Determination of resistance at zero and infinite frequencies in bioimpedance spectroscopy for assessment of body composition in babies.

Objective. Bioimpedance spectroscopy (BIS) is a popular technique for the assessment of body composition in children and adults but has not found extensive use in babies and infants. This due primarily to technical difficulties of measurement in these groups. Although improvements in data modelling have, in part, mitigated this issue, the problem continues to yield unacceptably high rates of poor quality data. This study investigated an alternative data modelling procedure obviating issues associated with BIS measurements in babies and infants.Approach.BIS data are conventionally analysed according to the Cole model describing the impedance response of body tissues to an appliedACcurrent. This approach is susceptible to errors due to capacitive leakage errors of measurement at high frequency. The alternative is to model BIS data based on the resistance-frequency spectrum rather than the reactance-resistance Cole model thereby avoiding capacitive error impacts upon reactance measurements.Main results.The resistance-frequency approach allowed analysis of 100% of data files obtained from BIS measurements in 72 babies compared to 87% successful analyses with the Cole model. Resistance-frequency modelling error (percentage standard error of the estimate) was half that of the Cole method. Estimated resistances at zero and infinite frequency were used to predict body composition. Resistance-based prediction of fat-free mass (FFM) exhibited a 30% improvement in the two-standard deviation limits of agreement with reference FFM measured by air displacement plethysmography when compared to Cole model-based predictions.Significance.This study has demonstrated improvement in the analysis of BIS data based on the resistance frequency response rather than conventional Cole modelling. This approach is recommended for use where BIS data are compromised by high frequency capacitive leakage errors such as those obtained in babies and infants.

Anthropometry and body composition of vertically HIV-infected children and adolescents under therapy with and without protease inhibitors.

OBJECTIVE: Although the benefits of highly active antiretroviral therapy (HAART) have been documented, it is thought to be associated to disturbances in nutritional status. These disturbances may occur early in life and are poorly understood. The present study aimed to investigate the relationship between anthropometric parameters and body composition of perinatally HIV-infected children and adolescents under HAART, according to use and non-use of protease inhibitors. DESIGN: Cross-sectional study undertaken between August and December 2007. Demographic, socio-economic, clinical and anthropometric data were collected from the patients. The χ 2 test, Wilcoxon rank sum test (Mann-Whitney) and t test were used to compare the following variables between users and non-users of protease inhibitors: age, gender, per capita income, HAART exposure, antiretroviral therapy adopted in the last three years, CD4 count, viral load, pubertal stage, nutritional status (BMI-for-age, height-for-age, waist and neck circumferences, triceps skinfold thickness, body fat percentage, upper-arm fat area and upper-arm muscle area). SETTING: An HIV/AIDS out-patient clinic, São Paulo, Brazil. SUBJECTS: One hundred and fifteen patients (children and adolescents aged 6-19 years). RESULTS: Protease inhibitors users had a higher prevalence of stunting (P=0.03), lower BMI (P=0.03) and lower percentage of body fat (P=0.05) compared with non-users. There was no statistically significant difference between the HAART regimens and measurements of fat adiposity. CONCLUSIONS: The findings of the study suggest that children and adolescents under protease inhibitors are at higher risk of growth and development deviations, but not at risk of body fat redistribution.

Dyslipidaemia and insulin resistance in vertically HIV-infected children and adolescents.

This cross-sectional study determined the influence of antiretroviral therapy (ART) on the lipid profile and insulin sensitivity of 119 perinatally HIV-infected Brazilian patients aged 6-19 years. Inadequate high-density lipoprotein cholesterol (HDL-c) concentrations were observed in 81.4% of patients. High concentrations of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-c) and triglycerides (TG) were found in 33.9%, 9.7% and 35.6% of patients, respectively. There were statistically significant differences in mean concentrations of TC (P=0.004), HDL-c (P=0.015) and LDL-c (P=0.028) among children (<10 years), early adolescents (10-14 years) and late adolescents (15-19 years). Children presented the highest mean concentrations of TC and LDL-c, and patients in late adolescence presented the lowest concentrations of HDL-c. Insulin sensitivity, assessed by the Homeostasis Model Assessment (HOMA) index, was diagnosed in 16.7% of patients, with a statistically higher proportion (P=0.034) of insulin-resistant children (33.3%) compared with adolescents (12.5%). There was a statistically significant association between TG concentrations and use of ART regimens containing protease inhibitors (PI) (P=0.0003). Children presented a higher prevalence of insulin resistance and dyslipidaemia compared with adolescents, suggesting that ART, especially PIs, may lead to metabolic complications.