Biomedical subjects

Dympna Gallagher

Publications and source records attributed to Dympna Gallagher.

42 records · Page 3Linked to original sources

PubMed2002

DXA: potential for creating a metabolic map of organ-tissue resting energy expenditure components.

OBJECTIVE: This study tested the hypothesis that tissue-organ components can be derived from DXA measurements, and in turn, resting energy expenditure (REE) can be calculated from the summed heat productions of DXA-estimated brain, skeletal muscle mass (SM), adipose tissue, bone, and residual mass (RM). RESEARCH METHODS AND PROCEDURES: Subjects were divided into five groups of adults <50 years of age. The specific metabolic rate of RM was developed in 13 Group I healthy subjects and a DXA-brain mass prediction formula in 52 Group II subjects. SM, adipose tissue, and bone models were developed based on earlier reports. The composite REE prediction model (REEp) was tested in 154 Group III subjects in whom REEp was compared with measured REE (REEm). Features of the developed model were determined in 94 normal-weight men and women (Group IV) and seven spinal cord injury patients and healthy matched controls (Group V). RESULTS: REEp and REEm in Group III were highly correlated (y = 0.85x + 233; r = 0.82, p < 0.001), and no bias was detected. Both REEm (mean +/- SD, 1,579 +/- 324 kcal/d) and REEp (1,585 +/- 316 kcal/d) were also highly correlated (r values = 0.85 to 0.98; p values < 0.001) and provided similar group values to REE estimated by the Harris-Benedict equations (1,597 +/- 279 kcal/d) and Wang's composite fat-free mass-based REE equation (1,547 +/- 248 kcal/d). New insights into the sources and distribution of REE were provided by analysis of the demonstration groups. DISCUSSION: This approach offers a new practical and educational opportunity to examine REE in subject groups using modeling strategies that reveal the magnitude and distribution of fundamental somatic heat-producing units.

Absorptiometry, Photon↗

PubMed2002

Total-body skeletal muscle mass: estimation by a new dual-energy X-ray absorptiometry method.

BACKGROUND: Skeletal muscle (SM) is an important body-composition component that remains difficult and impractical to quantify by most investigators outside of specialized research centers. A large proportion of total-body SM is found in the extremities, and a large proportion of extremity lean soft tissue is SM. A strong link should thus exist between appendicular lean soft tissue (ALST) mass and total-body SM mass. OBJECTIVE: The objective was to develop prediction models linking ALST estimated by dual-energy X-ray absorptiometry (DXA) with total-body SM quantified by multislice magnetic resonance imaging in healthy adults. DESIGN: ALST and total-body SM were evaluated with a cross-sectional design in adults [body mass index (in kg/m(2)) < 35] with an SM-prediction model developed and validated in model-development and model-validation groups, respectively. The model-development and model-validation groups included 321 and 93 ethnically diverse adults, respectively. RESULTS: ALST alone was highly correlated with total-body SM (model 1: R(2) = 0.96, SEE = 1.63 kg, P < 0.001), although multiple regression analyses showed 2 additional predictor variables: age (model 2: 2-variable combined R(2) = 0.96, SEE = 1.58 kg, P < 0.001) and sex (model 3: 3-variable combined R(2) = 0.96, SEE = 1.58 kg, P < 0.001). All 3 models performed well in the validation group. An SM-prediction model based on the SM-ALST ratio was also developed, although this model had limitations when it was applied across all subjects. CONCLUSION: Total-body SM can be accurately predicted from DXA-estimated ALST, thus affording a practical means of quantifying the large and clinically important SM compartment.

Absorptiometry, Photon↗

PubMed2002

Body-size dependence of resting energy expenditure can be attributed to nonenergetic homogeneity of fat-free mass.

An enduring enigma is why the ratio of resting energy expenditure (REE) to metabolically active tissue mass, expressed as the REE/fat-free mass (FFM) ratio, is greater in magnitude in subjects with a small FFM than it is in subjects with a large FFM. This study tested the hypothesis that a higher REE/FFM ratio in subjects with a small body mass and FFM can be explained by a larger proportion of FFM as high-metabolic-rate tissues compared with that observed in heavier subjects. REE was measured by indirect calorimetry, FFM by dual-energy X-ray absorptiometry (DEXA), and tissue/organ contributions to FFM by whole body magnetic resonance imaging (MRI) in healthy adults. Four tissue heat-producing contributions to FFM were evaluated, low-metabolic-rate fat-free adipose tissue (18.8 kJ/kg), skeletal muscle (54.4 kJ/kg), and bone (9.6 kJ/kg); and high-metabolic-rate residual mass (225.9 kJ/kg). Initial evaluations in 130 men and 159 women provided strong support for two key, developed models, one linking DEXA FFM with MRI FFM estimates and the other linking REE predicted from the four MRI-derived components with measured REE. There was an inverse association observed between measured REE/FFM and FFM (r(2) = 0.17, P < 0.001). Allometric models revealed a similar pattern of tissue change relative to body mass across males and females with greater proportional increases in fat-free adipose tissue and skeletal muscle than in FFM and a smaller proportional increase in residual mass than in FFM. When examined as a function of FFM, positive slopes were observed for skeletal muscle/FFM and pooled low-metabolic-rate components, and a negative slope for residual mass. Our linked REE-body composition models and associations strongly support the hypothesis that FFM varies systematically in the proportion of thermogenic components as a function of body mass and FFM. These observations have important implications for the interpretation of between-individual differences in REE expressed relative to metabolically active tissue mass.

