Acoustic analysis of voice in cochlear implant recipients with post-meningitic hearing loss.

The objective of this study was to evaluate the critical time period between the onset of sensorineural hearing loss and cochlear implantation with respect to normal voice production in children with post-meningitic hearing loss. Acoustic measures of voice production were obtained from ten paediatric cochlear implant recipients with post-meningitic hearing loss. Acoustic measures were obtained utilising the Multi-Dimensional Voice Program and Computerized Speech Laboratory (Kay Elemetrics Corp.). Measures were based on sustained phonation of the vowel /a/. Acoustic parameters included fundamental frequency, short- and long-term frequency perturbation, and short- and long-term amplitude perturbation. Measures of fundamental frequency and short-term frequency and amplitude perturbation were comparable to values of children with normal hearing. Long-term control of frequency was within normal limits for subjects with a period of auditory deprivation of less than four months. Measures of long-term amplitude perturbation were normal for all patients except those with cochlear ossification. Early restoration of auditory feedback with cochlear implantation, the absence of cochlear ossification, residual aided hearing following meningitis, and auditory-verbal therapy were identified as factors in preserving the long-term control of frequency and amplitude in the setting of post-meningitic hearing loss.

Amplitude modulation of DPOAEs by acoustic stimulation of the contralateral ear.

CONCLUSION: Otoacoustic emissions generated by outer hair cells (OHCs) are influenced by stimulation of the contralateral ear via a neural pathway involving the olivo-cochlear efferent system. This is often referred to as a contralateral 'suppression reflex', but we suggest that such a term is inappropriate since distortion product otoacoustic emissions (DPOAEs) can be both enhanced and suppressed, and there is continuous modulation with no threshold effects. OBJECTIVE: To characterize the continuous amplitude modulation of DPOAEs by contralateral sound stimulation. MATERIALS AND METHODS: In an animal model (chinchilla), DPOAEs were recorded in real time from one ear during presentation of acoustic stimuli to the opposite ear. RESULTS: DPOAE amplitude is suppressed by an increase in contralateral stimulation, and enhanced by a decrease in same, i.e. the emissions are continuously modulated by activity in the opposite ear. The input-output function shows a linear relationship to this system over a 40-50 dB range of contralateral stimulus levels. After a neural delay time of approximately 25 ms, DPOAE amplitude closely follows contralateral amplitude signals up to modulation frequencies of approximately 20 Hz. Thus, stimuli to one ear continually modulate the OHC system (and therefore the biomechanical amplification) of the contralateral cochlea.

Auditory brainstem activity and development evoked by apical versus basal cochlear implant electrode stimulation in children.

OBJECTIVE: The role of apical versus basal cochlear implant electrode stimulation on central auditory development was examined. We hypothesized that, in children with early onset deafness, auditory development evoked by basal electrode stimulation would differ from that evoked more apically. METHODS: Responses of the auditory nerve and brainstem, evoked by an apical and a basal implant electrode, were measured over the first year of cochlear implant use in 50 children with early onset severe to profound deafness who used hearing aids prior to implantation. RESULTS: Responses at initial stimulation were of larger amplitude and shorter latency when evoked by the apical electrode. No significant effects of residual hearing or age were found on initial response amplitudes or latencies. With implant use, responses evoked by both electrodes showed decreases in wave and interwave latencies reflecting decreased neural conduction time through the brainstem. Apical versus basal differences persisted with implant experience with one exception; eIII-eV interlatency differences decreased with implant use. CONCLUSIONS: Acute stimulation shows prolongation of basally versus apically evoked auditory nerve and brainstem responses in children with severe to profound deafness. Interwave latencies reflecting neural conduction along the caudal and rostral portions of the brainstem decreased over the first year of implant use. Differences in neural conduction times evoked by apical versus basal electrode stimulation persisted in the caudal but not rostral brainstem. SIGNIFICANCE: Activity-dependent changes of the auditory brainstem occur in response to both apical and basal cochlear implant electrode stimulation.

Middle ear instillation of gentamicin and streptomycin in chinchillas: electrophysiological appraisal of selective ototoxicity.

