Biomedical subjects

T H Simpson

Publications and source records attributed to T H Simpson.

At least 19 recordsLinked to original sources

PubMed2001

The effect of recreational gunfire noise on hearing in workers exposed to occupational noise.

Hearing sensitivity for an experimental group of 278 industrial workers who engaged in recreational shooting was compared with that of an age-matched control group of 278 nonshooting industrial workers to examine the effect of gunfire exposure on auditory thresholds. The influence of age and the number of unprotected gunshot exposures per year also was examined. The subjects in the experimental group completed a questionnaire to define the types of firearms used, the number of years shooting, and the number of protected and unprotected gunshot exposures per year. Results revealed that hearing sensitivity for frequencies 3.0, 4.0, and 6.0 kHz for both ears in the experimental group was an average of approximately 5 to 10 dB poorer than that of the control subjects. Although both subject groups demonstrated poorer 3.0-to-6.0-kHz hearing sensitivity for left-ear compared with right-ear listening, the degree of asymmetry between ears was greater for the experimental subjects. Older shooters had more hearing loss and greater threshold asymmetry than younger shooters, but there was no significant relationship between hearing sensitivity and the number of unprotected exposures per year. This latter finding was attributed to a fourfold increase in the number of unprotected annual exposures that were reported by younger shooters, who had inherently better hearing than did the older shooters.

Adult↗

PubMed1998

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.

Adult↗

PubMed1995

Audiometric referral criteria for industrial hearing conservation programs.

OBJECTIVES: To determine referral rates resulting from application of American Academy of Otolaryngology-Head and Neck Surgery audiometric referral criteria for occupational hearing conservation programs (HCPs) in a large industrial population and to estimate the efficacy of audiometric retesting in identifying false-positive referral flags. DESIGN: Retrospective, comparing referral rates between control and noncontrol HCPs from public domain data in the American National Standards Institute Draft American National Standard: Evaluating the Effectiveness of Hearing Conservation Programs. SETTING: Occupational HCPs from the United States and Canada. PATIENTS: A total of 45,055 baseline and 27,047 second chronologic audiograms were analyzed. A subset of 3958 employees who had baseline and seven subsequent tests were examined to confirm results. INTERVENTIONS: None. MAIN OUTCOME MEASURES: Percent of employees meeting referral criteria was calculated for unconfirmed (ie, single test) and confirmed (two consecutive tests) audiometric findings. No a priori hypotheses were formulated for referral rates for control or noncontrol HCPs. RESULTS: Noncontrol HCP referral rates were typically two to three times that of control HCPs. Control and noncontrol HCPs had about half as many audiometric referral flags when retests were used to confirm initial results. CONCLUSIONS: Mature industrial populations are likely to yield higher baseline referral rates than younger populations. Retesting may identify up to 50% of audiometric referral flags as false-positive and significantly reduce costly overreferrals. Annual referral rates of 1% to 2% seem to be achievable in well-run HCPs in which retesting is performed to identify false-positive audiometric outcomes.

Audiology↗

PubMed1995

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

Draft American National Standard "Evaluating the Effectiveness of Hearing Conservation Programs" identifies potentially important links between audiometric threshold variability outcomes and occupational hearing conservation program (HCP) practices. Unacceptable threshold variability in annual audiograms may identify poor testing practices and temporary threshold shifts. This preliminary investigation reveals pre-existing hearing loss to be a potentially important confounding viable to interpreting ANSI S12.13 outcomes. Poor hearing groups in this study consistently yielded greater threshold variability (i.e., "poorer" HCP performance) than better hearing groups. Gender may also be a confounding variable, however, to a far lesser degree. HCP managers should exercise caution when interpreting relative ANSI S12.13 outcomes among HCPs differing in baseline hearing sensitivity. Potential causes for these findings are discussed, and implications for future research are identified.

Adult↗

PubMed1994

Postnatal development of the hamster cochlea. II. Growth and differentiation of stereocilia bundles.

The postnatal development of stereocilia was studied in the Syrian golden hamster. The purpose was to describe the morphological changes underlying the differentiation of stereocilia bundles and to define the time course of their growth in different regions of the cochlea. Differentiation of the hair bundle occurred by progressive changes in stereocilia number, dimensions, and spatial relationships. The overall transformation of the bundle is interpreted as a four-stage process involving the initial production of stereocilia (stage I), differentiation into tall and short populations (stage II), formation of distinct ranks (stage III), and resorption of excess stereocilia (stage IV). The orientation and arrangement of stereocilia during stage II began to occur before the tectorial membrane grew over the hair cell field. Growth in the dimensions of stereocilia occurred continuously throughout these four stages with increases in length and width occurring simultaneously. The time frame of the growth process depended both on location along the organ of Corti and on the type of hair cell. Hair bundles in the basal turn began growing and reached maturity a few days earlier than those in the apical turn. Stereocilia of outer hair cells matured earlier than those of inner hair cells. Outer hair cell stereocilia reached their adult lengths by 14 days after birth, those of inner hair cells between 16 and 18 days after birth. A kinocilium was present on almost all hair cells on the day of birth, but most were eliminated by 14 days after birth. Tip links were observed as early as 4 days after birth, and their growth appeared to be synchronous with the growth of stereocilia. The spatial gradient of stereocilia length, which increased toward the apex in the adult, was nearly the reverse of that seen at birth. The gradient for inner hair cells was associated with a gradient in the rate of stereocilia growth. The data further expand the foundation for interpreting mechanisms underlying the morphogenesis of stereocilia bundles in mammals and for understanding structure-function relationships during development.

