Mean Threshold Level Research Articles

Impact of occupational noise exposure on the hearing level in hospital staffs: a longitudinal study.

The study aimed to evaluate the impact of occupational noise on hearing loss among healthcare workers using audiometry. A longitudinal study was conducted with a six-month follow-up period in a hospital with 21 participants, divided into high-noise-exposure (HNE) and low-noise-exposure (LNE) groups. Mean noise levels were higher in the HNE group (70.4 ± 4.5 dBA), and hearing loss was measured using pure-tone audiometry at baseline and follow-up. The HNE group had significantly higher mean threshold levels at frequencies of 0.25kHz, 0.5kHz, 4.0kHz, and an average of 0.5, 1, 2, and 4kHz (all p-values < 0.05) after the follow-up period. After adjusting for confounding factors, the HNE group had significantly higher hearing loss levels at 0.25kHz, 0.5kHz, and average frequencies of 0.5, 1, 2, and 4kHz compared to the LNE group at the second measurement. Occupational noise levels above 65 dBA over six months were found to cause significant threshold changes at frequencies of 0.25kHz, 0.5kHz, and an average of 0.5-4.0kHz. This study highlights the risk of noise-induced hearing loss among healthcare workers and emphasizes the importance of implementing effective hearing conservation programs in the workplace. Regular monitoring and assessment of noise levels and hearing ability, along with proper use of personal protective equipment, are crucial steps in mitigating the impact of occupational noise exposure on the hearing health of healthcare workers.

Round window versus conventional bony cochleostomy technique in pediatric cochlear implantation; A Randomized controlled double blinded trial.

&lt;p&gt;&lt;strong&gt;Background:&lt;/strong&gt; Objective of the study was to investigate the outcomes of cochlear implantation when done via two different techniques namely, the round window or the bony cochleostomy.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Methods:&lt;/strong&gt; A single-center, double-blinded randomized controlled trial including forty prelingual, bilateral severe to profoundly deaf children less than six years from the year 2014 to 2016 in a tertiary referral center in India were randomly allocated to round window and bony cochleostomy group. Our primary outcome measures were intraoperative neural response telemetry levels, behavioral threshold (t) and comfortable (c) loudness levels. The secondary subjective outcomes were measured via the category of auditory performance (CAP) and the meaningful auditory integration scale (MAIS) score. The cases were followed up for 9 months.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Results:&lt;/strong&gt; Intra-operative, electrically evoked compound action potentials (ECAP) showed comparable mean thresholds for both the techniques except intermediate electrodes (p~0.04) showed lower values for the round window. Similarly, a lower threshold (p~0.03) and comfortable mean current levels (p~0.03) were noticed for the round window group at 6 months post-implantation. Secondary speech perception outcome scores measured via category of auditory performance (CAP) and MAIS score were comparable. &lt;/p&gt;&lt;p&gt;&lt;strong&gt;Conclusions:&lt;/strong&gt; The round window insertion technique has physiological benefit as compared to the bony cochleostomy as evidenced by better stimulation levels in the intermediate electrodes and lower mean threshold and comfortable levels in the round window with more beneficial peri-modiolar position of electrode arrays. However, comparable speech perception outcomes revealed no clinical benefit in the cochlear implant performance depending on the technique of electrode insertion. &lt;/p&gt;

The relationship of cortical activity induced by pain stimulation with clinical and cognitive features of somatic symptom disorder: A controlled functional near infrared spectroscopy study

