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PubMedDate not supplied

Material properties of various intraocular lenses in an experimental study.

INTRODUCTION: With the recent introduction of small-incision cataract surgery, requirements for intraocular lens (IOL) flexibility, strength and hydrophilicity have rapidly evolved. The IOL surface, however, remains a critical factor influencing uveal biocompatibility. PURPOSE: To objectively quantify factors of material properties of various IOLs using contact angle measurements, differential scanning calorimetry, dynamic-mechanical measurements and scanning electron microscopy. MATERIAL AND METHODS: In our study, 17 currently available IOLs were investigated using contact angle measurements to assess hydrophilicity and biocompatibility, as well as differential scanning calorimetry for the estimation of glass transition temperature. Mechanical capacity and flexibility were investigated using dynamic-mechanical measurements. Additional analysis of the IOL surface was performed using scanning electron microscopy. RESULTS: The contact angle measurements of the studied IOLs revealed similar values within each group. The silicone IOLs had values between 106 and 119 degrees. The PMMA IOLs were found to have a narrower range of values, between 73.2 and 75.5 degrees. Lenses made of hydrogel had values between 59.2 and 69.1 degrees. The heparin-modified surface showed the lowest contact angle of 56.5 degrees. The glass transition temperature was determined by dynamic differential scanning calorimetry. The resulting values were between 118.8 and 113.5 degrees C for PMMA IOLs, 15.5 and 14.0 degrees C for acrylic IOLs, and -91.7 and -119.6 degrees C for silicone IOLs. The dynamic-mechanical measurements revealed that PMMA lenses manifested characteristics similar to glass, whereas silicone lenses had characteristics similar to rubber. Acrylic lenses were between rubber and glass. Scanning electron microscopy revealed smooth dispersion of fibrin on hydrophobic IOLs and a relative lack of fibrin adhesion on hydrophilic materials. CONCLUSION: These results demonstrate that material properties of various IOL materials are consistent within classes of IOL materials. This suggests that the intraoperative and postoperative behavior of an IOL is predictable and related to its composition, thus allowing surgeons to choose IOLs more appropriate for different surgical situations and individual patient characteristics.

Acrylates↗
PubMed1983

Nature and quantity of fuels consumed in patients with alcoholic cirrhosis.

Although alcoholism is a leading cause of morbidity and mortality of middle-aged Americans, there are no data available pertaining to the consequences of Laennec's cirrhosis on total body energy requirements or mechanisms for maintaining fuel homeostasis in this patient population. Therefore, we simultaneously used the techniques of indirect calorimetry and tracer analyses of [14C]palmitate to measure the nature and quantity of fuels oxidized by patients with biopsy-proven alcoholic cirrhosis and compared the results with values obtained from health volunteers. Cirrhotic patients were studied after an overnight fast (10-12 h). Normal volunteers were studied after an overnight fast (12 h) or after a longer period of starvation (36-72 h). Total basal metabolic requirements were similar in overnight fasted cirrhotic patients (1.05 +/- 0.06 kcal/min per 1.73 m2), overnight fasted normal subjects (1.00 +/- 0.05 kcal/min per 1.73 m2), and 36-72-h fasted normal volunteers (1.10 +/- 0.06 kcal/min per 1.73 m2). Indirect calorimetry revealed that in cirrhotic patients the percentages of total calories derived from fat (69 +/- 3%), carbohydrate (13 +/- 2%), and protein (17 +/- 4%) were comparable to those found in 36-72-h fasted subjects, but were clearly different from those of overnight fasted normal individuals who derived 40 +/- 6, 39 +/- 4, and 21 +/- 2% from fat, carbohydrate, and protein, respectively. These data are strikingly similar to data obtained through tracer analyses of [14C]palmitate, which showed that in overnight fasted patients with alcoholic cirrhosis, 63 +/- 4% of their total CO2 production was derived from oxidation of 287 +/- 28 mumol free fatty acids (FFA)/min per 1.73 m2. In contrast, normal overnight fasted humans derived 34 +/- 6% of their total CO2 production from the oxidation of 147 +/- 25 mumol FFA/min per 1.73 m2. On the other hand, values obtained from the normal volunteers fasted 36-72 h were similar to the overnight fasted cirrhotic patients. These results show that after an overnight fast the caloric requirements of patients with alcoholic cirrhosis are normal, but the nature of fuels oxidized are similar to normal humans undergoing 2-3 d of total starvation. Thus, patients with alcoholic cirrhosis develop the catabolic state of starvation more rapidly than do normal humans. This disturbed but compensated pattern for maintaining fuel homeostasis may be partly responsible for the cachexia observed in some patients with alcoholic cirrhosis. This study also showed remarkably good agreement between the results obtained with indirect calorimetry and those obtained with 14C tracer analyses.

