Amniotic fluid microviscosity determined by fluorescence polarization: methodology and relation to gestational age.

The fluorescence polarization of 116 amniotic fluid specimens obtained from 22 isoimmunized pregnant women was determined. The degree of fluorescence polarization of amniotic fluid provides an index of microvisocity in lipid aggregates that is dependent on the lecithin-to-sphingomyelin ratio and the degree of saturation of fatty acid side chains. We confirmed the reproducibility of the measurement of amniotic fluid microviscosity (coefficient of variation, 2.0%). The measurements are not effected by bilirubin concentration of amniotic fluid dilution. The pattern of change of amniotic fluid microviscosity during gestation parallels the expected development of the surfactant system. Amniotic fluid microviscosity is high during early gestation and abruptly and sequentially decreases between the 28th and 36th week of gestation. Since the measurements are an accurate reflection of the biochemical properties of amniotic fluid lipids and parallel the development of the surfactant system, we conclude that amniotic fluid microviscosity may well serve as an indicator of the process of fetal lung maturation.

Effect of dietary protein and carbohydrate on theophylline metabolism in children.

Theophylline metabolism can be altered by a variety of abnormal physiologic states as well as by exogenous factors. Adult studies demonstrate a significant influence of dietary composition on theophylline biotransformation. To examine this effect of diet, 14 children with bronchial asthma were studied during long-term theophylline administration. Each patient was maintained for 12 days on three separate diets with varying proportions of protein and carbohydrate and with constant calories and fat. Results showed significant differences in drug half-life and metabolic clearance rate parameters. Compared to the normal diet, high protein diet markedly decreased the half-life, and high carbohydrate diet greatly prolonged it (P < .001). Multiple regression analysis demonstrated these differences to correlate only with the dietary alterations. Adverse reactions and blood chemistry abnormalities were not detected during any test period. These findings firmly establish that nutritional factors exert a significant influence on theophylline pharmacokinetics in children.

Manual micromethods for bilirubin determination in sera of adults and children and investigation of reasons for observed differences.

This study compared three micromanual methods for determining bilirubin concentration. The two microchemical methods for total bilirubin, a Jendrassik-Grof procedure and a Unopette procedure, using dimethyl sulfoxide as an accelerator and protein solubilizer, gave comparable results in sera of adults and children. A microspectrophotometric method and the microchemical methods for total bilirubin gave similar results in plasmas of newborns with physiologic hyperbilirubinemia and in sera of older children with no hepatic abnormality. However, the microspectrophotometric method gave higher values in normal and hyperbilirubinemic adult sera. The results obtained with the Jendrassik-Grof and Unopette microchemical methods for direct bilirubin in sera of adults and children showed the values determined by the Unopette to be higher. Using the presently accepted normal range, this difference is significant enough to preclude recommendation of the use of the Unopette method for distinguishing normal from elevated levels of direct bilirubin. Direct bilirubin in newborn serum measured by the Unopette method is considerably higher than that measured by the Jendrassik-Grof method. An investigation to determine the reason for the difference in the direct bilirubin results indicated that the Unopette direct method measures diconjugated bilirubin in amounts similar to those measured by the Jendrassik-Grof method but significantly more monoconjugated bilirubin than the Jendrassik-Grof method.

Postmortem vitreous humor chemistry in sudden infant death syndrome and in other causes of death in childhood.

Postmortem vitreous humor concentrations reflect antemortem serum chemical values. The authors measured the postmortem vitreous humor concentrations of Na+, K+, Cl-, Ca+2, Mg+2, urea nitrogen, creatinine, and total protein of 127 children who died from sudden infant death syndrome (SIDS) and other causes. Forty-seven children, 1 hour to 13 years old, had died of medical or surgical causes; 21 children, 7 weeks to 11 years old, had died following acute trauma; 59 children, 8 days to 1 year old, had died of SIDS. There was no significant difference between mean postmortem vitreous humor concentrations of those who died of medical and surgical causes and those who died after acute trauma (non-SIDS). in both groups, the mean postmortem vitreous humor concentrations of Mg+2 and Ca+2 were significantly higher in premature infants. There was direct correlation of postmortem vitreous humor concentration and postmortem interval for K+, but the variation, +/- 26 hours, was too large to be of practical importance in estimating time of death in individual cases. The three patient groups were compared and the mean postmortem vitreous humor concentrations of all eight constituents in the SIDS and non-SIDS groups were in the same ranges. In SIDS, the mean postmortem vitreous humor concentrations of Mg+2, Cl-, and urea nitrogen were significantly different from values of the non-SIDS cases, but not enough to indicate SIDS or to be informative about the etiology of SIDS. Measurement of the concentrations of postmortem vitreous humor constituents may not aid in the diagnosis of SIDS, but may aid in discovering unsuspected antemortem serum chemical abnormalities.

