Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Mechanical filter wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Chirp spectrum wikipedia , lookup
Utility frequency wikipedia , lookup
Alternating current wikipedia , lookup
Mathematics of radio engineering wikipedia , lookup
Impedance matching wikipedia , lookup
Superheterodyne receiver wikipedia , lookup
Nominal impedance wikipedia , lookup
International Conference on Chemistry, Biomedical and Environment Engineering (ICCBEE'14) Oct 7-8, 2014 Antalya (Turkey) Implementation of Bioelectric Impedance Measurement System using Multi-Frequency Applying Method and Two-Electrode Method S. W. Baik, Y. J. Kim, J. H. Kim, W. Y. Jang, S. S. Kim, G. C. Park, J. M. Son, and G. R. Jeon configuration of impedance measuring circuit is complicated in four-electrode method. BIA is divided into single-frequency analysis and multi-frequency analysis depending on the frequency to be applied [5]. Single-frequency analysis is the method of measuring the BI while applying single-frequency to the living tissues and the biological material. Multi-frequency analysis is the method of measuring the impedance at each frequency by applying the chirp waveform in combination with multiple frequencies from low-frequency (LF) to high-frequency (HF). In addition, the method of measuring BI at each frequency has been also applied by selectively applying frequency in range of LF, middle-frequency and HF. Single-frequency analysis method has the advantage that the impedance can be measured in a short period of time when characteristics of the living tissue and biological samples are analyzed in a particular frequency bandwidth, but has the disadvantage that BI cannot be analyzed in various frequency bandwidth [6]. On the other hand, multi-frequency analysis method has the merit that characteristics of the living tissue and biological samples can be analyzed in various frequency bandwidth but the demerit that the measurement time is long in comparison with the single-frequency method and the measurement circuit is complicated [7]. Studies on the BIA have been carried out by many researchers to analyze the composition of the living tissue and the biological material [8-14]. Deurenberg et al [8] investigated the applicability of the BI method for determining changes in the body composition. The resistance of the human body to the conduction of an alternating electrical current is related to the volume of fluid within the body [9]. Bioelectrical impedance analysis (BIA) is based on this principle and is currently utilized to determine the extracellular water (ECW) and total body water (TBW) content in normal humans [10]. Scheltinga et al [11] measured electrical resistance across the whole body and its various segments before and after the intravenous administration of of saline. They also determined the effect of blood donation on body resistance. They reported that bioelectrical impedance analysis is a sensitive method which detected minimal alterations in body fluid volume. Miyatani et al [12, 13] investigated the validity of BI and ultrasonographic methods for predicting the muscle volume of upper arm. BI and series cross-sectional images of the forearm, upper arm, lower leg, and thigh on the right side were determined in 22 healthy young adult men using a specially designed BI acquisition system and magnetic Abstract— In order to measure the segmental impedance of the body, bioelectrical impedance measurement system (BIMS) was implemented in this study using multi-frequency applying method and two-electrode method. It was composed of constant current source unit, automatic gain control unit, and multi-frequency generation unit. Three experiments were executed using implemented BIMS and commercial impedance analyzer First, bioelectrical impedance (BI) was measured by applying multi-frequencies - 5, 10, 50, 100, 150, 200, 300, 400, and 500 KHz – to each circuit after composing 4 RC circuits connecting resistance and capacitor in serial and parallel in order to evaluate the performance of BIMS. BI values as a function of frequency for 4 RC circuits were compared to those obtained by using CIA. Second, after measuring BI at each frequency by applying multi-frequency to the left or