The Biagram Vector: A Graphical Relation between Reactance and Phase Angle Measured by Bioelectrical Analysis in Infants

Association between phase angle and height-to-age index classifications of children under five years of age

BACKGROUND & AIMS

The phase angle (PA) has been used as an indicator of prognosis and nutritional status because it reflects the integrity of the individuals' cellular function. In contrast to the investigations that assessed acute malnutrition (weight deficit) and PA in children, studies that evaluated the relationship of this indicator with stunting (height deficit) are still scarce and inconclusive. Thus, we aim to investigate whether there are differences in PA according to the classifications of the height-for-age (H/A) index of children under five years of age.

METHODS

This is a cross-sectional study carried out in a nutritional recovery center, in households, and in a daycare center in Maceió-Alagoas, Brazil. Anthropometric data were collected, and resistance and reactance were obtained through the use of tetrapolar electrical bioimpedance, from children aged 2-5 years. The PA and the percentage of body fat were calculated. Children were divided into 3 groups: adequate H/A, at-risk of stunting and stunted. Analysis of covariance for the main outcome was performed using age, sex, and the body mass index-to-age as covariates, and the H/A classification as the exposure.

RESULTS

The mean children's PA in the adequate H/A group was 3.9° [95% CI 3.6-4.2], while in the group at-risk of stunting and stunted it was 4.5° [95% CI 4.3-4.7] and 4.6° [95% CI 4.4-4.8], respectively, showing statistical difference (p < 0.01).

CONCLUSION

In the present sample, stunted children have higher PA values than children with adequate H/A.

The clinical use of longitudinal bio-electrical impedance vector analysis in assessing stabilization of children with severe acute malnutrition

BACKGROUND & AIMS

Severe Acute Malnutrition (SAM) in children is determined using anthropometry. However, bio-electrical impedance (BI) analysis could improve the estimation of altered body composition linked to edema and/or loss of lean body mass in children with SAM. We aimed to assess: 1) the changes in BI parameters during clinical stabilization and 2) whether BI parameters add prognostic value for clinical outcome beyond the use of anthropometry.

METHODS

This prospective observational study enrolled children, aged 6-60 months, that were admitted at Queen Elizabeth Central Hospital in Blantyre, Malawi, for complicated SAM (i.e., having either severe wasting or edematous SAM with a complicating illness). Height, weight, mid-upper arm circumference (MUAC), and BI were measured on admission and after clinical stabilization. BI measures were derived from height-adjusted indices of resistance (R/H), reactance (Xc/H), and phase angle (PA) and considered to reflect body fluids and soft tissue in BI vector analysis (BIVA).

RESULTS

We studied 183 children with SAM (55% edematous; age 23.0 ± 12.0 months; 54% male) and 42 community participants (age 20.1 ± 12.3 months; male 62%). Compared to community participants, the BIVA of children with edematous SAM were short with low PA and positioned low on the hydration axis which reflects severe fluid retention. In contrast, children with severe wasting had elongated vectors with a PA that was higher than children with edematous SAM but lower than community participants. Their BIVA position fell within the top right quadrant linked to leanness and dehydration. BIVA from severely wasted and edematous SAM patients differed between groups and from community children both at admission and after stabilization (p < 0.001). Vector position shifted during treatment only in children with edematous SAM (p < 0.001) and showed a upward translation suggestive of fluid loss. While PA was lower in children with SAM, PA did not contribute more than anthropometry alone towards explaining mortality, length of stay, or time-to-discharge or time-to-mortality. The variability and heterogeneity in BI measures was high and their overall added predictive value for prognosis of individual children was low.

CONCLUSIONS

BIVA did not add prognostic value over using anthropometry alone to predict clinical outcome. Several implementation challenges need to be optimized. Thus, in low-resource settings, the routine use of BI in the management of pediatric malnutrition is questionable without improved implementation.

Phase Angle From Bioelectrical Impedance Analysis: Population Reference Values by Age, Sex, and Body Mass Index

BACKGROUND

The use of bioelectrical impedance phase angle has been recommended as a prognostic tool in the clinical setting, but published reference data bases are discrepant and incomplete (eg, they do not consider body mass index [BMI], and data are lacking for children).

METHODS

Phase angle reference values stratified by age, sex, and BMI were generated in a large German data base of 15,605 children and adolescents and 214,732 adults, and the determinants of phase angle values were assessed. The reference values were applied to 3 groups of patients and compared with previously published reference values from the United States and Switzerland.

RESULTS

Gender and age were the main determinants of phase angle in adults, with men and younger subjects having higher phase angles. In children and adolescents, age and BMI were the main determinants of phase angle. In normal and overweight adults, phase angle increased with increasing BMI, but there was an inverse association at a BMI >40 kg/m2. In cirrhosis, the prevalence of a low phase angle increased with the state of disease, whereas it was not different between patients with the metabolic syndrome and controls. There are considerable differences between phase angle reference values from different populations. These differences are not explained by age or BMI and may be due to differences between impedance analyzers.

