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Biomedical subjects

M N Bronstein

Publications and source records attributed to M N Bronstein.

8 recordsLinked to original sources
PubMed1997

Technical and methodologic considerations for performance of indirect calorimetry in ventilated and nonventilated preterm infants.

OBJECTIVE: To evaluate and refine indirect calorimetry measurement techniques so that accurate metabolic measurements can be performed in mechanically ventilated and convalescing preterm infants who require supplemental oxygen. DESIGN: Laboratory validation of an indirect calorimeter; clinical and laboratory assessments of technical problems in performing metabolic measurements; and clinical indirect calorimetry studies in mechanically ventilated and nonventilated preterm infants. SETTING: Neonatal intensive care unit (ICU) in a tertiary care university hospital. PATIENTS: Level II and level III mechanically ventilated (n = 10) and nonventilated (n = 14) neonatal ICU patients who required FIO2 levels ranging from 0.21 to 0.42. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: System calibration was assessed by combustion of 100% ethanol; the mean respiratory quotient was 0.667 +/- 0.001 (SEM). In addition, oxygen consumption (Vo2) and CO2 production (Vco2) were simulated by CO2/nitrogen infusions within the range expected for 0.5- to 7-kg infants. Mean relative errors were 0.6 +/- 0.3% and 1.8 +/- 0.3% for expected Vo2 and Vco2 values, respectively. In 27 mechanically ventilated patients with no audible endotracheal tube leak, measured endotracheal tube leak ranged from 0.0% to 7.5%. Fluctuations in FIO2 during mechanical ventilation were monitored in 30-min studies, using wall-source (n = 27) or tank-source (n = 11) supplemental oxygen. Mean FIO2 variation was 0.00075 +/- 0.00013 vs. 0.00011 +/- 0.00001 using wall-source and tank-source oxygen, respectively. Some of the difficulties of obtaining accurate measurements in supplemental hood oxygen studies were overcome by using tank-source vs. wall-source oxygen and a unique hood design. CONCLUSIONS: Accurate indirect calorimetry studies can be performed in both ventilated and nonventilated infants weighing as little as 500 g, providing that sufficient attention is paid to technical and methodologic measurement details.

Calorimetry, Indirect↗
PubMed1996

Unexpected relationship between fat mass and basal metabolic rate in pregnant women.

We investigated the relationships between BMR, fat-free mass (FFM) and fat mass in pregnancy. BMR was measured by indirect calorimetry and body composition was assessed by densitometry in seventeen non-pregnant women (79.9 (SD 26.3, range 50.5-151.4) kg) and sixteen pregnant women (75.7 (SD 20.6, range 54.5-115.9) kg). The pregnant women were evaluated during weeks 31-35 of gestation. Multiple regression analysis of BMR with FFM and fat mass in the non-pregnant women showed that FFM was a highly significant predictor of BMR (P < 0.0001), but fat mass was not (P = 0.09). In contrast, in the pregnant women, multiple regression analysis revealed that fat mass was a highly significant predictor (P < 0.001), while FFM was not (P = 0.69). Evaluation of the interaction terms in the combined data set confirmed that the relationships of BMR with FFM and fat mass differ significantly in non-pregnant and pregnant women. It is proposed that pregnancy represents a unique condition during which BMR is regulated by maternal adipose reserves. An augmented BMR in overweight pregnant women may be protective, given that excessive weight gain may be detrimental to neonatal and maternal health.

Adipose Tissue↗
PubMed1995

Normal energy expenditure in the infant with presymptomatic cystic fibrosis.

To investigate whether a fundamental lesion in energy metabolism is a feature of cystic fibrosis, we measured total energy expenditure using the doubly labeled water technique in 19 infants with presymptomatic cystic fibrosis (0.8 to 6.6 months of age) identified through newborn screening. Total energy expenditure data collected in a cohort of healthy infants by the same method were used for comparison. Energy balance studies were additionally performed in 10 of the infants with cystic fibrosis. Total energy expenditure levels in infants with cystic fibrosis, expressed as either kilocalories per day or kilocalories per kilogram of fat free mass per day, did not differ from control levels. When expressed on the basis of body weight (in kilocalories per kilogram per day), expenditure levels in infants with cystic fibrosis were greater (p < 0.05) than control levels. No differences in expenditure were observed between those infants who were homozygous (n = 10) for the delta F508 mutation and the heterozygous infants (n = 7), regardless of how expenditure was expressed. Assessment of energy balance indicated that infants with cystic fibrosis grow at a normal rate for metabolizable energy intakes similar to those reported for healthy infants. We conclude that there are no differences in energy expenditure between infants with presymptomatic cystic fibrosis and healthy infants, once differences in body composition are taken into account. This finding indicates that the primary cystic fibrosis defect is not an energy-requiring one.

