Impedimed Bioimpedence Analysis (BIA) Machine

Bioimpedance analysis (BIA) has become a widely accepted method in healthy populations, for the determination of body composition due to its simplicity, speed and noninvasive nature. While BIA is recognized as one of the more reliable methods, not all devices or methods are able to achieve the level of accuracy required. The accuracy of a BIA device depends primarily on the number of frequencies at which measurements are taken. This is why the choice of instrument is so important.

Theory Behind Bioimpedance: The Science

BIA was first used over 30 years ago to measure the total water content of the body. The method involves passing an extremely low strength electrical current through the body and measuring the impedance to the flow of this current.

BIA is based on two key concepts:

  1. The Fact That the Body Contains Water and Conducting Electrolytes.
    When a current is passed through the body, the water-containing fluids primarily conduct the electrical current. Water is found both inside the cells, intracellular fluid (ICF) and outside the cells, extracellular fluid (ECF). At low frequency, current passes through the ECF space and does not penetrate the cell membrane. At high frequencies however the current passes through both the ICF and ECF (Figure 1).
  2. The Impedance of a Geometrical System is Related to Conductor Length, its Cross Sectional Area and Signal Frequency.
    Based on these concepts a value for impedance can be calculated from a fixed strength current being passed through the body, which is inversely proportional to the amount of fluid. By appropriate choice of signal frequency, this can be made specific for extracellular fluid or for total fluid determinations.

Courtesy of Metagenics