Biomedical subjects

ZiMian Wang

Publications and source records attributed to ZiMian Wang.

At least 19 recordsLinked to original sources

PubMed2006

Metabolically active portion of fat-free mass: a cellular body composition level modeling analysis.

The proportion of fat-free mass (FFM) as body cell mass (BCM) is highly related to whole body resting energy expenditure. However, the magnitude of BCM/FFM may have been underestimated in previous studies. This is because Moore's equation [BCM (kg) = 0.00833 x total body potassium (in mmol)], which was used to predict BCM, underestimates BCM by approximately 11%. The aims of the present study were to develop a theoretical BCM/FFM model at the cellular level and to explore the influences of sex, age, and adiposity on the BCM/FFM. Subjects were 112 adults who had the following measurements: total body water by (2)H(2)O or (3)H(2)O dilution; extracellular water by NaBr dilution; total body nitrogen by in vivo neutron activation analysis; and bone mineral by dual-energy X-ray absorptiometry. FFM was calculated using a multicomponent model and BCM as the difference between FFM and the sum of extracellular fluid and solids. The developed theoretical model revealed that the proportion of BCM to FFM is mainly determined by water distribution (i.e., E/I, the ratio of extracellular to intracellular water). A significant correlation (r = 0.90, P < 0.001) was present between measured and model-predicted BCM/FFM for all subjects pooled. Measured BCM/FFM [mean (SD)] was 0.584 +/- 0.041 and 0.529 +/- 0.041 for adult men and women (P < 0.001), respectively. A multiple linear regression model showed that there are independent significant associations of sex, age, and fat mass with BCM/FFM.

Adult↗

PubMed2006

Total body protein mass: validation of total body potassium prediction model in children and adolescents.

Protein is an important body component for monitoring growth, development, and nutritional status. We previously developed a total body potassium (TBK, in mmol) and bone mineral (Mo, in kg) model for predicting total body protein (TBPro, in kg) in adults (TBPro = 0.00252 x TBK + 0.732 x Mo). However, the applicability of the TBK-Mo model for children is unknown. The study aims were to develop a TBK-independent 6-component (6-C) TBPro approach as the criterion, and then to validate the TBK-Mo model in children. The following measurements were made in adolescents and children (n = 62, 38 boys and 24 girls, aged 5-17 y): body weight (BW, in kg), body volume (BV, in liters) by air displacement plethysmography, total body water (TBW, in kg) by 2H2O dilution, Mo by dual-energy X-ray absorptiometry, and TBK by whole-body counting. A 6-C model was derived as TBPro = 2.922 x BW - 0.301 x TBW - 2.039 x Mo - 2.632 x BV. The TBPro estimates did not differ between the 6-C and TBK-Mo models (mean +/- SD, 0.20 +/- 0.86 kg). There was a significant correlation between TBPro by the 6-C and TBK-Mo models (r = 0.94, P < 0.001). Bland-Altman analysis indicated that the differences between TBPro by 6-C and TBK-Mo models were not significantly correlated with the mean TBPro estimates by the 2 models (r = 0.032, P > 0.05). The TBK-Mo model can thus be used to estimate TBPro in healthy adults, adolescents, and children > 5 y old.

Absorptiometry, Photon↗

PubMed2005

Extracellular water: greater expansion with age in African Americans.

