the silver/silver chloride (Ag/AgCl) electrode?
Conducts current, slightly soluble, slow reaction, stable rate for precipitation and dissolution, charge neutrality.
p.4
Biopotential Electrodes: Function and Design
What is the primary function of biopotential electrodes?
To serve as an interface between the body and machine.
p.2
Bioelectric Phenomena at Cellular Level
What are the main topics covered in Chapter 2 of 'Biopotentials: the Origin and Measurements'?
Electrical activity at the cellular level and recordings of bioelectric signals.
p.5
Recording Bioelectric Signals: ECG, EMG, EEG
What is the general model to record the electrocardiographic signal?
It involves a bio-voltage source, impedance elements (Z1, Z2), and an amplifier (ZA).
p.5
Electrode-Electrolyte Interface Dynamics
What does the electrode–electrolyte interface consist of?
The electrode consists of metallic atoms (C), and the electrolyte is an aqueous solution containing cations (C+) of the electrode metal and anions (A-).
p.11
Polarizable vs Non-Polarizable Electrodes
Which materials make good polarizable electrodes?
Noble metals like gold (Au) and platinum (Pt), or other metal electrodes with oxidized surfaces.
p.6
Biopotential Electrodes: Function and Design
What are the components of the net current that crosses the interface from the electrode to the electrolyte?
1. Electrons moving in a direction opposite to that of the current in the electrode. 2. Cations (C+) moving in the same direction as the current. 3. Anions (A-) moving in a direction opposite to that of the current in the electrolyte.
p.15
Silver/Silver Chloride Electrode Characteristics
What reactions occur at the interface of a silver/silver chloride (Ag/AgCl) electrode?
Ag ↔ Ag⁺ + e⁻ and Ag⁺ + Cl⁻ ↔ AgCl ↓.
p.15
Silver/Silver Chloride Electrode Characteristics
What is the solubility product (Kₛ) for silver chloride?
Kₛ = aₐg⁺ × aₐl⁻ ~ constant.
p.18
Biopotential Electrodes: Function and Design
What is the function of biopotential electrodes?
They serve as an interface between the body and machine.
p.18
Silver/Silver Chloride Electrode Characteristics
What do the numbers attached to the curves in the graph indicate?
The number of mA·s for each deposit.
p.5
Biopotential Electrodes: Function and Design
What is the primary function of biopotential electrodes?
To act as an interface between the body and machine, transducing ionic currents in the body to electronic currents in the electrode and lead wire.
p.2
Recording Bioelectric Signals: ECG, EMG, EEG
What does an electrocardiogram (ECG) record?
The electrical activity of the heart.
p.11
Biopotential Electrodes: Function and Design
What is the role of biopotential electrodes?
They serve as an interface between the body and machine.
p.17
Silver/Silver Chloride Electrode Characteristics
Why is it not possible to use Ag⁺ ions to combine with e⁻ in the cathode reaction?
Because none are present.
p.21
Electrode-Skin Interface and Its Implications
What is the resistance of the skin/electrolyte/electrode interface for abraded skin?
Approximately 5,000 ohms.
p.20
Electrode-Skin Interface and Its Implications
How do the deeper layers of the epidermis compare to other tissues?
The deeper layers are similar to other tissues.
p.18
Silver/Silver Chloride Electrode Characteristics
What is the significance of the electrolytic deposition thickness in Ag/AgCl electrodes?
It affects the impedance characteristics of the electrode.
p.3
Biopotential Electrodes: Function and Design
What is the primary function of biopotential electrodes?
To serve as an interface between the body and machine.
p.10
Overpotential Mechanisms in Electrodes
What causes ohmic overpotential?
It is a direct result of the resistance of the electrolyte and depends on current, temperature, non-linearity, and individual variations.
p.10
Overpotential Mechanisms in Electrodes
What is activation overpotential?
It arises when the oxidation reaction requires different activation energy compared to the reversed reduction reaction, changing the equilibrium state.
p.10
Overpotential Mechanisms in Electrodes
What is the formula for total overpotential (Vp) of an electrode?