The purpose of this study was to investigate selective vestibular ototoxicity of gentamicin and streptomycin in the chinchilla model. In total, 10 chinchillas underwent left middle ear instillation of one of three agents: gentamicin, streptomycin and saline. Electrophysiological data (otoacoustic emissions (OAEs), auditory brainstem evoked response (ABRs), and ice-water electronystagmography were recorded before and after instillation. Animals were sacrificed for temporal bone studies using scanning electron microscopy. Morphological changes in the cochlear and vestibular neuroepithelia were correlated with electrophysiological changes. Widespread ipsilateral cochlear and vestibular neuroepithelial injuries were observed and correlated with loss of OAEs, ABRs and ice-water caloric response. This study provides no evidence of selective vestibular ototoxicity of gentamicin or streptomycin. Morphological damage correlates with, but precedes loss of electrophysiological parameters. Chinchillas, like other small mammals, may not be an ideal model for the study of human ototoxicity.

Binary partitioning for continuous longitudinal data: categorizing a prognostic variable.

We investigate a binary partitioning algorithm in the case of a continuous repeated measures outcome. The procedure is based on the use of the likelihood ratio statistic to evaluate the performance of individual splits. The procedure partitions a set of longitudinal data into two mutually exclusive groups based on an optimal split of a continuous prognostic variable. A permutation test is used to assess the level of significance associated with the optimal split, and a bootstrap confidence interval is obtained for the optimal split.

Contralateral suppression of DPOAE measured in real time.

The aim of this study was to measure contralateral suppression of distortion product otoacoustic emissions (DPOAE) in real time. A total of 10 human subjects were studied with a novel device to record DPOAE without signal time averaging, using digital narrow band pass filtering. Real time DPOAE levels were recorded at 2f1-f2 using primary tone settings of f2/f1 = 1.22 and L1 = 70 dB SPL, L2 = 65 dB SPL, at five values of f2 between 2.2 and 7.7 kHz. An acoustic stimulus was applied intermittently to the contralateral ear to cause DPOAE suppression. Characteristic features of contralateral suppression were identified and distinguished from small spontaneous variations in the real time DPOAE signal. Magnitude of suppression increased with contralateral stimulus intensity. Onset latency of suppression was around 43 ms (31-95 ms). Potential clinical applications are discussed in the light of these findings, including a role in improving the specificity of neonatal hearing screening.

Arterial blood supply to the auditory cortex of the chinchilla.

Utilizing optical imaging we identified and named the arteries that supply the primary auditory cortex in the chinchilla (Chinchilla laniger). The primary auditory cortex is located 2-3 mm caudal to the medial cerebral artery and is supplied by it. Using corrosion casts and scanning electron microscopy we visualized the capillary networks in the auditory cortex and found regional variations in the densities of the capillary bed. We hypothesize that the uneven capillary densities observed in the auditory cortex correspond to neurologically more active areas.

Guideline for the management of heart failure caused by systolic dysfunction: part II. Treatment.

Several large clinical trials conducted over the past decade have shown that pharmacologic interventions can dramatically reduce the morbidity and mortality associated with heart failure. These trials have modified and enhanced the therapeutic paradigm for heart failure and extended treatment goals beyond limiting congestive symptoms of volume overload. Part II of this two-part article presents treatment recommendations for patients with left ventricular systolic dysfunction. The authors recommend that, if tolerated and not contraindicated, the following agents be used in patients with left ventricular systolic dysfunction: an angiotensin-converting enzyme inhibitor in all patients; a beta blocker in all patients except those who have symptoms at rest; and spironolactone in patients who have symptoms at rest or who have had such symptoms within the past six months. Diuretics and digoxin should be reserved, as needed, for symptomatic management of heart failure. Other treatments or treatment programs may be necessary in individual patients.

Guideline for the management of heart failure caused by systolic dysfunction: Part I. Guideline development, etiology and diagnosis.

Over the past decade, the conceptual understanding of heart failure has changed significantly. Several large clinical trials have demonstrated that pharmacologic interventions can dramatically reduce the morbidity and mortality associated with heart failure. These trials have extended the therapeutic paradigm for treating heart failure beyond the goal of limiting congestive symptoms of volume overload. This two-part article presents an evidence-based guideline to assist primary care physicians in evaluating and treating patients with heart failure. Part I describes the new paradigm of heart failure and offers guidance for diagnostic testing. Part II presents a treatment guideline.

Assessment of vocabulary development in children after cochlear implantation.