right region of forearm and popliteal of the body, BI values were compared to those acquired by CIA. Third, when the distance between two electrodes was changed to 1, 3, 5, 7, 9, 11, 13, and 15 cm, BI measured at each frequency from 10 to 500 KHz was also compared to that from CIA. Keywords—Bioelectrical Impedance, Impedance analyzer, Multi-frequency impedance meter, extracellular fluid, intracellular fluid. I. INTRODUCTION Bioelectrical impedance analysis (BIA) is a non-invasive method of measuring a component of the biological tissues and biological samples with ease [1-4]. A method of measuring bioelectrical impedance (BI) is divided into two-electrode method, three-electrode method, and four-electrode method, depending on the number of electrodes attached to the human body. Four-electrode method has been widely used in order to overcome the interference problems that occur at the interface between the electrode and the skin. However, two-electrode method is widely used to measure the impedance since the Prof. Dr. S. W. Baik, Anesthesiology and Pain Medicine, Pusan National Univ. Yangsan, South Korea, email id: [email protected] Prof. Dr. Y. J. Kim, Anesthesiology and Pain Medicine, College of medicine, Inje Univ., South Korea, email id: [email protected] Prof. H. J. Kim, Computer simulation, Inje Univ., South Korea, email id: [email protected] Mr. W. Y. Jang, Mr. S. S. Kim, Mr. G. C. Park, Mr. J. M. Son, are with Biomedical Engineering, school of Medicine, Pusan National Univ. Yangsan South Korea, email id: [email protected], [email protected], [email protected], [email protected] Prof. G. R. Jeon, Biomedical Engineering, school of Medicine, Pusan National Univ. Yangsan, South Korea., email id: [email protected] http://dx.doi.org/10.17758/IAAST.A1014007 10 International Conference on Chemistry, Biomedical and Environment Engineering (ICCBEE'14) Oct 7-8, 2014 Antalya (Turkey) B. Impedance Measurement System As shown in Fig. 2, BIMS implemented in this study is composed of main control unit (MCU, ATmega128, Newtc Co., Korea), multi-frequency generation (MFG) unit, automatic gain control (AGC) unit, constant current source (CCS), electrode, preprocessing part, and PC. Fig 2 shows the configuration for measuring BI. The function of these units in Fig. 2 is as follows. MCU outputs the control command with respect to the frequency generated by MFG and controls the overall function of the implemented BIMS. Frequencies of 10, 50, 100, 150, 200, 300, 400, and 500 KHz are generated in MFG unit. The output voltage of frequency generated by MFG is automatically controlled in AGC unit. AC constant current of is generated in CCS part, where the current is to be output to the electrode. The body segmental BI is measured while the current applied from two electrodes attached to the body tissue is following into BI measuring region. The body segmental BI is transferred to PC after preprocessing. resonance imaging (MRI) method, respectively. Jeon et al [14] reported implementation of the blood pressure and blood flow variation rate detection system using impedance method. On the other hand, Thomasset et al [2] estimated the total body water in a living body. Chumlea et al [15] performed the study for analyzing the distribution of intracellular fluid (ICF) and extracellular fluid (ECF) within tissues in the human body. Studies were performed to analyze the distribution of ICF and ECF in the body tissues by Kanai et al [16]. Lorenzo et al [17] announced that while LF current was being applied to the human tissue, BI was increased since the LF current flew outside the cell, not passing through the cell membrane. While HF current was being applied to the human tissue, BI decreased since HF current flew in the inner cell. That is, ECF was determined from BI measured by applying LF current, the total body water was measured by applying HF current, and ICF was estimated from subtracting HF impedance value from LF impedance value [18, 19]. II. RESEARCH METHOD A. An Equivalent Circuit of Human Body Impedance Cell constituting the human organ consists of ICF and ECF that behave as electrical conductors, and cell membranes that act as electrical condensers and are regarded as imperfect reactive elements [20]. BI of the human