LeRoy C. Mims

Phototherapy for neonatal hyperbilirubinemia—a dose: response relationship

The relationship between irradiance (microwatts per square centimeter) from visible light in the blue spectral range and the serum bilirubin response was studied in 44 newborn infants with nonhemolytic hyperbilirubinemia. Patients were separated into study groups (1 to 4) on the basis of quantity of irradiance received. A significant positive correlation was noted in the decreases in the 24 hour serum bilirubin values and the amount of blue light irradiance received. The relationship is nearly linear. The importance of using a radiometer to measure light irradiance in microwatts per square centimeter per 420 to 470 nm. during phototherapy for neonatal hyperbilirubinemia is stressed.

Gastric Response in Low Birth Weight Infants Fed Various Formulas

Feeding techniques, delayed gastric emptying, volume overload, or reverse peristalsis may lead to regurgitation and aspiration in the premature infant. Noting these complications, various aspects of gastric function were studied in relation to the type of formula fed. 27 low birth weight infants (less than 2,000 g) were each fed one of three randomly assigned commercial formulas, which varied in osmolarity and MCT content. Gastric pH and emptying were monitored during the first 48 h of life. The fatty acid chain length of the triglyceride in the formula apparently did not influence either gastric pH or emptying. Infants fed formulas having a higher osmolar load (539 mosm/1) and containing protein hydrolysate showed greater gastric retention.

Riboflavin and Bilirubin Response during Phototherapy

Extract: Twenty-four jaundiced neonates were studied, 12 in the treatment group and 12 in the untreated group. Patients were randomly selected to receive oral riboflavin. The mean 24-hr bilirubin decrease was determined during phototherapy. Blue light (420–470 nm) energy ranged from 6–10 μW/cm2. The observed 24-hr bilirubin decrease was compared with the expected decrease based on an energy-dose-response relationship. Riboflavin-treated infants received either 6–7 μW/cm2 blue light energy or 8–10 μW/cm2 (same as control group). Those infants receiving less energy than the control group (8–10 μW/cm2) had a mean 24-hr bilirubin decrease (3.05 mg/100 ml/24 hr) equal to the control group (3.09 mg/100 ml/24 hr). Those riboflavin-treated infants receiving energy equal to the control group showed a greater decline (5.2 mg/100 ml/24 hr) in their mean 24-hr bilirubin. Although effective, additional in vivo studies are required to clarify the full effects, especially on DNA, of using photosensitizers such as riboflavin in the presence of bilirubin and blue light energy (420–470 nm).Speculation: Riboflavin may become an inportant adjunct to phototherapy for neonatal hyperbilirubinemia. As a producer of singlet oxygen it is capable of transferring enough energy to overcame the oxygen quenching effect of bilirubin in its rapid degradation.

The Significance of Circulating Glycerol as a Precursor of Pulmonary Phosphatidylcholine in the Developing Mammalian Lung

Extract: There is scant information regarding the contribution made by circulating precursors to pulmonary phosphatidylcholine synthesis in the developing mammalian lung. In situ pulmonary artery perfusions were performed in term New Zealand newborn rabbits with physiologic buffer containing either 3.6 mM or 10.8 mM glycerol. There was a twofold increase in nanomoles of glycerol-phosphatidylcholine synthesized at 30 min when the higher concentration of glycerol was used. Continuing with the higher concentration, a near three-fold increase was observed between the 30-min and 60-min perfusions. This data indicates that the de novo synthesis of pulmonary phosphatidylcholine is influenced by the concentration of glycerol in the perfusate as well as the duration of perfusion.Speculation: The observation that the concentration of circulating glycerol can influence the de novo synthesis of pulmonary phosphatidylcholine suggests that glycerol may also play a role in providing precursor for pulmonary surfactant synthesis. The biochemical similarity of lipid metabolism at birth between human newborn infants and the newborn rabbit encourages extrapolation of this data to humans. The question is raised as to the influence that intravenous glycerol at physiologic concentration would have on pulmonary phosphatidylcholine synthesis in the infant with hyaline membrane disease.