Adult↗
PubMedDate not supplied

Substrate oxidation in patients with cirrhosis: comparison with other nutritional markers.

BACKGROUND: Malnutrition in patients with hepatic cirrhosis is associated with abnormal fuel metabolism marked by reduced glucose oxidation and increased lipid oxidation. A low respiratory quotient (R/Q) indicates reduced glucose and increased lipid oxidation. The aim of this study was to determine if there is an association between substrate oxidation, using indirect calorimetry, and other markers of malnutrition in patients with cirrhosis awaiting liver transplantation. METHODS: Indirect calorimetry (MedGraphics) was used to determine resting energy expenditure and R/Q after an overnight fast. Anthropometric measurements including tricep skinfold thickness (TSF) and midarm muscle circumference (MAMC) were performed and expressed as a percentage of standard values. A 24-hour urinary creatinine excretion was collected to calculate creatinine height index (CHI) and serum albumin. A subjective global assessment (SGA) score was completed on each patient by a dietitian and physician. Spearman rank correlation was used for statistical comparison of R/Q to other nutritional markers. RESULTS: Fifteen patients (7 men, 8 women; mean age, 52 years) were studied. Mean values include: body mass index (BMI) 27.7 kg/m2 +/- 7.3, R/Q 0.78 +/- 0.04, serum albumin 2.97 g/dL +/- 0.56, TSF 71% +/- 27%, MAMC 85% +/- 13%, CHI 75% +/- 18%, and SGA median score A. There was a significant correlation (p < .05) between R/Q and serum albumin, CHI, and SGA score. There was a greater than 90% correlation of SGA estimation by a physician and dietitian. CONCLUSIONS: There is good correlation between R/Q values and serum albumin, CHI, and SGA score. BMI and anthropometric measurements may suggest normal nutrition when, in fact, indirect calorimetry (R/Q) suggests changes consistent with abnormal fuel metabolism and poor nutrition. R/Q can be a useful adjunct in the nutrition assessment of patients with hepatic cirrhosis.

Adult↗
PubMedDate not supplied

Validation of 2 approaches to predicting resting metabolic rate in critically ill patients.

BACKGROUND: Indirect calorimetry is the criterion method for determining resting metabolic rate for nutrition support in critically ill patients. However, calculation equations are more commonly used. In the current study we tested the validity of 2 such calculation systems. METHODS: Indirect calorimetry was performed with an open-circuit device in mechanically ventilated surgical, trauma, and medical patients at rest. Feedings were not stopped for the measurements. Two predictive equations by Ireton-Jones and 3 versions of a multivariate equation developed at our institution (referred to as Penn State equations) were then used to estimate resting metabolic rate. These estimates were compared on a percentage basis with the measured value of resting metabolic rate. Estimated resting metabolic rate within 10% of measured was considered accurate, whereas estimations >15% different from measured were considered large errors. RESULTS: Forty-seven subjects were measured. A larger percentage of subjects were estimated accurately by the Penn State equations (72% in the best equation) than by the Ireton-Jones equations (60% in the best equation; not significant). The incidence of errors >15% of measured was significantly lower in the Penn State equation (11% of subjects) compared with the Ireton-Jones equation (32% of subjects) (p < .05). CONCLUSIONS: The Penn State equation for resting metabolic rate in mechanically ventilated intensive care patients receiving nutrition support appears to be a valid clinical tool for determining energy goals in the absence of or as a supplement to indirect calorimetry. The Ireton-Jones equation performed less well, especially in that a higher number of large errors occurred.

Adolescent↗
PubMedDate not supplied

Effects of extra-carbohydrate supplementation in the late evening on energy expenditure and substrate oxidation in patients with liver cirrhosis.