Aging is associated with the onset of chronic diseases that lead to pathological expansion of the extracellular water (ECW) compartment. Healthy aging, in the absence of disease, is also reportedly accompanied by a relative expansion of the ECW compartment, although the studies on which this observation is based are few in number, applied different ECW measurement methods, included small ethnically homogeneous subject samples, and failed to adjust ECW for non-age-related influencing factors. The aim of the current study was to examine, in a large (n = 1,538) ethnically diverse [African American (AA), Asian, Caucasian, Hispanic] subject group the cross-sectional relationships between ECW and age after controlling first for other potential factors that may influence fluid distribution. ECW and intracellular water (ICW) were derived from measured total body water (isotope dilution) and potassium (40K whole body counting). The cross-sectional relationships between ECW, ICW, and ECW/ICW (E/I), and age were developed using multiple regression modelling methods. Body weight, weight squared, height, age, sex, race, and interactions were all significant ECW predictors. The slope of the observed race x age interaction was significantly greater in AA (beta = 0.0005, P = 0.005) than in the three other race groups. Race, sex, and age differences in fluid distribution persisted after adjusting for body composition in a subgroup (n = 994) with dual-energy X-ray absorptiometry lean soft tissue and fat measurements. A relative ECW expansion (i.e., E/I) was present with greater age in most sex-race groups, although the effect was not significantly larger in AA males (P > 0.05) compared with the other race groups, except Asians (P < 0.05). For females, a larger E/I-age effect was found in AA compared with the other race groups, but only the comparison against Hispanics was significant (P < 0.05). The ECW compartment and E/I are thus variably larger, according to race, in healthy older subjects independent of sex, lean soft tissue, and fat mass.

Black or African American↗

PubMed2005

Four-compartment cellular level body composition model: comparison of two approaches.

OBJECTIVE: The aim of this study was to develop and compare two DXA-based four-compartment [body weight=body cell mass (BCM)+extracellular fluid (ECF)+extracellular solids (ECS)+fat] cellular level models. RESEARCH METHODS AND PROCEDURES: Total body potassium (TBK) model: BCM from TBK by whole-body counting-ECF(TBK)=LST-[BCM(TBK)+0.73 x osseous mineral (Mo)]. Bromide model: ECF from sodium bromide dilution-BCM(BROMIDE)=LST-(ECF(BROMIDE)+0.73xMo); Mo and LST measurements came from DXA. The two approaches were evaluated in 99 healthy men and 118 women. RESULTS: BCM estimates were highly correlated (r=0.97, p<0.001), as were ECF estimates (r=0.87, p<0.001); a small statistically significant mean difference was present (mean+/-SD; BCM(TBK) model, 30.4+/-8.9 kg; BCM(BROMIDE), 31.4+/-9.3 kg; Delta=1.0+/-2.8 kg; p<0.001; ECF(TBK), 18.5+/-4.2 kg; ECF(BROMIDE), 17.5+/-3.6 kg; Delta=1.0+/-2.8 kg; p<0.001). A high correlation (r=0.97, p<0.001) and good agreement (38.9+/-9.5 vs. 38.9+/-9.5 kg; Delta=0.0+/-2.4 kg; p=0.39) were present between TBW, derived as the sum of intracellular water from TBK and ECW from bromide, and measured TBW by 2H2O dilution. DISCUSSION: Two developed four-compartment cellular level DXA models, one of which is appropriate for use in most clinical and research settings, provide comparable results and are applicable for BCM and ECF estimation of subject groups with hydration disturbances.

Absorptiometry, Photon↗

PubMed2005

Comparison of visceral adipose tissue mass in adult African Americans and whites.

OBJECTIVE: Previous studies have reported racial differences in the amount of visceral adipose tissue (VAT), a risk factor for metabolic diseases. These results are equivocal and have not controlled for hormonal influences on VAT mass. This study was designed to measure the extent to which race is associated with VAT, controlling for total adipose tissue (TAT) mass and testosterone. RESEARCH METHODS AND PROCEDURES: Using a cross-sectional study design, we measured TAT mass using DXA, VAT and subcutaneous adipose tissue mass using magnetic resonance imaging, and sex hormones using radioimmunoassay in 224 African-American and white men and women. RESULTS: White men had increased VAT mass, even when controlling for TAT and age, compared with African-American men. White women also had a higher VAT mass compared with African-American women, but only when controlling for TAT and age. When multiple linear regression was used to evaluate the racial differences in VAT mass in a subset of subjects (n=80), controlling for sex hormones, it was found that white men, but not women, had increased VAT mass compared with their African-American counterparts. DISCUSSION: Based on the results of this study, we conclude that, when controlling for TAT, sex hormone levels, and age, white men, but not women, have more VAT mass than African-American men and women. Additional studies are needed to explore possible environmental and genetic influences on fat distribution relative to race and sex.

