The ontogeny of sensory perception in preterm infants

Examining the effects of a targeted noise reduction program in a neonatal intensive care unit

OBJECTIVES

To determine whether implementation of a noise reduction policy followed by the addition of direct audit and feedback reduces noise levels in a tertiary-level neonatal intensive care unit (NICU).

STUDY DESIGN

Noise level data was collected in three phases: (1) baseline (preintervention), (2) immediately postimplementation of our noise reduction policy, (3) postunveiling of direct audit and feedback mechanism.

SETTING

A level 3 NICU in Ontario, Canada.

INTERVENTIONS

Noise reduction policy and a direct audit and feedback mechanism.

MAIN OUTCOME MEASURES

Average noise level.

RESULTS

The baseline level of noise in our unit consistently exceeds guidelines with an average baseline noise of 49 dB (±1.4). Our intervention resulted in a significant reduction in noise levels for one of the four areas in our NICU [-1.06 dB (-1.52, -0.6)], with a trend towards reduction in a second area (-0.21 dB (-0.6, 0.18)). Unexpectedly, two other areas experienced a significant increase in noise (2.05 dB (1.18, 2.94); 0.85 dB (0.11, 1.59)).

CONCLUSIONS

The baseline noise in the NICU consistently exceeds guidelines, but reductions in noise levels are achievable. Nonetheless, more work is needed to find the optimal NICU design and noise reduction strategy.

Extrauterine environment affects the cortical responses to verbal stimulation in preterm infants

Using optical topography, changes in the cerebral oxygenation were compared in the parieto-temporal lobe of preterm and term infants of equal postconceptional age in response to verbal stimulation. Eight preterm infants of gestational age 23-34 weeks were studied at postconceptional term age (38-46 weeks). Ten term infants were studied at 2-11 days after birth. Twenty-four-channel near-infrared optical topography (NIOT) was used to measure changes in concentration of oxyhemoglobin ([oxyHb]), deoxyhemoglobin ([deoxyHb]) and total hemoglobin ([totalHb]) in the bilateral temporal cortices. Verbal stimulation was provided by a recording of a Japanese fairy tale. The latency in response to verbal stimulation was significantly shorter in the preterm infants than in the term infants. This time is thought to reflect brain development, particularly the development of the neuro-vascular coupling mechanisms in the cerebral cortex. The present results indicate that the number of days after birth is more closely related to development of auditory system and neuro-vascular coupling than is postconceptional age. Thus, this suggests that early extrauterine environment affects the cortical responses to verbal stimulation in preterm infants.

Newborn auditory follow-up

Because hearing is a key component in the infant's development of speech, language, and cognition, early detection of infant hearing loss is critically important. The routine evaluation of hearing should include the identification of parental concerns regarding infant hearing as well as the assessment and diagnosis of infants with potential hearing impairment. Identification of hearing loss should be followed by early interventions to prevent developmental delays. This article promotes universal screening of newborn hearing. The article also provides a review of the embryogenesis of hearing and includes a breakdown of risks for hearing loss, recommendations for auditory testing, and suggestions for follow-up, early intervention, and support for families of infants with hearing impairment.

Maturation of the auditory brainstem in low risk-preterm infants: a comparison with age-matched full term infants up to 6 years

Whether preterm birth has a significant effect on the maturation of the human brain remains an equivocal issue. Since experience plays a crucial role in the development of the brain, it is conceivable that extra-uterine preterm exposure could exert some effects on the maturation of the developing human brain. The present study compared the post-term maturation of the central components of brainstem auditory evoked response (BAER) in low risk preterm infants with that of age-matched full term infants up to 6 years. The preterm infants demonstrated similar maturational profiles to those of the term infants in both interpeak intervals and amplitude measures. No systematic, statistically significant differences were found between the preterm and term infants in any of the BAER variables although the I-V interval tended to be slightly shortened in the prematurely born infants. These results suggest that preterm birth or earlier exposure to sound environment extra utero is unlikely to lead to significant neurophysiological consequence in the developing auditory brainstem of low risk infants.