Adult↗

PubMed2002

High-resolution magnetic resonance imaging tracks changes in organ and tissue mass in obese and aging rats.

Magnetic resonance imaging (MRI) has the ability to discriminate between various soft tissues in vivo. Whole body, specific organ, total adipose tissue (TAT), intra-abdominal adipose tissue (IAAT), and skeletal muscle (SM) weights determined by MRI were compared with weights determined by dissection and chemical analysis in two studies with male Sprague-Dawley rats. A 4.2-T MRI machine acquired high-resolution, in vivo, longitudinal whole body images of rats as they developed obesity or aged. Weights of the whole body and specific tissues were determined using computer image analysis software, including semiautomatic segmentation algorithms for volume calculations. High correlations were found for body weight (r = 0.98), TAT (r = 0.99), and IAAT (r = 0.98) between MRI and dissection and chemical analyses. MRI estimated the weight of the brain, kidneys, and spleen with high accuracy (r > 0.9), but overestimated IAAT, SM, and liver volumes. No differences were detected in organ weights using MRI and dissection measurements. Longitudinal MRI measurements made during the development of obesity and aging accurately represented changes in organ and tissue mass.

Aging↗

PubMed2002

Prepubertal Asians have less limb skeletal muscle.

Skeletal muscle mass in prepubertal Asian children has not been examined previously. The aims of this study were to test the hypotheses that 1) prepubertal Asians have less appendicular skeletal muscle (ASM) mass compared with African-Americans and Caucasians, and 2) ASM is less in prepubertal Asian girls compared with Asian boys. ASM was estimated by using dual-energy X-ray absorptiometry in healthy prepubertal girls (n = 170) and boys (n = 166). The results showed that, after adjusting for age, height, and body weight, 1) Asian girls and boys had less amounts of ASM than African-Americans (P < 0.001); 2) Asian girls had less amounts of ASM than Caucasian girls (P = 0.004); 3) there was a trend towards less ASM in Asian compared with Caucasian boys (P = 0.07); 4) and Asian girls had significantly less ASM than Asian boys (P < 0.001). This study indicates that skeletal muscle mass as a fraction of body weight is smaller in Asian compared with African-American and Caucasian children.

Black or African American↗

PubMed2002

Sex and race differences in fat distribution among Asian, African-American, and Caucasian prepubertal children.

Sexual dimorphism in fat distribution is thought to emerge during puberty. Truncal or android body fat distribution is characteristic of adult males but is also recognized as a human cardiovascular risk factor. Race differences in truncal fat are clearly evident in adults and have been described in prepubertal children but not between Asians and other race groups. The aim of this study in African-American, Asian, and Caucasian prepubertal children was to evaluate sex differences and race differences in body fat distribution. Analysis of covariance was used to explore fat distribution in 358 prepubertal children (176 girls and 182 boys; 143 Asians, 95 African-Americans, and 120 Caucasians), measured by skinfold thickness and dual-energy x-ray absorptiometry (DXA) in a cross-sectional study. Extremity and gynoid fat masses were evaluated after adjustment for trunk or android fat, respectively, and for covariates including age, weight, height, and interactions. In Asian children, sex differences were present in models for gynoid fat by DXA only (P < 0.001), with girls having greater gynoid fat than boys. In African-American and Caucasian children, sex differences were present in models for extremity and gynoid fat masses, measured by both methods. Among girls, Asians had generally lower adjusted extremity and gynoid fat than Caucasians and African-Americans. Among boys, Asians had lower adjusted extremity fat by DXA than Caucasians (P < 0.01) but greater gynoid fat by skinfolds than African-Americans (P < 0.01). This study of prepubertal children demonstrates that: 1) sex differences in body fat distribution are present in prepubertal children but that the specific characteristics for Asians differ from African-Americans and Caucasians, and 2) differences in body fat distribution in Asian children, compared with African-Americans and Caucasians, are present but vary by sex. This comparison of African-American, Asian, and Caucasian prepubertal children suggests phenotypic differences. Additional studies are needed to explore the metabolic and health risk implications of these findings.

Abdomen↗