OBJECTIVES: To assess vocabulary development in children following cochlear implantation and to evaluate the effect of age at implantation on performance. DESIGN: Retrospective study (mean follow-up, 3(1/2) years). SETTING: Tertiary center. PATIENTS: Children with prelingual deafness provided with a cochlear implant between 1988 and 1999, who serially performed the Peabody Picture Vocabulary Test-Revised (60 patients) and the Expressive One-Word Picture Vocabulary Test-Revised (52 patients). The children were subgrouped into those receiving implants at younger than 5 years and at 5 years or older. OUTCOME MEASURES: Age-equivalent vocabulary test score and gap index (chronological age minus the age-equivalent score, divided by the chronological age at the time of testing) were calculated. For each test, the following were performed: calculation of rate of change for age-equivalent score; comparison of earliest and latest gap indices means (the cohort and intergroup and intragroup comparison); and multiple regression analysis demonstrating the effect of age at implantation, sex, communication mode, etiology of deafness, and residual hearing on the rate of vocabulary development. RESULTS: Expressive and receptive vocabulary development rates were 0.93 and 0.71 (age-equivalent scores per year), respectively. Subgrouped by age at implantation, the children's rates (for both vocabularies) were not statistically different (Peabody Picture Vocabulary Test-Revised, P =.90; Expressive One-Word Picture Vocabulary Test-Revised, P =.23). The global latest gap indices were significantly less than the earliest (Peabody Picture Vocabulary Test-Revised, P =.048; Expressive One-Word Picture Vocabulary Test-Revised, P<.001), indicating an improvement in age-appropriate vocabulary development over time. The age subgroups demonstrated similar results, except for the younger group's receptive gap index. On multiple regression analysis, the significant predictive variables were residual hearing (Expressive One-Word Picture Vocabulary Test-Revised) and male sex and oral communication mode (Peabody Picture Vocabulary Test-Revised). CONCLUSIONS: Children with cochlear implants developed their vocabularies at rates that were sufficient to prevent an increase in their gap indices as related to ideal scores at testing. A late age at implantation does not singularly preclude beneficial development of vocabulary.

The effects of age of cochlear implantation on speech perception outcomes in prelingually deaf children.

We have made a retrospective analysis on 70 prelingually deaf children (78% congenital; age range 2-15 years) followed for up to 5 years post-implant during which both closed set speech perception tests (TAC, WIPI) and open set tasks (PBK, GASP) were administered. We used a binary partitioning algorithm to optimally divide our dataset on the basis of age at implantation This technique achieves an optimal split when the heterogeneity of the data is most reduced (maximal drop in deviance). For the closed set speech perception tests (TAC and WIPI) partitioning best divided-out data at age 4.4 years. For the open set tests optimal division was at a higher age of implantation (GASP word, 5.6 years; PBK word, 8.4 years). Using these partitioning values, we have found statistically significant differences between rate of improvement of scores in the younger implanted children compared with those implanted later.

Age-related tonotopic map plasticity in the central auditory pathways.

Inner hair cell lesions to the basal turn of the cochlea effectively result in a partial deafferentation of the auditory system. At the level of the midbrain (central nucleus of inferior colliculus) cochleotopic maps, based on single unit response characteristic frequency, are changed after such deafferentation. When a cochlear lesion is induced in a neonatal animal (chinchilla), the reorganization of the frequency map is more extensive than that resulting from similar deafferentation in the adult subject. Neonatal cochlear lesions result in an over-representation of sound frequencies corresponding to the border of the cochlear lesion, while similar lesions in the adult do not. The results suggest that significant plasticity exists in the auditory midbrain during early post natal development (even in a precocious species, such as chinchilla); however, this plasticity is largely lost in the mature animal. A conceptual model for the frequency map re-wiring is presented.

Vocabulary acquisition rate after pediatric cochlear implantation and the impact of age at implantation.

