改进的氦稀释法及其在体脂测定中的应用

为随时了解肺残气量（RV）的仪器测定误差，提高RV及其有关数据的实际可应用性，建立了改进的氦稀释法。改进的氦稀释法是在通用氦稀释法的基础上增加两个气体稀释程序，根据其加入的气体量（VS、Vb）和获得的氦浓度（原已知浓度He1、加入Va后浓度He2、加入Vb后浓度He3、终末浓度He4）来计算RV和RV的仪器测定误差。应用密度法测288名受试者体脂时采用改进的氦稀释法测RV，所有受试者RV的相对误差（RE）高限在5％以内，RV的绝对误差（AE）为34±27ml，体脂（F）误差0．14±0．11kg；若将RV的RE高限定为2％，受试者符合人数降至70％，RV的AE仅为19±13ml，F误差0．08±0．05kg。改进的氦稀释法在了解RV仪器测定误差和提高密度法的体脂测定精度等方面，均具有实际应用价值。     

Prediction accuracy of body density, lean body weight, and total body volume equations

The purpose of this study was to determine the accuracy of percent fat estimates derived from regression equations with functions of predicting body density (BD), lean body weight (LBW), and total body volume (TBV) from anthropometric variables. BD, LBW, and TBV equations were derived from the data of 95 young, adult men (percent fat X = 13.4%). The multiple correlations for these equations were: BD, 0.86-0.83; LBW, 0.96-0.95; and TBV, 0.99. The zero order correlations between laboratory determined percent fat and percent fat derived by the BD, LBW, and TBV equations ranged from 0.80 to 0.86 with standard errors from 3.1% to 3.7%. This shows that BD, LBW, and TBV equations have similar accuracy when transformed to percent fat. The derived equations were cross validated with three additional, but diverse, samples (percent fat X = 5.1%; 16.7%; 27.1%). The cross validations results revealed that all equations exhibited similar accuracy. With samples differing in percent fat, systematic prediction errors occurred. The results further confirm population specificity of prediction equations.     

Evaluation of simple methods to estimate total body fat in healthy women

Simple methods are needed to assess the total body fat (TBF) of individual human subjects. In addition to the commonly used skinfold thickness (SFT) technique, alternative methods to estimate TBF have recently been developed. In this comparative study the TBF content of healthy Swedish women was estimated by 3 simple methods: the SFT technique, near infrared interactance (NII) and bioelectrical impedance (BEI). The results were compared with estimates obtained by underwater weighing (UWW). The SFT technique was found to have the best accuracy and precision (UWW-SFT = 0.6±3.1% TBF, n =20; UWW-NII=-1.2±4.0% TBF, n =20; UWW-BEI=3.3 ± 3.6% TBE n = 16). The NII technique was found to overestimate TBF in lean subjects and TBF was underestimated in obese subjects.     

The estimation of body density in rugby union football players.

The general regression equation of Durnin and Womersley for estimating body density from skinfold thicknesses in young men, was examined by comparing the estimated density from this equation, with the measured density of a group of 45 rugby union players of similar age. Body density was measured by hydrostatic weighing with simultaneous measurement of residual volume. Additional measurements included stature, body mass and skinfold thicknesses at the biceps, triceps, subscapular and suprailiac sites. The estimated density was significantly different from the measured density (P < 0.001), equivalent to a mean overestimation of relative fat of approximately 4%. A new set of prediction equations for estimating density was formulated from linear regression using the logarithm of single and sums of skinfold thicknesses. Equations were derived from a validation sample (n = 22) and tested on a crossvalidation sample (n = 23). The standard error of the estimate (s.e.e.) of the equations ranged from 0.0058 to 0.0062 g ml-1. The derived equations were successfully crossvalidated. Differences between measured and estimated densities were not significant (P > 0.05), total errors ranging from 0.0067 to 0.0092 g ml-1. An exploratory assessment was also made of the effect of fatness and aerobic fitness on the prediction equations. The equations should be applied to players of similar age and playing ability, and for the purpose of identifying group characteristics. Application of the equations to individuals may give rise to errors of between -3.9% to +2.5% total body fat in two-thirds of cases.     

