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circuit model
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Water is the conductor in the body and determines the resistance.
Electrolytic fluid in fat-free mass consisting of water and charged ions readily conducts electrical current. Extracellular fluid (water and ionized sodium Na+) provides a low-resistance pathway. Intracellular fluid (water and ionized potassium K+) also provides a low-resistance pathway. Fat mass is non-conductive because it contains no water.
Cell membranes within intracellular mass determine the reactance.
The cell membranes consist of a layer of nonconductive, lipophilic material interposed between two layers of conductive molecules. They behave like tiny capacitors - storing electrical charge in the presence of an alternating current.
The extracellular pathway (sodium ionized water) is represented by a single resistance. The intracellular pathway (potassium ionized water and cell membranes) is represented by a resistance and a reactance.
The total resistance is proportional to the amount of fat-free mass. The reactance is proportional to body cell mass (intracellular mass).
Ultimately, the resistance seen by the bioimpedance meter is the total resistance, combining intracellular and extracellular resistance. The meter reports the total resistance and the total reactance to the microprocessor for analysis.
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