OBJECTIVE: studies of early vocabulary development after pediatric cochlear implantation show growth rates that approach normality. Do these growth rates continue to rise over time and, therefore, allow a 'catch up' with ideal scores for age, or do they decline after an initial peak. Could age at implantation be a decisive factor in that process? DESIGN: retrospective study (mean follow-up 4 years). PATIENTS: pre-lingually deaf children implanted between 1988 and1999, who serially performed Peabody Picture Vocabulary Test-Revised (PPVT), (37 patients) and Expressive One-word Picture Vocabulary Test-Revised (EOWPVT), (35 patients). OUTCOME MEASURES: the mean rates of age equivalent scores were determined for the whole follow-up period and analyzed further for two post-implant periods (the two halves of follow-up duration of individual patients). After sub-grouping by age at implantation (younger or older than 5 years old), the same analysis was executed for each subgroup. RESULTS: the mean EOWPVT rate of the earlier period was higher than that of the later period (1.33 vs. 0.67, P<0.01) and the mean PPVT rate of the earlier period was higher than that of the later period (0.72 vs. 0.5). The latter difference was not statistically significant (P>0.05). Within subgroups by age at implantation, the PPVT mean rates were stable for younger implanted patients (0.56 for both periods) and dropped for the older implanted sub-group (0.87-0.43, P>0.05). The EOWPVT mean rates declined significantly for the older patients group (1.72-0.55, P<0.01) but insignificantly for the younger patients (0.99-0.77, P>0.05). CONCLUSIONS: vocabulary acquisition rates decline in the post-implantation period. This is more pronounced with older implanted children and the EOWPVT rates. This information on the time course development of vocabulary after implantation would be valuable in counseling and planning habilitation in addition to candidate selection.

Differential vulnerability of inner and outer hair cell systems to chronic mild hypoxia and glutamate ototoxicity: insights into the cause of auditory neuropathy.

OBJECTIVE: To describe the effects of long-term mild hypoxia and of glutamate poisoning on the functional properties of the cochlea. METHODS: Outer hair cell activity was monitored using otoacoustic emissions and cochlear microphonics, and inner hair cell/cochlear afferent function was measured using neural responses (cochlear action potentials or auditory brainstem responses [ABRs]). RESULTS: In contrast to the effects of acute anoxia, in which all aspects of cochlear function are simultaneously lost, mild, long-term hypoxia results in a clear differential effect on outer versus inner hair cell systems. During a 2-hour period of mild hypoxia, ABR amplitude and threshold deteriorate significantly, whereas outer hair cell function, as reflected by otoacoustic emissions, shows little or no change. A similar dissociation between inner and outer hair cell function is observed during instillation of glutamate (1-10 mM), where the cochlear microphonic and the otoacoustic emissions are unchanged, whereas cochlear action potential amplitudes are reduced. CONCLUSION: These studies demonstrate a difference in vulnerability of inner and outer hair cell systems. The inner hair cell/cochlear afferent system is vulnerable to long-term, mild hypoxia; this may be an etiologic factor in hearing loss of cochlear origin, particularly in high-risk birth infants with auditory neuropathy.

Effect of residual hearing prior to cochlear implantation on speech perception in children.

We examined the impact of residual hearing prior to cochlear implantation on pre- and postimplantation speech perception outcomes in children. Stimulation of the auditory system prior to implantation because of the presence of residual hearing is important for development of the central auditory pathways, whereas, in the absence of such stimulation, the pathways show less development. We hypothesized that children who had some degree of residual hearing preimplantation achieve better speech perception skills than their peers with poorer hearing. From the 133 children followed in our program, we identified 37 children who had an audiometric pure-tone average of better than 95 dB HL in the better ear at any time preimplantation. Psychophysical speech perception measures, the Word Identification Picture Inventory and the Phonetically Balanced Kindergarten list, in these children were compared with those of 96 implanted children who had poorer hearing prior to implantation. Children with more residual hearing showed higher speech perception scores both before implantation and over their first year of implant use than children with poorer hearing, suggesting that there is an advantage in having a greater degree of residual hearing preimplantation. We suggest that this advantage is promoted, in part, by the greater potential for auditory stimulation provided by high-gain hearing aids in children with greater degrees of residual hearing. This advantage appears to be maintained at least over 1 year postimplantation, yet the rates of development of postimplantation speech perception are not different between the groups. We suggest that this may be due to the unique aspects of electrical stimulation from a cochlear implant. Our findings suggest that it is important to minimize the delay of speech perception skills in the preimplantation phase, particularly in children with poor residual hearing. This can be accomplished by implanting children with congenital severe to profound hearing loss at young ages and children with acquired hearing loss soon after the onset. Also, auditory stimulation prior to implantation should be maximized through the consistent use of hearing aids and therapy that emphasizes development of auditory skills.

Factors contributing to limited open-set speech perception in children who use a cochlear implant.