ObjectiveThe neurobiological correlates of Somatic Symptom Disorder (SSD) introduced in the DSM-5 has been the focus of a limited investigation. We aimed to examine the cortical response to painful stimuli and its relationship to symptom severity as well as cognitive and psychological characteristics in proposed models of somatoform disorders. MethodsWe measured hemodynamic responses by 52-channel functional near-infrared spectroscopy. We compared the cortical response to painful stimuli in index patients with SSD (N = 21) versus age, and gender matched healthy control subjects (N = 21). We used brush stimulation as the control condition. We analyzed the relationship of cortical activity with SSD symptom severity as well as somatosensory amplification (SSA), alexithymia, dysfunctional illness behaviour, worry, and neuroticism. ResultsPatients with SSD had higher somatic symptom severity, SSA, alexithymia, neuroticism, illness-related worry, and behaviour. Somatic symptom severity was predicted by a model including SSA and subjective feeling of pain in the index patients. Activity in the left-angular and right-middle temporal gyri was higher in the SSD subjects than the controls during pain stimulation. Positive correlations were detected between mean pain threshold levels and left middle occipital gyrus activity, as well as between SSA-scores and right-angular gyrus activity during pain condition in the index patients with SSD. ConclusionWe present the first evidence that representation of pain in terms of cortical activity is different in subjects with SSD than healthy controls. SSA has functional neuroanatomic correlates and predicts symptom severity in SSD and therefore is involved as a valid intermediate phenotype in SSD pathophysiology.

Efficacy of using NRT thresholds in cochlear implants fitting, in prelingual pediatric patients

ObjectiveTo evaluate the efficacy of using neural response telemetry (NRT) thresholds in predicting behavioural thresholds during programming of cochlear implant in prelingual children. MethodProspective study of 28 cochlear implants implanted with Nucleus 24 cochlear implant. We recorded NRT-thresholds on electrode numbers 1, 6, 11, 16 and 22 of the electrode array in each patient, the neural response thresholds were correlated with the behavioural map after six months of programming the device. ResultsThe mean neural response telemetry level was significantly higher than the mean threshold level (T-level) but lower than the comfortable level (C-level) in all the electrodes tested. NRT levels could statistically significantly predict T behavioural levels and comfortable behavioural levels, p < 0.01. There was a strong positive correlation between comfortable thresholds and neural response telemetry level measurements and behavioural threshold level and neural response telemetry threshold measurements. ConclusionThere is a useful role for neural response telemetry values in predicting the behavioural threshold and comfortable values in prelingual children. Combining the NRT values with behavioural observations can improve the programming of cochlear implants.

Noisy vestibular stimulation improves vestibulospinal function in patients with bilateral vestibulopathy.

To examine the mechanism underlying previously reported ameliorating effects of noisy galvanic vestibular stimulation (GVS) on balance performance in patients with bilateral vestibulopathy (BVP) and determine those patients (incomplete versus complete vestibular loss) that might benefit from this intervention. Vestibulospinal reflex thresholds were determined in 12 patients with BVP [2 with complete loss (cBVP) and 10 with residual function (rBVP)]. Patients were stimulated with 1Hz sinusoidal GVS of increasing amplitudes (0-1.9mA). Coherence between GVS input and stimulation-induced body motion was determined and psychometric function fits were subsequently used to determine individual vestibulospinal reflex thresholds. The procedure was repeated with an additional application of imperceptible white noise GVS (nGVS). All patients with rBVP but none with cBVP exhibited stimulation-induced vestibulospinal reflex responses with a mean threshold level of 1.26 ± 0.08mA. Additional nGVS resulted in improved processing of weak subthreshold vestibular stimuli (p = 0.015) and thereby effectively decreased the vestibulospinal threshold in 90% of patients with rBVP (mean reduction 17.3 ± 3.9%; p < 0.001). The present findings allow to identify the mechanism by which nGVS appears to stabilize stance and gait performance in patients with BVP. Accordingly, nGVS effectively lowers the vestibular threshold to elicit balance-related reflexes that are required to adequately regulate postural equilibrium. This intervention is only effective in the presence of a residual vestibular functionality, which, however, applies for the majority of patients with BVP. Low-intensity noise stimulation thereby provides a non-invasive treatment option to optimize residual vestibular resources in BVP.