Anthropometry↗
PubMed1995

The thermic effect of food in normal-weight and overweight pregnant women.

A defective thermic response to food may be an energy-sparing adaptation in both obesity and pregnancy. To evaluate the combined effect of obesity and pregnancy on postprandial thermogenesis, the thermic effect of food was assessed for a 240 min period following a high-carbohydrate meal and a typical mixed meal in nine normal-weight non-pregnant, eight overweight non-pregnant, eight normal-weight pregnant and six overweight pregnant women using indirect calorimetry. A test meal that provided 60% of each subject's measured daily requirement for basal metabolism was used. Pregnant women were studied during weeks 30-35 of gestation. Neither obesity nor pregnancy altered the thermic effect of food, although the response to the mixed meal was greater (P < 0.01) than that to the high-carbohydrate meal in all cases. The mean responses for the high-carbohydrate and mixed meals were 26.9 (SD 6.0) and 30.1 (SD 6.2) % baseline energy expenditure respectively, and 7.4 (SD 1.6) and 8.3 (SD 1.6) % of the meal energy load respectively. Obesity and pregnancy were associated with hyperinsulinaemia (P < 0.005) following both test meals, suggesting that postprandial thermogenesis was not altered by insulin resistance in this group. The incremental glucose response was elevated (P < 0.001) in the pregnant women following both test meals; overweight women tended to have a greater incremental glucose response following the high-carbohydrate meal, but it was not significant (P = 0.065). These results do not provide evidence of an impaired thermic response to food in either overweight or third trimester pregnant women.

Adult↗
PubMed1994

Energy metabolism during pregnancy: influence of maternal energy status.

Additional energy requirements for term pregnancies are traditionally estimated as 1200 kJ/d or 325 MJ. These estimates approximate measured energy costs for well-nourished women, but non-Western populations subsisting on limited diets have much lower expenditures. Based on recent studies of energy expenditure during pregnancy, this paper reviews the 1) association between gestational weight gain and fat gain, 2) the influence of maternal energy status on basal metabolic energy expenditure in late pregnancy, and 3) potential energy metabolism adaptations available to pregnant women and how adaptations vary with energy status. Available data suggest that additional energy requirements during pregnancy vary from 0 to 500 MJ and depend on maternal energy status. If energy supplies are limited, adaptations spare energy for fetal growth; if energy is abundant, energy balance may be achieved in different ways depending on individual behavioral changes in food intake or activity patterns and on adjustments in basal metabolism or fat deposition.

Adipose Tissue↗
PubMed1992

Pancreatic insufficiency, growth, and nutrition in infants identified by newborn screening as having cystic fibrosis.

To evaluate the impact of early pancreatic insufficiency on growth and nutritional status in cystic fibrosis, we studied 49 infants identified by a newborn screening program. Pancreatic insufficiency, determined by increased 72-hour fecal fat excretion, was present in 59% (23/39) of infants at diagnosis (7.0 +/- 0.8 weeks; mean +/- SEM). Before initiation of pancreatic enzyme replacement, growth and nutritional status of pancreatic-insufficient (n = 16) and pancreatic-sufficient (n = 13) infants were compared. Pancreatic-insufficient infants gained less weight from birth to diagnosis (13.4 +/- 3.4 vs 22.3 +/- 4.0 gm/day; p = 0.05), had decreased triceps skin-fold thicknesses (4.5 +/- 0.3 vs 6.1 +/- 0.4 mm; p less than 0.005), and had lower blood urea nitrogen (3.07 +/- 0.42 vs 4.62 +/- 0.65 mg/dl; p = 0.02) and albumin (2.99 +/- 0.14 vs 3.54 +/- 0.14 gm/dl; p less than 0.01) levels despite higher gross calorie (154 +/- 8 vs 116 +/- 13 kcal/kg per day; p less than 0.01) and protein intakes (2.81 +/- 0.21 vs 2.14 +/- 0.33 gm/kg per day; p = 0.03). Fecal nitrogen loss was correlated with fat loss (r = 0.79; p less than 0.001). Fat malabsorption was present in 79% (30/38) and 92% (33/36) of infants tested at 6 months and 12 months of age, respectively, indicating that pancreatic insufficiency persists and increases in frequency throughout infancy. We conclude that pancreatic insufficiency is prevalent in young infants with cystic fibrosis and has a significant impact on growth and nutrition.

Anthropometry↗