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Biomedical subjects

M B Sawyer

Publications and source records attributed to M B Sawyer.

16 recordsLinked to original sources
PubMed1997

Energy expenditure using isotope-labelled water (2H218O), exercise performance, skeletal muscle enzyme activities and plasma biochemical parameters in humans during 95 days of endurance exercise with inadequate energy intake.

Two men, R.F. and M.S., pulled sledges each with starting masses of 222 kg, 2300 km across Antarctica. Exercise was performed for approximately 10 h each day for 95 days. Despite an average energy intake of 21.3 MJ.day-1 both subjects lost more than 25% of body weight. Energy expenditure was measured using energy balance data (EB) and isotope-labelled water (2H218O). Isotope doses were taken on day 0 and day 50 of the expedition. During the first 50 days both methods gave reasonable agreement, giving energy expenditures of 38.3 (EB) and 35.5 (2H218O) MJ.day-1 in R.F. and 28.6 (EB) and 29.1 (2H218O) MJ.day-1 in M.S. The isotope data for days 20-30 yielded exceptional values of 44.6 MJ.day-1 in R.F. and 48.7 MJ.day-1 in M.S. Estimates of energy expenditure between day 51 and day 96 were much lower and although the methods were in agreement for R.F.-24.1 (EB) and 23.1 (2H218O) MJ. day-1, there was poor agreement for MS-26.8 (EB) and 18.8 (2H218O) MJ.day-1. However, some practical difficulties occurred during this second period and there were also problems arising from marked increases in body water that made estimates of body mass and composition change difficult to interpret. The latter problems were probably due to malnutrition, which may have also been responsible for surprising increases in urinary excretion of 2H and 18O observed in both men at around day 81. These increases may reflect the release of label incorporated into molecules other than water which do not normally freely exchange with the body water pool under the circumstances of marked malnourishment. Following the expedition, both men showed declines in maximal O2 consumption (VO2max, 53.6 to 41.2 ml O2 kg-1.min-1 in R.F., 58.1-46.0 ml O2 kg-1.min-1 in M.S.); maximal voluntary isometric force production in different muscle groups (up to 19.9% in R.F. and 55.8% in M.S.) and both cytoplasmic and mitochondrial skeletal muscle enzyme activities (up to 56% in R.F. and 63% in M.S.). Plasma samples taken during the expedition showed low glucose levels, inappropriately high insulin levels, and declines in testosterone and luteinizing hormone. Thyroxine, cholesterol, albumin and triglyceride levels remained normal.

Adult↗
PubMed1996

Components of total energy expenditure in free-living elderly men (over 75 years of age): measurement, predictability and relationship to quality-of-life indices.

Current recommendations for energy requirements in the elderly are based on assumed levels of physical activity relative to BMR (1.5 x BMR). The main aim of the present study was to establish whether these recommendations might be applicable to a randomly-selected group of free-living elderly men (all over 75 years of age). BMR was measured by indirect calorimetry and total energy expenditure (TEE) by the doubly-labelled-water technique. Further aims included evaluating the applicability of a variety of BMR prediction equations and whether assessed quality of life reflected any measured indices of energy expenditure. The mean value for daily energy requirement was found to be 1.5 x BMR (89 J/kg per min) but with substantial inter-individual variation (sd 0.2 x BMR; 14 J/kg per min). The bias between measured TEE and TEE estimated (1.5 x BMR) from the various BMR predictions varied according to which equation was used (-10- + 8% of the mean) with substantial 95% limits of agreement (28-30% of the mean). TEE and physical activity plus thermogenesis (TEE-BMR) were positively related to activities of daily living, but no relationships were apparent between these and perceived quality of life. It is concluded that, despite considerable inter-individual variability, national recommendations for energy requirements of elderly people are applicable to this randomly-selected group of free-living men over 75 years of age but that substantial variation exists when attempts are made to estimate TEE from measurements or predictions of BMR.

Activities of Daily Living↗
PubMed1996

A 3-year follow-up of the intellectual and academic functioning of children receiving central nervous system prophylactic chemotherapy for leukemia.

This prospective study compared the intellectual and academic functioning of two groups of children treated for cancer over the 3 years after their diagnosis. One group consisted of children who received central nervous system (CNS) prophylactic chemotherapy, and the other group consisted of children with cancer who did not receive CNS chemotherapy. The results suggest that the children who received CNS chemotherapy experienced more adverse effects from their treatment in the area of academic functioning than the children who did not receive CNS chemotherapy. Although there were no differences in the academic functioning of the two groups of children immediately after their diagnosis, 3 years postdiagnosis, the CNS-treated children scored more poorly on academic tests of reading, spelling, and arithmetic than the non-CNS-treated children. The results suggest that CNS chemotherapy prophylaxis may impede academic achievement.

Adolescent↗
PubMed1995

Energy expenditure and wasting in human immunodeficiency virus infection.

