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Biomedical subjects

S M Abel

Publications and source records attributed to S M Abel.

At least 19 recordsLinked to original sources
PubMed2001

The effect of the audallion BEAMformer noise reduction preprocessor on sound localization for cochlear implant users.

OBJECTIVE: To assess the effect of the Audallion BEAMformer noise reduction preprocessor on the sound localization ability of children fitted unilaterally with the Nucleus 22-channel cochlear implant. DESIGN: Eight children aged 11 to 14 yr participated. Using three arrays of six loudspeakers, each child was tested in a semi-reverberant sound proof booth representative of a small office environment. The six loudspeakers were positioned 30 degrees apart in the horizontal plane at a distance of 1 m, spanning 150 degrees either directly in front of or to the left or right of the subject. The stimulus to be localized was a 300 msec broadband noise with a rise/decay of 50 msec. Subjects were tested with the BEAMformer in four possible settings, including one single microphone control condition, with each of the three loudspeaker arrays. One block of 60 forced-choice speaker identification trials was presented for each of the 12 listening conditions. On each trial, the stimulus was emitted by one of the six loudspeakers, randomly selected. RESULTS: Results demonstrated that subjects were unable to discriminate among sound sources arrayed horizontally in space using the cochlear implant microphone alone, or in combination, with the BEAMformer microphone located on the other ear. Results also showed that using the BEAMformer did not bias the perception of spatial location. CONCLUSIONS: The localization of acoustic stimuli in pediatric cochlear implant users was unaffected by the use of the Audallion BEAMformer. The apparent origin of most sounds appears to be pulled toward the implanted ear. Further studies are needed to validate findings.

Acoustic Stimulation↗
PubMed2000

The role of high-frequency hearing in age-related speech understanding deficits.

An experiment was conducted to further explore the effect of ageing on speech understanding under degraded listening conditions. Two groups of subjects, aged 20-39 years and 50-75 years were tested. Measurements were made of hearing thresholds in each ear from 0.25-10kHz, consonant discrimination in quiet and continuous speech spectrum noise (S/N= -10 dB) and monophonic and stereophonic frequency selectivity. Neither group would have been diagnosed as hearing-impaired. Nonetheless, the older group had significantly higher hearing thresholds, which increased systematically with frequency. Poorer consonant discrimination in noise was observed for the older group. This outcome was correlated with high-frequency thresholds, not with age. There was no between-group difference in stereophonic frequency selectivity, minimizing the possibility of age-related changes in central auditory processing. Monophonic frequency selectivity, an index of cochlear processing, was correlated with speech understanding. The results support the conclusion that observed age-related effects are secondary to cochlear dysfunction.

Age Factors↗
PubMed2000

The effect of aging on horizontal plane sound localization.

An experiment was conducted to determine the effect of aging on sound localization. Seven groups of 16 subjects, aged 10-81 years, were tested. Sound localization was assessed using six different arrays of four or eight loudspeakers that surrounded the subject in the horizontal plane, at a distance of 1 m. For two 4-speaker arrays, one loudspeaker was positioned in each spatial quadrant, on either side of the midline or the interaural axis, respectively. For four 8-speaker arrays, two loudspeakers were positioned in each quadrant, one close to the midline and the second separated from the first by 15 degrees, 30 degrees, 45 degrees, or 60 degrees. Three different 300-ms stimuli were localized: two one-third-octave noise bands, centered at 0.5 and 4 kHz, and broadband noise. The stimulus level (75 dB SPL) was well above hearing threshold for all subjects tested. Over the age range studied, percent-correct sound-source identification judgments decreased by 12%-15%. Performance decrements were apparent as early as the third decade of life. Broadband noise was easiest to localize (both binaural and spectral cues were available), and the 0.5-kHz noise band, the most difficult to localize (primarily interaural temporal difference cue available). Accuracy was relatively higher in front of than behind the head, and errors were largely front/back mirror image reversals. A left-sided superiority was evident until the fifth decade of life. The results support the conclusions that the processing of spectral information becomes progressively less efficient with aging, and is generally worse for sources on the right side of space.

Adolescent↗
PubMed1999

Diagnostic value of infantile stridor: a perceptual test.