CONCLUSION

The determinants of phase angle differ between adults and children. In adults, the influence of BMI on phase angle depended on the BMI range. The prognostic value of phase angle may differ in different clinical settings. The use of population-specific and probably impedance-analyzer-specific reference values for phase angle is recommended.

Bioelectrical impedance analysis for assessment of fluid status and body composition in neonates--the good, the bad and the unknown

BACKGROUND/OBJECTIVES

There is a critical need for improved technologies to monitor fluid balance and body composition in neonates, particularly those receiving intensive care. Bioelectrical impedance analysis meets many of the criteria required in this environment and appears to be effective for monitoring physiological trends.

SUBJECT/METHODS

The literature regarding the use of bioelectrical impedance in neonates was reviewed.

RESULTS

It was found that prediction equations for total body water, extracellular water and fat-free mass have been developed, but many require further testing and validation in larger cohorts. Alternative approaches based on Hanai mixture theory or vector analysis are in the early stages of investigation in neonates.

CONCLUSIONS

Further research is required into electrode positioning, bioimpedance spectroscopy and Cole analysis in order to realise the full potential of this technology.

Obese related effects of inflammatory markers and insulin resistance on increased carotid intima media thickness in pre-pubertal children

Obesity in children appears to be associated with increased risk of cardiovascular and metabolic diseases later in life. Early development of insulin resistance and impaired oxidant-antioxidant status may lead to endothelial dysfunction and increased carotid intima media thickness (IMT) even in childhood. The aim of this study was to measure IMT and the relationship between IMT, insulin resistance and oxidant status in obese pre-pubertal children. In 53 obese pre-pubertal children (27M/26F, mean age 8+/-2 years), anthropometric measurements and inflammatory markers (hs-CRP and PGF-2 alpha), were evaluated compared with 41 healthy pre-pubertal subjects (21M/20F, mean age 7+/-2 years). OGTT was performed and insulin resistance (IR) indices (HOMA-IR, WBISI, G/I and QUICKI) were calculated in all patients. High-resolution ultrasound techniques were used to evaluate IMT. Obese children had higher levels of PGF-2 alpha and hs-CRP compared to healthy subjects (p=0.001 and p=0.005). Furthermore, fasting insulin levels and HOMA-IR were higher in obese children than in controls (p=0.001 and p=0.001) while WBISI was significantly lower (p=0.002). In addition, obeses had an increased IMT (p=0.001). In obese children there was a significant correlation between IMT and indices of IR (HOMA-IR: beta=-1.233, p=0.002; WBISI: beta=-0.921, p=0.008; G/I: beta=-0.811, p=0.003) and between IMT and PGF-2 alpha (beta=0.505, p=0.004). After categorizing subjects according to tertiles of body mass index (BMI) (<or=21.42, 21.42-26.23 and >or=26.23 kg/m(2)) and to waist circumference (WC) (<or=68.28, 68.28-79.04 and >or=79.04 cm), no influence of BMI or WC on IMT were found in the three groups. In conclusion, early changes in glucose metabolism and an alteration of oxidant-antioxidant status may be present in obese pre-pubertal children; this could lead to increase IMT and early cardiovascular disease.

Bioelectrical impedance analysis in clinical practice: a new perspective on its use beyond body composition equations

PURPOSE OF REVIEW

The bioelectrical impedance analysis is not a direct method for estimating body composition. Its accuracy depends on regression equations, and recent papers have suggested that this approach should not be used in several clinical situations. Another option is to obtain information about the electrical properties of tissues by using raw bioelectrical impedance measurements, resistance and reactance. They can be expressed as a ratio (phase angle) or as a plot (bioelectrical impedance vector analysis). This review describes their use in clinical practice.

RECENT FINDINGS

The phase angle changes with sex and age. It is described as a prognostic tool in many clinical situations. There are some controversies about considering it as a nutritional marker. Studies in burn victims and sickle-cell disease corroborate its ability to evaluate cell membrane function. Bioelectrical impedance vector analysis allows a semi-quantitative estimation of body composition from information from tissue hydration and soft-tissue mass in a plot. It can be used in healthy individuals or patients, for a population or individual evaluation of fluid imbalance or an assessment of soft-tissue mass. It has also been used as a prognostic tool in dialysis and cancer patients.

SUMMARY

The phase angle can be considered a global marker of health, and future studies are needed to prove its utility in intervention studies. Bioelectrical impedance vector analysis has increased its utility in clinical practice, even when the equations may be inaccurate for body composition analysis.