BACKGROUND: Increased expenditure of energy at rest has been considered a contributing factor to the negative energy balance and weight loss that occur in patients with human immunodeficiency virus (HIV) infection. However, the true determinant of energy balance is not resting but total energy expenditure. We sought to determine the contribution of total energy expenditure to weight changes in patients with HIV-associated wasting. METHODS: We performed 51 assessments of energy metabolism in 27 men with HIV infection at different stages of disease, including periods of both rapid and slow weight loss. Resting energy expenditure was measured by indirect calorimetry, total energy expenditure by the doubly-labeled-water technique, and energy intake by recording the weight of food consumed. The results were compared with the rate of weight loss or gain. RESULTS: The mean (+/- SD) total energy expended by the HIV-infected men was 2750 +/- 670 kcal per day, no more than that expended by normal men. There was a significant positive relation between total energy expenditure and the rate of weight change (r = 0.61, P < 0.001); thus, during rapid weight loss, total energy expenditure was reduced to 2180 +/- 580 kcal per day (P = 0.009), primarily because of reduced physical activity. During rapid weight loss, the negative energy balance (-850 +/- 580 kcal per day) was primarily the result of the reduction in energy intake, to 1330 +/- 610 kcal per day; intake correlated strongly with the rate of weight change (r = 0.84, P < 0.001). CONCLUSIONS: In patients with HIV infection, total energy expenditure is reduced during episodes of weight loss. Reduced energy intake, not elevated energy expenditure, is the prime determinant of weight loss in HIV-associated wasting.

Adult↗
PubMed1994

Comparative evaluation of body composition methods and predictions, and calculation of density and hydration fraction of fat-free mass, in obese women.

The objective of this study was to apply a three-component model of body composition to a group of obese women in order to (a) establish the relative value of a number of readily available prediction equations by comparison of the extent of agreement between these predictions and body composition estimated by the model and other reference methods and (b) evaluate density and hydration of fat-free mass. Estimation of body composition was carried out by reference methods and prediction equations and the usefulness of these prediction equations for application specifically to obese women was evaluated. The subjects were 15 obese, otherwise healthy, Caucasian women (body mass index > 30kg/m2 and body fat > 40% of body weight, as originally determined using densitometry). Body composition was estimated using three established reference methods (deuterium dilution which primarily measures total body water, densitometry for body fat and fat-free mass and total body potassium) and the three component model constructed from deuterium dilution and densitometry. Density and hydration fraction of the fat-free mass were calculated from appropriate values obtained as integral parts of the three-component model. In addition, body composition was predicted from various prediction equations incorporating weight and height (some of which include a factor for age), from a number of prediction equations utilizing different terms involving the same whole-body bio-electrical impedance measurement and from measurements of skinfold thickness and near infrared interactance. The extent of agreement between methods was assessed using bias and 95% limits of agreement. Mean density of fat-free mass was found to be 1.104 kg/l (s.d. 0.006kg/l) with a range of 1.093 to 1.117 kg/l, and mean hydration fraction was 0.712 (s.d. 0.016) with a range of hydration from 68.2% to 75.1% (all values were calculated from the three-component model). In general, the reference methods (densitometry, deuterium dilution, the three-component model and total body potassium) demonstrated better agreement with each other than with the prediction methods or equations. In these obese women, skinfold thickness measurements are apparently less reliable (large bias and 95% limits of agreement) than in the lean subjects of a variety of other studies. A majority of interpretations of weight and height measurements and predictions incorporating impedance/resistance measurements are apparently not applicable to this group of obese women, due to large values for both bias and 95% limits of agreement.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1993

Measurements of energy expenditure using isotope-labelled water (2H2(18)O) during an Arctic expedition.

Estimates of energy expenditure using both isotope-labelled (2H2(18)O) water and dietary intake/body composition changes were made during an attempt by two men (MS and RF) to walk to the North Pole. The isotope-labelled water technique gave mean estimates of daily energy expenditure for the 48-day expedition of 28.05 MJ (MS) and 32.38 MJ (RF), which compared with estimates of 25.66 MJ (MS) and 24.86 MJ (RF) from the intake/body composition measurements. Fluid retention and peripheral oedema probably caused a considerable underestimate of the losses in body energy stores when applying the energy balance method, whereas in the isotope method, uncertainty in the measurements of isotopic background led to minimum errors of -4.9% to +4.0% of the means for MS and -12.7% to +8.2% for RF (95% confidence limits).

Adult↗
PubMed1991

Longitudinal assessment of the components of energy balance in well-nourished lactating women.

The mechanisms by which well-nourished women meet the additional energy costs of lactation were studied by measuring energy intake (EI), basal metabolic rate (BMR), total energy expenditure by doubly labeled water (TEE), physical activity plus thermogenesis (TEE-BMR), changes in body fat stores, and milk energy transfer. Ten women were studied at 36 wk gestation; 4, 8, and 12 wk lactation (L4, L8, L12); and when nonpregnant and nonlactating (NPNL) after weaning. At L4, L8, and L12 the energy transferred in milk averaged 2245, 2225, and 2217 kJ/d with an additional 445 kj/d (106 kcal/d) estimated as being necessary for synthesis. EI was 1360, 1740, and 1275 kJ/d higher than the NPNL values, representing 56% of the costs of lactation. The remaining 44% was met by a reduction in TEE (-945, -688, and -826 kJ/d vs NPNL) caused largely by a reduction in physical activity because BMR was essentially unchanged (+29, -12, and -218 kJ/d). The energy-balancing strategies adopted by different women varied markedly.

