Body composition by DXA Shepherd, John A; Ng, Bennett K; Sommer, Markus J ...
Bone (New York, N.Y.),
11/2017, Letnik:
104
Journal Article
Recenzirano
Odprti dostop
Abstract Body composition measurements from DXA have been available since DXA technology was developed 30 years ago, but are historically underutilized. Recently, there have been rapid developments ...in body composition assessment including the analysis and publication of representative data for the US, official usage guidance from the International Society for Clinical Densitometry, and development of regional body composition measures with clinical utility. DXA body composition is much more than whole body percent fat. In this paper celebrating 30 years of DXA for body composition, we will review the principles of DXA soft tissue analysis, practical clinical and research applications, and what to look for in the future.
Clinical scores of mammographic breast density are highly subjective. Automated technologies for mammography exist to quantify breast density objectively, but the technique that most accurately ...measures the quantity of breast fibroglandular tissue is not known.
To compare the agreement of three automated mammographic techniques for measuring volumetric breast density with a quantitative volumetric MRI-based technique in a screening population.
Women were selected from the UCSF Medical Center screening population that had received both a screening MRI and digital mammogram within one year of each other, had Breast Imaging Reporting and Data System (BI-RADS) assessments of normal or benign finding, and no history of breast cancer or surgery. Agreement was assessed of three mammographic techniques (Single-energy X-ray Absorptiometry SXA, Quantra, and Volpara) with MRI for percent fibroglandular tissue volume, absolute fibroglandular tissue volume, and total breast volume.
Among 99 women, the automated mammographic density techniques were correlated with MRI measures with R(2) values ranging from 0.40 (log fibroglandular volume) to 0.91 (total breast volume). Substantial agreement measured by kappa statistic was found between all percent fibroglandular tissue measures (0.72 to 0.63), but only moderate agreement for log fibroglandular volumes. The kappa statistics for all percent density measures were highest in the comparisons of the SXA and MRI results. The largest error source between MRI and the mammography techniques was found to be differences in measures of total breast volume.
Automated volumetric fibroglandular tissue measures from screening digital mammograms were in substantial agreement with MRI and if associated with breast cancer could be used in clinical practice to enhance risk assessment and prevention.
The International Society for Clinical Densitometry (ISCD) convenes a Position Development Conference (PDC) every 2-3 yr to make recommendations for guidelines and standards in the field of ...musculoskeletal measurement and assessment. The recommendations pertain to clinically relevant issues regarding the acquisition, quality control, interpretation, and reporting of various aspects of musculoskeletal health metrics. Topics for consideration are developed by the ISCD Board of Directors and the Scientific Advisory Committee. For the 2013 PDC, body composition analysis was a central topic area for the first time and considered timely because of the scientific advances in measurement of fat and lean body mass by dual-energy X-ray absorptiometry (DXA). Indications for DXA and vertebral fracture assessment and use of reference data to calculate bone mineral density T-scores were also updated. Task Forces for each of these areas were assigned questions of relevance to a clinical audience and asked to conduct comprehensive literature reviews. Reports with proposed Position Statements were then presented to an international panel of experts. The Expert Panel included representatives of the International Osteoporosis Foundation, the American Society for Bone and Mineral Research, the National Osteoporosis Foundation, Osteoporosis Canada, and the North American Menopause Society. The PDC was held in Tampa, FL, contemporaneously with the Annual Meeting of the ISCD, March 21 through March 23, 2013. This report describes the methodology of the 2013 ISCD PDC and summarizes the results of the 2013 ISCD PDC for vertebral fracture assessment/DXA and National Health and Nutrition Survey (NHANES) Reference Database Task Forces. A separate article in this issue will summarize the results of the Body Composition Analysis Task Forces.
