A review of computerized electronystagmography technology.

Analysis of nystagmus using manual methods is time consuming, reliant on considerable experience and subject to observer bias. Like many electrophysiological responses, nystagmus waveforms are suited to acquisition and analysis by digital computer techniques. Development of computerized eye movement analysis procedures commenced in the late 1960s. Initially programs were mostly researched-based with the data often acquired on FM tape recorders and evaluated on mini-computers. As computer technology evolved and equipment prices decreased, development of portable software and hardware for use in general clinical assessment became feasible. The development of computer programs for the acquisition and analysis of eye movements is described and the limitations of analysis procedures discussed.

Reliability and effectiveness of screening for hearing loss in high risk neonates.

OBJECTIVE: To establish the reliability and effectiveness of screening for hearing loss by brainstem auditory evoked potential testing in high risk neonates. DESIGN: Seven year investigation of newborn babies admitted to a special care baby unit and monitored through a regional children's audiology unit. SETTING: Special care baby unit and children's audiology department, Belfast. SUBJECTS: 405 neonates admitted to the baby unit, during 1 October 1982 to 31 March 1987. MAIN OUTCOME MEASURES: Presence of hearing impairment, type and severity of hearing impairment, mortality. RESULTS: 85 children failed the screening test, 62 of whom were followed up. Five children had severe bilateral sensorineural impairment and 12 had conductive impairment requiring surgical intervention. A further 18 had severe neurological disorder detected. The sensitivity of screening was 100% and specificity was 88%. If the procedure was introduced into routine clinical practice the mean age at diagnosis for all children with severe perinatal hearing impairment would be 11 (median 1) months. The mean age at diagnosis with the health visitor screening service was 23 (19) months (difference 10 months, 95% confidence interval 6 to 16 months; p < 0.0001). CONCLUSION: Screening for hearing loss in high risk neonates is highly reliable and cost effective. It also provides valuable neurophysiological information. Routine testing of these infants would result in over half of all children with severe bilateral perinatal sensorineural hearing impairment being identified by 2 months of age. This would make an important contribution to the habilitation of this socially, emotionally, and educationally vulnerable group.

Microcomputer based analysis of nystagmus eye movement.

An algorithm to assist in the computation of routine peripheral nystagmus slow phase velocity (SPV) has been implemented on an Apple based data acquisition system. Waveforms stored by the computer may be output to a dot matrix printer to complement conventional strip-chart recorder output. An estimate of SPV is available after each caloric session. Analysis modes range from a summarized output for inclusion in the clinical report to a detailed beat by beat report comprising waveforms, markers and tabulated results. Problematic signals, beyond the scope of the automatic analysis, may be inspected interactively using a software controlled cursor.

Effects of nitrous oxide on auditory cortical evoked potentials and subjective thresholds.

This study has examined the effects of inhaled nitrous oxide on the N1 and P2 components of the cortical auditory evoked potentials (AEP) in the latency interval 80-300 ms after the stimulus. The amplitudes, latencies and thresholds of the AEP were measured at a range of end-tidal nitrous oxide concentrations (0%, 10%, 20%, 40%) in 10 subjects with normal hearing. Systematic decreases in amplitude and latency were observed with an increase in threshold. A study of the effect of stimulus intensity on AEP amplitude showed that the amplitude change with nitrous oxide was accounted for largely by systematic increase in evoked potential threshold. Subjective pure tone thresholds were not affected by the concentrations of nitrous oxide used, indicating that the AEP changes were independent of subjective hearing level.

The effects of diazepam on the auditory brain stem responses.

Sedation is widely used to improve the quality of auditory brain stem response (ABR) recording. This study demonstrated a small but significant increase in I-V interval following diazepam administration. There was no apparent effect on the ABR amplitudes.

Age and gender contributions to intersubject variability of the auditory brainstem potentials.

This study of auditory brainstem potentials in 123 normal hearing subjects examines the contributions of age and gender to intersubject variability of the response form and latency. The main features, wave I, wave III, and wave V, and the I-V interval were separately examined in premature infants, neonates, infants, children, and young adults. Perinatal changes in response latency were confirmed and significant additional shortening in the I-V interval was observed through childhood and adolescence. Significant gender differences in I-V interval were also observed in both children and adults. Whereas the age changes were consistent with the effects of myelination on conduction time, the nature and magnitude of the gender differences were in keeping with the differential growth changes in the central nervous system, reflected in the skull diameters of females and males. These two sources of intersubject variability, age and gender, should be considered when using the auditory brainstem potentials in clinical studies.