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R Letz

Publications and source records attributed to R Letz.

At least 55 records · Page 3Linked to original sources
PubMed1985

A computer-administered neurobehavioral evaluation system for occupational and environmental epidemiology. Rationale, methodology, and pilot study results.

To facilitate the conduct of epidemiologic studies of populations at risk for or suffering from central nervous system (CNS) dysfunction due to environmental agents, a computer-administered neurobehavioral evaluation system has been developed. The system includes a set of testing programs designed to run on a microcomputer and questionnaires to facilitate interpretation of results. Standard tasks evaluating memory, psychomotor function, verbal ability, visuospatial ability, and mood were selected and adapted for computer presentation following the recommendation of an expert committee of the World Health Organization and the National Institute for Occupational Safety and Health. In two pilot surveys, test performance was found to be influenced by age, education level, and socioeconomic status in ways consistent with prior research findings. Performance on tests of short-term memory and reaction time was negatively correlated with intensity of organic solvent exposure among industrial painters. In view of the ease of administration and data handling, high subject acceptability, and sensitivity to the effects of known neurotoxic agents, computer-based assessment of CNS function holds promise for future epidemiologic research.

Central Nervous System↗
PubMed1983

Estimating human exposure to nitrogen dioxide: an indoor/outdoor modeling approach.

Adverse health consequences associated with human exposure to nitrogen dioxide are well documented. In order for policymakers to assess health risks and implement appropriate control strategies, accurate information is required concerning (1) the number of people exposed, (2) the severity and patterns of exposure, and (3) the health-related effects of exposure. In the past, data from central monitoring sites have been used to establish air pollution exposures. However, it is now recognized that people spend much of their time indoors or in areas away from fixed monitors where pollutant concentrations may be drastically different. An attempt to provide a more realistic estimate of nitrogen dioxide exposures is made. A simple deterministic model is developed, relating exposure to background ambient levels, indoor values, and human activities. Ambient and indoor parameters are derived from monitoring programs in six U.S. cities. Results suggest indoor nitrogen dioxide concentrations in private dwellings vary primarily with outdoor levels and type of cooking fuel, but are also affected by factors such as air-exchange rates and strength of indoor sources. Estimates of population exposures are obtained by combining observed distributions of nitrogen dioxide concentrations from outdoor and indoor settings with information about number of people and time spent in each microenvironment.

Air Pollution↗
PubMed1979

Within-species variation in the development of ultrasonic signaling of preweanling rats.

The development of litter and individual differences in the rate of ultrasonic signaling of neonatal rats was studied. Systematic variations among litters and individuals emerged, without differential treatment. These differences were not correlated with variations in general development as indexed by body weight. Two experiments using a cross-fostering design showed that litter differences developed independently of variations in postnatal environment. These results indicate that the variations among litters in ultrasound rate have a prenatal, possibly genetic, etiology and may represent reliable indicants of response to environmental stress.

Animals↗
PubMed1977

Ultrasound emission in infant rats as an indicant of arousal during appetitive learning and extinction.

Infant rats rewarded for crawling by being allowed to suckle on the dry nipple of an anesthetized dam showed a decreasing rate of ultrasound production during acquisition and an increasing rate during extinction. These results suggest that infant rats can be stressed and are aroused as a result of successive nonrewards just as adult rats are. In addition, these results do not support the hypothesis that infant rats lack inhibitory mechanisms related to poorly developed neural centers.

Animals↗
PubMedDate not supplied

Neurobehavioral effects of acute styrene exposure in fiberglass boatbuilders.

A field investigation of the effects of acute exposure to styrene among fiberglass boatbuilders was performed. Personal samples of styrene in breathing zone air and postshift urinary mandelic acid were collected for 105 workers exposed and not exposed to styrene in 6 fiberglass boatbuilding companies in New England. Three tests from the computerized Neurobehavioral Evaluation System (NES) were performed by the subjects in the morning before exposure to styrene, near midday, and at the end of the work day. Duration of exposure averaged 2.9 years (SD = 4.6), 8-hour TWA styrene exposure averaged 29.9 ppm (SD = 36.2), and urinary mandelic acid averaged 347 mg/g creatinine (SD = 465). Regression analyses indicated a statistically significant relationship between postshift performance on the Symbol-Digit test and both acute styrene exposure and mandelic acid. Other analyses comparing workers exposed to less than 50 ppm and greater than 50 ppm styrene also showed a significant effect on Symbol-Digit performance. All three NES tests showed test-retest correlation coefficients above .80, and ease of use for collection of neurobehavioral data under field conditions was demonstrated.

