Segmental Impedance Research Articles

Identification of final fall in subglottal pressure contours of speech utterances

Subglottal pressure (Ps) contours for speech are described as having three phases: initial rise, constant or declining working phase, and final fall. The current work is part of a project to relate characteristics of the Ps contour to prosodic events. To that end, one must identify the three phases in a Ps contour. In past work, it was found that the initial phase is relatively easy to identify, but the transition from the working phase to final fall is less clear [J. Slifka (2000)]. Confounding issues could include segmental impedance, pitch accents, and phrase and boundary tones, all of which can have local effects on Ps. In this work, it is attempted to control tones and segments at the ends of utterances in order to better identify final fall. Lung pressure is estimated from esophageal pressure (corrected for lung volume). Pilot data from one subject indicate that the beginning of final fall is easier to identify when the phrase and boundary tones are low than when they are high. Results will be presented for additional subjects and it will be attempted to relate them to the distribution of pitch accents. [NIH grant DC04331.]

A new approach for detection of leg movement using segmental electrical impedance changes

The purpose of this paper is to provide a new approach for detection using bio-impedance. This impedance is measured by the four-electrode method. As the impedance changes resulting from ankle, knee, and hip movements depend on electrode placement, we determined the optimal electrode configurations for these movements by searching for high correlation coefficients, large impedance changes, and minimum interference in ten subjects (age: 20 ± 4). Our optimal electrode configurations showed very strong relationships between the ankle joint angle and ankle impedance (γ = − 0.913 ± 0.03), between the knee joint angle and knee impedance (γ = 0.944 ± 0.02), and between the hip joint angle and hip impedance (γ = 0.823 ± 0.08). This study showed that lower leg movement could be easily measured by the impedance measurement system with two pairs of skin electrodes.

부위별 생체 전기 임피던스법을 이용한 아동의 제지방 산출을 위한 예측 방정식

The purpose of this study was to developed the prediction equation for the determination of fat-free mass in 8~13 years children using segmental bioelectrical impedance analysis. For the purpose of study, 84 childrens(boys : 48, girls : 36) were measured. The reference method was used underwater weighing. The result follows as : First, The value of FFM obtained underwater weight(Dens-FFM) showed the highest correlation with the Ht²/R_(RL), Ht²/R_(RA), Ht²/Rt measured by SBIA. Second, Segmental impedance index(Ht²/R_(RA),Ht²/R+(T),Ht²/R_(RL)) was the best predictor of fat free mass than whole body impedance index(Ht²/(R_(RA)+R_(T)+R_(RL)). Third, The correlation coefficient between Segmental impedance index and fat-free mass was showed very high, and when the weight variable was included the correlation coefficient was increased and RMSE was decreased significantly. Fourth, children`s estimated equation developed by using Segmental impedance index and weight followed as : Uw-FFM was set up as a dependent variable, the equation showed ; FFM(SBIA)=FFM : O.O1Ht²/R_(RA)+O.O11Ht²/R_(T)+0.125Ht²/R_(RL),+0.252weight+0.24

Improved assessment of body cell mass by segmental bioimpedance analysis in malnourished subjects and acromegaly

Background: Estimation of body cell mass (BCM) has been regarded valuable for the assessement of malnutrition. Aim: To investigate the value of segmental bioelectrical impedance analysis (BIA) for BCM estimation in malnourished subjects and acromegaly. Methods: Nineteen controls and 63 patients with either reduced (liver cirrhosis without and with ascites, Cushing's disease) or increased BCM (acromegaly) were included. Whole-body and segmental BIA (separately measuring arm, trunk, leg) at 50kHz was compared with BCM measured by total-body potassium. Multiple regression analysis was used to develop specific equations for BCM in each subgroup. Results: Compared to whole-body BIA equations, the inclusion of arm resistance improved the specific equation in cirrhotic patients without ascites and in Cushing's disease resulting in excellent prediction of BCM ( R 2=0.93 and 0.92, respectively; both P <0.001). In acromegaly, inclusion of resistance and reactance of the trunk best described BCM ( R 2=0.94, P<0.001). In controls and in cirrhotic patients with ascites, segmental impedance parameters did not improve BCM prediction (best values obtained by whole-body measurements: R 2=0.88 and 0.60; P<0.001 and <0.003, respectively). Conclusion: Segmental BIA improves the assessment of BCM in malnourished patients and acromegaly, but not in patients with severe fluid overload.