tissue is measured differently depending on the frequency of the current to be applied. Current flows outside the cell membrane when LF current is applied to human tissue, whereas current flows into the cell through the cell membrane as well as outside the cell when HF current is applied to human tissue. That is, when the current with LF less than 10 KHz is applied to the cells, current only flows in the interstitial fluid i.e., ECF, but when the current with HF above 100 KHz is applied to the cells, the current flows in both ECF and ICF. This phenomenon is due to the fact that ECF performs as an electrical conductor in the LF bandwidth, ICF performs as an electrical conductor in the HF bandwidth, and the cell membrane acts a kind of capacitor filled with condenser dielectric substance [21]. Therefore, the equivalent circuit in Fig. 1 was proposed to analyze BI of the human tissue. The circuit in the top-right corner in Fig. 1 represents BI of interface between the electrodes and the gel. Ehc means a half cell potential, Cd and Rd mean capacitor and resistor, respectively. Rs means the impedance of skin. The central figure on the right illustrates capacitor and resister representing the BI components in the sweet and the duct of epidermis. Ru in the lower right represents the resistance in the skin and subcutaneous layer. Fig. 2. The configuration of the impedance measurement system C. Multi-Frequency Generation Unit A sine waves having multi-frequency should be applied to human tissue to measure the human segmental BI. It is possible to measure ICF, total body water, and ECF when multi-frequency is applied to the human body. Accordingly, eight kinds of multi-frequencies i.e., 10, 50, 100, 150, 200, 300, 400, and 500 KHz were generated using the frequency generating device (XR-2206, EXAR Co., USA). The process of generating multi frequencies in frequency generating device is as follows. Control command is output from MCU to digital to analogue converter (DAC, DAC0800, Texas Int. Co., USA). Control command has different digitalized values according to multi-frequency. These digitalized values are converted to analogue values in DAC. These analogue values are output to frequency generating device (FGD). Input analogue values are transferred to VCO included in FGD. Eight kinds of frequencies are generated according to input voltage values in VCO. Eight kinds of multi-frequencies generated from FGD were sequentially applied to the measurement sites of the human body. Fig. 3 shows the designed circuit of MFG unit. Fig. 1. The Equivalent circuit of electrode and the skin proposed for measuring BI. Fig. 3. A circuit designed for multi-frequency generation unit. http://dx.doi.org/10.17758/IAAST.A1014007 11 International Conference on Chemistry, Biomedical and Environment Engineering (ICCBEE'14) Oct 7-8, 2014 Antalya (Turkey) D.Automatic Gain Control Unit The output signal of MFG is automatically controlled in the automatic gain control (AGC) unit, which adjusts the amplification rate of the output signal of MFG. When AGC circuit is not used, experimental errors occur in measured impedance since the output voltage fluctuates. The designed circuit of AGC is shown in Fig. 4. It was designed to maintain a constant output voltage according to the selected multi-frequency. Since the output in Fig. 4 is current, it is converted to voltage by voltage follower circuit. form of graphs and tables, and then stored in PC using USB communication protocol. (a) (b) Fig. 6. PC program and monitoring screen implemented for BI measurement: (a) PC program using LabVIEW and (b) monitoring screen. III. RESULTS Multi frequency BIMS was implemented for measuring BI of the body segments in this study. Two-electrode method was applied to the embodied BIMS. Ag/AgCl electrode (Monitoring electrode, 3M Co., USA) commercialized for ECG measurement was used for electrode. Eight different frequencies generated from MFG unit were sequentially applied to the electrode attached to body surface through AGC and CCG. At this time, a current of 500uA was set to be supplied to the body surface at each frequency. In order to evaluate the performance of multi frequency BIMS, experiments were carried out 10 times using BIMS and CIA after configuring