An Approach to Combining Results From Multiple Methods Motivated by the ISO GUM.

The problem of determining a consensus value and its uncertainty from the results of multiple methods or laboratories is discussed. Desirable criteria of a solution are presented. A solution motivated by the ISO Guide to the Expression of Uncertainty in Measurement (ISO GUM) is introduced and applied in a detailed worked example. A Bayesian hierarchical model motivated by the proposed solution is presented and compared to the solution.

Regional differences in spectral EEG measures between healthy term and preterm infants.

State-specific spectral electroencephalographic (EEG) values were compared among 14 bipolar channel derivations between two healthy neonatal cohorts. Fifty-five healthy preterm neonates of < or = 32 weeks gestational age at birth were studied with 24-channel recordings over 3 hours at term conceptional age. These were compared with studies of 45 healthy term neonates. Five spectral measures for each channel (i.e., total spectral EEG, delta, theta, alpha, and beta frequency ranges) were calculated for each minute, which was identified as active or quiet sleep, based on visual analysis. Using multivariate analysis of variance, differences at each channel were assessed between neonatal cohorts for both states and cohorts; higher total EEG spectral values were noted during active sleep; whereas higher delta and theta spectral values were noted during quiet sleep. The term cohort had higher values for spectral theta, alpha, and beta power spectra in multiple channels, most significantly in the left central (i.e., C3O1) and sagittal regions (FzCz, CzPz) during both states (P < .0001, adj r2 > or = .2). Both interhemispheric and intrahemispheric differences in spectral values were present. For a healthy preterm cohort, lower spectral energies are expressed during sleep in specific head regions. Physiologic asymmetries exist in the newborn brain which are unique for the preterm infant, emphasizing functional alterations in brain development. How these asymmetries are altered by prenatal or postnatal stress or disease states needs to be explored.

Computer classification of state in healthy preterm neonates.

Nineteen electroencephalographic (EEG) sleep measures describing four physiologic aspects of sleep behavior (i.e. sleep continuity, EEG spectra, body and eye movements, and autonomic measures) were derived from visual and computer analyses of 71 24-channel, 3-hour EEG sleep recordings on 52 healthy preterm neonates from 28-36.5 weeks postconceptional age (PCA). Forty-eight subjects were neurodevelopmentally normal up to 2 years of age. Four electrographic states that comprise tracé discontinu of the preterm neonate were defined in terms of increasing seconds of EEG quiescence per minute. A regression analysis was performed after transformations of nonlinear data sets representing the 19 EEG sleep measures, with the four sleep states as outcome variables. Postconceptional age was also included in these analyses as the 20th explanatory variable. Four measures best defined the EEG sleep states, explaining 75% of the variance: decreasing rapid eye movements per minute, decreasing numbers of spontaneous arousals per minute, increasing spectral theta energies, and decreasing facial movements per minute. Other cerebral and noncerebral measures, including total spectral EEG energies, spectral EEG energies in three bandwidths (i.e. delta, alpha, beta), cardiac and respiratory measures, and body movements, did not contribute as significantly to the prediction. Inclusion of PCA into the regression equation with the four EEG measures, selected by the analysis procedure, indicated that its contribution to state prediction was also small; the effect of PCA on state was found to be explained by the four EEG sleep measures.

Prediction of lower developmental performances of healthy neonates by neonatal EEG-sleep measures.

Previous neurophysiologic studies from our laboratory have demonstrated altered EEG-sleep behavior at conceptional term ages in healthy preterm infant compared with a term cohort. Developmental assessments at 12 and 24 months of age of 16 children in each cohort were compared using MANOVA. Differences were detected on MANOVA between each cohort on Bayley mental and motor performance scores, while social skills (Vineland) and temperament (Carey) were similar. Healthy preterm infants had lower scores at 12 months of age (P < .0001) and 24 months (P < .04) than term infants before adjustment for prematurity. No group differences were observed after adjustment. For the combined cohort of 32 healthy neonates, specific neonatal EEG-sleep measures were included as predictor variables in regression analyses with Bayley mental scores as outcome variables. Lower Bayley mental scores at 12 and 24 months were associated with higher spectral EEG correlations, lower spectral EEG energies in the beta frequency ranges, fewer arousals per minute, lower rapid eye movements per minute, and shorter sleep latencies from awake state to active sleep. Significant associations were observed before adjustment for prematurity at both 12 and 24 months, and after adjustment at 12 months of age for lower spectral beta EEG energies. Lower socioeconomic class also correlated with lower developmental scores. Even in the absence of major neonatal illnesses, brain adaptation to prematurity influences later developmental outcome. Adjustment for "age equivalency" may be required up to at least 24 months of age even in a healthy preterm population.

Postnatal adaptation of brain function in full-term neonates as assessed by EEG sleep analyses.