BACKGROUND: The purpose of this study was to demonstrate the effects of extra-carbohydrate supplementation before bedtime on energy metabolism and substrate oxidation in patients with liver cirrhosis. METHODS: Sixteen cirrhotic patients and eight control subjects were included in this study. To compare the effect of energy metabolism and substrate oxidation with or without a bedtime snack, indirect calorimetry was assessed at 7 to 8 AM after overnight fasting, following either dinner (6 PM) or a bedtime snack (11 PM) the evening before. The bedtime snack contained about 50 g of carbohydrate. The energy expenditure and substrate oxidation were calculated from the indirect calorimetry measurement and 24-hour urinary nitrogen excretion. RESULTS: In those who fasted since dinner, the respiratory quotient (RQ) was significantly lower in cirrhotic patients than in control subjects. Also, the energy utilized by cirrhotic patients was derived primarily from fat oxidation (58%), whereas the main energy source for controls was carbohydrate (55%). An extra-carbohydrate supplement before bedtime did not influence the indirect calorimetry measurement in the controls, but there were significant increases in both RQ and carbon dioxide production (Vco2) in cirrhotic patients. The extra-carbohydrate supplementation did not significantly change the absolute resting energy expenditure utilization in control subjects; however, the utilization of carbohydrate significantly increased with a decrease in fat and protein oxidation in the cirrhotic patients. CONCLUSIONS: These preliminary data suggest that extra-carbohydrate supplementation before bedtime can shorten nocturnal fasting with a more economic fuel utilization and effectively diminish fat and protein oxidation in cirrhotic patients.

Adult↗
PubMed1984

Longitudinal studies on metabolic rate, heat loss, and energy cost of growth in low birth weight infants.

Longitudinal studies on total and resting metabolic rate and total heat loss were made in 14 LBW infants, age 1-58 d. Metabolic rate was calculated from indirect calorimetry, heat loss was measured by direct calorimetry. Total metabolic rate and total heat loss were lowest during the first week of life, 178.9 +/- 18.0 and 171.8 +/- 15.5 kJ X kg-1 X 24 h-1, respectively. During the age period of 8-58 d both total metabolic rate and heat loss showed a very slight increase with age: mean total metabolic rate was 278.8 +/- 2.6 and mean total heat loss 257.0 +/- 3.4 kJ X kg-1. during the first week of life and 248.0 +/- 2.5 during d 8-58. The energy cost of components of new tissue was calculated from the energy balance equation. Ecomponents during the second week of life was 25.5 +/- 4.9 kJ/g weight gain and 11.9 +/- 0.4 kJ/g weight gain over subsequent weeks. The net energy cost of tissue synthesis, calculated from the difference between indirect and direct calorimetry was 3.2 +/- 1.1 kJ/g weight gain during the second week and 1.1 +/- 0.1 kJ/g weight gain in the following weeks. A neonate who receives a caloric intake of 535 kJ X kg-1 X 24 h-1 and is growing at a rate of 17 g X kg-1 X 24 h-1 will use 42% of the caloric intake for maintenance and thermoregulation, 6% for activity, 38% for the components of new tissue, 4% for tissue synthesis and 10% for loss in faeces and urine.

Body Temperature Regulation↗
PubMed2004

Evaluation of the SenseWear Pro Armband to assess energy expenditure during exercise.

