Metabolic mapping of functional activity in human subjects with the [18F]fluorodeoxyglucose technique.

The 2-[18F]fluoro-2-deoxy-D-glucose technique was used to measure regional cerebral glucose utilization by human subjects during functional activation. Normal male volunteers subjected to one or more sensory stimuli (tactile, visual, or auditory) exhibited focal increases in glucose metabolism in response to the stimulus. Unilateral visual hemifield stimulation caused the contralateral striate cortex to become more metabolically active than the striate cortex ipsilateral to the stimulated hemifield. Similarly, stroking the fingers and hand of one arm with brush produced an increase in metabolism in the contralateral postcentral gyrus, compared with the homologous ipsilateral region. The auditory stimulus, which consisted of a monaurally presented factual story caused an increase in glucose metabolism in the auditory cortex in the hemisphere contralateral to the stimulated ear. These results demonstrate that the technique is capable of providing functional maps in vivo related to both body region and submodality of sensory information in the human brain.

Mapping of functional activity in brain with 18F-fluoro-deoxyglucose.

The efficacy of using the 18F-fluoro-deoxyglucose (18F-DG) for measuring regional cerebral glucose utilization in man during functional activation is demonstrated. Normal male volunteers subjected to sensory stimuli (visual, auditory, tactile) exhibited focal increases in glucose metabolism in response to the stimulus. Unilateral visual hemifield stimulation caused the contralateral striate cortex to become more active metabolically than the striate cortex ipsilateral to the stimulated hemifield. Similarly, stroking of the fingers and hand of one arm with a brush produced an increase in metabolism in the contralateral postcentral gyrus compared to the homologous ipsilateral region. The auditory stimulus, which consisted of monaural listening to either a meaningful or nonmeaningful story, caused an increase in glucose metabolism in the right temporal cortex independent of which ear was stimulated. These results demonstrate that the 18F-DG technique is capable of providing functional maps in vivo in the human brain.

Sensorineural hearing loss in patients with typical retinitis pigmentosa.

We performed detailed audiologic testing in 45 patients with retinitis pigmentosa and 45 age- and sex-matched controls. Ten (22%) of the retinitis pigmentosa patients had a sensorineural hearing loss that varied from mild to severe. None of the control subjects had a hearing loss. Audiograms measured over a ten- to 30-year period were available for four patients with retinitis pigmentosa and each showed progressive hearing loss. The results indicate the important role of audiologic evaluation in treating patients with retinitis pigmentosa.

Frequency selectivity in bird and man: a comparison among critical ratios, critical bands and psychophysical tuning curves.

The relative frequency selectivity of the internal auditory filters, as measured by critical bands or critical ratios, and psychophysical tuning curves, was compared in an avian species (parakeet) and human listeners. The results indicate that the critical band predicts the frequency selectivity of psychophysical tuning curves and vice versa. These findings suggest that there are similar mechanisms which contribute to the frequency selectivity measured by these two procedures and that these mechanisms operate in both the human and avian ear.

Central auditory imperception.

The development of clinically applicable techniques for the evaluation of hearing impairment caused by lesions of the central auditory pathways has increased clinical interest in the anatomy and physiology of these pathways. A conceptualization of present understanding of the anatomy and physiology of the central auditory pathways is presented. Clinical tests based on reduction of redundancy of the speech message, degradation of speech and binaural interations are presented. Specifically performance-intensity functions, filtered speech tests, competing message tests and time-compressed speech tests are presented with the emphasis on our experience with time-compressed speech tests. With proper use of these tests not only can central auditory impairments by detected, but brain stem lesions can be distinguished from cortical lesions.

The "plateau effect" of cis-platinum-induced hearing loss.

Cis-platinum-induced hearing loss has been reported to exhibit a "plateau effect" over the 2 to 8 kHz range. We examined serial audiometry data from 27 patients treated with cis-platinum. Although a plateau at 60 to 70 dB HL often occurred, this hearing loss was clearly exceeded in a number of patients. We identified 14 patients with sufficient cis-platinum-induced sensorineural hearing loss to evaluate a plateau limit to hearing loss over the 4 to 8 kHz range. Half of these 14 patients had hearing losses that exceeded the plateau level. More severe 4 to 8 kHz hearing losses did not correlate with number of treatments, cumulative dosages of cis-platinum, pre-existing hearing loss, radiation therapy, other chemotherapeutic agents, or even hearing losses below 4 kHz. Although cis-platinum therapy can induce a plateau of moderate hearing impairment for some patients over the 4 to 8 kHz range, a significant proportion of patients will experience more severe hearing impairment in this range, even after only one or two courses of cis-platinum.

Pseudohypacusis.

This article provides the basis for the techniques and interpretation of audiologic tests useful in evaluation of the patient with pseudohypacusis. Differences between the childhood and adult forms of the problem are discussed. The indications for currently popular conventional and special tests are presented. These include both behavioral and electrophysiologic measures for assessing auditory function.