INTRODUCTION: stridor is the most common presenting symptom of pediatric airway obstruction, yet its value in clinical diagnosis is undetermined. The purpose of this study was to determine what diagnostic information was available to clinicians based entirely on listening to infantile stridor. METHOD: ten taped samples of stridor and corresponding clinical summaries were independently scored by Pediatric Otolaryngologists and their trainees. Respondents were asked to score the 'perceived' severity of the stridor based on their aural perception. Participants were recruited by an advertisement on the Internet Pediatric Otolaryngology forum. Thirty-eight consultants and 22 trainees responded. The responses were compared to known outcomes in the ten patients presented. RESULTS: listening to stridor in isolation resulted in respondents performing at the level of chance when their score of 'perceived' severity was compared to the known clinical outcome. When the clinical summaries (of the same patients) were scored, the level of performance significantly improved (P < 0.001). There was no difference in the level of performance when responses of trainees were compared with consultants, although there was a trend towards improved performance by the consultants. CONCLUSION: the importance of infantile stridor judged in isolation is of limited diagnostic value. Clinical information contributes significantly to the rating of stridor severity. The combination of both clinical and auditory information will likely improve diagnostic acumen.

Clinical Competence↗
PubMed1998

Basic calcium phosphate crystal-induced collagenase production: role of intracellular crystal dissolution.

OBJECTIVE: To investigate the potential therapeutic effects of inhibiting intracellular dissolution of basic calcium phosphate (BCP) crystals in tissue culture by raising lysosomal pH using bafilomycin A1, a specific vacuolar pump inhibitor. DESIGN: 45Ca-labeled crystals were used to demonstrate intracellular crystal dissolution in human foreskin fibroblasts (HF). Mitogenesis was evaluated using [3H]thymidine incorporation assays and cell counts. Northern blot and Western blot were used to study collagenase [matrix metalloproteinase-1 (MMP1)] mRNA accumulation and protein secretion, respectively. RESULTS: Bafilomycin A1 inhibited intracellular dissolution of BCP crystals and caused a concentration-dependent inhibition of BCP crystal-induced mitogenesis. Doses of bafilomycin A1 which inhibited intracellular crystal dissolution and mitogenesis had no effect on BCP crystal-induced MMP1 mRNA accumulation or protein secretion. CONCLUSION: Raising lysosomal pH to inhibit intracellular BCP crystal dissolution attenuates the proliferative response to BCP crystals in HF but does not prevent metalloprotease synthesis and secretion. The therapeutic potential of lysosomotropic agents for preventing joint destruction in BCP crystal deposition disease is limited.

Anti-Bacterial Agents↗
PubMed1997

Active noise reduction versus conventional hearing protection. Relative benefits for normal-hearing and impaired listeners.

The benefits of active noise reduction (ANR) hearing protectors were assessed in two groups of normal-hearing subjects, under and over the age of 40 years, and one group with bilateral high-tone hearing loss. Subjects were tested with the ears unoccluded and fitted with conventional sound attenuating E-A-R foam plugs, E-A-R HI-FI plugs, and Bilsom Viking muffs; and one ANR muff, the Peltor 7004. Within each ear condition, measurements were made in quiet of hearing thresholds for frequencies between 0.25 kHz and 8 kHz, duration and frequency difference limens, and word recognition. Hearing thresholds and word recognition were also measured in a background of impulsive cable swager noise. The E-A-R foam plug provided the highest and the E-A-R HI-FI plug, the lowest attenuation. The Bilsom Viking and Peltor muffs were virtually identical and midway between. An additional 10 dB of sound reduction was realized at 0.25 kHz with ANR. The masking effect of the noise on hearing threshold decreased with an increase in attenuation. None of the devices compromised either duration or frequency discrimination. Word recognition in noise improved in normal listeners when protectors were worn. For the impaired subjects, word recognition with poor contextual cues decreased with an increase in sound attenuation, in both quiet and noise. Like older normal listeners, their scores were relatively higher with ANR.

Adult↗
PubMed1996

Sound localization. The interaction of aging, hearing loss and hearing protection.

The effect of conventional ear plugs and ear muffs, and muffs with limited dichotic amplification on the ability to localize one-third octave noise bands was investigated under semi-reverberant listening conditions. Forty-eight normal-hearing subjects, half over 40 years of age, and 23 subjects with bilateral sensorineural hearing loss participated. Sound localization was assessed using an array of six loudspeakers surrounding the subject at azimuth angles 60 degrees apart. One block of 120 forced-choice speaker identification trials was presented for each of 16 listening conditions defined by ear condition (unoccluded, E-A-R plug, E-A-R muff, and Bilsom 2392 muff), stimulus frequency (500 Hz and 4000 Hz), and background (quiet and continuous 65 dB SPL-white noise). Plugs and muffs, particularly active muffs, resulted in decrements in right/left judgments based on interaural intensity but not time-of-arrival differences. High-frequency front/back discrimination was affected more by muffs than by plugs. Error patterns for the conventional and active muffs were dissimilar. Aging resulted in a decrement in unoccluded front/back discrimination. Trends for the impaired subjects were the same as those for normal subjects at 500 Hz. Many could not hear 4000 Hz with conventional protectors. Their performance was no different from normal with the active muffs.