IMPORTANCE: The efficacy and safety of time-restricted eating have not been explored in large randomized clinical trials. OBJECTIVE: To determine the effect of 16:8-hour time-restricted eating on ...weight loss and metabolic risk markers. INTERVENTIONS: Participants were randomized such that the consistent meal timing (CMT) group was instructed to eat 3 structured meals per day, and the time-restricted eating (TRE) group was instructed to eat ad libitum from 12:00 pm until 8:00 pm and completely abstain from caloric intake from 8:00 pm until 12:00 pm the following day. DESIGN, SETTING, AND PARTICIPANTS: This 12-week randomized clinical trial including men and women aged 18 to 64 years with a body mass index (BMI, calculated as weight in kilograms divided by height in meters squared) of 27 to 43 was conducted on a custom mobile study application. Participants received a Bluetooth scale. Participants lived anywhere in the United States, with a subset of 50 participants living near San Francisco, California, who underwent in-person testing. MAIN OUTCOMES AND MEASURES: The primary outcome was weight loss. Secondary outcomes from the in-person cohort included changes in weight, fat mass, lean mass, fasting insulin, fasting glucose, hemoglobin A1c levels, estimated energy intake, total energy expenditure, and resting energy expenditure. RESULTS: Overall, 116 participants (mean SD age, 46.5 10.5 years; 70 60.3% men) were included in the study. There was a significant decrease in weight in the TRE (−0.94 kg; 95% CI, −1.68 to −0.20; P = .01), but no significant change in the CMT group (−0.68 kg; 95% CI, -1.41 to 0.05, P = .07) or between groups (−0.26 kg; 95% CI, −1.30 to 0.78; P = .63). In the in-person cohort (n = 25 TRE, n = 25 CMT), there was a significant within-group decrease in weight in the TRE group (−1.70 kg; 95% CI, −2.56 to −0.83; P < .001). There was also a significant difference in appendicular lean mass index between groups (−0.16 kg/m2; 95% CI, −0.27 to −0.05; P = .005). There were no significant changes in any of the other secondary outcomes within or between groups. There were no differences in estimated energy intake between groups. CONCLUSIONS AND RELEVANCE: Time-restricted eating, in the absence of other interventions, is not more effective in weight loss than eating throughout the day. TRIAL REGISTRATION: ClinicalTrials.gov Identifiers: NCT03393195 and NCT03637855
There have been many scientific advances in fracture risk prediction beyond bone density. The International Society for Clinical Densitometry (ISCD) convened a Position Development Conference (PDC) ...on the use of dual-energy X-ray absorptiometry beyond measurement of bone mineral density for fracture risk assessment, including trabecular bone score and hip geometry measures. Previously, no guidelines for nonbone mineral density DXA measures existed. Furthermore, there have been advances in the analysis of quantitative computed tomography (QCT) including finite element analysis, QCT of the hip, DXA-equivalent hip measurements, and opportunistic screening that were not included in the previous ISCD positions. The topics and questions for consideration were developed by the ISCD Board of Directors and the Scientific Advisory Committee and were designed to address the needs of clinical practitioners. Three task forces were created and asked to conduct comprehensive literature reviews to address specific questions. The task forces included participants from many countries and a variety of interests including academic institutions and private health care delivery organizations. Representatives from industry participated as consultants to the task forces. Task force reports with proposed position statements were then presented to an international panel of experts with backgrounds in bone densitometry. The PDC was held in Chicago, Illinois, USA, contemporaneously with the Annual Meeting of the ISCD, February 26 through February 28, 2015. This Executive Summary describes the methodology of the 2015 PDC on advanced measures from DXA and QCT and summarizes the approved official positions. Six separate articles in this issue will detail the rationale, discussion, and additional research topics for each question the task forces addressed.
Key points
Theoretical models suggest there is no benefit of high affinity haemoglobin to preserve maximal oxygen uptake in acute hypoxia but the comparative biology literature has many examples of ...species that are evolutionarily adapted to hypoxia and have high affinity haemoglobin.
We studied humans with high affinity haemoglobin and compensatory polycythaemia. These subjects performed maximal exercise tests in normoxia and hypoxia to determine how their altered haemoglobin affinity impacts hypoxic exercise tolerance.
The high affinity haemoglobin participants demonstrated an attenuated decline in maximal aerobic capacity in acute hypoxia.
Those with high affinity haemoglobin had no worsening of pulmonary gas exchange during hypoxic exercise but had greater lactate and lower pH than controls for all exercise bouts.
High affinity haemoglobin and compensatory polycythaemia mitigated the decline in exercise performance in acute hypoxia through a higher arterial oxygen content and an unchanged pulmonary gas exchange.
The longstanding dogma is that humans exhibit an acute reduction in haemoglobin (Hb) binding affinity for oxygen that facilitates adaptation to moderate hypoxia. However, many animals have adapted to high altitude through enhanced Hb binding affinity for oxygen. The objective of the study was to determine whether high affinity haemoglobin (HAH) affects maximal and submaximal exercise capacity. To accomplish this, we recruited individuals (n = 11, n = 8 females) with HAH (P50 = 16 ± 1 mmHg), had them perform normoxic and acute hypoxic (15% inspired oxygen) maximal exercise tests, and then compared their results to matched controls (P50 = 26 ± 1, n = 14, n = 8 females). Cardiorespiratory and arterial blood gases were collected throughout both exercise tests. Despite no difference in end‐exercise arterial oxygen tension in hypoxia (59 ± 6 vs. 59 ± 9 mmHg for controls and HAH, respectively), the HAH subjects’ oxyhaemoglobin saturation (Sa,O2) was ∼7% higher. Those with HAH had an attenuated decline in maximal oxygen uptake (V̇O2max) (4 ± 5% vs. 12 ± %, p < 0.001) in hypoxia and the change in V̇O2max between trials was related to the change in SaO2 (r = −0.75, p < 0.0001). Compared to normoxia, the controls’ alveolar‐to‐arterial oxygen gradient significantly increased during hypoxic exercise, whereas pulmonary gas exchange in HAH subjects was unchanged between the two exercise trials. However, arterial lactate was significantly higher and arterial pH significantly lower in the HAH subjects for both exercise trials. We conclude that HAH attenuates the decline in maximal aerobic capacity and preserves pulmonary gas exchange during acute hypoxic exercise. Our data support the comparative biology literature indicating that HAH is a positive adaptation to acute hypoxia.
