Impedance

Impedance is a measure of the opposition that a circuit presents to a current when a voltage is applied. In the context of medicine, impedance is often used in bioimpedance analysis and electrocardiography.

Definition

Impedance is a complex quantity, with the same units as resistance, for which the symbol Z is usually reserved. It includes both resistance (R) and reactance (X), and is given by Z = R + jX, where j is the imaginary unit.

Medical Applications

Impedance has a number of applications in the field of medicine.

Bioimpedance Analysis

Bioimpedance analysis is a method used for estimating body composition, and in particular body fat. Bioimpedance analysis is based on the principle that the resistance to an applied electric current is inversely related to the volume of the conductor (in this case, the human body).

Electrocardiography

In electrocardiography, impedance is used to measure heart rate, respiratory rate, and other parameters. Electrodes attached to the skin measure the impedance to an applied current, which changes with the cardiac and respiratory cycles.

See Also

• Bioimpedance
• Electrocardiography
• Resistance
• Reactance

References

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