Segmental bioelectrical impedance analysis in children aged 8-12 y: 2. The assessment of regional body composition and muscle mass.

To investigate the potential of segmental bioelectrical impedance analysis (BIA) for assessing regional composition and muscle mass in children. Strengths of relationships were determined between (a) BIA indices of trunk, limbs or limb segments and (b) segment fat or fat-free mass (FFM) assessed using dual-energy X-ray absorptiometry (DXA); the extent of agreement was established between two independent models, based on DXA and BIA, of limb muscle and adipose tissue (AT) mass. Eighteen boys and 19 girls aged 8-12 y. BIA and anthropometry of trunk, whole limbs, limb segments and defined sections were used to calculate segmental impedance indices and specific resistivities; segment fat and FFM were obtained using DXA; muscle and AT masses of limbs, segments and sections were estimated using DXA and BIA models, and by anthropometry. Segmental BIA indices were significantly related to composition of the segments assessed using DXA; although substantial bias was observed, there was fairly good agreement (low 95% limits of agreement) between the BIA and DXA models of muscle mass and estimates from each were similarly categorised in tertiles, as were estimates of AT. Segmental BIA appears to have potential for assessing in children the composition of body segments, as obtained using DXA, and the masses of muscle and AT in whole limbs, limb segments and defined sections.

Reversibility of artifacts of fluid volume measurements by bioimpedance caused by position changes during dialysis.

The effect of temporary position changes, sitting up from supine, on extracellular (ECW) and intracellular (ICW) resistances and fluid volumes calculated from whole body bioimpedance using a Xitron 4200 impedancemeter was investigated on 8 patients during dialysis for a total of 11 tests. It was found that ECW resistance decreased instantaneously by an average of 2.3% when the patient sits up, due to plasma and interstitial fluid shift into the legs which decreases leg resistance, the major contributor to total resistance. This drop in resistance is incorrectly interpreted by the device as an increase in ECW volume which averages 235 ml. But this effect is completely reversible and both ECW resistance and fluid volume rapidly resume their normal course when the patient returns to his initial position. No significant variation in ICW resistance was observed in any of the patients at the position change. We conclude that segmental impedance, which has been proposed to minimize this artifact, is not advisable in dialysis monitoring and that it is simpler to ignore or switch off measurements during the position change so that later data are not affected by it.

Validity of total and segmental impedance measurements for prediction of body composition across ethnic population groups.

To test the impact of body build factors on the validity of impedance-based body composition predictions across (ethnic) population groups and to study the suitability of segmental impedance measurements. Cross-sectional observational study. Ministry of Health and School of Physical Education, Nanyang Technological University, Singapore. A total of 291 female and male Chinese, Malays and Indian Singaporeans, aged 18-69, body mass index (BMI) 16.0-40.2 kg/ m2. Anthropometric parameters were measured in addition to impedance (100 kHz) of the total body, arms and legs. Impedance indexes were calculated as height2/impedance. Arm length (span) and leg length (sitting height), wrist and knee width were measured from which body build indices were calculated. Total body water (TBW) was measured using deuterium oxide dilution. Extra cellular water (ECW) was measured using bromide dilution. Body fat percentage was determined using a chemical four-compartment model. The bias of TBW predicted from total body impedance index (bias: measured minus predicted TBW) was different among the three ethnic groups, TBW being significantly underestimated in Indians compared to Chinese and Malays. This bias was found to be dependent on body water distribution (ECW/TBW) and parameters of body build, mainly relative (to height) arm length. After correcting for differences in body water distribution and body build parameters the differences in bias across the ethnic groups disappeared. The impedance index using total body impedance was better correlated with TBW than the impedance index of arm or leg impedance, even after corrections for body build parameters. The study shows that ethnic-specific bias of impedance-based prediction formulas for body composition is due mainly to differences in body build among the ethnic groups. This means that the use of 'general' prediction equations across different (ethnic) population groups without prior testing of their validity should be avoided. Total body impedance has higher predictive value than segmental impedance.