Absorptiometry, Photon↗

PubMed2005

Race-ethnicity-specific waist circumference cutoffs for identifying cardiovascular disease risk factors.

BACKGROUND: Waist circumferences (WCs) in white men and women that represent a risk of cardiovascular disease (CVD) equivalent to that of body mass indexes (BMIs; in kg/m2) of 25 and 30 have been identified. However, WC cutoffs for other race-ethnicity groups remain unknown. OBJECTIVE: The objective was to determine WC cutoffs for CVD risk in non-Hispanic blacks (blacks), Mexican Americans (MA), and non-Hispanic whites (whites). DESIGN: Data from 10,969 participants in the third National Health and Nutrition Examination Survey (1988-1994) were analyzed. The presence of CVD risk factors was the main outcome. Sex- and race-ethnicity-specific WC cutoffs were determined with logistic regression models by linking WC cutoffs with equivalent CVD risk based on BMI cutoffs for overweight and obesity. WC cutoffs for metabolic syndrome risk factors were similarly calculated. RESULTS: Correlations between WC and lipid profiles, blood pressure, and glucose were significantly higher than those between BMI and these same variables in all groups. The WC cutoffs were approximately 5-6 cm greater for white than for black men at BMIs between 25 and 40, and those for MA were intermediate. In women, few differences in WC cutoffs were observed between the groups. Simplified WC cutoffs corresponding to BMIs of 25 and 30, largely independent of age, for the 3 race-ethnicity groups were 89 and 101 cm for men and 83 and 94 cm for women. Minimal distances in receiver operating characteristic curves tended to be shorter when WC cutoffs rather than BMI cutoffs were used. CONCLUSIONS: WC is a better indicator of CVD risk than is BMI in the 3 race-ethnicity groups studied. The proposed WC cutoffs are more sensitive than are BMI cutoffs in predicting CVD risk.

Adult↗

PubMed2005

The end of body composition methodology research?

PURPOSE OF REVIEW: Over one century of research has led to methods for measuring all major body components at the atomic, molecular, cellular, and tissue-system levels. These remarkable developments have fueled a rapid and sustained increase in 'body composition' biological findings and related publications. Other than small, incremental improvements in available methods, is there no longer a need for developing new body composition methods? This review examines the question: are we approaching the 'end' of body composition methodology research? RECENT FINDINGS: Emerging and rapidly growing areas outside of 'traditional' body composition research are highlighting the need for new and innovative method development. Recently introduced technologies such as positron emission tomography and functional magnetic resonance imaging extend 'mass' estimates to corresponding 'function' and physiology in humans. Although all major components are now measurable in humans, large gaps remain when considering factors such as radiation exposure, invasiveness, static versus dynamic measurements, and laboratory versus clinic and field assessments. SUMMARY: The end of the first phase of body composition method development has now arrived: all major components are measurable in vivo. The accessibility of these methods is stimulating rapid advances in biological knowledge surrounding human body composition from in utero to old age. Sustaining advances in new body composition method development will require extending the boundaries of the field as it now exists.

Biomedical Research↗

PubMed2004

Total body skeletal muscle and adipose tissue volumes: estimation from a single abdominal cross-sectional image.