Vp = Vr + Vc + Va, where Vr is ohmic overpotential, Vc is concentration overpotential, and Va is activation overpotential.
p.9
Half-Cell Potential and Its Measurement
How is the half-cell potential (E) expressed in terms of standard conditions?
E = E0 + (KT/q) ln(ac+), where ac+ is the activity of cations.
p.15
Biopotential Electrodes: Function and Design
What is the primary function of biopotential electrodes?
To serve as an interface between the body and machine.
p.16
Half-Cell Potential and Its Measurement
Why is the half-cell potential of the Ag/AgCl electrode not strongly dependent on the silver ion concentration in body fluid?
Because the concentration of chloride ion in body fluid is relatively high and stable.
p.13
Biopotential Electrodes: Function and Design
What causes the time-varying offset in electrode signals?
The differences in half-cell potentials due to factors such as electrode corrosion, ion concentration changes, temperature fluctuations, skin contact, and current.
p.21
Electrode-Skin Interface and Its Implications
What does the electrode-skin interface represent?
An interface between the body and machine.
p.21
Electrode-Skin Interface and Its Implications
How does the resistance of the skin/electrolyte/electrode interface vary with time when using high-concentration NaCl electrolyte?
The resistance variation is greater than 10%.
p.12
Polarizable vs Non-Polarizable Electrodes
Are all electrocardiographic electrodes completely non-polarizable?
No, even the best available electrocardiographic electrode is polarizable to some extent.
p.8
Biopotential Electrodes: Function and Design
What is the role of biopotential electrodes?
They serve as an interface between the body and machine.
p.2
Recording Bioelectric Signals: ECG, EMG, EEG
What are the types of recordings of bioelectric signals discussed in Chapter 2?
Electrocardiogram (ECG), electromyogram (EMG), and electroencephalogram (EEG).
p.2
Recording Bioelectric Signals: ECG, EMG, EEG
What does an electromyogram (EMG) record?
The electrical activity of muscles.
p.2
Recording Bioelectric Signals: ECG, EMG, EEG
What does an electroencephalogram (EEG) record?
The electrical activity of the brain.
p.19
Electrode-Skin Interface and Its Implications
What is the purpose of the solid gel in disposable ECG electrodes?
To ensure good contact between the electrode and the skin.
p.17
Silver/Silver Chloride Electrode Characteristics
What chemicals are used in the electrolyte for making Ag/AgCl electrodes?
Hydrochloric acid (HCl) and Salt (NaCl).
p.20
Electrode-Skin Interface and Its Implications
What is the epidermis?
A constantly changing layer, with the outer surface consisting of dead material.
p.22
Biopotential Electrodes: Function and Design
What is the function of biopotential electrodes?
They serve as an interface between the body and machine.
p.22
Recording Bioelectric Signals: ECG, EMG, EEG
What does an Electroencephalogram (EEG) measure?
It measures the electrical activity of the brain.
p.2
Bioelectric Phenomena at Cellular Level
What are the key aspects of electrical activity at the cellular level?
Bioelectric phenomena at the cellular level, volume conductor potential distributions, and typical bioelectric sources such as the heart, brain, and muscle.
p.13
Biopotential Electrodes: Function and Design
Can the time-varying offset in electrode signals be removed?
No, the time-varying offset cannot be removed from the signal.
p.7
Half-Cell Potential and Its Measurement
How can the half-cell potential of an electrode affect its performance?
It can affect the performance to detect the potential signal.
p.19
Silver/Silver Chloride Electrode Characteristics
Why are Ag/AgCl electrodes preferred for biopotential measurements?
Because they provide stable and reliable measurements.
p.6
Biopotential Electrodes: Function and Design
What is the direction of electron movement in the electrode relative to the current?
Electrons move in a direction opposite to that of the current in the electrode.
p.12
Polarizable vs Non-Polarizable Electrodes
Why are non-polarizable electrodes ideal for potential signal measurement?
Because they allow current to pass freely across the electrode/electrolyte interface and develop low voltages.
p.15
Silver/Silver Chloride Electrode Characteristics
What does the solubility product (Kₛ) of silver chloride indicate?
