Direct Current Bioelectric Impedance Methods

Unlike A.C. bioelectric impedance, the electric current produced by D.C. bioelectric impedance methods specifically passes through the interstitial fluid compartment 23 (seeimage below). The interstitial fluid compartment represents approximately 16% of the body’s total water.24-26 Interstitial fluid is extra cellular water and solutes surrounding cells, but outside of the bloodstream and lymphatic system. Interstitial fluid forms the microscopic interface between cells and capillaries. Interstitial fluid differs from whole blood by the absence of red blood cells, and it differs from blood plasma in that there are far fewer proteins. Any substance passing between cells and the bloodstream must traverse the interstitial space. These substances include oxygen, carbon dioxide, glucose, as well as thousands of other compounds.27,28 The interstitial fluid’s role as a metabolic conduit and its proximity to the collective intracellular space of nearby cells suggests that the chemical composition of the interstitial fluid may reflect the physiology (or pathophysiology) of nearby cells.29-31 Since D.C. electric current primarily passes through the interstitial fluid, it has been proposed that an abnormality in the chemical composition of the interstitial fluid could be detected with an adequately sensitive D.C. BIM device.

General description of EIS system

The EIS system is non invasive device uses the bioelectrical impedance technique. 1.Trough the tactile electrodes, a current of 50KHz (R50), then a current of 1 KHz (Z1), and then a direct current (Z0) is sending alternatively and recording 22 parts of the human body. These measured parts represent the extracellular water resistance and the interstitial fluid resistance. 2. According to the formula of BIA (Body Index Analysis), the resistance can be converting in volume: •Total Body Water :TWB Formula of Hume and James •Extra cellular water volume : ECW = 0.229 (Ht2 /R1) + 4.5 (Deurenberg et al 1994) •Interstitial fluid volume: IFV 5-19 yr Davies et al 1988  0.60 (Ht2/R0) - 0.50 20-80 yr Lukaski and Bolonchuk 1988 0.372 (Ht2 /R0) + 3.05 (sex) + 0.142Wt - 0.069age 3. By application of mathematical formula (Venn diagram) and problem inverses issues of algorithms of the clinical tests Botkin 2003, the system allows a modeling of the human body which represents the body systems location according to the volume of the extracellular water and interstitial fluid 4. By extrapolation of the physiological knowledge of the interstitial fluid and the cells activity and ionic equilibrium, the volume of the interstitial fluid should be linked with estimation in percentage of some  physiological and biochemical ( Cottrell equation) tissue and microcirculation parameters.

Sequence and Volumes of measurement

During the initial test a AC 1 KHz is passed between the electrodes of the hands and foot according to a tetrapode measurement process

AC Measurements for Fat Mass and Total Body Water In sending a 1 KHz signal into the body The EIS Software then calculates the Extracellular water (ECW).   DC Measurements for Interstitial Fluid Analysis During the DC measurement process the examination is carried out between the 6 tactile electrodes placed on the forehead, hands and feet. Each electrode will alternate from a cathode to an anode to enable 22 volumes of the interstitial fluid of the human body to be measured. This measurement is conducted twice during the 2 minute test for 1 second and then for 3 seconds. The below diagram represents the 22 volumes being measured with the alternating anode and cathode.

The Process during the 1 second DC measurement: The intensity values are transmitted to The EIS Software via the USB port, in numerical form for each volume measured. The software converts these values into a conductivity value (application of the law of Ohm U=RI then C= 1/R) and displays this information on a graph format.     The graph of 22 volumes is called ElectroScanGram (ESG). This ESG graph was the subject of various clinical investigations and a statistical analysis in order to validate the examination as a marker or screening or follow up of certain pathologies and as a  modeling of the human body.             The process during the 3 second DC measurement: The intensity values are transmitted to The EIS Software via the USB port, in numerical form. The software converts these values into biochemical values by applying the Cottrell equation.