four kinds of circuits connected in series and (or) in parallel with resistor and capacitor as shown in Fig. 7. In particular, Fig 7(d) shows the equivalent circuit for biological tissues; Rout the resistance of ECF, Rin the resistance of ICF, and Cin the capacitance of cell membrane, which were reported by Cornish et al [22]. Fig. 4. A circuit designed for automatic gain control. E. Constant Current Source In order to measure the body composition such as ECF, the cell membrane, ICF, total body water, and body fat of the living tissue, AC constant current with a frequency from LF to HF should be applied to the body. In this study, AC constant current of 500uA was applied to the human body to measure the segmental BI of human body. The circuit as shown in Fig. 5 was designed to generate AC constant current. Fig. 5. A circuit designed for constant current source. ( ) (1) (2) Fig. 7. RC circuits suggested for impedance measurement: (a) resistor R, (b) R and C connected in parallel, (c) R and R and C connected in parallel and then connected in series with R, (d) R and C connected in series and then connected in parallel with R From Millman’s theorem, the output voltage is obtained from amplifying the input voltage according to Eq. 1. When output voltage is applied to the load resistor , constant current flows according to Ohm’s law . Fig. 8 illustrates the comparison of experimental results at each frequency from 10 KHz to 500 KHz, using BIMS and CIA. Fig. 8(a) shows the impedance which was observed to be constant regardless of the frequency for the circuit in Fig. 7(a). Error rate between the impedance values measured by BIMS and CIA was 0.04%. Fig. 8(b) indicates the impedance as a function of frequency for the circuit in Fig. 7(b), which decreased gradually with increasing frequency. BI values measured by BIMS were in good agreement with those obtained by CIA. Error rates of BI measured using BIMS and CIA were as follows: 1.39% for 10 KHz, 0.72% for 50 KHz, F. PC Program for Measuring Bioelectric Impedance PC program was developed using LabVIEW (LabVIEW 2010, National Instruments Co., USA) to control the BIMS and analyze the measured BI data. PC program was configured to set parameters such as starting frequency, frequency increment value, the number of increase, and the output voltage. The measured BI was displayed on the monitor in the http://dx.doi.org/10.17758/IAAST.A1014007 12 International Conference on Chemistry, Biomedical and Environment Engineering (ICCBEE'14) Oct 7-8, 2014 Antalya (Turkey) to be higher than that at the left. In addition, BI exhibited the different aspect from BI obtained from Fig. 8(d). In reality, the cell membrane is an imperfect capacitor because of ionic movement through the cell membrane, and the time constant is not the same. A comparison of BI measured at the left and right side of forearms and popliteal regions by BIMS and CIA indicated that the error rates at eight frequencies were as follows. As shown in Fig. 9(a), the error rates occurred in BI measurement at the left forearm: 0.59% for 10 KHz, 1.59% for 50 KHz, 4.12% for 100 KHz, 3.68% for 150 KHz, 4.7% for 200 KHz, 4.04% for 300 KHz, 4.52% for 400 KHz, and 1.72% for 500 KHz. The error rates occurred in BI measurement at the right forearm: 0.54% for 10 KHz, 2.1% for 50 KHz, 2.47% for 100 KHz, 3.43% for 150 KHz, 4.32% for 200 KHz, 3.85% for 300 KHz, 4.63% for 400 KHz, and 2.56% for 500 KHz. As shown in Fig. 9(b), the error rates occurred in BI measurement at the left popliteal region: 0.63% for 10 KHz, 1.63% for 50 KHz, 3.1% for 100 KHz, 3.09% for 150 KHz, 4.07% for 200 KHz, 3.19% for 300 KHz, 3.52% for 400 KHz, and 1.19 %for 500 KHz. The error rates occurred in BI measurement at the right popliteal region: 0.44% for 10 KHz, 1.9% for 50 KHz, 2.16% for 100 KHz, 2.81% for 150 KHz, 3.4% for 200 KHz, 3.13% for 300 KHz, 3.52% for 400 KHz, and 1.55% for 500 KHz. 2.78% for 100 KHz, 7.52% for 150 KHz, 2.88% for 200 KHz, 2.77% for 300 KHz, 4.55% for 400 KHz, and 0.87% for 500 KHz. Fig. 8(c) shows BI as a function of frequency for the circuit in Fig. 7(c). It was observed that BI decreased abruptly at LF between 10 KHz and 50 KHz, decreased gradually at frequency between 50 KHz and100 KHz, and decreased very slowly above 