Animals↗

PubMed1994

Early indicators of hearing conservation program performance.

Retrospective analysis of initial audiograms from 21 hearing conservation programs (HCPs) revealed several statistical protocols capable of identifying HCPs of known performance. American National Standards Institute (ANSI) and Occupational Safety and Health Administration (OSHA) protocols clearly identified 3 HCPs known to have demonstrated excellent overall programs. ANSI and OSHA outcomes appeared equivalent in ability to provide early warnings of potentially unacceptable HCP practices.

Audiometry↗

PubMed1993

Forward masking properties of neurons in the dorsal cochlear nucleus: possible role in the process of echo suppression.

The majority of single unit studies in the auditory system have been carried out using stimuli whose temporal and spectral contexts are held constant. Relatively little attention has been given to the influence of context on unit response properties. Indeed, auditory nerve fiber responses are known to be context-dependent due to the property of forward masking, a phenomenon by which the response to one sound results in a reduction in the response to a subsequent sound. Forward masking might be expected to be even more influential at central levels of the auditory pathway where the responses are reshaped by additional synaptic interactions. The purpose of the present study was to characterize the forward masking properties of neurons in the dorsal cochlear nucleus (DCN). A tool was developed for measuring the response to a probe tone as a function of delay following a previous tone-burst. The frequency of the probe was held constant at the unit's characteristic frequency while the frequency of the leading tone (masker) was varied. These measures provided a description of neural masking effects in different temporal and spectral contexts. The data yielded two patterns of suppression. In the first pattern (Type A), the suppression of the probe response became evident immediately following offset of the masker; the suppression bandwidth showed a gradual narrowing as the delay between masker and probe was increased. In the second class (Type B), the suppression of the probe response did not become evident until well after offset of the masker; this pattern appeared more circumscribed in that the suppression bandwidth gradually increased as a function of delay up to a maximum then decreased with further increases in delay. The results imply that mechanisms intrinsic to the DCN contribute to further modification and reshaping of the spectral and temporal context of masking effects beyond those seen in the auditory nerve. It is hypothesized that such properties may be specialized for suppressing the response to echoes thus facilitating communication and localization of sound in enclosed spaces.

Acoustic Stimulation↗

PubMed1993

Factors affecting laterality of standard threshold shift in occupational hearing conservation programs.

Although noise-induced hearing loss is generally characterized as bilaterally symmetrical, 80% of audiometric shifts meeting Occupational Safety and Health Administration (OSHA) criteria were unilateral in a large industrial sample. The primary factor related to unilateral OSHA shifts was asymmetric baseline hearing level. Better ears at baseline audiogram were more likely to demonstrate OSHA shifts than poorer ears. When hearing levels were symmetric at baseline, left ears were more likely to demonstrate OSHA shifts. Although OSHA shifts were primarily unilateral, cumulative effects of noise exposure were judged to be bilaterally symmetrical due to larger hearing shifts occurring in better ears of subjects with preexisting hearing asymmetries. Recovery from temporary threshold shift in second ears tested was judged not to be a significant determinant for high prevalence of unilateral shifts. Many factors likely interact to confound interpretive value of OSHA shift laterality in occupationally noise-exposed populations. This holds important implications for hearing conservation program professionals considering hearing shift laterality as a factor in shift etiology.

Adult↗

PubMed1993

Effects of audiometric threshold step size on proposed ANSI S12.13 outcomes for characterizing hearing conservation program effectiveness.

Audiometric records of 213 employees with low noise exposure were selected from the public domain data base underpinning Draft American National Standards Institute (ANSI) S12.13-1991 Standard Evaluating the Effectiveness of Hearing Conservation Programs. Records were selected from an ANSI S12.13 "control" group demonstrating raw audiometric thresholds in 1-dB steps, presumably resulting from self-recording audiometry. Raw audiometric data were rounded to the nearest 5-dB step, and ANSI S12.13 analysis protocols were applied to both raw and rounded data sets. The magnitude of all proposed ANSI test statistics increased with audiometric step size. Percent worse sequential and percent better or worse sequential protocols were markedly more sensitive to threshold step size than standard deviation of difference thresholds. The direction and magnitude of change in these outcomes supports the assumption that criterion ranges in the draft standard hold artifactual bias against hearing conservation programs (HCPs) collecting audiometric data in 5-dB steps.

Acoustic Stimulation↗

PubMed1992

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.

Acoustic Stimulation↗

PubMed1990

Flumazenil reverses sedation after midazolam-induced general anesthesia in ambulatory surgery patients.