Ototoxicity associated with topical administration of diclofenac sodium as an otic drop: An experimental animal study

ObjectivesThe aim of the study is to evaluate the ototoxicity of topical diclofenac sodium in comparison to positive and negative controls prior to the investigation of analgesic and anti-inflammatory efficacy of the agent in otic administration. MethodsTwenty four ears of 12 guinea pigs were included in the study. Wide myringotomy was performed on all tympanic membranes under general anesthesia and auditory brainstem responses (ABR) were evaluated. The subjects were separated into four groups, two groups received diclofenac sodium at low and high doses, positive controls received gentamicin and negative controls received isotonic sodium chloride topically for 14 days and ABRs were reevaluated. ResultsNo significant difference were observed between the pre and post-treatment click response, 1 kHz and 8 kHz response threshold levels after isotonic sodium chloride administration. All threshold levels were elevated in the positive control group. In the low and high dose diclofenac sodium groups, click response, 1 kHz and 8 kHz response threshold levels were significantly higher compared to the baseline values. Pre and post-treatment mean threshold level changes were not significantly different between the low and high dose diclofenac sodium groups. Pre and post-treatment mean threshold level changes in the gentamicin group were not significantly different from low or high dose diclofenac sodium groups. ConclusionDiclofenac sodium, considered as an analgesic and anti-inflammatory otic preparation, is shown to be as ototoxic as gentamicin in chronic use which may lead to loss of hearing especially when used topically in chronic otitis cases with tympanic membrane damage.

Evaluation of threshold response and appropriate electrode placement site for electric pulp testing in fluorosed anterior teeth: An in vivo study.

Accurate diagnosis is key to success. Diagnosing the pulpal status in varied clinical situations poses a challenge to the clinician. Electric pulp test (EPT) is one of the valuable attempts in evaluating the sensibility of pulp tissue. The aim of this study was to find out and compare the threshold levels and optimal electrode placement site for EPT in fluorosed and nonfluorosed anterior teeth. Eighty volunteers recruited for this study were divided into two groups based on the incidence of dental fluorosis. Electric pulp testing was done on either of the central incisors in fluorosed and nonfluorosed group. Four sites on each crown were tested 4 times with digitest electric pulp tester, and the mean of the threshold responses was recorded. The data were analyzed with SPSS, version 11. Means of variables from each location were compared using one-way ANOVA and Tukey's post-hoc test while the critical level of significance was set at P < 0.05. The mean and standard deviation of threshold levels in fluorosed teeth were greater when compared to that of nonfluorosed teeth at all sites with incisal edge showing the least mean threshold levels for both the groups (P > 0.05). Within the limitations of this study, it can be concluded that fluorosed teeth respond to higher threshold levels than the non-fluorosed teeth, and incisal edge was the optimal electrode placement site.

Dehydration and drinking behavior in true sea snakes (Elapidae: Hydrophiinae: Hydrophiini)

AbstractWater is an essential resource affecting behavior and the acquisition of energy, especially in environments where water is spatially or temporally restricted or unavailable. Recent investigations have shown that several species of marine snakes dehydrate at sea and are dependent on environmental sources of fresh water to maintain water balance. However, in this context, little is known concerning the majority of ‘true’ sea snakes (Hydrophiini). We investigated the dehydration and drinking responses of five species of hydrophiin sea snakes collected during the dry season in northern Australia. None of these snakes drank sea water, even when dehydrated. Dehydrated individuals of Hydrophis curtus, H. elegans and H. zweifeli drank fresh water, and the mean threshold levels of dehydration that first elicited drinking were deficits of −26, −29 and −27% of body mass, respectively. Individuals of Aipysurus mosaicus and H. peronii did not drink fresh water when similarly dehydrated. Few snakes that we collected following &gt;4 months of drought drank fresh water immediately after capture. Hydrophiin species appear to have a high resistance to dehydration, which they evidently tolerate in marine habitats for extended periods during drought. Thirst in these species is significantly less sensitive than in other species, suggesting that marine snakes have variable requirements for drinking fresh water. These data illustrate that sea snakes are characterized by diverse responses to dehydration and likely have different osmoregulatory strategies for survival, with implications for better understanding the evolutionary success of secondarily marine vertebrates and their potential responses to future changes in tropical precipitation.