Joint estimation of water/fat images and field inhomogeneity map

Water/fat separation in the presence of B₀ field inhomogeneity is a problem of considerable practical importance in MRI. This article describes two complementary methods for estimating the water/fat images and the field inhomogeneity map from Dixon‐type acquisitions. One is based on variable projection (VARPRO) and the other on linear prediction (LP). The VARPRO method is very robust and can be used in low signal‐to‐noise ratio conditions because of its ability to achieve the maximum‐likelihood solution. The LP method is computationally more efficient, and is shown to perform well under moderate levels of noise and field inhomogeneity. These methods have been extended to handle multicoil acquisitions by jointly solving the estimation problem for all the coils. Both methods are analyzed and compared and results from several experiments are included to demonstrate their performance. Magn Reson Med 59:571–580, 2008. © 2008 Wiley‐Liss, Inc.     

Independent estimation of T*2 for water and fat for improved accuracy of fat quantification

Noninvasive biomarkers of intracellular accumulation of fat within the liver (hepatic steatosis) are urgently needed for detection and quantitative grading of nonalcoholic fatty liver disease, the most common cause of chronic liver disease in the United States. Accurate quantification of fat with MRI is challenging due the presence of several confounding factors, including T*₂ decay. The specific purpose of this work is to quantify the impact of T*₂ decay and develop a multiexponential T*₂ correction method for improved accuracy of fat quantification, relaxing assumptions made by previous T*₂ correction methods. A modified Gauss‐Newton algorithm is used to estimate the T*₂ for water and fat independently. Improved quantification of fat is demonstrated, with independent estimation of T*₂ for water and fat using phantom experiments. The tradeoffs in algorithm stability and accuracy between multiexponential and single exponential techniques are discussed. Magn Reson Med 63:849–857, 2010. © 2010 Wiley‐Liss, Inc.     

Association between total and regional body fat to bone parameters of university athletes

Sport Sciences for Health - The purpose of this study was to investigate the association between total and regional body fat to BMD and BMC among university athletes. Cross-sectional study with 167...     

Error estimation on extracorporeal trajectory determination from body scans

This study explores the magnitude of two sources of error that are introduced when extracorporeal bullet trajectories are based on post-mortem computed tomography (PMCT) and/or surface scanning of a body. The first source of error is caused by an altered gravitational pull on soft tissue, which is introduced when a body is scanned in another position than it had when hit. The second source of error is introduced when scanned images are translated into a virtual representation of the victim’s body. To study the combined magnitude of these errors, virtual shooting trajectories with known vertical angles through five “victims” (live test persons) were simulated. The positions of the simulated wounds on the bodies were marked, with the victims in upright positions. Next, the victims were scanned in supine position, using 3D surface scanning, similar to a body’s position when scanned during a PMCT. Seven experts, used to working with 3D data, were asked to determine the bullet trajectories based on the virtual representations of the bodies. The errors between the known and determined trajectories were analysed and discussed. The results of this study give a feel for the magnitude of the introduced errors and can be used to reconstruct actual shooting incidents using PMCT data.

     

Impact of training and hypocaloric diet on fat oxidation and body composition in obese adolescents

ObjectiveWe undertook to evaluate the effects of training and hypocaloric diet on fat oxidation and weight loss in obese adolescents within a two-month program.MethodsThe longitudinal intervention of a two-month program was performed in 54 adolescents, whose body mass index was 30.3 ± 4.0 kg/m². They were divided into three groups: hypocaloric diet program (D), individualized training program at the level of maximal lipid oxidation Lipox_max (T) and hypocaloric diet combined with training program (D + T). The body composition, the substrate “crossover” point and the Lipox_max point were determined before and after each protocol.ResultsThe decreases in body weight and fat mass were more significant in the D + T group (p < 0.01) than in the D (p < 0.05) or T (p = 0.07) groups. In the D + T group, the crossover point was observed at a higher intensity at the end of the program (+ 19.7% ± 2.4 of W_max; p < 0.001), and the fat oxidation at Lipox_max has increased by 83.2 ± 15.3 mg/min (p < 0.01). A significant correlation between Lipox_max and weight was also observed after the program in D + T subject.     

An evaluation of a bioelectrical impedance analyser for the estimation of body fat content.