It indicates that the rate of precipitation and dissolution of silver chloride is a constant.
p.20
Electrode-Skin Interface and Its Implications
What is the stratum corneum?
The outermost layer of the epidermis with different electrical properties.
p.14
Silver/Silver Chloride Electrode Characteristics
What happens during the reduction process at the Ag/AgCl electrode interface?
Reduction leads to precipitation.
p.2
Bioelectric Phenomena at Cellular Level
What are typical bioelectric sources mentioned in Chapter 2?
Heart, brain, and muscle.
p.7
Half-Cell Potential and Its Measurement
What is half-cell potential?
It is the electric potential difference between the electrolyte surrounding the electrode and the rest of the solution.
p.19
Biopotential Electrodes: Function and Design
What is the primary function of biopotential electrodes?
To serve as an interface between the body and machine for biopotential measurements.
p.19
Biopotential Electrodes: Function and Design
What are the main components of a disposable ECG electrode?
Metal snap, label, base foam, Ag/AgCl, solid gel, and film.
p.12
Silver/Silver Chloride Electrode Characteristics
What type of metals act as non-polarizable electrodes?
Reactive metals, such as the Ag-AgCl electrode.
p.20
Biopotential Electrodes: Function and Design
What is the function of biopotential electrodes?
They serve as an interface between the body and machine.
p.20
Electrode-Skin Interface and Its Implications
What should be done to achieve better results with biopotential electrodes?
The stratum corneum should be removed.
p.8
Half-Cell Potential and Its Measurement
What is half-cell potential?
It is the electric potential difference between the electrolyte surrounding the electrode and the rest of the solution.
p.10
Overpotential Mechanisms in Electrodes
What is concentration overpotential?
It occurs when the equilibrium state of ion concentration in the vicinity of the electrode-electrolyte interface changes due to a non-zero current.
p.9
Electrode-Electrolyte Interface Dynamics
What is the Nernst equation for the electrode-electrolyte interface?
E = - (KT/q) ln(a1/a2), where a1 and a2 are the activity of ions in the electrode and electrolyte.
p.19
Silver/Silver Chloride Electrode Characteristics
What type of electrodes are commonly used for biopotential measurements?
Compact Ag/AgCl electrodes.
p.6
Biopotential Electrodes: Function and Design
What does the electrolyte represent in the context of biopotential electrodes?
The electrolyte represents the body fluid containing ions.
p.15
Silver/Silver Chloride Electrode Characteristics
What type of electrode is commonly used in biopotential measurements?
Silver/silver chloride (Ag/AgCl) electrode.
p.6
Biopotential Electrodes: Function and Design
What is the direction of anion (A-) movement in the electrolyte relative to the current?
Anions (A-) move in a direction opposite to that of the current in the electrolyte.
p.6
Biopotential Electrodes: Function and Design
What is the requirement for biopotential electrodes in terms of safety?
There should be no chemical and mechanical hazards.
p.18
Electrode-Electrolyte Interface Dynamics
What are the components of the equivalent circuit for a polarizable electrode?
Half-cell potential (Ehc), electrode capacitance (Cdl), leakage resistance (Rj), and series electrolyte and skin resistance (Rs).
p.8
Half-Cell Potential and Its Measurement
On what factors does the half-cell potential depend?
It depends on the metal involved and the concentration of its ion in the electrolyte.
p.5
Electrode-Electrolyte Interface Dynamics
How does the electric current pass from the body to the electrode?
The current crosses the electrode–electrolyte interface from left to right, with ions in the body and electrons in the electrode.
p.7
Electrode-Electrolyte Interface Dynamics
What does the surface electrode charge distribution indicate?
It shows the distribution of charge density across the electrode surface.
p.6
Biopotential Electrodes: Function and Design
What is the direction of cation (C+) movement in the electrolyte relative to the current?
Cations (C+) move in the same direction as the current.
p.6
Biopotential Electrodes: Function and Design
What are the chemical reactions at the interface between the electrode and the electrolyte?
Oxidation (leading to dissolution) and reduction (leading to precipitation).
p.14
Biopotential Electrodes: Function and Design
What is the primary function of biopotential electrodes?