100 KHz. A comparison of BI measured by BIMS and CIA indicated that the error rates were as follows: 1.57% for 10 KHz, 2.71% for 50 KHz, 3.84% for 100 KHz, 2.65% for 150 KHz, 1.18% for 200 KHz, 1.09% for 300 KHz, 0.89% for 400 KHz, and 1.09% for 500 KHz. In addition, Fig. 8(d) shows BI as a function of frequency for the circuit shown in Fig. 7(d). BI values as a function of frequency decreased from 10 KHz up to 50 KHz and were very similar above 50 KHz. Error rates of BI measured by BIMS and CIA were as follows: 1.24% for 10 KHz, 0.77% for 50 KHz, 0.59% for 100 KHz, 0.23% for 150 KHz, 0.32% for 200 KHz, 1.38% for 300 KHz, 1.54% for 400 KHz, and 1.94% for 500 KHz. Fig. 8 The comparison of BI measured by using BIMS and CIA for four kinds of RC circuits suggested in Fig. 7 In order to evaluate the clinical significance of BIMS, BI was measured at the left and right side of forearms and popliteal regions using BIMS, after the selection of the experimental subjects. The experimental subjects were ten male adults with a mean age of 27.5 (±2.5 years), average height of 173 cm (±3.2 cm), and average mass of 75 kg (±4.1 kg). Each experiment was conducted five times for 10 subjects using BIMS. Each measurement was conducted once again after taking 10-minute break. Fig. 9(a) shows the comparison of BI at the left and right side of forearms measured by using BIMS and CIA. Fig. 9(b) shows the comparison of BI of the left and right region of popliteal measured by using BIMS and CIA. Comparative analysis of the results measured by using BIMS and CIA indicated that BI exhibited a similar pattern. BI measured at forearms and popliteal regions was observed to be high at 10 KHz. The decreasing phenomenon of BI could be observed when HF was applied to the human body. BI was observed to be lowered since HF alternating current flew in ECF and ICF. BI values are slightly different in the forearm and popliteal regions, due to the amount of muscle of forearm and popliteal region, capacitance and resistance of the cell, the permeability of the cell membrane, the composition within the cell, size and shape of the cell, differences in tissue distribution. Fig. 9 shows that BI measured by BIMS was slightly lower than that by CIA. BI values measured at forearm were lower compared with those at popliteal region, and BI at the right was observer http://dx.doi.org/10.17758/IAAST.A1014007 (a) (b) Fig. 9. The comparison of BI using BIMS and CIA after applying eight kinds of frequencies to the left and right region of forearm and popliteal: (a) BI measured at left and right regions of forearms and (b) BI measured at left and right regions of popliteal. Figure 10 shows BI at the right forearm when the distance between the electrodes was changed to 1, 3, 5, 7, 9, 11, 13, and 15 cm. BI was measured to be about the same value, at 1 , regardless of the distance between the two electrodes. However, BI values showed a significant difference according to the distance between the two electrodes from 50 to 500 KHz. In addition, BI decreased in accordance with increasing frequency and decreasing distance between the electrodes. This corresponds well with the fact that the resistance is proportional to the resistivity and the length and inversely proportional to the cross section of the material as shown in the following equation of resistance, . These results are in good agreement with those reported by Scheltinga et al [11]. They measured the resistance of the whole body and its segments with two electrodes which apply alternating current of at 50 kHz. Initial whole body resistance was following an 8-hour overnight period of bed rest. In contrast, resistance determined by 13 International Conference on Chemistry, Biomedical and Environment Engineering (ICCBEE'14) Oct 7-8, 2014 Antalya (Turkey) proximal electrodes was and accounted for less than half of the whole body values. The resistance obtained from a single arm or a single leg was not significantly different from that obtained across the body using proximal electrodes (arm: , leg: proximal: ). The comparison between BI values measured by BIMS and Scheltinga’s work revealed that BI was strongly dependent on the frequency and the distance between electrodes, but do not depend on the location