Measuring Tissue Impedance and Resistivity
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Questions and Answers

What is the main factor that affects the resistivity of an electrolyte?

  • Temperature (correct)
  • Color of the solution
  • Solubility of the electrolyte
  • Size of the container

    • Which body tissues are classified as good conductors with low resistivity?

  • Cartilage and muscle
  • Bone and dry skin
  • Blood and lymph (correct)
  • Muscle and fat

    • When using a Wheatstone bridge to measure resistance, what condition indicates the balance of the circuit?

  • The resistance value changes
  • Buzzing increases
  • No current flows between C and D (correct)
  • Electrodes become polarized

    • What does the resistivity (ρ) of an electrolyte depend on?

    <p>Concentration and type of ions</p> Signup and view all the answers

    What equation is used to calculate the resistance (R) of the electrolyte in terms of resistivity (ρ)?

    <p>R = ρ × L/S</p> Signup and view all the answers

    Which type of source is used to avoid polarization of electrodes when measuring resistance?

    <p>Alternative current source</p> Signup and view all the answers

    What is the resistivity of a living organism primarily dependent on?

    <p>Presence of liquid and tissue type</p> Signup and view all the answers

    How does electrolytic dissociation occur?

    <p>Upon dissolving in water</p> Signup and view all the answers

    Which ions contribute to the low resistivity of body fluids?

    <p>Na+ and Cl-</p> Signup and view all the answers

    What can be inferred about tissues with low resistivity in the context of electrostimulation?

    <p>They respond effectively to electrical signals.</p> Signup and view all the answers

    What is the method used to calculate the electrolyte resistance R' in the experiment described?

    <p>By taking the mean values of l₁ and l₂ with specific R values</p> Signup and view all the answers

    In the thermoresistor section, what does the term ΔΕ represent?

    <p>The activation energy for the semiconductor</p> Signup and view all the answers

    What is needed to calculate the resistivity of the electrolyte in the experiment?

    <p>The values of diameter D, length L, and cross-sectional area S</p> Signup and view all the answers

    How is the slope β related to the activation energy ΔΕ in the thermoresistor experiment?

    <p>It represents the ratio of the change in resistance to the temperature change</p> Signup and view all the answers

    What is the purpose of adjusting R during the experiment with the thermoresistor?

    <p>To set the ammeter pointer to indicate no current flow</p> Signup and view all the answers

    What occurs to the overall current according to Ohm's law when considering polarization e.m.f.?

    <p>The total current is decreased by the e.m.f. of polarization.</p> Signup and view all the answers

    Which formula represents the current strength through a tissue when considering its impedance?

    <p>I = U/Z</p> Signup and view all the answers

    What is the procedure to establish tissue impedance using the adjusted resistance?

    <p>Moving the rheostat until the effect of current appears.</p> Signup and view all the answers

    What is the relationship derived from the impedances Z₁ and Z₂ in parallel according to the context?

    <p>Z₁ = sqrt(R² + (2n)²C²).</p> Signup and view all the answers

    Which frequency is used during the measurement of tissue impedance in the given procedure?

    <p>500 c/s</p> Signup and view all the answers

    If the resistance is adjusted to 5000 ohms after doubling the output voltage, what is the next step?

    <p>Reduce resistance until the current effect is felt.</p> Signup and view all the answers

    What does the relationship between resistance R and impedance Z simplify to at specific conditions?

    <p>R = Z.</p> Signup and view all the answers

    What is the primary function of the cathode-ray oscilloscope described?

    <p>To produce visual images of rapidly changing signals.</p> Signup and view all the answers

    According to the procedure, what happens when the rheostat is adjusted while observing the effects of current?

    <p>The observed resistance equals the impedance.</p> Signup and view all the answers

    What must be done before the tissue impedance measurement begins in the procedure outlined?

    <p>Ensure the circuit is connected and voltage is at zero.</p> Signup and view all the answers

    What primarily contributes to the high electrical resistance of living tissues?

    <p>Polarized dielectric water molecules</p> Signup and view all the answers

    Which of the following tissues is associated with high conductance?

    <p>Blood</p> Signup and view all the answers

    When measuring the resistance of a thermoresistor, what temperature interval is suggested for the experiment?

    <p>20° - 80°C</p> Signup and view all the answers

    What is meant by impedance in the context of living tissues?

    <p>The total opposition to the flow of current</p> Signup and view all the answers

    How does the cellular organization of tissue contribute to its electrical resistance?

    <p>By creating a potential difference across membranes</p> Signup and view all the answers

    What is the purpose of rheography in medical diagnostics?