PURPOSE: To assess the accuracy of the SenseWear Pro Armband for estimating energy expenditure during exercise. METHODS: : Forty subjects (age = 23.2 +/- 3.8 yr; body mass index = 23.8 +/- 3.1 kg x m) performed four exercises (walking, cycling, stepping, arm ergometry) with each exercise lasting 20-30 min and workload increasing at 10-min intervals. Subjects wore the SenseWear Pro Armband on the right arm, and energy expenditure was estimated using proprietary equations developed by the manufacturer. Estimated energy expenditure from the SenseWear Pro Armband was compared with energy expenditure determined from indirect open-circuit calorimetry, which served as the criterion measure. RESULTS: : When a generalized proprietary algorithm was applied to the data, the SenseWear Pro Armband significantly underestimated total energy expenditure by 14.9 +/- 17.5 kcal (6.9 +/- 8.5%) during walking exercise, 32.4 +/- 18.8 kcal (28.9 +/- 13.5%) during cycle ergometry, 28.2 +/- 20.3 kcal (17.7 +/- 11.8%) during stepping exercise, and overestimated total energy expenditure by 21.7 +/- 8.7 kcal (29.3 +/- 13.8%) during arm ergometer exercise (P < or = 0.001). At the request of the investigators, exercise-specific algorithms were developed by the manufacturer and applied to the data that resulted in nonsignificant differences in total energy expenditure between indirect calorimetry and the SenseWear Pro Armband of 4.6 +/- 18.1 kcal (2.8 +/- 9.4%), 0.3 +/- 11.3 kcal (0.9 +/- 10.7%), 2.5 +/- 18.3 kcal (0.9 +/- 11.9%), and 3.2 +/- 8.1 kcal (3.8 +/- 9.9%) for the walk, cycle ergometer, step, and arm ergometer exercises, respectively. CONCLUSIONS: It appears that it is necessary to apply exercise-specific algorithms to the SenseWear Pro Armband to enhance the accuracy of estimating energy expenditure during periods of exercise. When exercise-specific algorithms are used, the SenseWear Pro Armband provides an accurate estimate of energy expenditure when compared to indirect calorimetry during exercise periods examined in this study.

Adolescent↗
PubMed1993

Measurement of oxygen consumption after uncomplicated acute myocardial infarction.

BACKGROUND: Oxygen consumption (VO2) has been shown to be decreased after acute myocardial infarction (AMI) complicated by cardiogenic shock. STUDY OBJECTIVE: To evaluate early measurement of VO2 by indirect calorimetry after an uncomplicated AMI (UAMI). STUDY DESIGN: Prospective nonrandomized case study. SETTING: Emergency department of a large urban hospital. PARTICIPANTS AND INTERVENTIONS: Twenty-six consecutive patients presenting with confirmed UAMI. VO2 was measured by indirect calorimetry (Deletrac, Datex Ins,) which is noninvasive. All patients received buccal or intravenous nitroglycerin and thrombolytic therapy, and none received opiates before VO2 measurement. RESULTS: Two groups of patients were identified by subsequent development of cardiogenic shock. Group 1 did not develop cardiogenic shock, and group 2 developed shock within 24 h of admission. Group 1 (n = 22) had a significantly higher VO2 compared to group 2 (n = 4), mean 154(SD 25) vs mean 100(SD 13) ml/min.m2, p < 0.002. Group 1 had a significantly higher increase in basal metabolic rate than group 2, mean 30 percent (SD 11) vs mean 10(SD 15) percent, p < 0.007. There was no significant difference in age, heart rate (HR), shock index (SI), or rate-pressure product (RPP) between groups 1 and 2. All patients in group 2 developed cardiogenic shock despite thrombolytic therapy, and two died within 24 h of admission. CONCLUSION: VO2 is increased in UAMI and represents increased metabolic demands of peripheral tissues and not cardiac oxygen uptake. A reduction in VO2 (< 100 ml/min.m2) after AMI may be an early predictor of subsequent development of cardiogenic shock. Measurement of VO2 in UAMI by indirect calorimetry in the emergency department may be of value to identify patients at high risk and could influence their management.

Aged↗
PubMed1994

Predictors of total parenteral nutrition-induced lipogenesis.

OBJECTIVE: To evaluate the incidence and cause of parenteral nutrition-induced lipogenesis. DESIGN: Retrospective patient review. SETTING: A 40-bed predominantly surgical ICU. PATIENTS: One hundred forty patients receiving central venous nutrition and mechanical ventilatory support. INTERVENTIONS: Indirect calorimetry was used to determine patient's measured energy expenditure (MEE) and respiratory quotient (RQ). Additionally total caloric intake (TCAL), glucose infusion rate, basal energy expenditure (BEE), estimated stress factor, and calculated energy expenditure (CEE) were assessed in each patient. MEASUREMENTS AND MAIN RESULTS: Net fat synthesis was found as RQs exceeded 1 in 47 percent of patients. Statistically significant differences in oxygen consumption, CO2 production, measured energy expenditure, total and carbohydrate caloric intake, and glucose infusion rate were found between groups of patients with an RQ < or = or > 1. Seventy-three percent of patients with glucose infusion rates > 4 mg/kg-min had RQs > 1. CONCLUSIONS: Net fat synthesis was found in a surprisingly large number of critically ill patients receiving central venous nutrition. Many of these patients received carbohydrate calories in excess of their measured energy expenditure, even though it appeared that they needed this level of caloric intake by clinical assessment. The high carbohydrate total parenteral nutrition (TPN) solutions with lipids provided only for prevention of essential fatty acid depletion resulted in an unacceptably high incidence of fat synthesis. The results suggest that caloric intake may be optimized in critically ill patients using indirect calorimetry. When calorimetry is not available, a total caloric intake of up to 140 percent of the BEE with glucose infusion rates not exceeding 4 mg/kg-min and fats providing 40 to 60 percent of calories will meet the energy requirements of most critically ill patients without forcing the RQ > 1.