within segment. BI values measured by BIMS with AC current of and electrode distance of 7cm at 50 KHz in this study are as follows: at left forearm, 751.2 Ω at right forearm, 775.4 Ω at left region of popliteal, and 796.3 Ω at right region of popliteal. These BI values are different from those reported by Scheltinga’s study: 221±10 Ω at arm, 240±7 Ω at leg. The differences of BI values are partly due to the difference of the applied current- 500μA and 800μA, and due to the cross section of measuring region. (a) (b) Fig. 10. BI of the extracellular fluid and the intracellular fluid according to the frequency and the distance between electrodes: (a) impedance measurement system (b) commercial impedance analyzer. Table 1 shows BI of ECF and ICF at the right forearm according to the distance between the electrodes. BI of ECF was measured at 10 KHz. BI of ICF was calculated by subtracting BI values measured at 500 KHz from those measured at 10 KHz. BI of ICF and ECF increased as the distance between electrodes increase. Both ICF and BCF decreased when frequency increased from 10 to 500 KHz, but increased as the distance between two electrodes increased from 1 to 15 cm. TABLE I BI VALUES OF MEASURED ECF AND ESTIMATED ICF AT RIGHT FOREARM ACCORDING TO THE DISTANCE BETWEEN THE TWO ELECTRODES Frequency Dis. (cm) 1 3 5 7 9 11 13 15 10 KHz ECF ICF (KΩ) (KΩ) 50 KHz ECF ICF (Ω) (Ω) 100 KHz ECF ICF (Ω) (Ω) 150 KHz ECF ICF (Ω) (Ω) 200 KHz ECF ICF (Ω) (Ω) 300 KHz ECF ICF (Ω) (Ω) 400 KHz ECF ICF (Ω) (Ω) 1.51 1.52 1.53 1.54 1.55 1.55 1.56 1.56 586 676 683 730 738 786 818 858 443 536 553 580 588 610 623 648 393 483 505 525 540 568 588 608 366 440 468 488 513 536 556 573 341 405 430 453 470 486 515 525 316 371 396 413 436 456 476 480 0 0 0 0 0 0 0 0 286 321 323 323 338 348 368 392 143 161 163 165 168 170 173 182 93 115 117 118 120 128 138 142 IV. CONCLUSION In order to detect the trigger point for patients with chronic pain and MPS, BIMS of body segments was implemented. Multi-frequency method of sequentially applying selected eight frequencies from 10 KHz to 500 KHz was applied in BIMS with two-electrode method. The experimental results for evaluating the performance and verifying the efficiency of BIMS are as follows. 1. BI was measured for the circuit of four kinds of circuits consisting of passive elements, R and C. BI by BIMS was observed to be similar compared with that by CIA. 2. BI was measured at each frequency after attaching the electrode with the separation of 7 cm to the left or the right of forearm and popliteal regions of the human body. Experimental results measured by BIMS were compared with those acquired by CIA. Generally, BI values were observed to be higher in LF and lower in HF. BI measured using BIMS and CIA exhibited that the error rates were 1.2 % at LF and 1.74% at HF, respectively. 3. BI was measured at each frequency according to the distance between the two electrodes when the distance between the electrodes was changed from 1 to 15 cm. Experimental results measured by BIMS were compared with those acquired using CIA. The average errors of BI http://dx.doi.org/10.17758/IAAST.A1014007 14 66 85 88 90 93 96 106 107 41 45 48 50 52 57 65 59 16 16 16 16 16 16 17 14 500 KHz ECF ICF (Ω) (Ω) 0 0 0 0 0 0 0 0 300 355 380 407 420 440 450 466 measured using BIMS and CIA were 0.775% at LF (10 KHz) and 2.725% at HF (500 KHz), respectively. 4. BI of measured ECF and estimated ICF at the right forearm was acquired at each frequency according to the distance between two electrodes. BI of ICF and ECF increased as the distance between two electrodes increased from 1 to 15 cm, but decreased as frequency increased from 10 to 500 KHz. From experimental results, BIMS implemented in this study revealed to ensure the significance of clinical application. BIMS is expected to be applied to the detection of a trigger point of patients with chronic pain and MPS. ACKNOWLEDGMENT This work was financially supported from the basic research project (NO. 2013R1A2A2A04015325) by the National Research Foundation of Korea via the funds of Ministry of Education, Korea in 2013. REFERENCES [1] Horton JW, Van Ravenswaay AC. Electrical impedance of the human body, J Franklin Inst,, vol 20, 1935; pp. 557-572. http://dx.doi.org/10.1016/S0016-0032(35)90038-2 