A single abdominal cross-sectional computerized axial tomography and magnetic resonance image is often obtained in studies examining adipose tissue (AT) distribution. An abdominal image might also provide additional useful information on total body skeletal muscle (SM) and AT volumes with related physiological insights. We therefore investigated the relationships between abdominal SM and AT areas from single images and total body component volumes in a large and diverse sample of healthy adult subjects. Total body SM and AT volumes were derived by whole body multislice magnetic resonance imaging in 123 men [age (mean +/- SD) of 41.6 +/- 15.8 yr; body mass index of 25.9 +/- 3.4 kg/m(2)] and 205 women (age of 47.8 +/- 18.7 yr; body mass index of 26.7 +/- 5.6 kg/m(2)). Single abdominal SM and AT slice areas were highly correlated with total body SM (r = 0.71-0.92; r = 0.90 at L(4)-L(5) intervertebral space) and AT (r = 0.84-0.96; r = 0.94 at L(4)-L(5) intervertebral space) volumes, respectively. R(2) increased by only 5.7-6.1% for SM and 2.7-4.4% for AT with the inclusion of subject sex, age, ethnicity, scanning position, body mass index, and waist circumference in the model. The developed SM and AT models were validated in an additional 49 subjects. To achieve equivalent power to a study measuring total body SM or AT volumes, a study using a single abdominal image would require 17-24% more subjects for SM and 6-12% more subjects for AT. Measurement of a single abdominal image can thus provide estimates of total body SM and AT for group studies of healthy adults.

Abdomen↗

PubMed2004

Dual-energy X-ray absorptiometry lean soft tissue hydration: independent contributions of intra- and extracellular water.

Dual-energy X-ray absorptiometry (DEXA) provides a measure of lean soft tissue (LST). LST hydration, often assumed to be constant, is relevant to several aspects of DEXA body composition estimates. The aims of this study were to develop a theoretical model of LST total body water (TBW) content and to examine hydration effects with empirically derived model coefficients and then to experimentally test the model's prediction that, in healthy adults, LST hydration is not constant but varies as a function of extra- and intracellular water distribution (E/I). The initial phase involved TBW/LST model development and application with empirically derived model coefficients. Model predictions were then tested in a cross-sectional study of 215 healthy adults. LST was measured by DEXA, extracellular water (ECW) by NaBr dilution, intracellular water (ICW) by whole body (40)K counting, and TBW by (2)H(2)O dilution. TBW estimates, calculated as ECW + ICW, were highly correlated with (r = 0.97, SEE = 2.1 kg, P < 0.001) and showed no significant bias compared with TBW measured by (2)H(2)O. Model-predicted TBW/LST was almost identical to experimentally derived values (means +/- SD) in the total group (0.767 vs. 0.764 +/- 0.028). LST hydration was significantly correlated with E/I (total group, r = 0.30, SEE = 0.027, P < 0.001). Although E/I increased with age (men, r = 0.48; women, r = 0.37; both P < 0.001), the association between TBW/LST and age was nonsignificant. Hydration of the DEXA-derived LST compartment is thus not constant but varies predictably with ECW and ICW distribution. This observation has implications for the accuracy of body fat measurements by DEXA and the use of TBW as a means of checking DEXA system calibration.

Absorptiometry, Photon↗

PubMed2004

Three-compartment model: critical evaluation based on neutron activation analysis.

There is renewed interest in Siri's classic three-compartment (3C) body composition model, requiring body volume (BV) and total body water (TBW) estimates, because dual-energy X-ray absorptiometry (DEXA) and in vivo neutron activation (IVNA) systems cannot accommodate subjects with severe obesity. However, the 3C model assumption of a constant ratio (alpha) of mineral (M) to total body protein (TBPro) and related residual mass density (D(RES)) based on cadaver analyses might not be valid across groups differing in sex, race, age, and weight. The aim of this study was to derive new 3C model coefficients in vivo and to compare these estimates to those derived by Siri. Healthy adults (n = 323) were evaluated with IVNA and DEXA and the measured components used to derive alpha and D(RES). For all subjects combined, values of alpha and D(RES) (means +/- SD, 0.351 +/- 0.043; 1.565 +/- 0.023 kg/l) were similar to Siri's proposed values of 0.35 and 1.565 kg/l, respectively. However, alpha and D(RES) varied significantly as a function of sex, race, weight, and age. Expected errors in percent body fat arising by application of Siri's model were illustrated in a second group of 264 adults, including some whose size exceeded DEXA limits but whose BV and TBW had been measured by hydrodensitometry and (2)H(2)O dilution, respectively. Extrapolation of predictions by newly developed models to very high weights allows percent fat error estimation when Siri's model is applied in morbidly obese subjects. The present study results provide a critical evaluation of potential errors in the classic 3C model and present new formulas for use in selected populations.