Heart-rate variability in low-risk prematurely born infants reaching normal term: a comparison with full-term newborns

To investigate the influence of prematurity and postnatal age on the maturation of the autonomic nervous system function, we analysed heart-rate and heart-rate variability in twelve prematurely born infants (< 37 weeks gestational age) reaching the conceptional age of 37-41 weeks. These neonates were compared with sixteen 37-41 week conceptional age newborns (< 10 days postnatal age). Heart-rate variability was analysed by spectral analysis of interbeat intervals using Short-Time Fourier Transform. We found that during both active and quiet sleep, the durations of RR-intervals were shorter and the amplitude of heart-rate variability in different frequency bands was lower in prematures reaching term than in newborns of the same conceptional age (P < 0.001). Between-state comparison showed differences in both groups. In both groups, low-frequency heart-rate variability was higher in active sleep than in quiet sleep. Between-state differences of RR-intervals and high-frequency heart-rate variability were present only in newborns (P < 0.01). Discrimination between newborns and prematures reaching term, based on RR-intervals and heart-rate variability, was correct in both sleep states with errors between 7 to 16%. However, in both newborns and prematures reaching term, between-state discrimination showed less reliable results, especially for quiet sleep discrimination with 24% (in PRT) and 20% (in NB) of errors. Our results, especially information given by factor analysis, suggest that the differences between newborns and prematures reaching term, concerning RR-interval and heart-rate variability, may be related to a changed balance between the sympathetic and parasympathetic nervous systems with a diminished parasympathetic component of heart rate control in prematures reaching term, as compared to newborns.

Assessment of Sitting in Children with Cerebral Palsy from Videofilm

The purpose of this study was to investigate the reliability of two dependent measures, (1) counting of pathologic movements (CPM) and (2) the Sitting Assessments Scale (SAS). The measures were intended for use in clinical physiotherapy practice, to provide both quantifiable and qualitative information from videofilm concerning functional sitting in children with cerebral palsy (CP). Two separate groups of final term physiotherapy students (three students in each group) tested one technique each for interrater reliability. The SAS-measure also was tested for interrater reliability. Videofilm of twelve children with CP ranging in age from 2 to 16 years were assessed. The students' results were compared to earlier results by experiences physiotherapist. The results demonstrated excellent interrater reliability for SAS (p<0.001) and good interrater reliability for the CPM technique. The degree of user experience seems to play a role in the use of the CPM measure. Considering evaluation of postural control and functional performance over all, SAS appears to be superior to CPM.

The effect of preterm birth on brainstem, middle latency and cortical auditory evoked responses (BMC AERs)

Recent studies on the maturation of auditory brainstem evoked responses (ABRs) present conflicting results, whereas only sparse reports exist with respect to the maturation of middle latency auditory evoked responses (MLRs) and auditory cortical evoked responses (ACRs). The present study reports the effect of preterm birth on the maturation of auditory evoked responses in low risk preterm infants (27-34 weeks conceptional age). The ABRs indicate a consistent trend towards longer latencies for all individual ABR components and towards longer interpeak latencies in preterm infants. The MLR shows longer latencies for early component P0 in preterm infants. The ACRs show a remarkable difference between preterm and term infants. At 40 weeks CA the latencies of ACR components Na and P2 are significantly longer in term infants, whereas at 52 weeks CA the latencies of the same ACR components are shorter in term infants. The results support the hypothesis that retarded myelination of the central auditory pathway is partially responsible for differences found between preterm infants and term infants with respect to late ABR components and early MLR component P0. Furthermore, mild conductive hearing loss in preterm infants may also play its role. A more complex mechanism is implicated to account for the findings noted with respect to MLR component Na and ACR components Na and P2.