International Conference on Chemistry, Biomedical and Environment Engineering (ICCBEE'14) Oct 7-8, 2014 Antalya (Turkey) [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] Thomasset A, Bio-electrical properties of tissue impedance measurements, Lyon Med., vol. 207, 1962; pp. 107-118. Lingwood BE, Colditz PB, Ward LC, Biomedical applications of electrical impedance analysis, Proc. of ISSAP., vol. 1, 1999, pp. 367-370. http://dx.doi.org/10.1109/ISSPA.1999.818188 Lukaski HC, Methods for the assessment of human body composition: traditional and new, Am J Clin Nutr., vol. 46, 1987; pp. 537-556. Deurenberg P, Tagliabue A, Schouten FJ, Multi-frequency impedance for the prediction of extracellular water and total body water, Br J Nutr., vol. 73, no.3, 1995, pp. 349-358.. http://dx.doi.org/10.1079/BJN19950038 Lusseveld EM, Peters ET, Deurenberg P, Multi-frequency bioelectrical impedance as a measure of differences in body water distribution, Ann Nutr Metab., vol. 37, no. 1, 1993, pp. 44-51 http://dx.doi.org/10.1159/000177748 McNeill G, Fowler PA, Maughan RJ, McGaw BA, Fuller MF, Gvozdanovic D, Body fat in lean and overweight women estimated by six methods. Br J Nutr., vol. 65, no. 2, 1991, pp. 95-103. http://dx.doi.org/10.1079/BJN19910072 Deurenberg P, Weststrate JA, Hautvast J.GAJ, Changes in fat-free mass during weight loss measured by bioelectrical impedance and densitometry, Am J Clin Nutr., vol. 49, 1989, pp. 33-36 Hoffer, E.C., Meador, C.K., Simpson, D.C., Correlation of whole-body impedance with total water volume, J. Appl. Physiol., vol. 27, 1969; pp. 531-534. .Kushner, R.F., Schoeller, D.A., Estimation of total body water by bioelectrical impedance analysis, Am. J. Clin. Nutr., vol. 44, 1986, pp. 417-424. Scheltinga MR, M.D., Jacobs DO, Kimbrough TD, Wilmore DW, Alternations in body fluid content can be detected by bioelectrical impedance analysis, Journal of surgical research, vol. 50, 1991, pp. 461-468. http://dx.doi.org/10.1016/0022-4804(91)90025-H Miyatani M, Kanehisa H, Fukunaga T, Validity of bioelectrical impedance and ultrasonography methods for estimating the muscle volume of the upper arm, Eur J Appl Physiol., vol. 82 2000, pp. 391-396. http://dx.doi.org/10.1007/s004210000213 Miyatani M, Kanehisa H, Masuo Y, Ito M, Fukunaga T, Validity of estimating limb muscle volume by bioelectrical impedance. J Appl Physiol., vol. 91, 2001, pp. 386-394. Ro JH, Bae JW, Ye SY, Shin BJ, Jeon GR, Implementation of the Blood Pressure and Blood Flow Variation Rate Detection System using Impedance Method, Korea Academia-Industrial Cooperation Society, vol. 10, no. 8, 2009, pp. 1926-1938. http://dx.doi.org/10.5762/KAIS.2009.10.8.1926 Chumea, WC, Guo, SS, Bioelectrical impedance and body composition: present status and future directions, Human Biology, vol. 59, 1999; pp. 221-234. Kanai H, Haeno M, Sakamoto K, Electrical measurement of fluid distribution in legs and arms, Medical progress through technology, vol. 12, 1987, pp. 159-170. http://dx.doi.org/10.1007/978-94-009-3361-3_14 De Lorenzo A., SassoGf., Andreoli A., Sorge R., Candeloro N, Cairella M, Improved prediction formula for total body water assessment in obese women, International J. of obesity and related metabolic disorders; 1995, pp. 535-538. Rush S, Abildskov JA, McFee R, Resistivity of body tissues at low frequencies, Circ Res., vol. 12, 1963; pp. 40-50. http://dx.doi.org/10.1161/01.RES.12.1.40 Ackmann JJ, Seitz MA, Methods of complex impedance measurements in biologic tissue, Crit Rev Biomed Eng., vol. 11, 1984; pp. 281-311. Lukaki HC, Johnson PE, Bolonchuk WW, Lykken GI, Assessment of fat-free mass using bioelectrical impedance measurements of the human body, The American Journal of Clinical Nutrition, vol. 41, 1985, pp. 810-817. Cole KS, Cole RH, Dispersion and absorption in dielectrics: I. alternating current characteristics, Journal of chemical physics, vol. 9, 1936; pp. 341-351. http://dx.doi.org/10.1063/1.1750906 Cornish BH, Thomas BJ, Ward LC, Improved prediction of extracellular http://dx.doi.org/10.17758/IAAST.A1014007 and total body water using impedance loci generated by multiple frequency bioelectrical impedance analysis, Phys. Med. Biol., vol. 38, 1993, pp. 337-346. http://dx.doi.org/10.1088/0031-9155/38/3/001 15