Flumazenil, a specific competitive benzodiazepine antagonist, was evaluated for reversal of residual sedation after midazolam-induced ambulatory general anesthesia. Endotracheal anesthesia was begun with midazolam (mean +/- SD dose 12.4 +/- 2.4 mg), followed by nitrous oxide in oxygen, fentanyl, and succinylcholine, for gynecologic surgery lasting 38.6 +/- 12.5 min. After surgery, 29 women were given repeated injections of small amounts of either flumazenil or placebo until awake and calm. The mean flumazenil dose was 0.83 +/- 0.04 mg. Assessment of recovery was based on psychodiagnostic tests (visual analog sedation scale, Trieger dot, digit symbol substitution), pulse oxygen saturation, and end-expired carbon dioxide tension. Patients given flumazenil scored significantly better than did those given placebo on the psychodiagnostic tests for 5-60 min, but the groups were no longer different 120 and 180 min after the conclusion of surgery. All scores did not return to preoperative values by 180 min. Pulse oxygen saturation and end-expired carbon dioxide tension showed improvement from postoperative levels at 15 min after flumazenil injection. A controllable degree of midazolam reversal was achieved with flumazenil, but the duration of reversal was limited. Caution is needed to avoid premature discharge of ambulatory patients after midazolam-induced general anesthesia during the time that flumazenil is effective.

Adult↗

PubMed1986

The interrelationship of cortisol, gill (Na + K) ATPase, and homeostasis during the Parr-Smolt transformation of Atlantic salmon (Salmo salar L.).

Serum cortisol concentrations were measured in juvenile Atlantic salmon (Salmo salar L.) undergoing the parr-smolt transformation in fresh water, at either 1 year (S1 population) or 2 years (S2 population) after hatching. Serum cortisol levels were generally low (less than 10 ng ml-1), but during smoltification became significantly elevated in both populations. In addition, the S2 population showed a small cortisol peak in the autumn prior to smoltification. Simultaneous measurement of gill (Na + K) ATPase activity and serum cortisol concentrations in S2 salmon juveniles revealed that both features rose during smoltification in fresh water. The rise in gill (Na + K) ATPase activity was independent of cortisol levels, and preceded the rise in cortisol titer by approximately 1 month. After seawater transfer, gill enzyme levels remained high while cortisol titers fell sharply. Serum cortisol levels, but not gill (Na + K) ATPase activities, were progressively reduced by acclimation of smolts to increasing salinities. Linear regression studies indicated that, at any one level of gill (Na + K) ATPase, cortisol titer increased with increasing surface area: volume ratio. Extracellular fluid volume (sodium space) was found to decline with increasing gill (Na + K) ATPase activity, and to increase with serum cortisol titers. These results indicate that high serum cortisol levels represent a secondary response caused by the development of hypoosmoregulatory ability while still resident in fresh water. Cortisol does not appear to directly stimulate gill (Na + K) ATPase activity in Atlantic salmon smolts.

Animals↗

PubMed1978

A radio-gas chromatographic method for the determination of 11-oxotestosterone in fish plasma: its use in confirming estimations by radioimmunoassay.

A radio-gas chromatographic method has been devised for the estimation of 11-oxotestosterone (17beta-hydroxyandrost-4-ene-3, 11-dione) in fish plasma samples which provides an independent means of validating the radioimmunoassay described earlier. Estimates of the concentration of 11-oxotestosterone in a sample of male rainbow trout plasma by radio-gas chromatography using peak height and peak weight measurements were 6.9 microgram/100 ml and 7.4 microgram/100 ml respectively, in good agreement with that of 7.1 microgram/100 ml determined by radioimmunoassay.

Animals↗

PubMed1977

A radioimmunoassay for 11-oxotestosterone: its application in the measurement of levels in blood serum of rainbow trout (S. Gairdneri).

17beta-Hydroxyandrost-4-ene-3,11-dione was linked via its 3-(O-carboxymethyl) oxime to bovine serum albumin to give a conjugate which was used to generate antiserum in rabbits. The antiserum, at an overall dilution of 1 in 16,000, together with [1,2-3H] 17beta-hydroxyandrost-4-ene-3,11-dione synthesized from [1,2-3H] cortisone have been used to develop a radioimmunoassay for the parent steroid. The assay incorporates a purification step in which serum or plasma extracts are chromatographed on silica gel layers bound to plastic or aluminum sheets and the steroid containing zones cut out and eluted directly with assay buffer. The cross-reactivities of several steroids with the antiserum and the specificity, sensitivity, accuracy and precision of the assay are described. Blood sera from immature male rainbow trout contain ca 0.2-0.4 mature, serum levels rise sharply to reach values of 2 to greater than 9 microng/100 ml of 17beta-hydroxyandrost-4-ene-3,11 dione. As male fish mature, serum levels rise sharply to reach values of 2 to greater than 9 microng/100 ml. Levels in immature females rarely exceeded the assay sensitivity but serum from three ripe females showed low but detectable levels (ca 0.2 microng/100 ml) of steroid. The assay has found application in sexing live fish for experimental purposes.

Age Factors↗

PubMed1975