Detectability of auditory evoked response components in preterm infants

In determining the detectability of brainstem, middle latency and cortical auditory evoked responses in preterm newborns, one has to deal with the ongoing maturation of the auditory system. In the preterm period the detectability of evoked responses is closely related to the appearance of the individual evoked response components. The detectability of the individual evoked response components in preterm infants is important, because low detectability rates make the absence of a particular evoked response component irrelevant with respect to the clinical-neurophysiological correlation. In a longitudinal study we determined the detectability and cumulative detectability, i.e. the presence of individual evoked response components in one or more recordings of evoked response components in 37 low risk preterm infants between 30 and 41 weeks conceptional age (CA). On the basis of their detectability it is concluded that evoked response components, determined between 30 and 34 weeks CA, are generally of limited use for clinical application, except for auditory brainstem response (ABR) components I, IIn, V and Vc and middle latency response (MLR) component Na. Our study made clear that improvement can be achieved by performing more than one examination within a period of approximately 4 weeks between the recording sessions. The cumulative detectability rates after two recordings showed improvement for all components involved in this study. The cumulative detectability rates of ABR components I, II, IIN, III, V, IIc, IIINc, Vc, MLR components Na and P0, and auditory cortical response (ACR) components PbP1 and N2p are sufficient to use as measures in the neurophysiological judgement of functional integrity of the central auditory pathway in preterm infants.

Gross and fine motor development of preterm infants at eight and 12 months of age

Forty-five neurologically normal preterm infants were allocated to one of two groups according to their gestational age at birth (less than 32 weeks; 32 to 36 weeks). Their gross and fine motor development was assessed at eight and 12 months chronological age and eight and 12 months adjusted age. At eight months chronological age the two groups differed significantly in both gross and fine motor development, but at eight and 12 months adjusted age and 12 months chronological age they differed significantly only in fine motor development.

The maturation of the central auditory conduction in preterm infants until three months post term. V. The auditory cortical response (ACR)

Auditory cortical evoked responses (ACRs) were recorded in 65 preterm infants, at least on 3 occasions in 48 of them. The infants were divided into 5 groups according to their gestational age (GA). The recording sessions were performed at 8 conceptional age (CA) levels, defined as the gestational age added to the chronological age. The last recordings were obtained at 50-52 weeks CA. The ACRs were analyzed for the primary complex containing middle latency components (MLR) and the secondary complex, containing the slow late components. The ACR records first appear at about 25 weeks CA, initiating the premature stage followed by a transitional stage around term date and the gradual development into the mature stage, achieved at 50-52 weeks CA. The detectability rate of the various components generally increased with increasing conceptional age, for some of the components, especially N2p and N2, this rate achieved a value of about 80%. The degree of prematurity did not influence appreciably the development of the ACR. The waveforms, and to a lesser extent the latency and amplitude values, are strongly age dependent. Remarkable topographic differences between the ACR parameter latency and more importantly amplitude values are found between the derivations from the vertex and the central temporal areas, supporting the theory of different generation sites for the ACR components. The premature and mature ACR appeared relatively insensitive to changes in the states of vigilance. The ACR in premature infants are useful in developmental studies with respect to the central audition in premature infants and might contribute in the clinical assessment on the quality of the premature central auditory system.

The maturation of the central auditory conduction in preterm infants until three months post term. IV. Composite group averages of the cortical auditory evoked responses (ACRs)

Composite group averages were constructed from cortical auditory evoked responses (ACRs), which are recorded sequentially at maximally 8 conceptional age levels in 5 groups of 49 preterm infants, with additional inclusion of the records of 16 prematures obtained at different conceptional age levels. The group averages for the 5 gestational age groups showed replicable waveforms at all conceptional age (CA) levels reflecting the intragroup stability of the ACR complex. From the earliest age levels, from 25 weeks CA on, ACR group averages can be obtained, containing relative low voltage fast waves and high voltage slow waves. The most outstanding developmental changes in the ACR complex are the waveform changes. Until about 36 weeks CA a premature waveform is found, followed by a transitional phase with low voltage noisy records. Finally the adult waveform is found in the measurements at three months after term date. The latency values of the group averages are determined by the waveform changes. Persistent amplitude differences are found for the slow late waves between the vertex and the central temporal derivations.