Adaptive Gluconeogenesis in Preterm and Term Rabbits

Summary: Carbohydrate metabolism in the developing rabbit was investigated for deficiencies that may be responsible for the failure of many preterm (281/2–291/2 day) animals to survive the first hours of life. The preterm animal shows an inability to reverse glycogenolysis or initiate gluconeogenesis from lactate or alanine in the first hours of life. This impairment, coupled with 50% less liver glycogen stores than the term animal, places the preterm animal at jeopardy for energy substrate early on in life. Unexpected was the early, rapid conversion of glycerol to glucose by the preterm animal. This ability seemed to be the primary difference in carbohydrate metabolism between the surviving and nonsurviving preterm rabbit.Speculation: Impaired glyconeogenesis from lactate and alanine in the preterm animal coupled with active gluconeogenesis from glycerol suggests that substrates from lipolysis may be very important for early adaptation. Preterm animals endowed with limited fat stores, thus, minimal available glycerol, would be incapable of survival.

Glycerol as a Phosphatidyl Choline Precursor in the Developing Mammalian Lung

In vitro evidence demonstrates that glycerol is actively incorporated by the developing mammalian lung into phosphatidyl choline (PC synthesis) and such incorporation is a good indi

A New Model for Neonatal Pulmonary Hemorrhage Research

Extract: Hemorrhagic atelectasis was successfully produced in newborn rabbits by pharmacologically narrowing airways leading to alveoli ventilated with oxygen-enriched gas. Between 48% and 62% of alveoli filled with blood cells. Areas of lung with a tendency to collapse were measured by pressure volume studies. Animals given supplemental oxygen retained 56% of total lung volume compared with 79% in the pilocarpine group, which suggested increased effectiveness of antiatelectasis factors in the latter. Less total lung gas was present in the pilocarpine group (4.0 ± 0.4 cc/g) compared with oxygen controls (5.1 ± 0.81 cc/g), which indicated more noninflatable lung. Neither surfactant deficiency nor heart failure needed to be present for pulmonary hemorrhage to occur.Speculation: Neonates are at increased risk of pulmonary hemorrhagic atelectasis because of their incomplete pulmonary anatomic development, if their airways become obstructed while breathing high concentrations of oxygen.

Cold Stress Influence on Lung Lecithin in the Newborn Rabbit

Term, food-water deprived newborn rabbits exposed to a cold environment for 48 h demonstrated a significant decrease in total lung lipid (p less than 0.01), total triglyceride (p less than 0.001), total phospholipid (p less than 0.05), and total phosphatidylcholine (p less than 0.025). Disaturated phosphatidylcholine remained unchanged. Fatty acid methyl esters of total and disaturated phosphatidylcholine were not influenced by cold stress. Likewise, there was no alteration in pulmonary function as determined by deflation pressure-volume relationships.

INHIBITION OF FETAL PULMONARY SURFACTANT APPEARANCE AFTER MATERNAL METYRAPONE INFUSION

Pulmonary maturity was measured in fetal rabbits after continuous infusion of metyrapone (M)(7 mg/ml at 2 ml/hr × 24 hrs) to 24 day gestation females and compared to placebo treated controls (C). 27.5 day gestation animals (total N = 56) were compared for body weight in gm (BW), wet lung weight expressed as % of body weight (LW%), mg DNA per lung (DNA), minimal surface tension of minced lung in dynes per cm (MST), distensibility expressed as cc per gm of wet lung at peak distending P of 35 cm H2O (cc/gm), and deflation stability expressed as % of maximal volume upon deflation to a P of 10 cm H20 (%Vmax). All results are mean ± standard deviation; * = p < .001.Decreased %Vmax and increased MST after M are similar to findings in 26 day gestation fetal rabbits (JAP 30:358, 1971). Two additional M litters delivered at term (31 days) and 15 out of 17 bunnies survived to one month of age. Previously reported (Amer. Rev. Resp. Dis. 107:1109, 1973) accelerated appearance of pulmonary surfactant after intermittent metyrapone (300 mg I.M. Q8HX12) may have been due to incomplete block of adrenal 11-β hydroxylation.