Adolescent↗
PubMed1995

Prevention of noise-induced hearing loss in the Canadian military.

A prospective study was undertaken to investigate the development of noise-induced hearing loss in Canadian military recruits, and to assess the effectiveness of the hearing conservation program currently in place. The participants were 134 men and women, 20 to 30 years of age, employed in four trades, three of these (infantry, artillery, and armour) associated with high noise levels. The data comprised audiometric measurements made at the time of entry and after 3 years of employment, and responses to a questionnaire mainly relating to noise exposure in the workplace and during leisure activities, and the utilization of personal hearing protective devices. The findings showed that group audiograms at entry and at the 3-year recall were characterized by a 6-kHz notch that was indicative of noise-induced hearing loss, although mean threshold values were within normal limits. By the 3-year recall, 11% of the infantry had sustained a mild-to-moderate hearing loss in the left ear, greater than 25-dB HL, that was consistent with the use of small-calibre weapons. Responses to the questionnaire indicated that, while subjects appreciated the potential benefit of wearing hearing protectors, instructions in their proper use and education on the hazards of noise exposure were poor. The results suggested methods to strengthen the existing scheme for hearing conservation to further minimize risk.

Adult↗
PubMed1994

Frequency selectivity in patients with acoustic neuroma.

Frequency selectivity was compared in subjects with hearing loss due to acoustic neuroma and cochlear pathology, and normal listeners. A particular interest was the role of probe tone parameters on the shape of the tuning curve. Psychophysical tuning curves (PTCs) were measured for each of two equal energy 2000-Hz probe tones (10 dB SL/300 msec and 17 dB SL/60 msec), using simultaneous 1/3-octave narrow-band noise maskers centered at 1, 1.25, 1.6, 2.5, 3.15, and 4 kHz. The results showed that the critical masker levels obtained for impaired listeners were significantly greater than those from normal subjects. The slope of the low-frequency limb of the PTC was steeper for normal compared to hearing-impaired listeners but there was no difference due to site of lesion. In all three groups, the critical masker levels obtained with the short probe were significantly greater than those for the long probe, negating the hypothesis that equal energy probes would yield the same outcomes. Tuning in listeners with hearing loss was highly correlated with audiometric threshold but not with tumor size, width of the internal auditory canal, or tumor location within the cerebellopontine angle. The main conclusion was that cochlear and retrocochlear hearing loss are similar with respect to their effect on frequency selectivity.

Acoustic Stimulation↗
PubMed1993

Nonpalpable occult and metastatic papillary thyroid carcinoma.

The results of palpation, ultrasound, and detailed pathology were compared in 50 patients undergoing total thyroidectomy. Of the 211 nodules recognized by pathology, palpation detected 24% and ultrasound detected 43%. There were 14 patients with palpable papillary carcinomas, and 12 of these 14 had metastatic foci in other portions of the gland. Metastatic foci would have been left in 10 patients if only a lobectomy had been performed and would have been left in 6 patients if only a subtotal thyroidectomy (as defined in this report) had been performed. Of the 33 patients with benign palpable nodules, 5 had occult papillary carcinomas. In 2 of those 5 patients, the occult carcinomas would not have been removed if a less-than-total thyroidectomy had been performed. The significance of these occult and metastatic papillary carcinomas is discussed.

Carcinoma, Papillary↗
PubMed1993

Cortisol metabolism in vitro--II. Species difference.