Validation of skinfold thickness and hand-held impedance measurements for estimation of body fat percentage among Singaporean Chinese, Malay and Indian subjects.

Body fat percentage (BF%) was measured in 298 Singaporean Chinese, Malay and Indian men and women using a chemical four-compartment model consisting of fat, water, protein and mineral (BF%4C). In addition, weight, height, skinfold thickness and segmental impedance (from hand to hand) was measured. Body fat percentage was predicted using prediction equations from the literature (for skinfolds BF%SKFD) and using the manufacturer's software for the hand-held impedance analyser (BF%IMP). The subjects ranged in age from 18-70 years and in body mass index from 16.0 to 40.2 kg/m2. Body fat ranged from 6.5 to 53.3%. The biases for skinfold prediction (BF%4C-BF%SKFD, mean +/- SD) were -0.4+/-3.9, 2.3+/-4.1 and 3.1+/-4.2 in Chinese, Malay and Indian women, respectively, the Chinese being different from the Malays and Indians. The differences were significant from zero (P < 0.05) in the Malays and Indians. For the men, the biases were 0.5+/-3.8, 0.0+/-4.8 and 0.9+/-4.0 in Chinese, Malays and Indians, respectively. These biases were not significantly different from zero and not different among the ethnic groups. The biases for hand-held impedance BF% were -0.7+/-4.5, 1.5+/-4.4 and 0.4+/-3.8 in Chinese, Malay and Indian women. These biases were not significantly different from zero but the bias in the Chinese was significantly different from the biases in the Malays and Indians. In the Chinese, Malay and Indian men, the biases of BF%IMP were 0.7+/-4.6, 1.9+/-4.8 and 2.0+/-4.4, respectively. These biases in Malay and Indian men were significantly different from zero and significantly different from the bias in Chinese men. The biases were correlated with level of body fat and age, and also with relative arm span (arm span/height) for impedance. After correction, the differences in bias among the ethnic groups disappeared. The study shows that the biases in predicted BF% differ between ethnic groups, differences that can be explained by differences in body composition and differences in body build. This information is important and should be taken into account when comparing body composition across ethnic groups using predictive methods.

Prediction of lean body mass from multifrequency segmental impedance: influence of adiposity.

The aim of the study was to determine the influence of adiposity on the relationship between bioelectrical impedance (BIA) measurements of body segments and estimation of body composition by dual-energy X-ray absorptiometry (DXA). Multiple frequencies of whole body and segmental impedances were measured in 68 normal-weight and obese subjects (46 women and 22 men), mean age 37.2+/-14.8 years (range, 18-69). Total and appendicular lean body mass (LBM) assessed by DXA correlated significantly with total and segmental impedance values adjusted for stature in both obese and normal-weight subjects. Best fitting equations for the prediction of appendicular LBM from segmental impedance measurements were derived for the arm and leg with and without the inclusion of adiposity (the percentage of body fat measured by DXA) in the regression models. Best prediction was obtained at low frequency for the arm and high frequency for the leg. Adiposity appears to significantly influence the prediction of leg LBM by BIA. These preliminary observations need further validation to provide an accurate assessment of appendicular LBM assessment by BIA.

Use of single-frequency bioimpedance at 50 kHz to estimate total body water in patients with multiple organ failure and fluid overload.

To investigate the relationship between single-frequency bioimpedance at 50 kHz (both total body impedance and segmental impedance) and total body water, measured using tritiated water in the presence of the severe fluid retention seen in multiple organ failure. Prospective, controlled study. General intensive care unit. Twenty patients with multiple organ failure and 30 normal volunteers, of whom a subgroup of ten had total body water measured. None. Total body water and total and segmental bioimpedance values at 50 kHz were measured using tritiated water and a Holtain body composition analyzer in 20 patients with multiple organ failure and in ten normal volunteers. An additional 20 normal volunteers also had segmental and total body impedance measured. There was no difference in the linear regression lines constructed for the patients and the volunteers, but the SEM in the patients (7.6 L) was four times that seen in the normal subjects (1.9 L). In a further seven patients, the impedance technique overestimated the change in total body water, deduced from acute changes in weight, by between 0% and 46% (median, 12%). In the patients, who were supine, the knee-ankle segment contributed significantly more to total body impedance than it did in the normal volunteers (42.5% vs. 34.4%; p < .001), who were upright and mobile immediately before the measurement. Although single-frequency bioimpedance does give an indication of total body water and change in total body water, it is neither precise nor accurate enough to be the sole guide to fluid therapy. The proportion of total impedance contributed by the knee-ankle segment, which contains relatively little water, was significantly greater in the patients than in the controls, probably reflecting better drainage of fluid from the lower limb in the supine position.

