Behavioural and physiological reactivity to noise in the newborn.

OBJECTIVE: To assess the electromyographic (EMG) and behavioural reactivity of a group of newborn infants exposed to noisy stimulation of various intensity recorded in the Paediatric intensive care Unit (PICU). METHODS: The study was performed at the nursery of the Paediatrics Department (University of Padova) on a group of 21 healthy newborns (mean 39 weeks of gestation), assessed between 24 and 72 h after birth. The study involved taking EMG recordings of the corrugator supercilii muscle and assessing the infant's behaviour at the baseline (15 seconds before stimulation), during noisy stimulation (for 1-2 seconds) and during recovery (15 seconds in three subphases). The noises, previously recorded in PICU, had four different intensities and were administered in random order to all infants. Descriptive analysis and repeated-measures analysis of variance (anova) were performed on the EMG and behavioural data. RESULTS: The infants demonstrated a significant reaction to the noises both in the EMG recordings and in behavioural changes, especially during intense noisy stimulation. The reaction lasted longer than the stimulation period, preventing the infants from returning to the baseline condition. CONCLUSIONS: Exposure to high-intensity noise produced in PICU causes evident behavioural and physiological effects (EMG). This is a field of study that could have important repercussions, given the medium- and long-term effects of repeated noise stimulation.

Electrocochleography potentials evoked by condensation and rarefaction clicks independently derived by a new numerical filtering approach.

The cochlear microphonic potential (CM) and the compound action potential (CAP) cannot be measured separately but only in combination. In the literature their individual estimates are conventionally recovered by the so-called CM cancellation technique. This method averages the potential obtained in response to rarefaction and condensation clicks under the assumption that changing the polarity of the clicks only affects the CM sign and does not alter the CAP in any way. However, both theory and evidence suggest that these hypotheses can be critical. In addition, recent contributions in the electrocochleography (ECochG) literature suggested that assessing the influence of stimulus polarity on the evoked CAP may constitute an indicator of clinical usefulness which the CM cancellation method cannot supply. In this work we propose a new algorithm to estimate the cochlear potentials evoked from positive clicks, CAP+ and CM+, and those evoked from negative clicks, CAP- and CM-, by processing the same kind and amount of data employed in the CM cancellation method. The application to real data taken from 3 subjects exhibiting quantitatively and qualitatively different ECochG responses at various levels of stimulation intensity is presented. In addition, simulated problems where the true CAP and CM are known are studied to permit a fair assessment of the proposed technique. Results suggest that the new algorithm is potentially able to point out small differences between CAP+ and CAP-. This encourages its further employment on a larger scale.

Evaluation of noise in the neonatal intensive care unit.

This study evaluated the noise level inside the incubators in a neonatal intensive care unit and identified its sources in order to attempt to reduce it. Although noise is not a proven risk factor as far as the sensory integrity of newborns is concerned, it is certainly an important cause of stress to them and a source of serious and dangerous changes in their behavioral and physiologic states. Noise recorded inside the incubators had two components. The first was background noise from the incubator motors, which varied from 74.2 to 79.9 dB, and was similar to environmental noise. The second source was impulsive events beyond 80 dB. These events were the result of voluntary and involuntary contact with the incubators' Plexiglas surface or to the abrupt opening and closing of their access ports. Considering its decibel levels and frequency, this latter component is undoubtedly an important source of stress to newborns. Moreover, these data reveal the need to train health care personnel on how to reduce such noise by taking more care in the handling of infants.

[Noise exposure in neonatal intensive care units]. / Esposizione a rumore nelle terapie neonatali intensive.

This study evaluates the exposure of newborn babies in neonatal intensive care units (NICU) to noise which can cause hearing lesions directly (acoustic trauma) as well as indirectly (hypoxia). Moreover, noise can have an aggravating effect when combined with other potentially harmful factors in the NICU, such as ototoxic medication or stress due to other external stimuli, such as excessively bright light, lack of a day/night rhythm or pain. Sound pressure levels were measured in the NICU and inside the cribs in various experimental conditions, classified under 3 different types of sound events: constant background noise, variations in background noise and impulsive events. The main sources of noise detected were crib noise generated by ventilation and temperature control systems, ambient noise in the room, noise caused by the staff in the NICU, noise generated by crib alarm systems and NICU apparatus and noise caused by activity on the crib cover or on its plexiglas top. Findings revealed that the influence of ambient noise is fairly irrelevant. Background noise and its variations concerned with activities in the department never exceeded the limits considered potentially harmful to adults (DRC), whereas the impulsive noise generated by staff on the cribs or on the plexiglas tops was considerable and potentially harmful. These findings demonstrate that it is feasible and relatively easy to control noise in the NICU and significantly reduce the impulsive noise component by training staff to be more careful and avoid any unnecessary jolting and rough handling on and near the cribs.

Brainstem auditory evoked potentials in rats with streptozotocin-induced diabetes.

