Gladys R. Rios

Temperature measurement in term and preterm neonates

Body temperatures of 99 term and 44 preterm infants were measured at four sites: core (5 cm beyond the anus, with an electronic telethermometer), rectum (2 cm, with a mercury-in-glass thermometer), axilla, and between the skin and mattress. Temperatures measured at the four sites agreed closely in this group of largely normothermic infants. However, five of seven term infants with abnormal core temperature (greater than 1.5 SD below or above the mean) would have been judged to be normothermic by each of the three other measurements. The temperatures in preterm infants were lower and varied less with the site of measurement, indicating a smaller core-surface temperature gradient because of their relative lack of thermal insulation by body fat. Axillary temperature was as reliable as rectal temperature measured in the usual way with a mercury-in-glass thermometer. Measurement of the temperature between the skin and mattress was nearly as accurate as the other more frequently used methods. Ninety percent of temperatures were within 0.1 degree C of their final stabilization readings by 5 minutes for each type of thermometer and measurement site.

A Double-Walled Incubator Alters the Partition of Body Heat Loss of Premature Infants

Summary: Partitional calorimetry was used to assess the influence of a double-walled incubator (Air-Shields C-86 Isolette) on the body heat loss of eight premature newborn infants (birth weights 1.44–1.89 kg, ages 6–19 days). Each infant was studied in the same incubator with and without the inner wall. Incubator heater output was regulated by servocontrol to maintain the abdominal skin temperature at 36.5°C. Operative environmental temperature was the same (mean 33.0°C) in both incubators. There were no differences in body temperatures, oxygen consumption, carbon dioxide production, respiratory quotient, or evaporative water and heat losses. The double-walled incubator reduced radiant heat loss but increased convective heat loss, so that the total rate of body heat loss was unchanged.

Estimation of 24-Hour Energy Expenditure from Shorter Measurement Periods in Premature Infants

ABSTRACT. We performed continuous indirect calorimetry for 24 h on nine occasions in small premature infants. Oxygen consumption, carbon dioxide production, respiratory quotient, and energy expenditure were calculated for each 2-h period. The mean energy expenditure during the first 6 h was within 6.5% of the mean for the whole 24-h period in all but one case. The mean error in estimating total daily energy expenditure from 6-h measurements was 0.9%. Because positive and negative errors tend to offset each other, we also calculated the mean absolute error, which was 5.6%. The mean coefficient of variation in energy expenditure among the 2-h periods was 11.0%. The mean coefficients of variation in oxygen consumption, carbon dioxide production, and respiratory quotient were 12.8, 9.9, and 14.1%, respectively. Total daily energy expenditure of small premature infants can be estimated from measurements as short as 6 h with sufficient accuracy for most purposes.

Air versus skin temperature servocontrol of infant incubators

Air temperature servocontrol was compared with skin temperature servocontrol and manual control as methods for regulating the heat output of a single-walled incubator (Air-Shields C-86) (1) when optimally used in the laboratory and (2) when operated by staff nurses in the nursery. The subjects were eight premature infants with birth weights between 1.07 and 1.54 kg. When the three methods were used to produce neutral air and skin temperatures during 2-hour measurement periods in the laboratory, there were no differences in mean air, skin, or rectal temperature, metabolic heat production, or body heat loss. There were also no differences among the three methods in mean air, skin, or rectal temperature when used by the nurses in the nursery for periods of 24 hours. When incubator wall temperature is stable, air temperature servocontrol can be used as effectively as skin temperature servocontrol to operate infant incubators.

FOLATE AND FOLATE-DEPENDENT ENZYMES ASSOCIATED WITH RAT CNS DEVELOPMENT

Folic acid and its derivatives are important mediators in growth-related cellular processes. The concentration of folate and two folate-dependent enzymes, 10-formyltetrahydrofolate synthetase (10-FTHFS) and 10-formyltetrahydrofolate dehydrogenase (10-FTHFDH), was determined in brain regions over the early period of rat development. Folate concentrations determined at birth were high in all brain regions studied. During the first 2 weeks, folate concentrations declined steadily, followed by a period of significant increase. High and invariant activity of 10-FTHFS was found throughout the period of study. Low amounts of 10-FTHFDH were seen for the first 2 weeks, but increased significantly from postnatal days 14 to 28. These changes correlated with changes determined in the concentration of folate, supporting the idea that this protein is involved with folate uptake and/or storage. Furthermore, immunohistochemical expression of 10-FTHFDH in different rat brain regions revealed glial cells as a preferential cellular location for this folate-binding protein.