Assessment of early auditory and visual abilities of extremely premature infants

The early auditory and visual abilities of 47 extremely premature infants (31 born less than or equal to 28 weeks gestation) were assessed with a bell, a light and an optokinetic nystagmus drum. All the infants altered to the bell and blinked to the light from 25 weeks postconceptional age (PCA) and beyond. A few infants at first had only a change in heart rate or respiratory rate in response to the bell, or required a high-intensity light to elicit a blink. The majority appeared to habituate to the bell and light during their first examination at one week of age. None of the infants blinked in response to a threatening gesture. Optokinetic nystagmus could be elicited as early as 30 weeks PCA, could be elicited in the majority by 36 weeks PCA, and universally by term (40 weeks PCA). The responses of 15 fullterm newborn infants were not significantly different from those of the preterm infants at term. Alerting to a bell, blinking to light and habituation to both are simple bedside maneuvers for assessing extremely premature infants less than 30 weeks PCA. Optokinetic nystagmus may be useful in assessing the visual abilities of premature infants closer to term.

First magnetoencephalographic recordings of the brain activity of a human fetus

Using a one-channel neuromagnetometer adjusted to a special site on the mother's abdomen, we succeeded in recording prenatally, for the for the time, human fetal brain activity in late pregnancy. It was possible to record both the fetal auditory-evoked neuromagnetic field and to detect fetal brain activity by analysis of the frequency spectrum. Such measurements may soon prove valuable for the noninvasive investigation of human brain function.

Differential maturation of cortical auditory evoked potentials to speech sounds in normal fullterm and very low-birthweight infants

Cortical auditory evoked potentials (AEP) to the consonant-vowel syllables/da/and/ta/and 800Hz tone were recorded at 40 weeks post-conceptional age and at one, two and three months after term in normal fullterm and very low-birthweight infants. As a group, the very low-birthweight infants exhibited significantly less mature AEPs to consonant-vowel syllables than the normal-birthweight infants at 40 weeks post-conceptional age. Consistent but statistically non-significant differences also were found for tones at 40 weeks post-conceptional age, and for all stimuli at one and two months after term. By three months, all the infants exhibited mature AEP morphology and topography.

The very low birth weight infant after discharge from intensive care: anticipatory health care and developmental course

Despite intensive research, the data available on the long-term effects of prematurity on development of the child have not led to clearcut conclusions, particularly when the investigations are based on infant or perinatal factors alone. Previous research does indicate that the infant is "at risk" through school age and that the parents' perception of the child and the harmony between the child and his environment are powerful determinants of outcome. The implications for medical care, however, are clear. The developing low birth weight infant is best served by close medical supervision, particularly during the turbulent early years. Health care should be planned to include ongoing developmental assessment and screening at least through school entrance so that emerging vulnerabilities or deficits may be addressed as early as possible, thus impeding developmental progress minimally. An optimal care plan includes active partnership with the parents in detection of weaknesses, reinforcement of strengths, and formulation of recommendations for behavioral and educational management. For the physician this will require clinical acumen, an understanding of the child within the context of his environment, an attitude of supportive realism and a long view.

The etiology of neurosensory hearing defects in preterm infants

We retrospectively investigated the influence of gestational age, perinatal risk, and the duration of incubator care periods in 193 surviving preterm infants with a gestational age between 28 and 36 weeks raised in our intensive care nursery incubators from 1965--1967. 24 (12.4%) of the children showed definite neurosensory hearing defects, which were particularly encountered in the high frequencies. No correlation could be substantiated between hearing difficulties and hyperbilirubinemia, streptomycin application and gestational age. This study does not support the assumption that the duration of noise exposure in currently used incubators is a major determinant for the development of deafness in otherwise healthy preterm infants. Our study did show, however, a strong correlation between the sum of all perinatal risk factors and neurosensory hearing loss.