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Background Air-displacement plethysmography ( ADP) systems can either measure or predict lung volume ( LV) in their test trials. The repeatability of the predicted and the measured value is an important factor in the accuracy of the final test result. Objective Compare the variability and accuracy of ADP tests using predicted and measured LV over a protracted period of time. Methods Twenty-four adults (18-30 years) participated in the study. Each subject underwent three ADP tests over a period of 3 weeks, with 1 week between tests. At each testing session, subjects were tested using a predicted LV protocol and a measured LV protocol in random order. LV, body volume ( BV) and per cent body fat (% BF) were compared between testing modes and between assessment times. Results A two-way ANOVA examined the effect of the mode of LV assessment (measured or predicted) and trial (week) for LV and BV and the effect of the LV mode assessment (measured or predicted) and trial (week) on % BF results. LV and BV did not differ significantly ( P>0·05) between the two modes of assessment (measured or predicted). Time (day of assessment) also was not significantly different between trials ( P>0·05). Neither mode nor trial was significant ( P>0·05), therefore neither had an effect on the % BF results. Conclusion In this investigation, the method used to determine LV during ADP testing did not significantly affect the final % BF result. Also, tests performed over an extended period of time was not affected by LV measurement method. [ABSTRACT FROM AUTHOR]

Objective. Air diplacement plethysmography (ADP) has become increasingly popular to assess body composition in children. The aim of this study was to compare ADP with deuterium dilution and to investigate the effect of using child-specific prediction equations to correct raw body volume from ADP for thoracic gas volume (TGV) and body surface area (BSA). Methods. Thirty-seven healthy Dutch children (17 girls, 20 boys) aged 10–13 years were recruited. Body volume was measured using the Bod Pod®. Both adult and child-specific prediction equations were used to correct raw body volume from the Bod Pod® for TGV and BSA. Total body water (TBW) was assessed using deuterium dilution. Child-specific densities and hydration fractions of fat-free mass were used to convert body volume and TBW to percentage fat mass (%FM). Correlation and agreement between methods was assessed using linear regression analysis and Bland-Altman plots. Results. Despite a high correlation between the Bod Pod® and deuterium dilution (R=0.91, p <0.001), a significant difference was found between %FM obtained using the Bod Pod® and deuterium dilution (p <0.001), regardless of the equation used to correct raw body volume for TGV and BSA. Bland-Altman plots showed a systematic bias towards a smaller difference between techniques at higher %FM. Conclusion. Significant differences in %FM were found between both methods. Given the underlying assumptions to translate body volume or TBW to %FM, it is recommended to use a 3- or 4-compartment model when assessing body composition in children. [ABSTRACT FROM AUTHOR]

Objective:This study was designed to compare measured and predicted thoracic gas volume (V TG) after weight loss and to analyze the effect of body composition confounders such as waist circumference (WC) on measured V TG changes.Design:Prospective intervention study.Setting:Outpatient University Laboratory, Lisbon, Portugal.Subjects:Eighty-five overweight and obese women (body mass index=30.0±3.5 kg/m2; age=39.0±5.7 years) participating in a 16-month university-based weight control program designed to increase physical activity and improve diet.Methods:Body weight (Wb), body volume (Vb), body density (Db), fat mass (FM), percent fat mass (%FM) and fat-free mass (FFM) were assessed by air-displacement plethysmography (ADP) at baseline and at post-intervention (16 months). The ADP assessment included a protocol to measure V TG and a software-based predicted V TG. Dual-energy X-ray absorptiometry (DXA) (Hologic QDR 1500) was also used to estimate FM, %FM and FFM. Maximal oxygen uptake (VO2 max) was assessed with a modified Balke cardiopulmonary exercise testing protocol with a breath-by-breath gas analysis.Results:Significant differences between the baseline and post-weight loss intervention were observed for body weight and composition (Vb, Db, %FM, FM and FFM), and measures of V TG (measured: Δ=0.2 l, P<0.001; predicted: Δ=0.01 l, P<0.010) variables. Measured V TG change was negatively associated with the change in the WC (P=0.008), controlling for VO2 max and age (P=0.007, P=0.511 and P=0.331). Linear regression analysis results indicated that %FM and FM using the measured and predicted V TG explained 72 and 76%, and 86 and 90% respectively, of the variance in %FM and FM changes using dual-energy x-ray absorptiometry.Conclusions:After weight loss, measured V TG increased significantly, which was partially attributed to changes is an indicator of body fat distribution such as WC. Consequently, measured and predicted V TG should not be used interchangeably when tracking changes in body composition. The mechanisms relating the reduction of an upper body fat distribution with an increase measured V TG are worthy of future investigation.European Journal of Clinical Nutrition (2008) 62, 444–450; doi:10.1038/sj.ejcn.1602709; published online 28 March 2007 [ABSTRACT FROM AUTHOR]

