Year: 2013
Type: article
Study design: Observational Study
Abstract: Background. Improvements in postnatal care provided in neonatal intensive care units have resulted in increasing survive percentage of children born at the limits of viability. A large number of premature infants experienced major impairment and/or minor neurodevelopmental disabilities, such as cognitive, psychiatric and motor disorders. The etiology of these developmental deficits still remains not completely understood, but they may be the result of neonatal brain injury as well of interruption of the normal process of brain maturation that occurs during the last trimester of pregnancy, a critical period of prenatal ontogenesis. Prediction of the outcome of individual preterm infants is difficult. Although a premature infant may be asymptomatic for abnormal clinical signs, he may exhibit subtle alterations in brain activity which often remain unrecognized. A neurophysiologic evaluation of brain activity in the third trimester of gestation would probably be of great benefit for early detection of pathological processes or subclinical alterations. Electroencephalogram and cortical auditory evoked potentials turned out to be simple and useful techniques in evaluation of brain maturation. Aims. We conducted cross-sectional and longitudinal investigations at early crucial phases of development (35 and 40 weeks post-conception) in order to identify differences in cerebral activity between premature infants born at different gestational ages and full-term neonates, using electroencephalogram (EEG) at rest and cortical auditory evoked potentials (CAEP). We further aimed to correlate the neonatal data with later neurodevelopment. Methods. The research is divided into three studies: Study 1: EEG spectral activity was recorded at 35 post-conception weeks in 40 premature infants and compared between groups of infants born at different gestational age (“extremely low gestational age”, ELGA: 23–27+6, ‘‘very low gestational age’’, VLGA: 28–31+6 and “low gestational age”, LGA: 34-35). The results were correlated with behavioral developmental scores obtained at 12 months corrected age from 20 infants. Study 2: a subgroup of 10 infants of Study 1 repeated the EEG recording at 40 post-conception age. EEG spectral activity of this subgroup was compared longitudinally and further the activity recorded at 40 GA were compared with those of a group of 10 full-term infants. Study 3: CAEP were recorded in active sleep at 35 post-conception weeks in response to an auditory stimulation in 36 premature infants and compared between groups of infants born at different gestational age (ELGA, VLGA, LGA). The results were correlated with behavioral developmental scores obtained at 12 months corrected age from 20 infants. Methodology Study 1 and 2. Electrical brain activity was recorded for 40 minutes on 5 bipolar channels. Data were transformed into the frequency domain using a Fast Fourier Transform algorithm. Frequency spectrum was divided into the following bands: δ (0.5-4 Hz, comprising δ1 0.5-1 Hz and δ2 1-4 Hz), θ (4-8 Hz), α (8-13 Hz) and β (13-20 Hz). Statistical analysis were performed on absolute and relative power values only on central sites (C3-C4, C3-T3, C4-T4). Methodology Study 3. 1000 Hz (paradigm 1) and 500 Hz (paradigm 2) auditory stimulations were performed on continuous EEG recording. Design consisted of 300 tones for each paradigm. Inter-stimulus interval randomly varied between 600 and 900 ms; 12 monopolar channels were recorded, referenced to the bilateral linked ear lobes. 600 ms epochs were divided for statistical analysis in time windows of 100 ms. Statistical analysis were performed only on central sites (Fz, Cz). Results. Study 1. On C3-C4, relative spectral power values differed significantly between ELGA and LGA groups. Infants born at lower gestational ages had a higher amount of power in the δ and a lower amount of α and β spectral power. The preliminary data on those infants attaining 12 months of corrected age showed that higher amount of δ and a lower amount of β and α resulted associated with poor relational skills and personal self autonomies. Study 2. At 40 post-conception age, premature infants showed on C3-C4 a decrease in δ activity and a mild, not significant, increase in higher frequencies; no significant differences in spectral power values were found with full-term neonates. Study 3. In response to 1000 Hz tones no waveforms became evident on Fz in ELGA infants, while LGA presented a wide and slow positive response; the groups differed significantly. VLGA’s grand average waveform resembled that of LGA group, but characterized by a high variability. Responses to 500 Hz resulted highly variable and not reliable. Conclusions. We found early subtle brain electrical alterations in premature infants experiencing different developmental pathways, suggesting a different cortical organization; these differences seem to be associated with later development. The potential of neurophysiological methodologies is to provide a useful indicator of good prognosis or poor developmental outcomes.
Author: Elisa Cainelli
Language: English
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W79475535