Metabolism of Endobiotics and Xenobiotics by UDP-Glucuronosyltransferase

Publisher Summary All organisms are exposed to a number of chemical compounds that are toxic were it not for metabolic mechanisms available to the organism to moderate their effects. Chemical substances may be xenobiotics, such as drugs, or compounds presented to the organism from environmental or dietary sources. The elimination of many such compounds and their detoxification involves different types of metabolic reactions. One of them is conjugation through glucuronic acid catalyzed by UDP-glucuronosyltransferases (UGTs). In addition to xenobiotics; endobiotics, such as steroids or bilirubin, are glucuronidated. Formation of glucuronides from xeno- and endo- biotics generally results in the formation of products that are more hydrophilic and more readily excreted by the kidney or liver. A number of UGTs have been purified to homogeneity from liver of several species, including humans. Recently identified are a number of UGTs that are important for the metabolism of xenobiotics and endobiotics, such as steroids and estrogen catechols. This chapter discusses the metabolism of important amines, opioids, and endobiotics, such as steroids and their catechol derivatives. There are details on glucuronidation of amines, glucuronidation of opioid compounds, and glucuronidation of catechol estrogens by UGTs. Many isoforms of UGT catalyze the glucuronidation of primary and secondary amines. In humans, many important therapeutic agents, such as the antihistamines, antipsychotics, and tricyclic antidepressants, are tertiary amines. Many of these tertiary amines, in humans, are converted to and excreted as quaternary ammonium-linked glucuronides. Stably expressed human UGT1.4 protein has been discovered to catalyze the N-glucuronidation of a variety of tertiary amines. To date, only human UGT1.4 has been identified to catalyze the formation of quaternary ammonium-linked glucuronides from tertiary amines. UGT2B1 and UGT1.1 have been demonstrated to catalyze the glucuronidation of opioid substances. UGT2B1 has high activity toward many opioid substrates, whereas UGT1.1 catalyzes the glucuronidation the oripavine-type opioid compounds.

Effects of formula temperature on postprandial thermogenesis and body temperature of premature infants

To study the effect of formula temperature on the thermogenic response to gavage feeding, we fed formula at room temperature (mean 24.0 degrees C, SD 1.1) and at body temperature (mean 36.9 degrees C, SD 1.7) to premature infants in a crossover design while monitoring their metabolic heat production and gastric, rectal, and skin temperatures. After feeding with room temperature formula, stomach temperature fell by 6.9 degrees C, rectal temperature by 0.2 degree C, and mean skin temperature by 0.6 degree C, and metabolic rate increased by 16% in the first postprandial hour. After body temperature feedings, mean skin temperature fell by 0.2 degree C, but stomach and rectal temperatures did not change appreciably. The metabolic rate rose by 12% in the first hour, which was not significantly less than the rise after room temperature feeding. The heat required to warm the formula to body temperature did not result in a detectably greater rise in metabolic rate after cool feeding than after warm feeding. The effects of feed temperatures below room temperature were not studied, but it remains possible that cooler feedings might produce even greater body cooling and a greater thermogenic response.

Tympanic membrane temperature of term and preterm neonates

Deep body temperatures of 70 term and 24 preterm newborn infants were measured at two sites: deep rectum (5 cm beyond the anus) and tympanic membrane. A significant correlation was found between deep rectal and tympanic membrane temperatures in both term and preterm infants. Mean deep rectal and tympanic membrane temperatures in term infants were 37.01 degrees C and 36.83 degrees C, respectively. Mean deep rectal and tympanic membrane temperatures in preterm infants were both 36.69 degrees C.

Performance characteristics of two double-walled infant incubators

Two double-walled incubators, the Air Shields C-100 and the Ohio IC, were evaluated for performance characteristics. The Ohio incubator heated more rapidly from room temperature to 36 degrees C, but overshot the preset air temperature and produced greater fluctuation in air temperature due to the operation of the servocontrol system at equilibrium. Neither incubator produced excessive air currents, sound levels, or carbon dioxide accumulation.

Heme biosynthesis in the heart

The rates of biosynthesis of heme a and heme b in hearts of fed and fasted rats were measured using an isolated heart perfusion system. delta-Aminolevulinic acid synthetase activity was decreased in hearts of fasted rats to about 30% of values in hearts obtained from fed rats. [14C] Glycine incorporation into hemes a and b of cardiac tissue obtained from fasted rats was also decreased to about 30% of values obtained in hearts from fed rats. Cobalt addition to the perfusion fluid led to a decrease in cardiac delta-aminolevulinic acid synthetase activity just as cobalt administration to rats does in vivo. These studies strongly suggest that delta-aminolevulinic acid synthetase activity regulates the rate of synthesis of hemes a and b in the heart.