Bioimpedance Measurements

Bioimpedance Measurements Sverre Grimnes and 0rjan G. Martinsen.10-1... 

Cornish BH, Jacobs A, Thomas BJ, Ward LC. 1999. Optimising electrode sites for segmental bioimpedance measurements. Physiol Meas 20,241-250. 

This study examines the possibility of the use of spectroscopic bioimpedance measurements to assess BAC. 

Bioimpedance measurements were conducted with a BIS device (SFB7, ImpediMed, Pinkeba, Australia) covering a frequency range of 5 kHz to 1 MHz. This device has an impedance accuracy of 1% and a phase resolution of 0.1° using adhesive electrodes. To ensure rehable measurements, the body position was not altered and electrode sites were cleaned before attaching the electrodes. For this trial, the whole-body and hand-to-hand bioimpedance is analyzed. Extracellular resistance intracellular resistance (i ,) and capacitive effects CJ are calculated using the Cole model [6]. 

Additional trials with more participants (of both sexes, and of varying weight) are required. To avoid possible bias, a change in role with respect to water and/or alcohol consumption, and a repeat measurement for both groups, should be taken into account. In case of a contactless device, analysis focusing on the signal-to-nose ration (SNR) is necessary because it is known that, for example, inductive bioimpedance measurements can achieve only low SNRs (between 20 dB and 50 dB) [9]. 

G. Medrano, F. Eitner, M. Walter, et al, Model-Based Correction of the Influence of Body Position on Continous Segmental and Hand-to-Foot Bioimpedance Measurements, Medical Biological... 

Meat quality assessments are made with bioimpedance measurements and multivariate analysis. Fermentation can be monitored in brewery industries. Plant properties can be determined in the living or dead state (wood quality). 

A dielectric may be defined simply as a volume of material placed between the plates of a capacitor for examination by an applied electric field. Traditionally, there is an important difference between dielectric and bioimpedance measurements with respect to the role of water. Etymologically, a dielectric is a material that the electric field penetrates (Greek dia meaning through). Conductors do not allow static electric field penetration, and basically a perfect dielectric is a substance without free charges. Synonyms for a perfect dielectric may then be an insulator or a nonconductor antonyms may be a conductor or an electrolyte. 

The initial drop in resistance is due to the warming up of the cool tissue sample, and the subsequent drop in 10-MHz resistance is probably caused by accumulation of metabolic products in the tissue (as mentioned previously). The 100-Hz resistance rises steeply after a period of approximately 3 h, indicating the onset of tissue damage. This damage is nonreversible when the upper plateau is reached and the organ cannot be revived. In addition, Salazar (2004) found that bioimpedance measurements enabled differentiation among... 

Aliau-Bonet and Pallas-Areny (2012, 2013) have studied the effect of body capacitance to ground in four-electrode bioimpedance measurements and found that stray capacitance between the measured body and ground could lead to inductive artifacts and resonance behavior. 

For bioimpedance measurements a bipolar electrode may be used covered by an insulating layer of Teflon or glass. This is further analyzed by FEM (see Section 5.5). Another example of capacitive electrode coupling is diathermy, see the following section. 

However, manual bridges are slow and not suited for measurements on dynamic systems. Although automated bridges are commercially available, they have given way to other methods for bioimpedance measurements, such as lock-in amplifiers. 

This chapter gives an overview of relevant statistical methods for the analysis of bioimpedance measurements, with an aim to answer questions such as How do I begin with planning an experiment How many measurements do I need to take How do I deal with large amounts of frequency sweep data Which statistical test should I use How do I validate my results ... 

The topic of time-series is relevant for bioimpedance and especially bioelectricity analysis, but is not covered in this chapter on statistical methods. The methods covered are applicable for time-series after a suitable approach is employed for parameterization. All the examples in the text are given for bioimpedance measurements. 

These classification methods use different principles and rules for learning and prediction of class membership, but wiU usually produce a comparable result. Some comparisons of the methods have been given (i.e., Kotsiantis, 2007 Rani et al., 2006). Although the modem methods such as SVM have demonstrated very good performance, the drawback is that the model becomes an incomprehensible black-box that removes the explanatory information provided by, for example, a logistic regression model. However, classification performance usually outweighs the need for a comprehensible model. PCA has been used for classification based on bioimpedance measurements. Technically, PCA is not a method for classification but rather a method of data reduction, more suitable as a parameterization step before the classification analysis. 

Until now, we have been dealing with exploratory methods, in which file bioimpedance measurements have been used to explore differences between groups of measurement, effects of different factors, or associations between bioimpedance and other parameters. We have also been dealing with predictions of either continuous or discrete outcomes, but not the validation of these. If we have come one step further and developed a potentially... 

Studies on humans have shown that reproducibility and sensitivity of the bioimpedance measurement—including REG—were comparable to the sensitivities of the pulse oximeter, laser Doppler, and Doppler ultrasound. Results demonstrated that bio-impedance offers potential for use as a multifunctional, continuous, noninvasive life sign monitor for both military and civilian purposes (Bodo et al., 2006). 

ICG is impedance plethysmography based upon the measurement of thoracic electrical bioimpedance. It may also include a component from the resistivity dependence on blood flow (Sigman effect). If so this is not a plethysmographic but a blood velocity component. Usually a measuring frequency of 50—100 kHz has been used. A thoracic electrical bioimpedance measurement picks up both cardiac and respiration signals. The ambition is that the SV [L] and therefore CO [L/min] can be calculated with ICG, as well as the total thoracic fluid volume, for example, according to Eq. 10.1 v = GpL. ... 

Aliau-Bonet, C., Rallas-Areny, R., 2012. On the effect of body capacitance to ground in tetrapolar bioimpedance measurements. IEEE Trans. Biomed. Eng. 59, 3405—3411. 

Cornish, B.H., Thomas, BJ., Ward, L.C., 1993. Improved prediction of extracellular and total body water using impedance loci generated by multiple frequency bioelectrical impedance analysis. Phys. Med. Biol. 38, 337. Cornish, B.H., Jacobs, A., Thomas, BJ., Ward, L.C., 1999. Optimising electrode sites for segmental bioimpedance measurements. Physiol. Meas. 20, 241—250. 

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