Measuring Tissue Impedance Flashcards
State body tissues with good conductance.
blood, lymph, spinal liquid, urine.
State body tissues with medial conductance.
internal organs, muscle tissues
State body tissues with low conductance.
dry skin, bones
What kind of resistance do living organisms normally have?
they have high electric resistance, reminding of dielectrics
Why do living organisms have high electric resistance?
Due to the property of living organisms whose main constituents are polarized dielectric water molecules.
What creates an action potential across the cell?
The cell membrane. The cell has an asymmetric ion distribution due to the selective properties of the membrane.
Why does tissue have high resistance?
Due to its capacitance and ohmic resistance.
What is capacitance?
The ability of a system to store an electric charge.
What is ohmic resistance?
The sum of multiple different types of resistances:
the electrolyte resistance, the resistance of the current collector, the active mass, and the transition resistance between the current collector and active mass.
What is impedance?
The total opposition to the flow of current.
What is the symbol of impedance
Z
What method is based on tissue impedance?
Rheography
What is the current when a tissue is put across the A.C. source?
I = U / Z
U = voltage
Z = impedance
What is the threshold of perception?
Increasing the current until something is felt.
What to do after the tissue reaches the threshold of perception?
double the voltage and connect the resistor R. Adjust R in such a way that the current circuit is the same.
What is the final equation used to measure tissue impedance?
R = Z
R = tissue resistance
Z = impedance
Explain the procedure of measuring tissue impedance.
1) Connect the circuit.
2) Switch on the generator.
3) Adjust the output voltage at zero value.
4) Set output frequency at 500c/s.
5) Put the rheostat slider position at R=0 Ohms.
6) put two cloths moistened in NaCL solution at 5-10cm separation on the forearm. Then fix electrodes P1 and P2.
7) Switch on and off the knob K each 0.5-1s. Note the voltmeter reading when the person feels the sensation.
8) Adjust the rheostat at 5000 Ohms and double the voltage output.
9) switch off and on K every 0.5-1s, reducing the resistance by moving the rheostat slider to the left until the effect disappears.
10) note the rheostat slider position (resistance value). magnitude = resistance at f=500 c/s.
11) Take measurements of impedance Z at f=2000c/s.
12) Calculate R and C using the following formulae:
I = 2* U / (R+Z)
R = Z
13) Draw conclusions.