Aged↗
PubMed1987

Determination of resting energy expenditure utilizing the thermodilution pulmonary artery catheter.

Accurate determination of the resting energy expenditure (REE) for patients in intensive care units has assumed increasing importance as the adverse effects of underfeeding or overfeeding have become clearer. As a result, indirect calorimetry is frequently used to determine the REE. This technique, however, is neither universally available nor inexpensive. Furthermore, it requires meticulous measurements of gas exchange and technical expertise. Because of this, we have developed a method to determine REE for those patients in intensive care units who have thermodilution pulmonary artery catheters in place. This method requires determining the oxygen consumption from data obtained from such a catheter. The REE is then calculated by multiplying the determined oxygen consumption by the caloric value for oxygen (4.86 kcal/L at a nonprotein respiratory quotient of 0.85). We made 20 simultaneous measurements of REE, comparing our method with indirect calorimetry in 19 patients. There was excellent agreement between both methods (r = 0.90; p less than 0.0001). Therefore, for those patients in intensive care units who require thermodilution pulmonary artery catheters, this method will allow accurate determination of REE and thus caloric requirements, without the need for indirect calorimetry using measurements of gas exchange.

Calorimetry, Indirect↗
PubMed1992

[Estimation of energy utilization in patients based on catabolism of endogenous proteins].

The authors describe their own methodical procedure used for estimation of energy requirements of patients with a defined nutrition. They ascribe importance to the quantitative assessment of the degree of catabolism of endogenous proteins the value of which they transform mathematically to calculate the catabolic factor with which they multiply the basal energy output calculated according to Harris-Benedict equations. At the same time they take into account also the thermogenic action of nutrients. In 28 patients with gastroenterological diseases they confronted their own procedure with indirect calorimetry and theoretical calculations using Jabor's catabolic factor and Nejedly's formula. Differences between values of their own and other theoretical calculations, as compared with the results of indirect calorimetry, nor the results of Jabor's and Nejedly's calculation as compared with those of the authors did not reach the level of statistical significance. With regard to the assembled results the authors consider the suggested procedure for estimation of energy requirements as feasible, in particular when indirect calorimetry is not available.

Calorimetry, Indirect↗
PubMed1991

Energy turnover and heat exchange in mature lean and obese Zucker rats acutely exposed to three environmental temperatures for 24 hours.

Differences between lean (FA/?, n = 6) and obese (fa/fa, n = 6) mature male Zucker rats' energy turnover and heat storage were compared during a 24-h period when the animals were exposed to ambient temperatures of 30, 15 or 5 degrees C. Energy turnover was examined through measurements of heat production rates via indirect calorimetry and heat loss rates via direct calorimetry. Heat storage rates were calculated as the difference between heat production and heat loss rates. Predicted heat storage rates were also calculated as the product of the change in core temperature and the calculated specific heat of the animal based on body composition (carcass) analysis. A minimal heat loss rate was determined for each animal representing a period of least activity. Various comparisons were made: between groups (lean/obese), temperature (30, 15, 5 degrees C), calorimetry method (indirect/direct), period (light/dark), heat storage (experimental/predicted), and minimal heat loss. Immediately before a test, pretest weight and colonic temperature were obtained. Then, the animal was placed into the calorimeter chamber and remained there unrestrained for 24 h. Normal light/dark periods were maintained. On removal from the calorimeter, core temperature and body weight measurements were again obtained. Upon completion of all tests, body composition was analyzed and surface area determined. Energy turnover, i.e. both heat production and heat loss in the lean and obese animals differed among the 30, 15 and 5 degrees C exposures. The obese animals had relatively greater heat production rate and heat loss rate (kcal/day or kcal/kg (FFM)/day than the lean animals at 30, 15 and 5 degrees C. But, on a relative basis, the increments in heat production in the cold environments were greater for the lean animals. Both the lean and obese animals tended to be more active during the dark period when at 30 degrees C, but the difference was less at 15 degrees C and even less at 5 degrees C. Experimental heat storage rates did not differ significantly from predicted values at any of the temperatures with the possible exception of the animals at 5 degrees C. It was concluded that the mature obese Zucker rats had no major discernible defect in thermoregulation as revealed by rates of heat production and loss, although three of the obese rats did elicit a drop in colonic temperature during exposure to 5 degrees C, i.e. their excessive subcutaneous adiposity and thermal insulation did not prevent a fall in colonic temperature.(ABSTRACT TRUNCATED AT 400 WORDS)