A new method for determining the optimal CT threshold for extracting the upper airway

The purpose of this study was to evaluate the optimal upper threshold levels of a number of individuals and determine the most suitable upper threshold. A phantom model and ten patients were used in this study. The phantom was made of acrylic resin and urethane resin and had nine pillar-shaped air spaces. The subjects were ten female patients with jaw deformities who were not affected by respiratory disease. The optimal threshold levels were determined using the "calculation of CT value disparities" (CCTD) technique, which we devised. In other words, the mean CT values along two lines (air space and soft tissue) were calculated and the optimal threshold level was determined as the level that produced the maximum difference between the CT values measured inside and outside of the air-space border. The optimal upper threshold levels of the nine phantom holes calculated using the CCTD technique in the front-on standing position and side-on standing position were -434 HU and -456 HU, respectively. The optimal upper threshold level of the ten patients calculated using the CCTD technique was -472 HU. The true threshold level of each patient was defined as the optimal threshold level calculated using the CCTD technique. The mean threshold level was defined as -472 HU. The absolute differences between the volume measurements obtained with these two measures were considered. Therefore, the no error values were -460 HU and -470 HU. We consider that the most suitable upper threshold level for extracting the airway is from -460 HU to -470 HU.

The Relationship between Thresholds of Electrically Evoked Compound Action Potential and Speech Perception in Children with Cochlear Implants

Background and ObjectivesZZNeuropathology around the cochlea could create variation from site to site in physiological thresholds of cochlear implant users. This variability would be detrimental to speech recognition with a cochlear implant for a variety of reasons, including distortion of the place code and variation in the number of neurons. The purpose of this study is to examine the relationship between thresholds of electrically evoked compound action potential (ECAP) and speech perception in children implanted with the Nucleus Freedom devices. Subjects and MethodZZFifty-seven children implanted with the Nucleus Freedom device participated in this study. ECAP thresholds were recorded using the automated neural response telemetry test protocol. We then calculated mean threshold and three metrics to assess acrosssite variation within subjects: 1) the variance of T levels for all tested sites, 2) the range of T levels (highest minus lowest) across all tested sites and 3) site-to-site variation. For each subject, these measures were compared with performance on tests of word recognition. ResultsZZThere was considerable across-site (within-subject) and across-subject variability in thresholds. However, we found no significant correlation between speech recognition and across-site variation of thresholds as well as mean threshold levels. ConclusionZZThese data suggest that the ECAP measures of thresholds may not be an accurate predictor of speech perception ability. � Korean J Otorhinolaryngol-Head Neck Surg 2011;54:688-92 Key WordsZZCochlear implant ㆍElectrically evoked compound action potential ㆍ Key WordsZZThreshold ㆍSpeech perception.

Linear Versus Nonlinear Signal Transmission in Neuron Models With Adaptation Currents or Dynamic Thresholds

Spike-frequency adaptation is a prominent aspect of neuronal dynamics that shapes a neuron's signal processing properties on timescales ranging from about 10 ms to >1 s. For integrate-and-fire model neurons spike-frequency adaptation is incorporated either as an adaptation current or as a dynamic firing threshold. Whether a physiologically observed adaptation mechanism should be modeled as an adaptation current or a dynamic threshold, however, is not known. Here we show that a dynamic threshold has a divisive effect on the onset f-I curve (the initial maximal firing rate following a step increase in an input current) measured at increasing mean threshold levels, i.e., adaptation states. In contrast, an adaptation current subtractively shifts this f-I curve to higher inputs without affecting its slope. As a consequence, an adaptation current acts essentially linearly, resulting in a high-pass filter component of the neuron's transfer function for current stimuli. With a dynamic threshold, however, the transfer function strongly depends on the input range because of the multiplicative effect on the f-I curves. Simulations of conductance-based spiking models with adaptation currents, such as afterhyperpolarization (AHP)-type, M-type, and sodium-activated potassium currents, do not show the divisive effects of a dynamic threshold, but agree with the properties of integrate-and-fire neurons with adaptation current. Notably, the effects of slow inactivation of sodium currents cannot be reproduced by either model. Our results suggest that, when lateral shifts of the onset f-I curve are seen in response to adapting inputs, adaptation should be modeled with adaptation currents and not with a dynamic threshold. In contrast, when the slope of onset f-I curves depends on the adaptation state, then adaptation should be modeled with a dynamic threshold. Further, the observation of divisively altered onset f-I curves in adapted neurons with notable variability of their spike threshold could hint to yet known biophysical mechanisms directly affecting the threshold.