    <p>To gauge blood flow in tissues</p> Signup and view all the answers

    How does the resistance of a thermoresistor change with temperature?

    <p>It can increase or decrease depending on the temperature range</p> Signup and view all the answers

    What formula can be used alongside the graph of InR = f(1/T) to calculate ΔΕ in eV?

    <p>ΔΕ = kT ln(R)</p> Signup and view all the answers

    Study Notes

    Measuring Tissue Impedance

    • Living tissues have varying electrical conductance due to their composition and cell structure.
    • Good conductors include fluids like blood, spinal fluid, and urine.
    • Medial conductors are internal organs and muscle tissues.
    • Poor conductors are bones and dry skin.
    • Tissues resemble dielectrics due to polarized water molecules and cellular membranes.
    • Cell membranes act as capacitors, with values around 0.5-1 µF/cm².
    • Tissue impedance is determined by factors like blood supply.
    • Rheography involves measuring tissue impedance to understand blood flow.
    • Direct current (DC) decreases over time through living tissue, reaching a constant value lower than its initial value.
    • The method involves measuring the potential difference across an electrode pair placed on the body.

    Measuring Resistivity

    • Electrolytes conduct electricity due to the presence of ions.
    • Electrolytic dissociation involves the separation of substances into ions (anions and cations).
    • Resistivity is the resistance of a material per unit length and cross-sectional area.
    • It is measured in ohm-meters (Ω·m) and indicates the opposition to electric current flow.
    • Resistivity of electrolytes depends on factors like concentration, temperature, and type.
    • Living tissues have varying resistivity depending on their liquid content.
    • Good conductors include fluids like blood, lymph, and spinal liquid.
    • Muscle has moderate conductivity.
    • Poor conductors include bone and dry skin.

    Resistivity Measurement Procedure

    • A U-shaped glass tube filled with an electrolyte and electrodes is used to measure resistivity.
    • The distance between electrodes (L) and the cross-sectional area of the tube (S) are used to calculate resistance (R).
    • A Wheatstone bridge is used to measure the resistance.
    • AC source is used to avoid electrode polarization.
    • Polarization creates an opposing electromotive force (EMF) that affects current flow.
    • Subthreshold AC frequencies (20-30 kHz) are used in reography.

    Principle of the Method:

    • An AC voltage is applied to the tissue, and the current is measured.
    • The current is proportional to the voltage and inversely proportional to the impedance.
    • By adjusting the voltage and a resistor in series with the tissue until the current is the same as the initial measurement, the impedance can be determined.
    • The resistor value then represents the tissue impedance.
    • Impedance values are determined at different frequencies to analyze tissue properties.
    • Formulas are used to calculate tissue resistance (R) and capacitance (C) based on impedance measurements at two frequencies.

    The Oscilloscope:

    • The oscilloscope is a device that visualizes rapidly changing electrical signals.
    • The cathode-ray oscilloscope is the most common type.
    • It uses a cathode-ray tube (CRT) to display the signal as a waveform.

    Resistivity of an Electrolyte Experiment

    • A circuit with a Wheatstone bridge is used to measure electrolyte resistance.
    • Electrodes are placed in a U-shaped tube containing the electrolyte.
    • The balance point of the bridge is adjusted to determine resistance.
    • By changing the electrode positions, the resistance is measured at different heights.
    • The resistivity is calculated based on the measured resistance and the dimensions of the tube.

    Thermoresistor:

    • Thermoresistors, also known as thermistors, are semiconductor devices whose resistance changes with temperature.
    • The resistance of a thermoresistor is exponentially related to temperature.
    • The activation energy (ΔΕ) is a key parameter that governs the sensitivity of the thermoresistor to temperature.
    • A graph of ln(R) versus 1/T can be used to determine ΔΕ.
    • The slope of the graph is related to ΔΕ, and the activation energy can be calculated using the equation: ΔΕ = 2k·tan(β), where k is Boltzmann's constant and β is the angle of the slope.

    Thermoresistor Experiment:

    • Circuit setup involves a Wheatstone bridge, power supply, and ammeter.
    • The thermistor is connected in the bridge circuit.
    • The temperature of the thermistor is changed, and the resistance is measured.
    • The measurements are used to plot ln(R) versus 1/T, and ΔΕ is determined from the graph.

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    Description

    This quiz explores the principles of tissue impedance and resistivity in living organisms. It covers the conductance of various tissues, the role of cell membranes, and the methods of measuring impedance, particularly through rheography. Additionally, it delves into electrolytic dissociation and the conduction of electricity through electrolytes.

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