Key points
Theoretical models suggest there is no benefit of high affinity haemoglobin to preserve maximal oxygen uptake in acute hypoxia but the comparative biology literature has many examples of species that are evolutionarily adapted to hypoxia and have high affinity haemoglobin.
We studied humans with high affinity haemoglobin and compensatory polycythaemia. These subjects performed maximal exercise tests in normoxia and hypoxia to determine how their altered haemoglobin affinity impacts hypoxic exercise tolerance.
The high affinity haemoglobin participants demonstrated an attenuated decline in maximal aerobic capacity in acute hypoxia.
Those with high affinity haemoglobin had no worsening of pulmonary gas exchange during hypoxic exercise but had greater lactate and lower pH than controls for all exercise bouts.
High affinity haemoglobin and compensatory polycythaemia mitigated the decline in exercise performance in acute hypoxia through a higher arterial oxygen content and an unchanged pulmonary gas exchange.
Body Mass Index has traditionally been used as a measure of health, but Fat Mass Index (FMI) and Lean Mass Index (LMI) have been shown to be more predictive of mortality and health risk. Total body ...FMI and LMI reference curves have particularly been useful in quantifying sarcopenia and sarcopenic obesity. Research has shown regional composition has significant associations to health outcomes. We derived FMI and LMI reference curves of the regions of the body (leg, arm, and trunk) for 15,908 individuals in the 1999-2004 National Health and Nutrition Examination Survey data for each sex and ethnicity using the Lambda-Mu-Sigma (LMS) method and developed software to visualize this regional composition. These reference curves displayed differentiation between males and females during puberty and sharper limb LMI declines during late adulthood for males. For adults ages 30-50, females had 39%, 83%, and 47% larger arm, leg, and trunk FMI values than males, respectively. Males had 49%, 20%, and 15% higher regional LMI values than females for the arms, legs, and trunk respectively. The leg FMI and LMI of black females were 14% and 15% higher respectively than those of Hispanic and white females. White and Hispanic males had 37% higher trunk FMI values than black males. Hispanic females had 20% higher trunk FMI than white and black females. These data underscore the importance of accounting for sex and ethnicity in studies of regional composition. This study is the first to produce regional LMI and FMI reference tables and curves from the NHANES dataset. These reference curves provide a framework useful in studies and research involving sarcopenia, obesity, sarcopenic obesity, and other studies of compositional phenotypes. Further, the software tool we provide for visualizing regional composition will prove useful in monitoring progress in physical therapy, diets, or other attempts to attain healthier compositions.
In humans, β-adrenergic receptor activation causes a substantial portion of hypoxic vasodilation in skeletal muscle at rest and during forearm exercise. Recent evidence suggests that β-adrenergic ...receptors are either more sensitive or upregulated in young women vs. men. Therefore, we examined whether sex influences hypoxic vasodilation in 31 young subjects (15 women/16 men; 26 ± 1 yr). We also examined whether potential sex-related differences existed in a group of older adults (6 women/5 men; 61 ± 2 yr). All subjects performed forearm exercise at 10 and 20% of maximum under normoxic and hypoxic 80% arterial O2 saturation (So2) conditions. Forearm vascular conductance (FVC; ml · min(-1) · 100 mmHg(-1)) was calculated from blood flow (ml/min) and blood pressure (mmHg). At rest, young women demonstrated a greater vasodilator response to hypoxia compared with men (39 ± 12 vs. 13 ± 6%, P < 0.05). The absolute compensatory vasodilator response (hypoxic FVC-normoxic FVC) during exercise was similar between sexes, but the relative change was greater in young women at 10% (28 ± 5 vs. 17 ± 3%, P < 0.05) and 20% exercise (29 ± 4% vs. 15 ± 3%, P < 0.01). Additionally, the absolute changes in vasodilation after normalizing the response to forearm volume or workload were greater in young women during exercise (P < 0.05). Interestingly, the compensatory vasodilator responses between older women and men were similar at 10 and 20% exercise, regardless of whether the response is expressed as absolute, relative, or absolute change normalized for forearm volume or workload (P = 0.054-0.97). Our data suggest that the compensatory vasodilator response to hypoxic exercise is greater in young women compared with men. However, sex-specific differences appear to be lost with aging.
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