Objective. The aim of the study was to evaluate air-displacement plethysmography (ADP) thoracic gas volume (TGV) prediction equations in children representing a wide range of body mass index (BMI). Methods. 254 children (5 to 17 years) were recruited from two centres (England and the United States). Subjects were stratified into three BMI categories according to the International Obesity TaskForce (IOTF) criteria: lean (48 male, 42 female), overweight (15 male, 29 female), and obese (52 male, 68 female). As part of the normal ADP procedure, TGV was measured (TGVMeas), predicted using child specific equations developed by Fields (TGVFields) and adult derived equations by Crapo (TGVCrapo) with percentage body fat (PF) estimates subsequently calculated (PFMeas, PFFields, PFCrapo). Results. Compared with the mean TGVMeas, the TGVFields estimates were within±0.2 L in all groups, except obese males (+0.5 L), while the mean TGVCrapo estimates were greater than±0.3 L in all groups except lean males (+0.1 L). When converted to PF, the mean PFFields estimates were within±1% of the measured value in all groups, except obese males (+1.1%), while the mean PFCrapo estimates were greater than±1% in all groups, except lean males (+0.5%). Using either prediction equation, Bland-Altman analysis revealed that the greatest PF±95% limits of agreement were in the lean and overweight groups and lowest in the obese groups. Conclusion. The Fields child-specific TGV prediction equations provide accurate mean PF estimates and appear better than using the Crapo equations if a measured TGV cannot be achieved in children of a wide range of BMI. However, individual predictions may result in large PF errors especially in lean children. [ABSTRACT FROM AUTHOR]

Air-displacement plethysmography (ADP) is now widely used for body composition measurement in pediatric populations. However, the manufacturer's software developed for adults leaves a potential bias for application in children and adolescents, and recent publications do not consistently use child-specific corrections. Therefore we analyzed child-specific ADP corrections with respect to quantity and etiology of bias compared with adult formulas. An optimal correction protocol is provided giving step-by-step instructions for calculations. In this study, 258 children and adolescents (143 girls and 115 boys ranging from 5 to 18 y) with a high prevalence of overweight or obesity (28.0% in girls and 22.6% in boys) were examined by ADP applying the manufacturer's software as well as published equations for child-specific corrections for surface area artifact (SM), thoracic gas volume (TGV), and density of fat-free mass (FFM). Compared with child-specific equations for SM, TGV, and density of FFM, the mean overestimation of the percentage of fat mass using the manufacturer's software was 10% in children and adolescents. Half of the bias derived from the use of Sin's equation not corrected for age- dependent differences in FFM density. An additional 3 and 2% of bias resulted from the application of adult equations for prediction of SAA and TGV, respectively. Different child-specific equations used to predict TGV did not differ in the percentage of fat mass. We conclude that there is a need for child-specific equations in ADP raw data analysis considering SAA, TGV, and density of FFM. [ABSTRACT FROM AUTHOR]