Differences in electroencephalographic (EEG) sleep between preterm and full-term neonatal cohorts at matched postconceptional ages have been previously presented by our study group. These differences may have occurred, however, because of postnatal brain adaptation of the full-term infant after a more recent delivery. EEG sleep analyses, therefore, were performed on only the full-term cohort to determine if EEG sleep measures changed over the first three days after birth, which might account for the differences with the preterm group. Twelve full-term infants studied on the first day of life were compared with 17 full-term infants who were studied on days of life 2 and 3. Using multivariate analysis of variance (MANOVA), comparisons were performed among 13 EEG sleep measures. No EEG sleep differences were seen between full-term children born by Cesarean section versus those born by vaginal presentation. No statistical differences were noted between day 1 compared to days 2 and 3 with respect to 10 measures concerning sleep architecture, phasic, continuity, spectral EEG, and autonomic features. In three EEG sleep measures, changes occurred between days 1 and 2-3, but two of the three measures were in a direction that strengthen our claim that differences exist between preterm and full-term cohorts: more body movements and lower percentages of quiet sleep were noted for full-term infants on days 2-3. EEG sleep differences between preterm and full-term infants at matched postconceptional term ages are more likely to be due to conditions associated with prematurity rather than postnatal brain adaptation in the full-term group who experienced a more recent delivery.

Maturational trends of EEG-sleep measures in the healthy preterm neonate.

Five physiologic groupings of 45 EEG-sleep measures were acquired from serial 24-channel EEG-sleep recordings (i.e., sleep architecture, continuity, EEG spectral, phasic, and autonomic measures), utilizing 129 studies on 56 healthy preterm infants from 28 to 43 weeks postconceptional age (PCA) who were neurodevelopmentally normal on follow-up. Regression analyses chose the least number of measures that best reflected maturation. Four of 45 variables (i.e., spectral alpha energy during quiet sleep, total spectral EEG energy, arousal number during active sleep, and percentage of EEG discontinuity) most significantly explained brain maturation in neonates < 36 weeks PCA. Three of 45 variables (i.e., spectral theta and beta energies during active sleep and spectral alpha energy during quiet sleep) were most representative after 36 weeks PCA. Spectral EEG energies were the strongest indicators of maturation compared with other measures, particularly in near-term neonates.

Comparative estimates of neonatal gestational maturity by electrographic and fetal ultrasonographic criteria.

We previously reported a high correlation between electrographic and postmortem neuroanatomic (i.e., sulcal-gyral) estimates of maturity in sick preterm neonates who were clinically abnormal because of neonatal medical illnesses. Electroencephalographic studies have not yet been compared with ultrasonographic measurements in healthy fetuses who subsequently had normal neurodevelopmental outcome. Twenty-five EEG recordings on healthy neonates (28-43 weeks postconceptional age) had EEG estimates of gestational maturity without knowledge of obstetric, neonatal, or ultrasonographic criteria. Thirteen recordings from this cohort were obtained on very premature neonates (i.e., < 32 weeks estimated gestational age). Fetal ultrasonographic determinations of gestational maturity for these 13 subjects were also obtained prior to birth. Ultrasonographic estimates were assigned without knowledge of other clinical data. Gestational age estimates based on electroencephalographic analyses were compared with 5 ultrasonographic estimates of gestational age maturity using multivariate regression (i.e., biparietal diameter, abdominal circumference, femur length, transcerebellar diameter, and head circumference), as well as the mother's last menstrual period. No significant differences were detected between the electrographic and obstetric/ultrasonographic estimates of gestational maturity. An electroencephalographer's assessment of gestational age is as accurate as the fetal ultrasonographic estimates in the asymptomatic preterm neonate whose gestational age is < 32 weeks at birth.

Comparisons of EEG sleep state-specific spectral values between healthy full-term and preterm infants at comparable postconceptional ages.

Differences in state-specific electroencephalographic (EEG) spectral values are described between groups of preterm and full-term neonates at comparable postconceptional term ages. Eighteen healthy preterm neonates of < or = 32 weeks gestation were selected from an inborn population of a neonatal intensive care unit. Twenty-four-channel recordings were obtained at a full-term age and compared with studies of 22 healthy full-term neonates. The initial three hours of each 12-hour study were recorded on paper from which EEG sleep state scores per minute were visually assessed. Six mean spectral values (i.e. total EEG, electromyogram, delta, theta, alpha and beta energies) were calculated from each corresponding minute of digitized data, which was also assigned one of six EEG sleep states. Each neonatal group displayed statistically significant differences among sleep-state segments for all spectral values. The alpha- and beta-range spectral values of the preterm group, compared to the full-term control group, were lower during all sleep state segments. Spectral values for the theta band were lower during both quiet sleep segments only, whereas spectral values for delta were lower during all sleep stages, except tracé-alternant quiet sleep. Significant differences in EEG spectral values were noted among states of sleep for both preterm and full-term infants of similar postconceptional term ages. These data also suggest differences in central nervous system maturation between neonatal populations. These findings strengthen our previously stated contention that there is a functional alteration in brain development of the preterm infant as reflected in sleep organization that results from a prolonged extrauterine experience and/or prematurity.

Changes in personality associated with changes in aerobic and anaerobic fitness in women and men.

Thirty-nine females and 63 males participated in a 10-week physical conditioning class involving aerobic (running) and anaerobic (weight training) exercise. Aerobic fitness, anaerobic fitness, and personality were measured before and after the 10-week training period. Multiple regression analyses revealed that changes in personality were generally associated with changes in aerobic rather than anaerobic fitness, and that the relationship were most likely to be found with women. Possible explanations were offered.