ImpediMed

[ImPoster]

Single frequency, multi-freqency and bioimpedance spectroscopy

Bioimpedance is often referred to generically as BIA (Bioelectrical Impedance Analysis) but a variety of different approaches exist. For the purpose of standardization, I would like to suggest the following definitions:

Bioimpedance - generically includes any of the methods defined below.

Single-frequency bioimpedance - uses only one frequency of current.

Multiple- or multi-frequency bioimpedance - generally use 2 to 10 different frequencies of current.

Bioimpedance Spectroscopy or BIS - use a spectrum of 256 different frequencies when taking readings. Devices using BIS most often will employ a Cole-Cole plot of resistance (R) versus Reactance (Xc) to determine Rinf, or the theoretical resistance at infinity and Rnaught or Rzero (Ro), the theoretical resistance at a zero frequency. Rinf provides a measure of Total Body Water (TBW) while Ro provides a measure of Extra-cellular fluid (ECF). The level of fluids lying inside the body's cells, or Intra-cellular fluid (ICF) can be derived by subtracting ECF from TBW.


Single frequency devices rely on the use of algorithms to estimate body composition parameters. Algortihms, also called prediction equations, are mathematically derived by studying a population while using both bioimpedance and the reference method for the parameter of interest, TBW for example. The basic assumption when using a single frequency bioimpedance device is that the subject or patient is similar that those that made up the population from which the prediction equation was derived. Since body composition can vary by gender, ethnicity and race, matching the subject to a proper algorithm is critical. ImpediMed's single frequency device, the DF50, provides the choice of three agrorithms. (#msg-9790870)

Bioimpedance spectroscopy or BIS is a direct measure and does not rely on the use of algorithms to determine the subject's TBW and ECF. This makes BIS more robust across different genders, ethnic groups and races.