A Comparison of the Military Entrance Processing Station Screening Audiogram with the Defense Occupational and Environmental Health Readiness System Reference Audiogram at Fort Sill, Oklahoma, in 2000

The Department of Defense Hearing Conservation Program requires that a reference audiogram be performed at initial entry training (IET), before noise exposure. In the Army, only Fort Sill, home of the field artillery, and Fort Benning, home of the infantry, are in compliance. All military applicants receive a screening audiogram at a military entrance processing station (MEPS) to qualify for service. This audiogram does not meet the Defense Occupational and Environmental Health Readiness System-Hearing Conservation (DOEHRS-HC) standard. Nevertheless, it has been proposed that the MEPS screen be used as the reference because of limited resources and time during IET medical in-processing. A total of 11,816 individual reference audiograms performed at Fort Sill 95th Adjutant General Recruit Reception Center in 2000 were identified in the DOEHRS-HC database. Results of the MEPS screening audiograms were found for 11,311 (96%) of these individuals. The two audiograms were compared by frequency and ear and by using the two Department of Defense criteria for threshold shift. A total of 14.49% (95% confidence interval, 14.48-14.50%) of audiograms using the three-frequency average difference and 23.19% (95% confidence interval, 23.18-23.20%) using the four-frequency difference in either ear demonstrated a threshold shift. The mean difference in intensity between the two audiograms ranged from 5 to 12 dB and varied by frequency and ear, with the greatest differences being seen at 500 and 6,000 kHz and in the left ear, compared with the right ear. The mean threshold level was higher for each frequency in the DOEHRS-HC audiogram, compared with the MEPS audiogram. Approximately 15% of soldiers at Fort Sill in 2000 showed a clinically significant threshold difference between their MEPS screening and the DOEHRS-HC baseline audiogram. Methodological variations in testing and interval noise-induced hearing loss could account for these differences. The results do not support the use of the MEPS screening audiogram as the reference audiogram. Compliance with the Hearing Conservation Program in the Army would require either improving MEPS testing to DOEHRS-HC standards or performing baseline audiograms at all five IET sites.

Across-Site Threshold Variation in Cochlear Implants: Relation to Speech Recognition

Functional implications of across-site variation in detection thresholds in subjects with cochlear implants were evaluated by comparing thresholds to speech recognition performance. Detection thresholds for bipolar (BP) and monopolar (MP) stimulation of all available stimulation sites were assessed in 21 subjects with Nucleus^® CI24M and CI24R(CS) implants. We found significant negative correlations between speech recognition and within-subject across-site threshold variance for both BP and MP stimulation, but no significant correlation of speech recognition with mean threshold levels. These results suggest that across-site variance of detection thresholds could provide a useful early indication of the prognosis for speech recognition and might serve as an indicator for specific therapeutic approaches in individual subjects.

Blood pressure relates to sodium taste sensitivity and discrimination in adolescents.