Absorptiometry, Photon↗

PubMed2004

Combination of BMI and Waist Circumference for Identifying Cardiovascular Risk Factors in Whites.

OBJECTIVE: BMI (kilograms per meters squared) and waist circumference (WC) (measured in centimeters) are each associated with the risk of developing cardiovascular disease (CVD). Therefore, a combination of the two may be more effective in identifying subjects at risk than either alone. The present study sought to identify the combination of BMI and WC that has the strongest association with CVD risk factors in whites. RESEARCH METHODS AND PROCEDURES: Subjects were 8712 white men and women from the Third National Health and Nutrition Examination Survey. The optimal combination of BMI and WC was developed using logistic regression models with BMI and WC as predictors and CVD risk factors as outcomes. The combined measure of BMI and WC using current cut-off points was also examined. Sensitivity, specificity, and receiver operating characteristics curves were compared between the combined measures and BMI alone. RESULTS: For white men, the optimal combination of BMI and WC for identifying CVD risk factors was 0.68 x BMI + 0.32 x WC. This combination generated a score that better estimated the odds of having CVD risk factors than either alone. For white women, WC alone largely determined the likelihood of having CVD risks. The combination of BMI and WC using current cut-off points may provide an improved measure of CVD risk. Combined measures showed a higher sensitivity or a shorter distance in receiver operating characteristic curves in the identification of CVD risk factors. DISCUSSION: Combined measures of BMI and WC may provide a higher overall test performance for CVD risk factors and may be useful in some ethnic groups as an improved means of screening subjects for further evaluation in the clinical setting.

Body Constitution↗

PubMed2004

Body-composition differences between African American and white women: relation to resting energy requirements.

BACKGROUND: Body composition differs between African American (AA) and white women, and the resting metabolic rate (RMR) is likely to be lower in AA women than in white women. OBJECTIVE: We tested 2 hypotheses: that AA women have a greater proportion of low-metabolic-rate skeletal muscle (SM) and bone than do white women and that between-race musculoskeletal differences are a function of body weight. DESIGN: Hypothesis 1 was tested by comparing SM, bone, adipose tissue, and high-metabolic-rate residual mass across 22 pairs of matched AA and white women. Magnetic resonance imaging and dual-energy X-ray absorptiometry were used to partition weight into 4 components, and RMR was both calculated from tissue-organ mass and measured. Hypothesis 2 was evaluated by measuring SM, bone, fat, and residual mass in 521 AA and white women with the use of dual-energy X-ray absorptiometry alone. RESULTS: Hypothesis 1: AA women had greater SM ( +/- SD group difference: 1.52 +/- 2.48 kg; P < 0.01) and musculoskeletal mass (1.72 +/- 2.66 kg; P < 0.01) than did white women. RMR calculated from body composition and measured RMR did not differ; RMR estimated by both approaches tended to be lower (approximately 160 kJ/d) in AA women than in white women. Hypothesis 2: SM was significantly correlated with weight, height, age, and race x weight interaction; greater SM in the AA women was a function of body weight. CONCLUSIONS: Lower RMRs in AA women than in white women are related to corresponding differences in the proportions of heat-producing tissues and organs, and these race-related body-composition differences increase as a function of body weight.

Adipose Tissue↗

PubMed2004

Visceral adipose tissue: relations between single-slice areas and total volume.

