The Biagram vector: a graphical relation between reactance and phase angle measured by bioelectrical analysis in infants

BACKGROUND: Biagram vector is derived by plotting direct measurements of reactance and phase angle from the analyzer, which are not dependent on anthropometric characteristics of the subject and it can be considered an emerging method for evaluating the nutritional status in clinical practice. AIM: To calculate and plot the Biagram vector in a sample of healthy infants in their first year of life. METHODS: 174 healthy infants (99 male, 75 female) aged under 1 year, born at full term and adequate for gestational age, were enrolled in a cross-sectional study. The sample was divided into three age groups: 0-3.99 months (group A), 4-7.99 months (group B), and 8-11.99 months (group C). Bioelectric impedance analysis (BIA) was performed by a tetrapolar single frequence phase-sensitive impedance analyzer (STA/BIA; Akern Srl, Firenze, Italy). RESULTS: Biagram vector showed an increasing trend (p < 0.05) in the first year of life (group A: 27.9 ± 12.6; group B: 32.1 ± 9.7; group C: 37.2 ± 9.5). Females showed Biagram vector values significantly higher than males in group A (34.7 ± 15.0 vs. 24.0 ± 9.1; p < 0.05). 95% confidence ellipses of Biagram vector for each age group were calculated and plotted and a comparison of our results with published data calculated in older children was conducted. CONCLUSION: The bivariate analysis of BIA measurements, plotted as a vector in relation to the age, showed an increasing trend with a higher gain rate under 1 year with respect to the following age periods. These data could reflect the variation of body composition in the first years of life and could be of interest to assess the nutritional status for clinical practice.