Estimation of body composition from bioelectrical impedance of body segments

This study provides values of anthropometric measurements and specific impedance, for a sample of 104 adults. The hypothesis that the body composition can be estimated more accurately from measurements of lengths and impedance values of the body segments than from the whole body was tested. The impedance of upper and lower extremities (arm and leg) and trunk were used to compute estimates of body composition parameters (FFM, FM, %F, TBW, ECW). The results were compared with those estimated by the impedance of the whole body. These comparisons demonstrated that significative differences resulted from body composition obtained by segmental impedance and by the whole body.

Optimizing electrode sites for segmental bioimpedance measurements

Recent advances in the application of bioelectrical impedance analysis (BIA) have indicated that a more accurate approach to the estimation of total body water is to consider the impedance of the various body segments rather than simply that of the whole body. The segmental approach necessitates defining and locating the physical demarcation between both the trunk and leg and the trunk and arm. Despite the use of anatomical markers, these points of demarcation are difficult to locate with precision between subjects. There are also technical problems associated with the regional dispersion of the current distribution from one segment (cylinder) to another of different cross-sectional area. The concept of equipotentials in line with the proximal aspects of the upper (and lower) limbs along the contralateral limbs was investigated and, in particular, the utility of this concept in the measurement of segmental bioimpedance. The variation of measured segmental impedance using electrode sites along these equipotentials was less than 2.0% for all of the commonly used impedance parameters. This variation is approximately equal to that expected from biological variation over the measurement time. It is recommended that the electrode sites, for the measurement of segmental bioelectrical impedance in humans, described herein are adopted in accordance with the proposals of the NIH Technology Assessment Conference Statement.

Bedside determination of fluid accumulation after cardiac surgery using segmental bioelectrical impedance.

Bioelectrical impedance analysis (BIA) is based on the physical property of tissues to conduct electrical currents, impedance being inversely related to tissue fluid content. At high frequency, the electrical current flows across both intracellular and extracellular pathways, making the assessment of fat-free mass possible while a low-frequency current flows through the extracellular space. Similarly, segmental BIA may be used to assess segmental body fluid repartition. The aim of this study was to assess fluid accumulation after cardiac surgery by multiple frequency segmental BIA. Observational, clinical study. A 17-bed, surgical intensive care unit in a university hospital. Twenty-six patients before and after open-heart surgery with cardiopulmonary bypass. None. After surgery, fluid accumulation resulted in a decrease in whole-body and segmental bioelectrical impedance in the arm and in the trunk. There was a good correlation between the fluid accumulation measured by fluid balance and by whole-body or segmental impedance changes. The major part (71%) of fluid accumulation occurred in the trunk. Multiple frequency measurements did not indicate a fluid shift between the intra- and extracellular compartments. Cardiac surgery produced a significant decrease in segmental trunk BIA, reflecting fluid accumulation at the trunk level.

Letters to the Editor

The following is the abstract of the article discussed in the subsequent letter: Bracco, David, Daniel Thiébaud, René L. Chioléro, Michel Landry, Peter Burckhardt, and Yves Schutz.Segmental body composition assessed by bioelectrical impedance analysis and DEXA in humans. J. Appl. Physiol. 81(6): 2580–2587, 1996.—The present study assessed the relative contribution of each body segment to whole body fat-free mass (FFM) and impedance and explored the use of segmental bioelectrical impedance analysis to estimate segmental tissue composition. Multiple frequencies of whole body and segmental impedances were measured in 51 normal and overweight women. Segmental tissue composition was independently assessed by dual-energy X-ray absorptiometry. The sum of the segmental impedance values corresponded to the whole body value (100.5 ± 1.9% at 50 kHz). The arms and legs contributed to 47.6 and 43.0%, respectively, of whole body impedance at 50 kHz, whereas they represented only 10.6 and 34.8% of total FFM, as determined by dual-energy X-ray absorptiometry. The trunk averaged 10.0% of total impedance but represented 48.2% of FFM. For each segment, there was an excellent correlation between the specific impedance index (length2/impedance) and FFM ( r = 0.55, 0.62, and 0.64 for arm, trunk, and leg, respectively). The specific resistivity was in a similar range for the limbs (159 ± 23 cm for the arm and 193 ± 39 cm for the leg at 50 kHz) but was higher for the trunk (457 ± 71 cm). This study shows the potential interest of segmental body composition by bioelectrical impedance analysis and provides specific segmental body composition equations for use in normal and overweight women.

