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bioimpedance measurements
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Impedance (Z) is the overall propensity of an object to conduct electrical current and is defined as the ratio of the voltage in an object to the current in an object. Its units are ohms, after the physicist.
The constituent components of impedance are resistance (R) and reactance (X). Resistance is a direct indicator of a material's propensity to dissipate energy; reactance is an indicator of energy storage. All materials both dissipate and store energy.
The following electrical characteristics are measured and used to evaluate body composition:
Impedance (Z)
Impedance is a measurement of the ability of a medium to conduct current. It is the ratio of induced voltage to injected current in a conductive medium and has two components: resistance and reactance.
Resistance (R)
Resistance is the component of impedance related to the dissipation of energy in a conductive medium.
Reactance (X)
Reactance is the component of impedance related to the storage of energy in a conductive medium.
Phase Angle (α)
The phase angle is the time delay between a stimulating current and the voltage generated by an alternating current in a conductive medium. The phase angle is expressed in degrees of phase shift.
How do these electrical characteristics relate to each other?
The time relationship of voltage, current, and phase is shown in the first figure below. The vector relationship between impedance, resistance, reactance, and phase angle, represented with polar coordinates is shown in the second figure.
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