It has been suggested that cortisol 6 beta-hydroxylase activity specifically reflects cytochrome P4503A (CYP3A) levels in the liver. However, we have previously reported that the metabolism of cortisol in human liver fractions in vitro is extremely complex and variable, and therefore complete metabolite analysis must be undertaken if 6 beta-hydroxycortisol is to be used as a marker of CYP3A activity. In the present study, the metabolism of [3H]cortisol by hepatic microsomes from various animal species, and by cytosol from male and female rats, has been defined and compared with metabolites formed by human liver microsomes. Metabolites were characterized by co-chromatography with authentic standards, mass spectrometry, and quantified by radiometric HPLC. The results show that all microsomes prepared from animal species studied (male and female rat, male and female guinea-pig, male hamsters and mice) can metabolize cortisol, although the metabolic profiles are both quantitatively and qualitatively different from that obtained with human microsomes. In general the metabolic profiles for animal microsomes are simpler: hamster, mouse and guinea pig show only 6 beta-hydroxylase and 11 beta-dehydrogenase activity, although male rat shows both of these and 20 beta-reductase activity while the female rat possesses all of the above as well as the ability to reduce the A-ring (delta 4-reductase and 3-oxidoreductase activities). The female rat also produces two metabolites undetected in humans. Incubations with male rat cytosol generated 20 beta-dihydrocortisone as the major metabolite, and several unidentified minor polar metabolites, whereas female cytosolic products were identical to those generated by human cytosol, the major metabolite being 3 alpha,5 beta-tetrahydrocortisol. In conclusion, our studies have shown that hepatic cortisol metabolism is extremely variable amongst the species investigated and that the hamster provides the simplest model with which to explore cortisol 6 beta-hydroxylase activity.

Animals↗
PubMed1993

Cortisol metabolism in vitro--III. Inhibition of microsomal 6 beta-hydroxylase and cytosolic 4-ene-reductase.

The in vitro metabolism of cortisol in human liver fractions is highly complex and variable. Cytosolic metabolism proceeds predominantly via A-ring reduction (to give 3 alpha,5 beta-tetrahydrocortisol; 3 alpha,5 beta-THF), while microsomal incubations generate upto 7 metabolites, including 6 beta-hydroxycortisol (6 beta-OHF), and 6 beta-hydroxycortisone (6 beta-OHE), products of the cytochrome P450 (CYP) 3A subfamily. The aim of the present study was, therefore, to examine two of the main enzymes involved in cortisol metabolism, namely, microsomal 6 beta-hydroxylase and cytosolic 4-ene-reductase. In particular, we wished to assess the substrate specificity of these enzymes and identify compounds with inhibitory potential. Incubations for 30 min containing [3H]cortisol, potential inhibitors, microsomal or cytosolic protein (3 mg), and co-factors were followed by radiometric HPLC analysis. The Km value for 6 beta-OHF and 6 beta-OHE formation was 15.2 +/- 2.1 microM (mean +/- SD; n = 4) and the Vmax value 6.43 +/- 0.45 pmol/min/mg microsomal protein. The most potent inhibitor of cortisol 6 beta-hydroxylase was ketoconazole (Ki = 0.9 +/- 0.4 microM; n = 4), followed by gestodene (Ki = 5.6 +/- 0.6 microM) and cyclosporine (Ki = 6.8 +/- 1.4 microM). Both betamethasone and dexamethasone produced some inhibition (Ki = 31.3 and 54.5 microM, respectively). However, substrates for CYP2C (tolbutamide), CYP2D (quinidine), and CYP1A (theophylline) were essentially non-inhibitory. The Km value for cortisol 4-ene-reductase was 26.5 +/- 11.2 microM (n = 4) and the Vmax value 107.7 +/- 46.0 pmol/min/mg cytosolic protein. The most potent inhibitors were androstendione (Ki = 17.8 +/- 3.3 microM) and gestodene (Ki = 23.8 +/- 3.8 microM). Although both compounds have identical A-rings to cortisol, and undergo reduction, inhibition was non-competitive.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1993

Cortisol metabolism by human liver in vitro--IV. Metabolism of 9 alpha-fluorocortisol by human liver microsomes and cytosol.

The oxidative and reductive biotransformations of 9 alpha-fluorocortisol (fluorocortisol) by human liver microsomes and cytosol have been characterized. 9 alpha-Fluorination greatly simplified cortisol metabolism in microsomes: dehydrogenation of the 11 beta-hydroxyl group and A-ring (4-ene-5 beta and 3 alpha-keto) reduction, the principle pathways, were completely blocked. Fluorocortisol was essentially metabolized by the remaining pathways, 20 beta-reduction and 6 beta-hydroxylation. In cytosol, 20 beta-reduction replaced the A-ring reduction of cortisol as the sole biotransformation. The major structure-metabolism relationships of fluorocortisol in man, i.e. complete and extensive inhibition of 11 beta-dehydrogenation and 4-ene-5 beta-reduction, respectively, were attributed to hepatic enzyme systems. Their mechanistic basis is discussed with reference to the electronic and conformational changes induced by 9 alpha-fluorination.

Adult↗
PubMed1993

Sound localization: effects of reverberation time, speaker array, stimulus frequency, and stimulus rise/decay.