Measurement of body composition is an important part of any assessment of health or fitness. Hydrostatic weighing is generally accepted as the most reliable method for the measurement of body fat content, but is inconvenient. Electrical impedance analysers have recently been proposed as an alternative to the measurement of skinfold thickness. Both these latter methods are convenient, but give values based on estimates obtained from population studies. This study compared values of body fat content obtained by hydrostatic weighing, skinfold thickness measurement and electrical impedance on 50 (28 women, 22 men) healthy volunteers. Mean(s.e.m.) values obtained by the three methods were: hydrostatic weighing, 20.5(1.2)%; skinfold thickness, 21.8(1.0)%; impedance, 20.8(0.9)%. The results indicate that the correlation between the skinfold method and hydrostatic weighing (0.931) is somewhat higher than that between the impedance method and hydrostatic weighing (0.830). This is, perhaps, not surprising given the fact that the impedance method is based on an estimate of total body water which is then used to calculate body fat content. The skinfold method gives an estimate of body density, and the assumptions involved in the conversion from body density to body fat content are the same for both methods.     

Energy absorption, lean body mass, and total body fat changes during 5 weeks of continuous bed rest

Inactivity causes profound changes. We determined the nature of the body composition changes due to inactivity, and sought to determine if these changes are secondary to changes in energy absorption. Volunteers were 15 healthy males who lived on a metabolic research ward under close staff supervision for 11 weeks. Subjects were ambulatory during the first 6 weeks and remained in continuous bed rest for the last 5 weeks of the study. Six male volunteers (age 24-61 years, height 175.7 +/- 4.2 cm) were selected for body composition measurements. Nine different male volunteers (age 21-50 years, height 177.7 +/- 5.0 cm) were selected for energy absorption measurements. The volunteers were fed weighed conventional foods on a constant 7-d rotation menu. The average daily caloric content was 2,592 kcal. Comparing the 5 weeks of continuous bed rest with the previous 6 weeks of ambulation we observed: no change in energy absorption or total body weight during bed rest, but a significant decrease in lean body mass and a significant increase in total body fat (p less than 0.05).     

Rapid automated measurement of body fat distribution from whole-body MRI

OBJECTIVE: The purpose of this article is to determine the feasibility of using computer-assisted diagnosis (CAD) techniques to automatically identify, localize, and measure body fat tissue from a rapid whole-body MRI examination. CONCLUSION: Whole-body MRI in conjunction with CAD allows a fast, automatic, and accurate approach to body fat measurement and localization and can be a useful alternative to body mass index. Whole-body fat analysis can be achieved in less than 5 min.     

Regional and total body bone mineral density in elite collegiate male swimmers.

BACKGROUND: To examine the role of long-term swimming exercise on regional and total body bone mineral density (BMD) in men. METHODS: Experimental design: Cross-sectional. Setting: Musculoskeletal research laboratory at a medical center. Participants: We compared elite collegiate swimmers (n = 11) to age-, weight-, and height-matched non-athletic controls (n = 11). MEASURES: BMD (g/cm2) of the lumbar spine (L2-4), proximal femur (femoral neck, trochanter, Ward's triangle), total body and various subregions of the total body, as well as regional and total body fat and bone mineral-free lean mass (LM) was assessed by dual-energy X-ray absorptiometry (DXA, Hologic QDR 1000/W). RESULTS: Swimmers, who commenced training at 10.7 +/- 3.7 yrs (mean +/- SD) and trained for 24.7 +/- 4.2 hrs per week, had a greater amount of LM (p < 0.05), lower fat mass (p < 0.001) and percent body fat (9.5 vs 16.2%, p < 0.001) than controls. There was no significant difference between groups for regional or total body BMD. In stepwise multiple regression analysis, body weight was a consistent independent predictor of regional and total body BMD. CONCLUSIONS: These results suggest that long-term swimming is not an osteogenic mode of training in college-aged males. This supports our previous findings in young female swimmers who displayed no bone mass benefits despite long-standing athletic training.     

Bromide space,total body water,and sick cell syndrome

Displacements of the bromide space (Br-82-C, as a marker for the extracellular fluid compartment) are caused by an enhanced anatomical space and/or increased permeability of cells to bromide. The ratio Br-82-C: total body water (TBW) was evaluated to be 0.83±0.17 in critically ill patients (n=38) compared with the normal value of 0.46±0.04 (n=10). Because of normal TBW in critically ill patients (TBW=505±68 ml/kg), an increased bromide penetration into cells seems to be responsible for the enlarged ratio Br-82-C: TBW. Taking into consideration measurements in patients with malabsorption (Br-82-C: TBW=0.56±0.13; n=13) and carcinoma of the rectum and colon (Br-82-C: TBW=0.66±0.24; n=18) we think that the bromide space is a good measurement of the effective extracellular water.