Measurement of urinary constituents with the Astra-8 Multichannel Analyzer.

The Beckman Astra-8 is a computerized, discrete-microsample, multiple-test clinical chemistry analyzer. We have examined its capability to measure urine Na+, K+, Cl-, urea nitrogen, glucose, and creatinine and found that (a) the Astra measurements are linear, accurate, and precise in concentration ranges of urine analytes; (b) urine analyte concentrations measured with the Astra correlate well with those by comparison micromethods (p < 0.001); and (c) the Astra has no significant carryover from adjacent urine samples or from adjacent urine and serum samples.

Recommended site and depth of newborn heel skin punctures based on anatomical measurements and histopathology.

The heels of 40 children (0.56--13.15 kg), 35 of whom were newborn infants and 28 of whom had 2--20 visible skin punctures, were examined at necropsy, and the thickness of the tissue layers was measured with a metric vernier caliper. Histological examination showed that uncomplicated skin-puncture wounds heal with minimum scarring and no neuroma formation. 1 infant had an infected puncture track extending into the calcaneus and resulting in cellulitis and focal calcaneal necrotising chondritis. The skin's primary blood-supply is located at the junction of the dermis and subcutaneous tissue, and the distance from the surface of the heel to this junction was quite constant (0.35--1.6 mm). However, the distance from the skin surface to the calcaneus increased with infant weight (in the smallest infant it was 2.4 mm), and at the posterior curvature of the heel it was half that from the plantar surface to the calcaneus. The calcaneus rarely extended lateral to a line drawn posteriorly from a point midway between the 4th and 5th toes and running parallel to the lateral aspect of the heel or medial to a line extending posteriorly from the middle of the great toe and running parallel to the medial surface of the heel. Therefore, in order to avoid calcaneal puncture and the risk of osteochondritis, heel puncture in the newborn should be done: (1) on the most medial or lateral portions of the plantar surface of the heel; (2) no deeper than 2.4 mm; (3) not on the posterior curvature of the heel; and (4) not through previous puncture sites that may be infected.

Simultaneously obtained skin-puncture serum, skin-puncture plasma, and venous serum compared, and effects of warming the skin before puncture.

Specimens of skin-puncture serum and plasma and venous serum were simultaneously obtained from healthy adults and in each specimen the concentrations of 12 chemical constituents were measured. No clinically important difference was found in the concentrations of the constituents measured in skin-puncture serum and plasma with or without warming the skin before puncture. When the concentration of each of the measured constituents was compared in skin-puncture specimens and venous serum there were important differences in the concentrations of glucose, potassium, total protein, and calcium. Except for glucose, the concentrations of these were higher in venous serum. The degree of hemolysis was the same in skin-puncture serum and plasma, but less in venous serum. The greater hemolysis in skin-puncture specimens was not reflected in a clinically important increase in the values of lactate dehydrogenase and potassium. We conclude that there is a difference in the concentration of some chemical constituents in skin-puncture specimens and venous serum and that these differences should be considered when results for these types of specimens are compared.

Microviscosity of amniotic fluid phospholipids, and its importance in determining fetal lung maturity.

Fluorescence polarization measurements of microviscosity (apparent viscosity within the hydrophobic center of lipid bilayers) of amniotic fluid correlate well with lecithin/sphingomyelin ratios determined by thin-layer chromatography. In addition to lecithin, phosphatidylglycerol and phosphatidylinositol are important for determining fetal lung maturity, but the lecithin/sphingomyelin ratio gives no information concerning these other phospholipids. The microviscosity of sphingomyelin significantly exceeded that of lecithin over the temperature range 25--37 degrees C; values for phosphatidylglycerol, phosphatidylinositol, and phosphatidylserine were lower. Phosphatidylglycerol, phosphatidylinositol, and phosphatidylserine, added individually, significantly decreased the microviscosity of dispersions with lecithin/sphingomyelin ratios corresponding either to fetal lung immaturity or maturity. Phosphatidylglycerol caused the greatest decrease in both. Mixtures of the three phospholipids in the proportions found in term amniotic fluid decreased the microviscosity of fluids with either mature or immature lecithin/sphingomyelin ratios by 23--27%. When each was present in the proportion found in tracheal aspirate (twice that of term amniotic fluid), the decreases uere 46--50%. This technique quickly and precisely indicates not only fetal lung maturity but also the presence of important phospholipids other than lecithin and sphingomyelin.