Analysis of Variance↗
PubMed1989

Enthalpy changes and heat production induced by a meal.

In 1974 Pittet and coworkers measured the thermic effect of glucose and amino acids by both direct and indirect calorimetry. Their results have been re-analysed in this paper. Only about 20 per cent of the substrate ingested was combusted during the period of observation (2 1/2 h). The change in enthalpy due to combustion, as measured by indirect calorimetry, can be divided into two parts. Direct calorimetry shows that about 40 per cent represents heat lost from or stored in the body; the form in which the remainder is stored cannot be evaluated from the data, but it is likely that it is in chemical form, resulting from reactions that increase the enthalpy content of the substrate that was not combusted within 2 1/2 h.

Calorimetry↗
PubMed1989

Thermal stability and folding of type IV procollagen and effect of peptidyl-prolyl cis-trans-isomerase on the folding of the triple helix.

Intact, monomeric type IV procollagen was isolated from the medium of PF-HR9 cells. Its stability was measured by optical rotatory dispersion, differential scanning calorimetry, and trypsin susceptibility of the partially unfolded molecules. At neutral pH, a complex transition between 35 and 42 degrees C and a smaller transition at 48 degrees C are observed by optical rotatory dispersion, using a heating rate of 10 degrees C/h. Reduction of the heating rate to 1.6 degrees C/h resulted in a 1 degree C lowering of the apparent melting temperatures. A similar curve is observed in 10 mM acetic acid, with transitions about 2 degrees C lower. Differential scanning calorimetry revealed transitions at 36.0, 42.1, and 48.0 degrees C at neutral pH, with a total transition enthalpy of 17.1 kJ/mol tripeptide units. In 10 mM acetic acid, transitions at 35.6, 38.9, 41.7, and 50.0 degrees C are observed. The transition enthalpy is 16.4 kJ/mol tripeptide units. The transition enthalpy is similar to values found for interstitial collagens. Results from trypsin digestion experiments are consistent with the stability found by optical methods and calorimetry. The rate and completeness of refolding after melting were measured. In neutral buffer, the initial rate was found to be 0.041 min-1, faster than the refolding rates observed with types pN III and III collagen. Peptidyl prolyl cis-trans-isomerase increased the refolding rate to 0.083 min-1, indicating that cis-trans-isomerization is the rate-limiting step, despite the interruptions in the triple helix. Trypsin digestion experiments indicated that the refolding mechanism is similar in the presence and absence of the enzyme. Refolding was nearly complete in neutral buffer. In 10 mM acetic acid, folding was considerably slower and went to about 74% completion. In both solvents, the refolded material was only slightly less stable than the native material. Electron microscopy of partially refolded samples showed that most refolding started at the COOH terminus, but some was initiated at other sites.

Amino Acid Isomerases↗
PubMed1980

Lipid dynamics and lipid-protein interactions in rat hepatocyte plasma membranes.