Cochlear implants have enabled many children with severe to profound sensorineural hearing loss to develop speech perception skills. However, some children experience few gains while others develop high levels of speech perception. We identified potential factors contributing to poor performance with an implant by studying implanted children who do not develop functional speech perception. Five children were identified as developing no open-set word recognition skills after at least 2 years of implant use. This study group was compared to a randomly selected control group (n=10) and an age-matched control group (n=5). Pre-implant factors were examined using a Graded Profile Analysis and post-implant factors were assessed in a retrospective chart review. A greater number of pre-implant concerns were raised in the study group than in randomized controls (P<0.01). Chronological age and duration of deafness were pre-implant concerns in all study group subjects. A greater number of post-implant concerns were found in the study group than in randomly selected controls (P<0.005). We conclude that while appropriate selection of candidates for cochlear implantation is important in predicting speech perception outcomes, post-implant follow-up is also essential and must include regular monitoring of equipment, monitoring of stimulation levels with use of objective measures of stimulation levels if necessary, and consistent habilitation.

Projections from the medial geniculate body to primary auditory cortex in neonatally deafened cats.

In the present study, anatomical projections from the medial geniculate body (MGB) to primary auditory cortex (AI) were investigated in normal adult cats and in animals that were neonatally deafened with the ototoxic drug amikacin. Cochleotopic/tonotopic maps in AI (based on neural response characteristic frequency) were obtained with microelectrode recording techniques, and single or multiple injections of retrograde tracers (horseradish peroxidase and fluorescent dyes) were introduced into AI. The AI maps of the amikacin-treated cats had an abnormal cochleotopic organization, such that deprived cortical areas exhibited an expanded representation of intact regions of the damaged cochlea. However, retrograde tracer injections into different regions of AI produced a normal pattern of labeling in the ventral division of the medial geniculate body (MGBv). In both experimental and control animals, the main mass of labeled thalamic cells was found in the MGBv. Different isofrequency contours in AI receive input from different portions of the MGBv. Thus, cell arrays labeled by anterior AI injections were situated medially in MGBv, and injections into posterior AI labeled MGBv more laterally. Furthermore, the deafened cats did not develop a more divergent thalamocortical projection compared with normal control animals, indicating that an abnormal spread of the thalamocortical afferents across the frequency domain in AI (anterior-posterior axis) is not responsible for the altered cochleotopic map in these neonatally deafened animals. The relatively normal thalamocortical projection pattern suggests that, after neonatal cochlear lesions, the major reorganization of cochleotopic maps occurs at subthalamic levels.

Tonotopic mapping in auditory cortex of the adult chinchilla with amikacin-induced cochlear lesions.

We have found a reorganization of tonotopic maps (based on neuron response thresholds) in primary auditory cortex of the adult chinchilla after amikacin-induced basal cochlear lesions. We find an over-representation of a frequency that corresponds to the border area of the cochlear lesion. The reorganization observed is similar in extent to that previously seen in a developmental model. The properties of neurons within the over-represented area were investigated in order to determine whether their responses originated from a common input (an indication of true plasticity) or represented only the result of truncating the activity of the sensory epithelium ("pseudo-plasticity"). Some aspects of our data fit with a true plasticity model and indicate the potential for the deafferented cortex of the mature cortex to regain connections with the surviving sensory epithelium.

Improving HEDIS measurement: linking managed care organization and health system ambulatory care data.

This article describes one health system's efforts to improve HEDIS measurement by integrating claims information from its managed care organization with data from its medical center's automated billing, scheduling, and clinical information systems. The authors discuss problems encountered while establishing an integrated measurement process and offer suggestions for others considering such an approach.

Three distinct auditory areas of cortex (AI, AII, and AAF) defined by optical imaging of intrinsic signals.

Using pure-tone sound stimulation, three separate auditory areas are revealed by optical imaging of intrinsic signals in the temporal cortex of the chinchilla (Chinchilla laniger). These areas correlate with primary auditory cortex (AI) and two secondary areas, AII and the anterior auditory field (AAF). We have distinguished AI on the basis of concurrent single-unit electrophysiological recording; neurons within the AI intrinsic signal region have short (<15 ms) onset-response latencies compared with neurons recorded in AII and the AAF. Within AI, AII, and AAF we have been able to define cochleotopic or tonotopic organization from the differences in intrinsic signal areas evoked by pure tones at octave-spaced frequencies from 500 Hz to 16 kHz. The maps in AI and AII are arranged orthogonal to each other.