Body impedance

There is therefore a threshold, a dose below which there will be no effects, either desirable or poisonous. This is a very important concept which is used in the assessment of risk from chemicals (see Chapter 12). For some chemicals, in particular those that cause cancer, there is uncertainty over whether there is a threshold. Consideration of the factors that restrict and impede entry of chemicals into the body, impede... 

Deurenberg, R, Kooy K., and Leenen, R. (1989a). Differences in body impedance when measured with different inslrument.s. Ejrr. /. Clin. Nutr. 43,885-886. 

Mattar, J.A. (1996) Application of Total Body Impedance to the Critically lU Patient, New Horiz. 4,493-503. 

The most validated method is prediction of TBW from four-electrode whole-body transfer impedance measurements at 50 kHz. It is not really a whole-body measurement because the results are dominated by the wrist and ankle segments with very little influence from the chest because of the large cross-sectional area. By using more than four electrodes, it is possible to measure more than one body segment. With two electrodes at each hand and foot, the body impedance can, for instance, be modeled in five segments arms, legs, and chest. 

TBW method). Although body impedance reflects tissue hydration, soft-tissue mass (lean and fat) can also be empirically derived by correlation in healthy subjects because the compartments of soft tissue are correlated with each other through physiological constants. However, physiological constants become flawed in patients with fluid disorders, which accounts for some of the conflicting results in the literature (Kyle et al., 2004). 

Nordbotten, B.J., Tronstad, C., Martinsen, 0.G., Grimnes, S., 2011. Evaluation of algorithms for calculating bioimpedance phase angle values from measured whole-body impedance modulus. Physiol. Meas. 32, 755-765. 

The phase voltage at the substation transformer will be a little higher than 230 V to allow for the inevitable voltage drop in the distribution cables. In urban areas, the line/neutral and the line/earth loop impedances will be comparable and will probably be only a small fraction of an ohm, whereas the victim s hand-to-hand impedance will be in the order of 2000 ohms. Under these circumstances the effects of the circuit impedances can be ignored. The victim s touch voltage will be about 230 V and, for a total body impedance of 2000 ohms, the shock current would be 230/2000 = 0.11 A. This is high enough to cause ventricular fibrillation in many people should the current flow for about 0.5 s. 

Low-Cost Body Impedance Analyzer for Healthcare Applications... 

Fig. 2 Schematic of the body impedance analyzer, where PA is the phase angle, Iout+ is the inject current and lout- is the return current.

Bioimpedance is a non-invasive, safe and relatively inexpensive technique to assess body composition of both healthy and illness patients. The body impedance analyzer developed in this work was conducted according to the requirements of healthcare applications, such as portability and low cost. These characteristics are considered very important for large-scale use, benefiting the National Health System (NHS) and homecare users. It can be concluded that the developed system can be used for body composition assessment over a wide aging range. 

Foster KR, Lukaski HC (1996) Whole-body impedance-what does it measure . Am J Clin Nutr 64(Suppl) 388S - 396S... 

The whole-body impedance was measured in a supine position on the right side of the body according to a conventional tetrapolar measurement scheme by the bioimpedance analyzer ABC-01 Medas (SRC Medas, Moscow, Russia) at a frequency of 50 kHz using disposable Ag/AgCl Schiller bioadhesive electrodes. 

Long term recording of body weight and possibly body composition would result in data for the substrate flow to or from body stores. The dietary food intake can be assessed by questionnaires or prediction formulas, provided by earlier measurements. So energy expenditure and substrate oxidation rates can be calculated from energy and substrates balances. All these approaches would not need calorimetry at all it could however be used to verify some of the results of these methods. Body composition can be assessed by various established methods like dual energy X-ray analysis (DEXA), skin fold measurements, underwater weighing and body impedance measurements. 

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