To serve as an interface between the body and machine.
p.14
Silver/Silver Chloride Electrode Characteristics
What happens during the oxidation process at the Ag/AgCl electrode interface?
Oxidation leads to dissolution.
p.3
Biopotential Electrodes: Function and Design
What is the general problem addressed by biopotential electrodes?
How to transduce ionic currents in the electrolytes in the body fluid into electronic currents in wires.
p.4
Recording Bioelectric Signals: ECG, EMG, EEG
What significant award did Willem Einthoven receive for his invention?
The Nobel Prize in Medicine in 1924.
p.13
Biopotential Electrodes: Function and Design
What is the ideal case for an electrode pair in a series-parallel circuit?
Two electrodes are electrically identical, leading to the same half-cell potential and cancellation of half-cell potential.
p.8
Half-Cell Potential and Its Measurement
How is half-cell potential measured?
Half-cell potential is measured using a setup involving a voltmeter, an electrolyte, and electrodes, as shown in the diagram.
p.11
Polarizable vs Non-Polarizable Electrodes
How does a perfectly polarizable electrode respond to a current?
It responds as a perfect capacitor would, with no charge crossing the electrode-electrolyte interface.
p.9
Half-Cell Potential and Its Measurement
What is the half-cell potential equation at high cation concentration?
E = E0 + (KT/q) ln(a2), where a2 is the activity of ions.
p.16
Biopotential Electrodes: Function and Design
What type of electrode is commonly used as an interface between the body and machine?
Silver/silver chloride (Ag/AgCl) electrode.
p.16
Silver/Silver Chloride Electrode Characteristics
Why must the activity of Ag ion be very low in the Ag/AgCl electrode?
Because the electrolyte has a relatively high concentration of Cl- ions.
p.21
Electrode-Skin Interface and Its Implications
What is the initial resistance of the skin/electrolyte/electrode interface for 'pre-rub' skin?
Approximately 100,000 ohms.
p.14
Electrode-Electrolyte Interface Dynamics
What is the Nernst equation used for?
To describe the potential of a general oxidation-reduction reaction.
p.4
Biopotential Electrodes: Function and Design
What is the general problem addressed by biopotential electrodes?
How to transduce ionic currents in the electrolytes in the body fluid into electronic currents in wires.
p.7
Biopotential Electrodes: Function and Design
What is the role of biopotential electrodes?
They serve as an interface between the body and machine.
p.9
Electrode-Electrolyte Interface Dynamics
What does the ionic activity represent in the context of the electrode-electrolyte interface?
The ionic activity represents the availability of the ions for the reaction.
p.11
Polarizable vs Non-Polarizable Electrodes
What is the relationship between current and voltage in a perfectly polarizable electrode?
Current and voltage are not linearly related.
p.12
Biopotential Electrodes: Function and Design
What is the function of biopotential electrodes?
They serve as an interface between the body and machine.
p.21
Electrode-Skin Interface and Its Implications
How does the resistance of the skin/electrolyte/electrode interface vary with time when using low-concentration NaCl electrolyte?
The resistance variation is less than 0.5%.
p.12
Polarizable vs Non-Polarizable Electrodes
How are current and voltage related in non-polarizable electrodes?
Current and voltage are linearly related (I = V/R).
p.18
Silver/Silver Chloride Electrode Characteristics
What type of electrode is Ag/AgCl?
It is a silver/silver chloride electrode.
p.20
Electrode-Skin Interface and Its Implications
What does the total equivalent circuit represent in the context of biopotential electrodes?
It represents the electrical model of the electrode-skin interface.
p.16
Silver/Silver Chloride Electrode Characteristics
What makes the electrical characteristics of the Ag/AgCl electrode relatively stable?
The high and stable concentration of chloride ion in body fluid.
p.18
Silver/Silver Chloride Electrode Characteristics
What does the graph in the image represent?
Impedance as a function of frequency for Ag electrodes coated with an electrolytically deposited AgCl layer.
p.22
Recording Bioelectric Signals: ECG, EMG, EEG
What does an Electromyogram (EMG) measure?
It measures the electrical activity of muscles.
