In biomedical engineering, bioimpedance is the response of a living organism to an externally applied electric current. It is a measure of the opposition to the flow of that electric current through the tissues, the opposite of electrical conductivity.[1] The measurement of the bioimpedance (or bioelectrical impedance) of the humans and animals has proved useful as a non-invasive method for measuring such things as blood flow (often referred to as bioimpedance plethysmography) and body composition like TBW and fat content(known as bioelectrical impedance analysis or simply BIA).Can precisely define changes in body composition during weight loss.

In bioimpedance plethysmography, the measure is sometimes based on pulsatile blood volume changes in the aorta. Bioimpedance is relevant to the development of devices to measure cardiac output and circulating blood volume. Electrical conductivity can vary as a result of breathing. Because of this and other sources of variability, the reliability of bioimpedance for obtaining accurate data has been called into question. Nevertheless, the technique is used in both routine clinical medicine and research.

BIA has found a much sounder footing and is the basis of a number of commercially available body composition analysers. See Bioelectrical impedance analysis for more details.

BIA has been widely researched all over the world. Research results have been published on many specialized journals and conferences. See the I Latin American Conference on Bioimpedance for more details.

There is a good explanation about bioimpedance in chapter 73 of Bronzino's Biomedical Engineering Handbook: http://upload.sm-7.net/Detali%20mashin/bmt/The%20Biomedical%20Engineering%20Handbook%20-%202Ed%20-%20Bronzino/ch073.pdf

Bioimpedance is about the electrical properties of your body (or other biomaterials), e.g. to what extent you are a good conductor. Bioimpedance is a measure of how well the body impedes electric current flow. Fat has high resistivity, blood lower resistivity.

Impedance is measured by applying a small electric current e.g. via 2 electrodes and picking up the resulting small voltage with another pair of electrodes: The lower the voltage the lower the tissue impedance for a given current.

Tissue consists of cells and membranes, and membranes are thin but have a high resistivity and do electrically behave as small capacitors. By using high measuring frequencies the current passes right through these capacitors, and the result is dependent on tissue and liquids both inside and outside the cells. At low frequencies, however, the membranes impede current flow, and the results are dependent only on liquids outside the cells.

In an ideal model like Fig. 7.43 the impedance Z is given by:

Z = ρ L / A

where ρ is the resistivity of the tissue, L is the distance between the pick-up electrodes, and A is the cross-sectional area (the equation is actually only correct if the tissue is homogeneous and the current is applied by band electrodes far away from the pick-up electrodes. For the real setup with 4 band electrodes the mathematics are more complicated.)? It is clear that by measuring impedance, either r or L or A may be found if the two other quantities are known. Bioimpedance can therefore be used to measure volumes, shapes or tissue electrical properties. Geddes and Baker (Principles of Applied Biomedical Instrumentation, 1989) wrote about bioimpedance:

"The elegantly simple technique requires only the application of two or more electrodes, and it has been used successfully for many years to detect a remarkable variety of physiological events."

Bioimpedance applications include e.g.:

Skin water content

Impedance imaging (tomography)

Body composition (training, nutrition)

Impedance Cardiography (ICG)

Cardiac Output monitoring

Ablation monitoring

Blood volume

Meat quality assessment

Tissue ischemi monitoring

CO2 catheter transducer

Single cell motion microscope

Single cell counting and characterisation

Fingerprint sensors

A complete introduction to the field of bioimpedance can be found in Grimnes & Marinsen (2008): Bioimpedance and Bioelectricity Basics, 2. ed., Academic Press.

Please remember that impedance is a more general concept than resistance (i.e. it is a function of frequency) . As we have cells with membranes the Bioimpedance of living tissue tends to be capacitive.

@Peter Husar

But that webpage is in German! :-))

Dear Peter

If you really want it to be useful, please post the full link to the lecture as most of us are not good with German and are unable to navigate the website of your institution and find the lecture... All I found was a notice of cancellation of the lecture at http://www.tu-ilmenau.de/bmti/mitteilungsarchiv/einzelmitteilung/newsbeitrag/13243/

Mit freundlichen Grüßen

Fernando

Bioimpedance is about the electrical properties of your body (or other biomaterials), e.g. to what extent you are a good conductor. Bioimpedance is a measure of how well the body impedes electric current flow. Fat has high resistivity, blood lower resistivity.