Basal Metabolism↗
PubMed1982

Breast-milk intake measurement in mixed-fed infants by administration of deuterium oxide to their mothers.

Breast-milk intakes in infants can be estimated from measurements of water turnover rates after the oral administration of small doses of deuterium oxide (2H2O) to the infant or its mother. However, when the former method is used it is not possible to distinguish water intakes from milk and those from other sources. Giving a 2H2O dose to the mother avoids this problem. The theoretical basis for these techniques is examined and useful compromises between the requirements of theory and practice are suggested. Results obtained for breast-milk intakes of Gambian and Papua New Guinean children are used to illustrate the potential value of the procedures.

Administration, Oral↗
PubMed1979

New method for measuring milk intakes in breast-fed babies.

A method for the measurement of milk intake in young breast-fed babies is described in which heavy water (2H2O) enrichment in saliva is measured on only two occasions after a single oral dose of 2H2O. Values obtained by this method are compared with those obtained by test-weighing. This new method is ideal for routine surveys since it does not interfere with feeding habits and maternal life style, and no technical expertise is required of the mother.

Breast Feeding↗
PubMed1977

Whole-body albumin mass and distribution in rats fed on low-protein diets.

1. From 5 weeks of age, control and experimental rats were given diets containing 210 and 31 g protein/kg respectively, and killed for analysis at 0, 2, 5, 8, 12 and 20 d after the start of the experiment. At these times estimates were made of plasma albumin concentration, plasma volume and total vascular and extravascular albumin mass. 2. Plasma albumin concentrations were significantly lower in the experimental animals when compared to controls at 8, 12 and 20 d but plasma volumes (ml/kg body-weight) tended to be greater in the former animals. Total vascular albumin mass (g/kg body-weight) was significantly less in experimental animals compared to controls at 8 and 20 d, but was significantly reduced below values at 0 d only at 20 d. 3. extravascular albumin mass (g/kg body-weight) was significantly lower in experimental animals in comparison with controls at 2, 5, 8, 12 and 20 d and significantly reduced below values at 0 d at 5, 8, 12, and 20 d. 4. Whole-body albumin mass was significantly reduced at 5, 8, 12 and 20 d when compared both with controls killed at the same time and animals killed at 0 d. Measurement of the ratio, extravascular albumin mass: vascular albumin mass indicated a significant redistribution of whole-body albumin mass at 5 and 20 d and mean values for this ratio were always lower in experimental animals than in controls. 5. It was concluded that measurement of plasma albumin concentration does not indicate the true extent of whole-body albumin losses in protein deficiency since total vascular albumin mass is, to some extent, maintained at the expense of extravascular albumin mass.

Albumins↗
PubMedDate not supplied

Prediction of body composition in elderly men over 75 years of age.

A comprehensive number of body composition predictions (involving weight, height, skinfold thicknesses, bioelectrical impedance and near-infrared interactance-NIRI) were evaluated against total body water (TBW from isotope dilution), in 23 randomly selected men over 75 years old, and dual-energy X-ray absorptiometry (DXA), in 15 volunteers from this group. Comparisons were made between anthropometric and impedance methods for estimating limb muscle mass (obtained using DXA). Bias and 95% limits of agreement between measured TBW and DXA estimates were -2.1 kg and 3.1 kg, respectively (for fat, 5.4% and 6.1% body weight). Agreement between TBW predictions and reference measurements was remarkably variable, irrespective of whether TBW was predicted from TBW-specific equations or indirectly from estimates of fat or fat-free mass: for predictions using anthropometry, bias ranged from -4.7 kg to 1.6 kg and 95% limits of agreement from bias +/- 3.8 kg to +/- 5.0 kg; using impedance, bias was -8.8 kg to 3.2 kg and 95% limits of agreement were bias +/- 3.6 kg to +/- 7.8 kg; corresponding values for NIRI were -5.3 kg and +/- 5.4 kg. Although some non-age-specific equations appeared valid, age-specific equations generally predicted TBW better. Limb muscle mass (DXA) was predicted better using the segmental impedance method, from indices of limb muscle area (r = 0.76; SEE = 1.9 kg) and volume (r = 0.86; SEE = 1.6 kg), than by anthropometry alone (r = 0.61 and 0.71; SEE = 2.3 kg and 2.1 kg, respectively). In conclusion, some body composition predictions are unacceptable (at least for TBW) in older men, and care is recommended when selecting from these methods or equations. Also, the segmental impedance method is as good as, if not better than, anthropometry alone in predicting limb muscle mass (DXA) in older men.

Absorptiometry, Photon↗
PubMedDate not supplied

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Models, Theoretical↗