Effects of pre-existing hearing loss on proposed ANSI S12.13 outcomes for characterizing hearing conservation program effectiveness: follow-up investigation.

Draft ANSI S12.13 1991 Standard Evaluating the Effectiveness of Hearing Conservation Programs presents statistical protocols purportedly sensitive to temporary threshold shift (TTS) in occupational hearing conservation program (HCP) audiometric databases. Because it is well established that less TTS is found in humans with hearing loss than in those with essentially normal hearing, one might predict baseline hearing level to be a confounding variable in interpreting ANSI S12.13 outcomes, with better-hearing industrial populations tending to demonstrate greater year-to-year audiometric variability than poorer-hearing groups. However, in a large industrial sample from the public domain audiometric database, poorer-hearing groups systematically demonstrated greater audiometric threshold variability than better-hearing groups, and ANSI S12.13 outcome magnitudes were highly positively correlated to baseline hearing levels. These findings generally do not support notions that ANSI S12.13 outcomes clearly provide indirect measures of TTS. HCP managers should exercise extreme caution in interpreting ANSI S12.13 outcomes to rate overall program performance. In particular, HCP managers should not rely upon these outcomes for decisions regarding hearing protection policies without careful consideration of pre-existing hearing loss in the populations involved.

Audiometric test criteria in the detection of cisplatin ototoxicity.

Audiometric criteria establishing the ototoxic effects of cisplatin (CDDP) vary widely in the literature. Normal test-retest variability in audiometric thresholds resulting from serial audiometry is likely a confounding variable in the over-reporting of ototoxic effects. This study investigated the variability of serial audiometry for a group of 21 head and neck cancer patients receiving no known ototoxic drugs in an effort to establish guidelines for determining reasonable audiometric criteria for CDDP therapy. Comparison of this group to a similar group of 31 patients receiving high dose (100+ mg/m2) bolus administration of CDDP suggests that audiometric shift criteria developed from Receiver Operating Characteristic analysis and employing multiple frequency averaging above 1000 Hz may lead to more universally accepted audiometric criteria for ototoxicity, which should in turn lead to more reliable reports of disease incidence.

Transient evoked otoacoustic emissions and pseudohypacusis.

The audiologic diagnosis of pseudohypacusis continues to challenge the clinical audiologist. The introduction of otoacoustic emissions (OAEs) to the test repertoire of the audiologist may prove valuable in the evaluation of pseudohypacusis. This report highlights five cases in which transient evoked otoacoustic emissions (TEOAEs) were used to cross-check the validity of subjective audiologic thresholds. Relationships of TEOAEs to other objective measures of audiologic threshold are shown to substantiate the value of the procedure for the diagnosis of pseudohypacusis. Suggestions for the use of OAEs in cases of pseudohypacusis are discussed.

Comparison of pure-tone, warble-tone and narrow-band noise thresholds of young normal-hearing children.

Pure-tone, warble-tone, and narrow-band noise thresholds were compared in terms of sensitivity and clinical test-retest reliability. Eighty normal-hearing young children, equally divided in four discrete age levels (3 1/2, 4 1/2, 5 1/2, and 6 1/2 years) were examined. Thresholds were ranked from most to least sensitive as follows: warble-tone, pure-tone, and narrow-band noise. Test-retest reliability was equivalent for all three stimuli. Clinical implications are discussed.

The influence of audiometric configuration on pure-tone, warble-tone and narrow-band noise thresholds of adults with sensorineural hearing losses.

Thresholds measurements for pure tones, warble tones, and narrow-band noise were compared for adult sensorineural hearing-impaired subjects with gradual and sharp audiometric configurations. Results demonstrated that audiometric configuration does not significantly affect the relationship between pure tones and warble tones but does affect the relationship between pure tones and narrow-band noise. Differences were most apparent at the higher frequencies. Clinical implications are discussed.

Perception of time-compressed consonant-nucleus-consonant monosyllables by non-native speaker/listeners of English.

Recent investigations of time-altered speech have dealt with the effect of time compression and sensation level on intelligibility scores of native speaker/listeners of English. In the present investigation, the intelligibility of time-compressed consonant-nucleus-consonant monosyllables was studied using English speaker/listeners whose native languages are Spanish or Indo-Dravidian. Results supported earlier findings in that intelligibility decreased as a function of increasing percentage of time compression and decreasing sensation level. This effect was more prominent for the Indo-Dravidian than for Spanish speaker/listeners. The Spanish group of subjects showed generally lower difference scores than did the Indo-Dravidian group when compared to native English speaker/listeners.

Articulation functions and test-retest performance of normal-hearing children on three speech discrimination tests: WIPI, PBK-50, and NV Auditory Test No. 6.