BACKGROUND: Visceral adipose tissue (VAT), which is linked with the metabolic consequences of obesity, is usually characterized by measuring VAT area at the L4-L5 vertebral interspace. However, the location of the slice with the strongest relation to VAT volume is not established. OBJECTIVE: We sought to investigate the relations between cross-sectional VAT areas at different anatomic locations and VAT volume in a large, diverse sample of healthy subjects. DESIGN: VAT volume was derived from slice areas taken at 5-cm intervals from magnetic resonance images in 121 healthy men [x +/- SD age: 41.9 +/- 15.8 y; body mass index (BMI; in kg/m(2)): 26.0 +/- 3.2; VAT: 2.7 +/- 1.8 L] and 198 healthy women (age: 48.1 +/- 18.7 y; BMI: 27.0 +/- 5.4; VAT: 1.7 +/- 1.2 L). Regression models were developed to identify the best single slice for estimating VAT volume. RESULTS: The VAT area 10 cm above L4-L5 (A(+10)) in men (R(2) = 0.932, P < 0.001) and 5 cm above L4-L5 (A(+5)) in women (R(2) = 0.945, P < 0.001) had the highest correlation with abdominal VAT. R(2) increased by only 3.8% in men and 0.5% in women with adjustment for age, race, scanning position, BMI, and waist circumference. Studies using A(+10) in men and A(+5) in women will require 14% and 9% fewer subjects, respectively, than those using slices at L4-L5 and will have equivalent power. CONCLUSION: Measurement of slice areas at A(+10) in men and A(+5) in women provides greater power for the detection of VAT volume differences than does measurement at L4-L5.

Abdomen↗

PubMed2004

Dual-energy x-ray absorptiometry-measured lean soft tissue mass: differing relation to body cell mass across the adult life span.

Lean soft tissue (LST) measured by dual-energy X-ray absorptiometry (DEXA) is used as a metabolic measure in aging research despite evidence of extracellular fluid expansion and a corresponding reduction in body cell mass (BCM) in older participants. We investigated the hypothesis that the fraction of LST as BCM is smaller with greater age. Men and women (n = 2043) had DEXA and 40K-counting for body potassium and BCM measured on the same day. Both BCM and LST were lower with greater age but the relative lowering was larger for BCM. A multiple linear regression model was fitted with BCM/LST as the dependent variable, and age, sex, and interaction terms as independent variables. Men had a mean BCM/LST greater (p < .001) than women; quadratic and cubic age terms were also significant or approached significance. Thus, the fraction of LST as BCM is smaller in older adults, a finding that has implications for the interpretation of DEXA results.

Absorptiometry, Photon↗

PubMed2003

Body cell mass: model development and validation at the cellular level of body composition.

Existing models to estimate the metabolically active body cell mass (BCM) component in vivo remain incompletely developed. The classic Moore model is based on an assumed BCM potassium content of 120 mmol/kg. Our objectives were to develop an improved total body potassium (TBK)-independent BCM prediction model on the basis of an earlier model (Cohn SH, Vaswani AN, Yasumura S, Yuen K, and Ellis KJ. J Lab Clin Med 105: 305-311, 1985), to apply this improved model in subjects to explore the sex and age dependence of the TBK/BCM ratio, to develop a new TBK/BCM model on the basis of physiological associations between TBK and total body water (TBW) at the cellular level of body composition, and to fit this new model with available reference data. Subjects were 112 healthy adults who had the following components measured: TBW by 2H2O or 3H2O, extracellular water by NaBr, total body nitrogen by in vivo neutron activation, bone mineral by dual-energy X-ray absorptiometry, and TBK by whole body counting. Human reference data were collected from earlier published reports. The improved Cohn model-derived TBK/BCM ratio was (mean +/- SD) 109.0 +/- 10.9 mmol/kg and was not significantly related to sex and age. A simplified version of the new TBK-TBW model provided a TBK/BCM ratio almost identical (109.1 mmol/kg) to that derived by the improved Cohn model. The TBK-BCM prediction formula derived from the improved and new models [BCM (kg) = 1/109 x TBK (mmol); or BCM = 0.0092 x TBK] gives BCM estimates approximately 11% higher than the classic Moore model (BCM = 0.0083 x TBK) formulated on rough tissue composition estimates. The present analyses provide a physiologically based, improved, and validated TBK-BCM prediction formula that should prove useful in body composition and metabolism research.