To investigate salt perception and discrimination and their possible association with blood pressure (BP), 72 healthy adolescents (42 boys) aged 9-21 years (mean 16.1 years) were studied. BP was measured with a standardized technique. Anthropometric measurement and conventional renal function tests were performed. Sensitivity tests to recognize the presence of salt when given simultaneously distilled/deionized water and a low sodium concentration water solution, and discrimination tests consisting of six graded samples of different saline solutions presented in randomized order were used to assess individual gustatory sensitivity. Average systolic BP values were 113.2+/-1.6 mmHg in boys and 109.6+/-1.9 mmHg in girls. Mean threshold level for salt sensitivity was 4.55+/-0.6 mmol/l. Systolic BP and salt sensitivity showed a significant correlation ( r=-0.33, P<0.01) even when adjusting for weight. Discrimination score was correlated with salt sensitivity ( r=0.27, P<0.05). There is a significant association between gustatory perception and BP in Spain adolescents, although a real cause-effect relationship has not been established.

Recurrent laryngeal nerve monitoring in thyroid and parathyroid surgery: the University of Michigan experience.

Intraoperative monitoring of the recurrent laryngeal nerve (RLN) is finding increasing acceptance during thyroidectomy. Recently, a laryngeal surface electrode was introduced to enable another form of noninvasive monitoring of the RLN. The present report examines the University of Michigan experience with RLN monitoring using the postcricoid surface electrode. All patients undergoing partial or total thyroidectomy or parathyroidectomy from January 1999 to July 2001 were considered candidates for the study. Audiologists trained in intraoperative electrophysiological techniques performed all of the monitoring. Data collected on each patient included 1) stimulation threshold for a laryngeal compound muscle action potential on initial RLN identification, 2) stimulation threshold of the laryngeal compound muscle action potential on completion of the procedure, and 3) flexible fiberoptic evaluation of the larynx at the initial postoperative visit and at the 3-month follow-up visit. The average duration of follow-up was 9.8 months with a range of 3 to 60 months. The average minimum current required for stimulation on first identification of all nerves was 0.57 mA (+/-0.48 mA). After completion of the procedure a mean threshold level of 0.42 mA (+/-0.55 mA) was obtained during direct RLN stimulation. Post-dissection stimulation of the RLN on the side of tumor dissection was 0.92 mA (+/-0.65 mA) compared with a stimulation threshold of 0.76 mA (+/-0.57 mA) for the nontumor side. Electromyographic monitoring of the RLN using a postcricoid surface electrode provides a safe, simple, and effective method for intraoperative monitoring during thyroid or parathyroid surgery. Further, evoked electromyography confirms RLN integrity at the conclusion of surgery.

Association of clinical features with mutation of TECTA in a family with autosomal dominant hearing loss.

The TECTA gene, which encodes alpha-tectorin, has recently been cloned. alpha-Tectorin is a major component of the noncollagenous matrix of the tectorial membrane. Nonsyndromic hearing impairment caused by TECTA mutations has been reported in Austrian, Belgian, Swedish, French, and Lebanese families. The phenotypes and genotypes were different among these families. Our study family displayed autosomal dominant hearing impairment through 3 generations. We sequenced the coding exons of the TECTA gene in 4 affected individuals, and we report the clinical features in a Japanese family with nonsyndromic hearing impairment and a mutation in the TECTA gene. The 5-frequency average of 250, 500, 1000, 2000, and 4000 Hz in 4 affected individuals was 42.2 +/- 3.7 (mean +/- SD) dB in the right ear and 42.3 +/- 4.5 dB in the left ear. The mean age at onset of hearing impairment was 5 years. The progression of hearing impairment was not confirmed for a 15-year period, from the age of 6 to 21 years, in 1 affected member. The 4 patients had a G-->A missense mutation at nucleotide 6063 in exon 20. This mutation replaces arginine at residue 2021 with histidine (R2021H). All 4 affected members showed symmetrical and stable bilateral mild to moderate hearing impairment in the midfrequencies. The mean threshold level of 2000 Hz was the worst among the 5 frequencies. All the affected members had normal vestibular function. The mutation in the TECTA gene, localized in the zona pellucida domain, was detected in all 4 affected individuals. The localization of the mutation in the different modules of the protein may have caused the different clinical features.