This research assessed the ability of human listeners to localize one-third octave noise bands in the horizontal plane. The effects of reverberation time (absorbent versus reverberant room), stimulus center frequency (500, 1000, 2000, and 4000 Hz), stimulus rise/decay time (5 vs 200 ms) and speaker array (frontal versus lateral) were investigated for four subjects using a forced-choice speaker-identification paradigm. Sound localization scores were consistently lower in the reverberant room than in the absorbent room. They also revealed strong frequency and azimuthal effects. The benefit of a shorter rise/decay time was small and limited to low frequencies. The identification of a speaker position depended strongly upon the array in which it was embedded, primarily because localization in the lateral array led to frequency-dependent front/back confusions and response bias. The results also illustrated the importance of choosing a coordinate system based on the auditory cone-of-confusion to analyze localization data for speaker arrays spanning the aural axis.

Auditory Perception↗
PubMed1993

Auditory perception with level-dependent hearing protectors. The effects of age and hearing loss.

Auditory perception with hearing protectors was assessed in three groups of subjects, two with normal hearing, but differing in age, and one with moderate bilateral sensorineural hearing loss. Individuals were tested with the ears unoccluded, and fitted with each of two level-dependent ear muffs and their conventional level-independent counterparts. One of the former devices provided limited amplification. In each of these five ear conditions, the threshold of audibility for one-third octave noise bands centered at 500, 1,000, 2,000 and 4,000 Hz, consonant discrimination, and word recognition were measured in quiet and in a continuous impulse noise background. The results showed that the attenuation of sounds (i.e. the difference between protected and unoccluded thresholds) in quiet did not vary as a function of age or hearing loss for any of the four protectors. In noise, the difference between protected and unoccluded listening was close to zero, as long as hearing was normal. With hearing loss as a factor, there was a significant increment in the protected threshold, the amount determined by the device. Word recognition in quiet was adversely affected in normal-hearing listeners by the three attenuating devices but improved in noise relative to unoccluded listening. Amplification had a deleterious effect for both consonant discrimination and word recognition in noise. In hearing-impaired listeners, speech perception was impeded by all four muffs but less so in quiet with limited amplification.

Adult↗
PubMed1993

Incidence and types of non-palpable thyroid nodules in thyroids removed for palpable disease.

The purpose of this study was to determine the number, size and types of non-palpable and ultrasound undetected thyroid nodules in thyroid glands removed for a single palpable nodule. Twenty patients undergoing partial (hemi- and subtotal) thyroidectomy and 40 patients having a total thyroidectomy were analyzed. Patients had no more than one palpable nodule, no cervical adenopathy and no history of previous thyroid surgery. An ultrasound was performed routinely within four months of surgery. Forty-six nodules were detected by final pathology in the partial thyroidectomy group but only 42% were detected by palpation and 59% by ultrasound. The median diameter of non-palpable and ultrasound undetected partial thyroidectomy nodules was 0.5 cm and all were benign except for one case of lymphoma. Pathology detected 186 nodules in the total thyroidectomy group although palpation only detected 22% of these and ultrasound 42%. The median diameters of the benign and malignant non-palpable nodules were 0.4 cm and 0.25 cm respectively. Most of the undetected nodules in the total thyroidectomy group were benign but there were 20 non-palpable and 18 ultrasound undetected papillary carcinomas.

Adolescent↗
PubMed1993

Sound localization with hearing protectors.

A preliminary investigation was conducted of the ability of normal-hearing subjects to localize sound while wearing hearing protective devices. Performance with Bilsom 2392 level-dependent stereophonic muffs with limited amplification was compared with that of conventional level-independent E-A-R 3000 muffs and E-A-R plugs. Sound localization was assessed using an array of six speakers, positioned in the horizontal plane, 1 m from the subject at azimuth angles of 30 degrees, 90 degrees, 150 degrees, 210 degrees, 270 degrees and 330 degrees. The stimulus was an 80 dB SPL 300-ms one-third octave noise band centered at 500 Hz or 4000 Hz. The experiment was conducted in quiet and in a 65 dB SPL white noise background. The results indicated that at 500 Hz, the wearing of protectors resulted in a 20% decrease in the accuracy of speaker identification but the three types of device were indistinguishable. At 4000 Hz, performance was best in the unoccluded condition and relatively worst with the level-dependent muff. Error patterns depended on the interaction of stimulus frequency, speaker azimuth and protector. Front/back errors in localizing the high-frequency stimulus were greatest with the conventional muff, whereas right/left errors were greatest with the level-dependent muff. Protected listening was generally unaffected by the presence of a noise background for both of the frequencies tested.

Adult↗