Rat hepatocyte plasma membranes were isolated and examined by differential scanning calorimetry and by steady state fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene, 12-anthroyl stearate, and 2-anthroyl stearate. Calorimetry of the intact membranes revealed a reversible lipid thermotropic transition with lower and upper critical temperatures of 18 degrees and 31 degrees C, respectively. The transition was also observed in lipid extracts of the membrane, both dried and rehydrated. The transition enthalpies estimated for intact membranes, dried membrane lipids, and rehydrated lipids, respectively, were approximately 0.3, 1.2 to 1.4, and 0.5 to 0.7 cal/g of lipid. The transition observed in the native membranes is broad and of low enthalpy, owing in part to the relatively high cholesterol content and to protein-lipid interactions. Fluorescence polarization studies detect the lower critical temperature of the transition in the membranes and in sonicated dispersions of the membrane lipid. Arrhenius studies of membrane 5'-nucleotidase and alkaline phosphatase give two-slope plots with breakpoints, respectively, of approximately 17 degrees and 26 degrees C. These break points and others reported for a number of hepatocyte membrane protein activities cluster uniformly at either the lower or the upper critical temperature of the lipid transition observed by differential scanning calorimetry.

Animals↗
PubMed1995

[Role of energy metabolism in nutrition management of critically ill patients].

Indirect calorimetric measurements were made with a MedGraphics Critical Care Monitor (CCM) desktop analysis system in the observation of critically ill and malnourished patient's energy expenditure. In 15 critically ill patients, predicted energy requirements based on 1.75 times BEE calculated by Harris-Benedict formula or corrected Harris-Benedict formula averaged 32.7% and 27.8% greater than metabolic expenditure measured by indirect calorimetry respectively. In the 20 unstressed malnourished patients, predicted energy requirements based on the Harris-Benedict (BEE) formula averaged 15% to 20% higher than metabolic expenditure measured by indirect calorimetry. When the critically ill patients' total energy intakes were 1.2 times resting energy expenditure, their nutritional state could be maintained in normal conditions. While the malnourished patients were provided with 1.5 x REE in energy intake, the malnourished state could be reversed. We believed that the critically ill and malnourished patients' energy expenditures are better measured than predicted and their nutritional regimens should be guided under the computerized indirect calorimetry.

Adult↗
PubMed1978

Thermodynamics of mercaptopurine dehydration.

The hydrate form of mercaptopurine was shown to undergo peritectic decomposition of its water molecule, localized dissolution, and dehydration around 125 degrees. The anhydrate form was prepared by a thermal method, whose effectiveness was confirmed by X-ray diffraction, NMR spectroscopy, and differential scanning calorimetry. The activation energy for mercaptopurine dehydration calculated by various methods ranged from 45.74 to 63.04 kcal/mole. The dehydration enthalpy was calculated to be 8.27 kcal/mole by differential scanning calorimetry. The solution enthalpy for the hydrate was calculated to be 4.85 kcal/mole from its saturation solubility and differential scanning calorimetry. Anhydrate solubility in water was calculated based on initial dissolution rate data since the anhydrate converts to hydrate in aqueous media. The high degree of stability against interconversion of the hydrate and anhydrate forms and the higher solubility of the anhydrate suggest that use of the anhydrate might improve mercaptopurine bioavailability.

Desiccation↗
PubMed1998

Comparison of measured and predicted energy expenditure in mechanically ventilated children.

OBJECTIVE: To determine the energy requirements in mechanically ventilated pediatric patients using indirect calorimetry and to compare the results with the predicted metabolic rate. DESIGN: In 50 mechanically ventilated children with a moderate severity of illness, energy expenditure was measured by indirect calorimetry. Daily caloric intake was recorded for all patients. Total urinary nitrogen excretion was determined in 31 patients. RESULTS: Although there was a close correlation between the measured total energy expenditure (mTEE) and the predicted basal metabolic rate (pBMR) (r = 0.93, p < 0.001), Bland-Altman analysis showed lack of agreement between individual mTEE and pBMR values. The ratio of caloric intake/mTEE was significantly higher in the patients with a positive nitrogen balance (1.4 +/- 0.07) compared with those with a negative nitrogen balance (0.8 +/- 0.1; p < 0.001). CONCLUSIONS: Standard prediction equations are not appropriate to calculate the energy needs of critically ill, mechanically ventilated children. Individual measurements of energy expenditure and respiratory quotient by means of indirect calorimetry in combination with nitrogen balance are necessary for matching adequate nutritional support.

Adolescent↗