Transcranial magnetic stimulation confirms hyperexcitability of occipital cortex in migraine

We hypothesized that the hyperexcitability of occipital cortex neurons may predispose migraine subjects to develop spreading depression, the putative basis of migraine with aura (MwA). To date there is no direct physiologic correlate confirming this in patients. Accordingly, we evaluated the differences in the threshold of occipital cortex excitation between MwA patients and normal controls (C) using transcranial magnetic stimulation (TMS). TMS was performed using the Cadwell MES 10 stimulator. A circular coil 9.5 cm in diameter was applied to the occipital scalp (7 cm above the inion). Stimulator intensity was increased in 10% increments until subjects reported visual phenomena or 100% intensity was reached. Stimulation intensity was then fine-tuned to determine the threshold at which phosphenes were just visualized. Eleven MwA patients, mean age 37 +/- 7 years, were compared with 11 C, mean age 37.7 +/- 7 years. The difference in the proportion of subjects with phosphene generation between MwA patients and C was significant (MwA patients 100% versus C 27.3%, p = 0.001). The mean threshold level for MwA patients was 44.2 +/- 8.6 versus 68.7 +/- 3.1 for C (p = 0.0001). All threshold levels for MwA patients were lower than the lowest threshold for C; the MwA patient with the lowest threshold had an aura after stimulation. The threshold for excitability of occipital cortex is lower in MwA patients compared with C. This is a direct neurophysiologic correlate for clinical observations that have indicated hyperexcitability of the occipital cortex in migraineurs.

Immuno-injury to the inner ear auditory system following secondary endolymphatic sac immune response

This study investigated immuno-injury to the inner ear auditory system following inner ear immune response in the guinea pig. The endolymphatic sac (ES) was directly challenged with keyhole limpet hemocyanin (KLH). Auditory brainstem response with click sound stimulation was assessed pre and post KLH challenge of the ES. In systematically presensitized animals, secondary KLH challenge to the ES produced significant elevation of the mean threshold level on day 3 and 17 as compared to that of pre challenge levels. However, no significant prolongation of the latency (N1-N3) was observed. On the other hand, neither phosphate buffered saline injection into the ES nor primary KLH challenges of the ES were capable of elevating the threshold level and changing the latency. These results indicate that elevation of threshold was apparently induced by a secondary immune response of the ES, not by nonspecific mechanical damage to the ES, the central auditory system or KLH toxicity to the inner ear, suggesting that local immune response of the ES is a possible pathogenesis of sensorineural hearing loss.

Repeated Infant Thresholds in Operant and Nonoperant Audiometric Procedures

This study examined test-retest reliability of infant auditory thresholds in a single evaluation session. Eight- to 11-month-olds were assessed in both operant and nonoperant audiometric procedures. Operant testing produced an average of 8.5 thresholds. Mean threshold level did not shift significantly over the course of the operant session, although some individual threshold functions varied from the group trend. Nonoperant assessment yielded two or more measures of threshold for only a portion of the subject group. The pattern of repeated measures for this subgroup showed a significant upward shift in threshold level.

On cantilever loading of vital and non-vital teeth. An experimental clinical study.

Three healthy subjects with neighboring or contralateral vital and root-filled teeth requiring crown therapy were selected as test persons. All teeth had optimal alveolar bone support. The root-filled teeth were furnished with individual cast posts and cores, and veneer crowns were made on both the vital and non-vital teeth. Buccal extension bars were then soldered to the occlusal surfaces of these crowns, and weights were applied in different positions along the bars until the test persons experienced pain. The experiments were repeated under local anesthesia. The results showed that non-vital teeth had mean pain threshold levels that, on cantilever loading, were more than twice as high as those of their neighboring or contralateral vital teeth. The positions of the centers of rotational deformations of the loaded teeth, which were assumed to be mainly rotational, were calculated and found to be located inside the peripheries of the crowns for the vital teeth but extracoronally in markedly more peripheral positions for the non-vital teeth.