Association of electrical bioimpedance vectors with the nutritional classification of vulnerable multiethnic children.

BACKGROUND & AIMS: Monitoring growth and body composition in childhood is vital for early detection of health and nutrition problems during child development. The bioelectrical impedance vector analysis (BIVA) revealed its effectiveness as an indicator of nutritional status. This study aimed to measure the bioimpedance vectors of a sample of multiethnic children and evaluate the utility of BIVA for the classification of the nutritional status in a group of children with greater vulnerability, including in the presence of obesity. METHODS: This is a cross-sectional study that analyzed the bioelectrical impedance of a sample of 321 children from public daycare centers, aged 1-4 years, using the RXc graph method (tetrapolar analysis at 50 kHz frequency). The 95%, 75%, and 50% tolerance ellipses were plotted by age group. The Z-scores of bioimpedance parameters (Xc/H-Z and R/H-Z) were calculated regarding age, which were used to build reference tolerance ellipses for a single group, regardless of age. Such ellipses were evaluated for their ability to recognize the pattern and classify the deviations, using individual vectors of obese children. RESULTS: The mean impedance vectors showed progressively higher reactances and lower resistances with age. In the group of obese children, the individual vectors located outside the 95% baseline tolerance ellipse were 12.5%, 18.75%, and 11.1% of the cases for the WHZ, WAZ, and BMIZ criteria, respectively, all above the expected 5%, but much below expectations. This may be a problem with the obesity criteria used, as WHZ, WAZ, and BMIZ do not differentiate fat from lean mass. CONCLUSION: Bioimpedance vector analysis reflects differences in the bioelectric patterns of children classified as obese. Provided the obesity criteria are constructed based on fat measurements, rather than lean mass, the use of tolerance ellipses in the BIVA chart is promising as a tool for monitoring nutritional status where measuring body composition is difficult, because constant tissue hydration cannot be assumed.

Valores do vetor de impedância bioelétrica em crianças multiétnicas em situação de vulnerabilidade social / Bioelectrical impedance vector values in multiethnic children in situations of social vulnerability

Introdução: A importância da avaliação do estado nutricional de crianças, em especial as que vivem em situação de vulnerabilidade social, ganhou reconhecimento na última década. A análise do vetor de impedância bioelétrica revelou sua eficácia como um indicador do estado nutricional. Os objetivos do presente estudo foram descrever o conjunto de valores brutos dos componentes da bioimpedância (resistência e reatância) monofrequencial, a distribuição do vetor de bioimpedancia e avaliar o estado nutricional das crianças segundo esses padrões bioelétricos, especialmente aquelas classificadas com obesidade. Métodos: Trata-se de um estudo transversal que analisou a impedância bioelétrica de uma amostra de 321 crianças de creches públicas, com idade entre 1 a 4 anos, usando o método gráfico RXc (análise tetrapolar na frequencia de 50 kHz). As elipses de tolerância de 95%, 75% e 50% foram plotadas por faixa etária. Foram calculados os escores Z dos parâmetros de bioimpedância (Xc/H-Z e R/H-Z) em relação a idade, utilizados na construção das elipses de tolerância de referência de um único grupo, independente da faixa etária. Tais elipses foram avaliadas quanto a sua capacidade de reconhecer o padrão e classificar os desvios, utilizando vetores individuais de crianças obesas. Resultados: Os vetores de impedância média apresentaram reatâncias progressivamente mais altas e resistências mais baixas a medida que a idade aumentava. No grupo das crianças obesas, os vetores individuais situados fora da elipse de tolerância de referência de 95% totalizaram 12,5%, 18,75% e 11,1% dos casos, para os critérios z-score de peso/estatura (WHZ), z-score de peso/idade (WAZ) e z-score de IMC/idade (BAZ), respectivamente, todos acima dos 5% esperados. Conclusões: Nossos resultados confirmaram a importância da definição de valores de referência do vetor de impedância corporal segundo a idade da criança; e que os valores de referência de um determinado país não devem ser adotados acriticamente por outros, tendo em vista a considerável diversidade étnica. Também foi verificado que a análise vetorial da bioimpedância reflete diferenças nos padrões bioelétricos de crianças classificadas com obesidade. O uso das elipses de tolerância do gráfico da BIVA é promissor como ferramenta para o monitoramento do estado nutricional.

Introduction: The importance of assessing the nutritional status of children, especially those living in situations of social vulnerability, has gained recognition in the last decade. Analysis of the bioelectrical impedance vector (BIVA) revealed its effectiveness as an indicator of nutritional status. The objectives of the presente study were describe the raw values of the mono-frequency bioimpedance componentes (resistance and reactance), the distribution of the bioimpedance vector in a sample of ethnically diverse children from 1 to 4 years of age in a situation of social vulnerability in the periphery favelas in Rio de Janeiro and assess nutritional status acoording to these bioelectric standardas, especially those classified as obesity. Methods: This is a cross-sectional study that analyzed the bioelectrical impedance of a sample of 321 children from public daycare centers, aged 1-4 years, using the RXc graph method (tetrapolar analysis at 50 kHz frequency). The 95%, 75%, and 50% tolerance ellipses were plotted by age group. The Z-scores of bioimpedance parameters (Xc/H-Z and R/H-Z) were calculated regarding age, which were used to build reference tolerance ellipses for a single group, regardless of age. Such ellipses were evaluated for their ability to recognize the pattern and classify the deviations, using individual vectors of obese children. Results: The mean impedance vectors showed progressively higher reactances and lower resistances with age. The mean bioimpedance vectores of the presente sample of Brazilian children were diferente from children of other nationalities of the same age group. In the group of obese children, the individual vectors located outside the 95% baseline tolerance ellipse were 12.5%, 18.75%, and 11.1% of the cases for the z-score weight/ height (WHZ), z-score weight/age (WAZ) and z score IMC/age (BAZ), respectively, all above the expected 5%. Conclusions: Our results confirm the importance of defining reference values for the body impedance vector according to the child's age; and that the reference values of a given country should not be adopted uncritically by others, in view of the considerable ethnic diversity. We also demonstrated that the vectorial analysis of bioimpedance reflects diferences in the bioelectric patterns of children classified with obesity. The use of tolerance elipses in the BIVA char tis promising as a tool for monitoring nutritional status.