Body Impedance

TODO: body impedance

Body impedance

The aim of the work is to present results of our ongoing research focused on the influence of body hydration on the body impedance measurements and also on the influence of the frequency used for the measurement. The performed measurements showed certain influence which must be verified by repeated experiments.

The most popular and publicly well-known are the studies using the Body Mass Index (BMI) as a single parameter indicating the degree of obesity (or slimness). However it cannot tell anything about the body composition. It is known that density of bones and quality of muscles influences the weight to a certain degree. That means that two persons having the same height and waist size might have relatively high difference in weight due to the differences in body composition. Thus, a method allowing measurement of more informative quantities is necessary in order to evaluate the amount of body fat more objectively and precisely.

The Body Impedance Analysis (BIA) represents one of the methods for classification of body composition. Obesity does not refer to excessive body weight but it refers to the condition in which the individual has an excessive amount of body fat. Many laboratory and field assessment techniques exist for estimating a person's body composition.

Obesity is characterized by Body Mass Index (BMI) > 30kg/m² and by body fat increase. It is possible to use a number of methods including the measurement of body impedance for observing the body fat mass. Body impedance depends on body composition, i.e. on the amount of water in individual tissues. Some impedance values of a human body are shown on figure 1.

Fig 1: Values of body impedance of relevant parts of a body

For calculating body composition parameters such as FFM (fat free mass), TBW (total body water), etc. there are used equations that unfortunately contain several parameters that were acquired experimentally. Thus one of our goals is also to improve these equations and to fit them for Czech population.

Basic theoretical models are very simply based on a cylinder model shown in figure 2. This model uses only tissue properties, length and area. Therefore this model is not only used for body impedance modeling but it can be used in any modeling. In this case the equation is. But when we are using this model we must consider that human body is not composed of homogenous parts therefore different body parts have different properties.

Fig 2.: Cylindrical model of human body

To take this into account we must use some advanced models that consider also other parameters of a human tissue, such as conductive and inductive properties of human tissue.  Some better models are e.g. Cole or Extended Cole-Fricke-Cole (ECFC) model. These models are much better for estimating human body composition parameters. But also these models do not consider all aspects of a human body.

Fig 3.: -Fricke-Cole (ECFC) model , Re-extracellular rezistence,Ri-intracellular rezistence, C- membrane capacity, L-inductive part, R-rezistence

We are using InBody 720 and Tanita MC-180 MA devices. These devices must be able to measure on various frequencies because of inductive and capacitive characteristics. From this range of frequencies not all are usable for body composition evaluation because some studies show that frequencies below 5 kHz are not suitable for calculations.

InBody 720                                                                    Tanita MC 180 - MA

These devices are body composition analyzers so they are able to calculate TBW, FFM, fat mass and so on. So we can measure importance of hydration of human body. These devices are multifrequency devices so we can measure dependence of body impedance on frequencies. These outcomes are compared in graphs. Example of a graph is shown in figure 4.

Fig 4.: Results of measurements

In this part of our laboratory research we are trying to measure and evaluate body composition. For this purposes there are used body impedance values. Also we are trying to cooperate with several medical institutions and medical experts. We all are well aware of the fact that obesity and problems connected with body composition are major problems of present time and for sure they will be in focus of attention of future medical research.