Brainstem acoustic evoked potentials (BAEPs) were studied in streptozotocin (STZ)-diabetic rats and age-matched controls at 3 and 5 months from induction of the pathology. The diabetic status of the animals was kept uncontrolled throughout the study. Body weight and glycosylated hemoglobin were markedly altered in the diabetic animals (-42%, and +120% of control values, respectively). Neurophysiological results showed an increase in the latency of the major components of BAEPs; this increase was clearly time-dependent for the peripheral component (peak I). The central component (peak IV) was also significantly delayed. However, no significant impairment of the central conduction time was demonstrated by examining the interpeak I-IV latency. In conclusion, BAEPs prove to be a useful non-invasive neurophysiological technique that may help unravel both the relative involvement of the peripheral and central nervous systems in the course of diabetes mellitus, and the evolution of diabetic neuropathy.

Comparative ototoxic potential of hyaluronic acid and methylcellulose.

In experimental animal studies, exogenous hyaluronan (HA) has been shown to exert beneficial effects on the healing of tympanic membrane perforation. As any other exogenous substance, HA may prove potentially toxic, by filling the middle ear cavity, to the sensory cells of the organ of Corti. Electrophysiological (ABR) and morphological studies were carried out in the rat to examine the auditory function and the structure of the sensory epithelium. Rats received either HA or hydroxy-propyl-methyl-cellulose by trans-tympanic injection (middle ear cavity was completely filled up) and were compared to untreated, age- and weight-matched rats. In both treated groups ABR revealed transitory, mild conduction hearing loss, in particular for high frequencies, until day 7 postinjection. This loss recovered completely within the 15th day. Morphologically, no significant degenerative/necrotic lesions were observed in the organ of Corti, from both treated groups.

Auditory brainstem and middle latency evoked responses in the clinical evaluation of diabetes.

The measurement of auditory brainstem evoked responses and middle latency evoked responses may improve the evaluation of diabetic neuropathy. Twenty diabetic patients were studied (12 males, 8 females), aged 21 to 63 years with normal hearing, together with 20 age- and sex-matched normal subjects (10 males, 10 females). Auditory brainstem evoked responses were induced by rarefaction clicks of 0.1 ms at a repetition rate of 21.1 CPS and an intensity of 75 dB hearing level. Middle latency evoked responses were induced with clicks of 0.1 ms, a repetition rate of 7.7 CPS and an intensity of 75 dB hearing level. Diagnostic criteria were: a I-V interval latency shift greater than 2SD of the control group for the auditory brainstem evoked response test or the interval difference of wave V greater than 0.2 ms. Middle latency evoked response was diagnostic if the latency of the Pa component was greater than 2SD of normals. Twenty-five per cent of subjects had retrocochlear impairment (absence of I wave) even in the absence of symptoms. The combined technique of auditory brainstem evoked response and middle latency evoked response improved the detection rate of central nervous system dysfunction. Auditory brainstem response is important for detecting desynchronization of the auditory response, whereas middle latency evoked response detects abnormalities in the more rostral regions of the central nervous system. In conclusion, there is a role for auditory brainstem evoked response and middle latency evoked response in the global assessment of diabetic neuropathy.

Auditory evoked responses (ABR, MLR, SVR) and brain mapping in the elderly.

The influence of age on evoked auditory brainstem responses (ABRs) is still a matter of controversy. It is well known that in the elderly the ABRs show a progressive latency shift of the principal components. While many authors have reported a I-V internal latency shift, others claim that there is not a delay in the central conduction time (CCT) with ageing. Middle latency auditory evoked responses (MLRs) are also reported to be impaired in the elderly, but the few results published need further investigations. This study investigates some of the controversial aspects of electrophysiological assessment of the auditory system in the elderly. 36 healthy subjects (18 males and 18 females), mean age 67.2 years +/- 5.8, underwent ABRs, MLRs and SVRs and SVRs brain mapping evaluation. All the data were compared with our normative data for young adults. Our results confirm previous reports of a latency shift of all principal components of ABR, but do not demonstrate a significant CCT impairment in the elderly. The MLRs, SVRs and brain mapping analysis also support this conclusion.

Topographic brain mapping of middle latency auditory evoked potentials in normal subjects.

Topographic brain mapping of auditory middle latency evoked responses (MLR) were obtained from 20 subjects (10 males and 10 females), all right-handed and with normal pure tone audiograms. Clicks with alternative polarity, with a rate of 7.7/sec. were delivered at an intensity of 75 dB HL monoaurally to both ears. Responses from 21 channels were amplified and band-pass filtered (3-150). All the surface maps were analyzed with a Bio-Logic Brain Atlas III system. MLR maps obtained show a quite small intrasubjective variability at the latencies of the principal components Na and Pa. The grand averages of MLR maps at the corresponding latencies in males and females were compared each other. All the entire temporal window has been segmented into some subepochs, showing similar spatial characteristics of the maps, like location of maxima and minima and, overall, shape.