Effect of intermittent phototherapy on bilirubin dynamics in Gunn rats.

To determine whether continuous phototherapy is necessary to control neonatal jaundice, groups of jaundiced (Gunn) rats were exposed to four blue light regimens: continuous light, 30 min light/30 min dark, 6 min light/6 min dark, and 6 min light/18 min dark. An exponential decrease in serum bilirubin concentration (SBC) was found with all regimens. A logarithmic dose response curve was obtained with a 50% light dose exhibiting 75% efficacy, and a 25% light dose exhibiting 59% efficacy compared to continuous phototherapy. The time constants of the decrease in serum bilirubin concentration also varied logarithmically with doses with continuous therapy having a time constant of 1.4 days, and 6 min light/18 min dark therapy having a time constant of 3 days.

Bilirubin dynamics in the Gunn rat. Dose response of intermittent and continuous phototherapy.

Jaundiced Gunn rats underwent continuous and intermittent phototherapy with white and blue lights. Irradiances ranged from 0.088 to 1.4 mW/cm2 in the blue (415-465 nm) wavelengths. Changes in serum bilirubin concentration were analyzed by a single exponential model. Dose-response curves for 10 days of phototherapy indicated similar logarithmic relationships between light dose and serum bilirubin decline for intermittent and continuous blue light and continuous white light phototherapy. The dose-response curve for intermittent white light showed a low slope and correlation coefficient.

Amniotic fluid fluorescence polarization value as a predictor of respiratory distress syndrome.

Fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene in amniotic fluid lipid aggregates was measured to determine the ability of this technique to prospectively predict respiratory distress syndrome. Prior retrospective studies have shown that an FP value of less than or equal to 0.336 correlated best with a lecithin to sphingomyelin ratio of greater than 2.0. Fluorescence polarization values of amniotic fluid samples obtained within 48 hours of birth from 161 pregnancies were correlated with neonatal outcome. Samples from 149 pregnancies had FP values of less than or equal to 0.336 and samples from 12 pregnancies had FP values of greater than or equal to 0.336. No infants delivered from the former group developed RDS and eight of 12 infants from the latter group developed RDS (P less than 0.001). In the entire population the test had a sensitivity of 100% and a specificity of 97%. When 37 infants with birth weights less than 2,500 gm were studied, the FP value remained a highly reliable predictor of the infant at risk for developing RDS (P less than 0.001). In this subset the test had a sensitivity of 100% and a specificity of 90%. L-S ratios were performed on 96 samples and the results correlated well with FP values (P less than 0.001). We conclude that the amniotic fluid FP value is a reliable index of fetal lung maturity and the risk for developing RDS. The FP value also has specific technical and diagnostic advantages over the L-S ratio.

Selected chronic disease 'risk factors' in two elementary school populations. A pilot study.

Ninety-five first-grade elementary school students (aged 5 to 6 years) in two New York City area schools participated in a pilot test of a chronic disease primary prevention program stressing nutrition, antismoking, and physical activity. Program components included a health knowledge questionnaire; measurement of height, weight, skin-fold thickness, total serum cholesterol level, and blood pressure; and a modified Harvard step test of pulse rate recovery after exercise and subsequent classroom health education. The proportion of students with test values higher than specified critical levels was much greater in school M compared with school S. These measures will be repeated after one year to determine the feasibility and potential effectiveness of certain classroom health education activities.

Determination of fetal lung maturity by fluorescence polarization of amniotic fluid.

The degree of fluorescence polarization (P value) of 1,6-diphenyl-1,3,5-hexatriene has been shown to be an excellent indicator of the lecithin/sphingomyelin (L/S) ratio in laboratory prepared liposomal dispersions. In order to test the validity of this technique in amniotic fluid, the L/S ratio and P value of 161 amniotic fluid specimens were determined. In 127 the P value was less than or equal to 0.336 and the L/S ratio was greater than or equal to 2. In 26 the P value was greater than 0.336 and the L/S ratio was less than 2 (P less than 0.05). The amniotic fluid P value is affected by blood or meconium but not by surgical lubricants or bilirubin. We concluded that the degree of fluorescence polarization of amniotic fluid indicates fetal lung maturity as reliably as the L/S ratio. However, this method has important technical and practical advantages that make it more applicable for a clinical laboratory.