Shifts in blood volume alter the perception of posture

Recent experiments have shown that somatic graviceptors exist in humans. Traditionally, extravestibular gravity information has been thought to originate from mechanoreceptors in the joints, muscles and skin. Experiments with normal, paraplegic and nephrectomized subjects revealed that the kidneys and the cardiovascular system are involved in providing truncal gravity information. The present study intends to determine the influence of shifts in body fluid, especially of the distribution of blood along the subjects' spinal (Z-) axis, on the perception of posture. To this end, the distribution of body fluids was altered by means of the technique of lower body negative and positive pressure (LBNP and LBPP). LBNP leads to venous pooling of blood in the legs, whereas LBPP prevents venous blood from pooling, increasing central volume. Changes in blood distribution were measured by segmental impedance cardiography for four body segments: the upper torso (thoracic cavity), lower torso (abdominal and pelvic region), thigh and calf. Seventeen healthy subjects (mean age: 27.3 years) participated in the experiment. They were positioned on the side (right-ear-down head position) on a tilt table which the subjects and the experimenter could tilt via remote control around an axis parallel to the subjects' visual (X-) axis. The experimenter set the initial tilt in total darkness to arbitrary angles, while strictly alternating between head-up and head-down tilts. Subjects were then asked to rotate the board until they felt they were in a horizontal posture. Means and variances of eight pairs of settings were taken as a measure of the subjective horizontal posture (SHP). During LBNP (−30 mmHg), subjects perceived being tilted head-up, whereas LBPP (+30 mmHg) led them to feel tilted head-down. The results corroborate the hypothesis of an effect of the blood's mass on graviception and also indicate supplementary contributions of other visceral afferences. © 1997 Elsevier Science B.V.

The effect of arteriovenous fistulae in haemodialysis patients on whole body and segmental bioelectrical impedance.

Bioelectrical impedance (BIA) is a potentially useful method for measuring body water and soft-tissue composition in patients with chronic renal failure. The majority of whole body impedance is derived from the limbs with only a small contribution from the trunk, and thus abnormalities of the limbs could have an exaggerated effect on estimates of total body impedance. This study investigated the effect of arteriovenous fistulae in the arm in haemodialysis patients on body composition measurement by whole body BIA. Body composition estimates from measurements on fistula and non-fistula sides of the body were compared and segmental impedance measurements of the arms were also performed. Whole body resistance was markedly lower on the fistula side of the body compared with the nonfistula side at 517.1 (124.3) omega compared with 561.5 (121.2) omega, P < 0.0005. This difference was accounted for by differences in the arm segments. This was attributed to swelling of the fistula arm which had a greater mid-arm circumference at 28.5 (2.1) cm compared with the contralateral side at 27.5 (2.0) cm, P < 0.05. This resulted in greater estimates for total body water from the fistula side at 38.6 (10.0) kg compared with 36.6 (8.6) kg from the non-fistula side, P < 0.05 and fat-free mass at 51.1 (11.8) kg from the fistula side compared with 49.1 (11.2) kg from the non-fistula side, P < 0.005. Estimates of body fat from the fistula side, 13.1 (6.9) kg, were less than the nonfistula side, 15.0 (6.0), P < 0.005. The presence of arteriovenous fistulae for vascular access in haemodialysis patients may have a significant effect on estimates of body composition by BIA.

Segmental body composition assessed by bioelectrical impedance analysis and DEXA in humans.