Adult↗

PubMed2003

Adipose tissue quantification by imaging methods: a proposed classification.

Recent advances in imaging techniques and understanding of differences in the molecular biology of adipose tissue has rendered classical anatomy obsolete, requiring a new classification of the topography of adipose tissue. Adipose tissue is one of the largest body compartments, yet a classification that defines specific adipose tissue depots based on their anatomic location and related functions is lacking. The absence of an accepted taxonomy poses problems for investigators studying adipose tissue topography and its functional correlates. The aim of this review was to critically examine the literature on imaging of whole body and regional adipose tissue and to create the first systematic classification of adipose tissue topography. Adipose tissue terminology was examined in over 100 original publications. Our analysis revealed inconsistencies in the use of specific definitions, especially for the compartment termed "visceral" adipose tissue. This analysis leads us to propose an updated classification of total body and regional adipose tissue, providing a well-defined basis for correlating imaging studies of specific adipose tissue depots with molecular processes.

Adipose Tissue↗

PubMed2003

Volume estimates by imaging methods: model comparisons with visible woman as the reference.

OBJECTIVE: To compare the accuracy of four volume estimation models to actual tissue and organ volumes measured in the visible woman. METHODS: Actual volumes were calculated from 1-mm-thick visible woman images that were segmented for five major components including subcutaneous and visceral adipose tissue across the 1730 available slices. Four available models resolved to two equations: truncated cone/truncated pyramid vs. two-column/parallel trapezium. Between-slice interval and initial slice were systematically varied when deriving component volumes using the two equations in four regions. RESULTS: For each compartment and each between-slice interval, the means of the two-column model were always the same as the corresponding reference volumes, whereas those of the truncated cone model were smaller than the reference volumes. Similarly, the coefficient variation for the two-column model was always smaller than for the truncated cone model. DISCUSSION: The equation based on the parallel trapezium and the two-column models is more accurate in estimating tissue volumes than the corresponding equation for truncated pyramid and truncated cone models. This finding has important implications for the volume calculations of imaging-based body compartments such as adipose tissue.

Anatomy↗

PubMed2003

Whole-body skeletal muscle mass: development and validation of total-body potassium prediction models.

BACKGROUND: A substantial proportion of total body potassium (TBK) in humans is found in skeletal muscle (SM), thus affording a means of predicting total-body SM from whole-body counter-measured (40)K. There are now > 30 whole-body counters worldwide that have large cross-sectional and longitudinal TBK databases. OBJECTIVE: We explored 2 SM prediction approaches, one based on the assumption that the ratio of TBK to SM is stable in healthy adults and the other on a multiple regression TBK-SM prediction equation. DESIGN: Healthy subjects aged >or= 20 y were recruited for body-composition evaluation. TBK and SM were measured by whole-body (40)K counting and multislice magnetic resonance imaging, respectively. A conceptual model with empirically derived data was developed to link TBK and adipose tissue-free SM as the ratio of TBK to SM. RESULTS: A total of 300 subjects (139 men and 161 women) of various ethnicities with a mean (+/- SD) body mass index (in kg/m(2)) of 25.1 +/- 5.4 met the study entry criteria. The mean conceptual model-derived TBK-SM ratio was 122 mmol/kg, which was comparable to the measurement-derived TBK-SM ratios in men and women (119.9 +/- 6.7 and 118.7 +/- 8.4 mmol/kg, respectively), although the ratio tended to be lower in subjects aged >or= 70 y. A strong linear correlation was observed between TBK and SM (r = 0.98, P < 0.001), with sex, race, and age as small but significant prediction model covariates. CONCLUSIONS: Two different types of prediction models were developed that provide validated approaches for estimating SM mass from (40)K measurements by whole-body counting. These methods afford an opportunity to predict SM mass from TBK data collected in healthy adults.

Absorptiometry, Photon↗