This study investigates the performance of normal-hearing children on three types of speech discrimination tasks: (1) a multiple-choice, closed-message set test requiring no verbal response, the WIPI; (2) an open-message set test for adults, Northwestern University Aue talker were administrated to 60 normal-hearing children, divided qually between the ages three-and-one-half, five-and-one-half, seven-and-one-half, nine-and-one-half, and 11-and-one-half years. The number of tests and sensations levels administered varied by age. The WIPI test yielded the highest discrimination scores, the PBK-50 was intermediate, and the NU-6 was most difficult. A small number of items on the WIPI test accounted for a large percentage of the errors. For three-and-one-half years olds, the WIPI appears to be the instrument of choice. For children aged five-and-one-half years, both the WIPI and the PBK-50 appear to be appropriate clinical tools. Children aged seven-and-one-half scored similar to children aged nine-and-one-half on the WIPI and to children aged nine-and-one-half and 11 and-one-half on the PBK-50 and NU-6. Test-retest differences were small on all three tests.

Intelligibility of time-compressed sentential stimuli.

Time-compressed monosyllables have been studied relative to the assessment of central auditory disorders. In certain instances, sentential stimuli may be more useful than word lists in central auditory testing, particularly when results may be contaminated by concomitant peripheral hearing losses. Central Institute for the Deaf (CID) and Revised CID sentence lists and a contrived sentential approximation task were presented to 96 normal hearing young adults at time-compression ratios of 0%, 40%, 60%, and 70%, under sensation levels of 24 and 40 dB. The CID and RCID stimuli were more intelligible than the sentential approximations. The results are presented and discussed as they pertain to central auditory testing and are compared to earlier data using consonant-nucleus-consonant monosyllabic stimuli.

Performance of noise-induced hearing-impaired listeners on time-compressed consonant-nucleus-consonant monosyllables.

The effects of time compression on the intelligibility of consonant-nucleus-consonant (CNC) monosyllables was investigated by presenting six conditions of a time-compressed versions of the Northwestern University Auditory Test no. 6; at four sensation levels, to nine subjects with noise-induced sensorineural hearing impairments. Results indicated that intelligibility gradually decreased as the ratio of time compression increased, with a dramatic breakdown at the highest ratio of time compression. A typical roll-over phenomenon was also found. Results are related to data on normal listeners.

Vancomycin during pregnancy: does it cause hearing loss or nephrotoxicity in the infant?

Vancomycin was administered intravenously to 10 pregnant women for the treatment of methicillin-resistant Staphylococcus aureus infections. Auditory brainstem response testing and renal function studies were performed on the 10 babies in the experimental group and 10 babies in each of two control groups to determine the safety of vancomycin use during pregnancy. Auditory brainstem responses were not normal at birth in six infants from the three different groups studied (N = 30) but were normal at 3 months in five. The sixth infant had conductive hearing loss unrelated to vancomycin use that spontaneously disappeared at 12 months of age. Renal function was normal in all infants. Vancomycin was detected in cord blood in two patients and in breast milk in one. Adequate serum levels were achieved with routine doses in eight mothers tested; no adverse reactions occurred. It appears that vancomycin use during the second and third trimesters of pregnancy does not produce sensorineural hearing loss or nephrotoxicity in the infant.

Renal and auditory toxicity of high-dose, prolonged therapy with gentamicin and tobramycin in pseudomonas endocarditis.

The nephrotoxicity and auditory toxicity of high-dose (mean, 28.6 g) and prolonged (mean, 61.6 days) courses of gentamicin and tobramycin were monitored in 15 patients receiving 17 courses of treatment for pseudomonas endocarditis. Doses were adjusted in a manner that maintained peak levels of aminoglycoside in serum at 12-15 micrograms/ml and trough levels at less than 2 micrograms/ml. Drug-related renal dysfunction and auditory toxicity occurred in 63% and 44%, respectively, of gentamicin-treated patients and in 43% and 25%, respectively, of tobramycin-treated patients. Mean maximal rises (+/- SEM) in serum creatinine levels were 0.8 (+/- 0.4) mg/dl in the group given gentamicin and 1.6 (+/- 0.7) mg/dl in the group given tobramycin. Mean maximal decreases in pure-tone hearing threshold levels were greater in gentamicin-treated patients (58.3 dB) than in those given tobramycin (22.5 dB). Both forms of toxicity appeared earlier and at a smaller dose with gentamicin than with tobramycin.

The dichotic rhyme task: results in split-brain patients.

Monosyllabic rhyme words were dichotically presented to normal and complete split-brain subjects. In the normal adult population, only one of the words in the dichotic condition was identified. Hence, normal performance was about 50%, with a small but significant right-ear advantage. The split-brain patients yielded the expected marked left deficit, as seen on other dichotic speech tests, and demonstrated a right-ear enhancement, producing a large interear difference. This right-ear enhancement on the dichotic rhyme task (DRT) may suggest a release from central auditory competition in the left hemisphere. The dichotic rhyme task's normative data results and sensitivity to lack of callosal transmission make it worthy of further clinical and basic research.