The present study assessed the relative contribution of each body segment to whole body fat-free mass (FFM) and impedance and explored the use of segmental bioelectrical impedance analysis to estimate segmental tissue composition. Multiple frequencies of whole body and segmental impedances were measured in 51 normal and overweight women. Segmental tissue composition was independently assessed by dual-energy X-ray absorptiometry. The sum of the segmental impedance values corresponded to the whole body value (100.5 +/- 1.9% at 50 kHz). The arms and legs contributed to 47.6 and 43.0%, respectively, of whole body impedance at 50 kHz, whereas they represented only 10.6 and 34.8% of total FFM, as determined by dual-energy X-ray absorptiometry. The trunk averaged 10.0% of total impedance but represented 48.2% of FFM. For each segment, there was an excellent correlation between the specific impedance index (length2/impedance) and FFM (r = 0.55, 0.62, and 0.64 for arm, trunk, and leg, respectively). The specific resistivity was in a similar range for the limbs (159 +/- 23 cm for the arm and 193 +/- 39 cm for the leg at 50 kHz) but was higher for the trunk (457 +/- 71 cm). This study shows the potential interest of segmental body composition by bioelectrical impedance analysis and provides specific segmental body composition equations for use in normal and overweight women.

Segmental bioelectrical impedance in patients with chronic renal failure

We studied changes in hydration by whole body and segmental (arm, leg and trunk)bioelectrical impedance analysis (BIN in patients with chronic renal failure (CRF) undergoing haemodialysis and continuous ambulatory peritoneal dialysis (CAPD). Mean (SD) fluid removal by haemodialysis of 1.38 (0.81) kg was overestimated by whole body BIA at 1.83 (1.13) I, P < 0.005. Peritoneal fluid drained from the CAPD patients of 1.88 (0.36) kg was underestimated by whole body BIA at 0.59 (0.35) I, P < 0.0001. Resistance and reactance significantly increased for the whole body and all segments (except trunk reactance) after haemodialysis. Drainage of CAPD fluid resulted in smaller increases in trunk resistance and whole body resistance. The increase in trunk resistance was less in CAPD than haemodialysis patients, even though the volume of fluid drained from the peritoneum in CAPD patients exceeded that removed from the whole body during haemodialysis. We conclude that whole body BIA does not estimate changes in body fluid with sufficient accuracy to be of use in clinical practice. Segmental impedance may be a potentially useful method for investigation of regional changes in body fluid, though is insensitive to changes within the peritoneal cavity.

Mechanical and physiologic modifiers and bioelectrical impedance spectrum determinants of body composition

Fat-free mass and total and percentage body fat were determined by dual-energy X-ray absorptiometry (DXA) and total-body and segmental impedance measures were taken at 16 frequencies from 5 to 1300 kHz in a sample of white men and women aged 18-30 y. Plots of total-body and segmental impedance against frequency for each individual indicated that the general shape of these curves was described by the same mathematical function consisting of three components-ai, bi, and ci,-that contain information derived from the individual measurements of impedance summarized across the spectrum of current frequencies. Total-body and segmental multifrequency impedance were significantly correlated with hemoglobin, hematocrit, and serum sodium, potassium, creatinine, and osmolality. Regression models of body composition with total-body or segmental impedance measures at discrete frequencies or the impedance spectrum variables were similar to corresponding findings for impedance models at 50 kHz. The segmental impedance spectrum variables for total and percentage body fat and the ratios of low- to high-frequency impedance from the trunk were significantly associated with total body fatness as measured by DXA.

A multifrequency multichannel electrical impedance data acquisition system for body fluid shift monitoring

Discusses some important issues for the design of electrical impedance measurement systems intended for body fluid shift monitoring, in particular during dialysis treatments. The authors have studied two common signal generation systems: digital synthesis and carrier recovery. They have found that in prolonged measurement applications, digital synthesis yields the best performance. On the demodulation side, they balance the demodulator errors between the real and imaginary parts by rotating the demodulation axes. The authors use segmental multifrequency impedance measurements to estimate the values of intracellular and extracellular impedance by adjusting the parameters of a Cole-Cole model for each segment measured. They stress the need to perform segmental measurements in order to accurately measure the segments of interest, in particular the trunk during dialysis treatments. Their results show that there is a sharp disequilibrium between the intracellular and extracellular compartments in the very first dialysis period. This fact generates the need to continuously measure segmental impedance instead of comparing initial and final values.