Adult↗
PubMedDate not supplied

Covariates of human peripheral nerve function: I. Nerve conduction velocity and amplitude.

A systematic investigation of covariates of nerve conduction measures was performed on data collected by the U.S. Centers for Disease Control. Nerve conduction velocity and amplitude were obtained for the median motor, median sensory, ulnar sensory, peroneal motor, and sural sensory nerves on 4,462 subjects. The magnitude of effect of skin temperature, height, body mass index, age, race, place of military service, smoking status, alcohol consumption, income, and EMG examiner was estimated for all 10 conduction outcomes. The major covariates were skin temperature, height, and examiner. Covariates with smaller but not unimportant effects on conduction outcomes were age, race, smoking status, and income. Alcohol consumption was associated with only small effects on conduction measures. These results provide an empirical basis for selection of variables to control in studies employing nerve conduction measures.

Adult↗
PubMedDate not supplied

Covariates of human peripheral nerve function: II. Vibrotactile and thermal thresholds.

A systematic investigation of covariates of quantitative sensory thresholds was performed on data collected by the U.S. Centers for Disease Control. Vibrotactile and thermal sensory thresholds were obtained from the index finger and great toe of 4,462 male Vietnam-era veterans. The magnitude of effect of skin temperature, height, body mass index, age, race, place of military service, smoking status, alcohol consumption, income, and examiner was estimated for the four outcomes. The major covariates of finger and toe vibrotactile threshold were age, height, body mass index, and examiner. The major covariates of toe thermal threshold were height, income, and examiner, and of finger thermal threshold were age, income, examiner, race, and smoking status. Alcohol consumption had only small effects on vibrotactile thresholds and essentially no effect on thermal thresholds. These results provide an empirical basis for selecting variables to control in studies employing vibrotactile and thermal threshold measures.

Adult↗
PubMedDate not supplied

Covariates of human peripheral nerve function: III. Effects of reported drinking.

A cross-sectional epidemiologic study of the relationship between alcohol consumption and peripheral nerve function was performed using data from a cohort of 4462 male Vietnam-era Army veterans selected independently of either alcohol consumption history or clinical disorders associated with excessive alcohol use. Self-reported alcohol consumption, expressed as current drinking intensity (drinks per month), was the primary measure of alcohol use. The dependent variables were: (a) conduction velocity and amplitude of the median motor, median sensory, ulnar sensory, peroneal motor, and sural sensory nerves; (b) vibrotactile and thermal thresholds of the index finger and great toe. Drinkers who reported consuming < 180 drinks per month had, in general, slightly faster mean nerve conduction velocities, slightly greater evoked response amplitudes, and slightly lower vibrotactile thresholds than did both never drinkers and drinkers reporting consuming more than 179 drinks per month. The heaviest drinking category (> 179 drinks/month) had slightly slower mean conduction velocities and slightly smaller mean amplitudes than all other drinking categories. No consistent associations were observed between thermal thresholds and alcohol consumption. These results suggest that consuming up to 6 drinks per day alone does not cause slowed nerve conduction velocity, diminished amplitude of the evoked response, or elevated sensory thresholds in 35- to 45-year-old men.

Adult↗
PubMedDate not supplied

Neurobehavioral test methods for environmental health studies of adults.

The Agency for Toxic Substances and Disease Registry convened a workshop in Atlanta, GA, that evaluated approaches and methods to ascertain whether there are neurobehavioral sequelae to children and adults exposed to hazardous substances in the environment. This article, developed from that Workshop, recommends testing methods [to identify neurotoxic insult] for immediate use in environmental health field studies of adults. A list of broad functional domains or modalities affected by chemicals was identified from the occupational and related literature (learning and memory, coding, sustained attention, higher intellectual function, strength, coordination, speed, vision, somatosensory, and affect). A core set of tests was selected that should assess those functions with the greatest demonstrated sensitivity to established neurotoxic chemicals, and a secondary set was selected to assess a broader group of functions. The core tests should be used in all investigations where neurotoxic effects would be targeted for identification; secondary tests would be used where suggested by questionnaire or symptom data or by knowledge of the effects of chemicals at the hazardous waste site.

Adult↗
PubMedDate not supplied

Standing steadiness measurements: empirical selection of testing protocol and outcome measures.

A variety of methods for measuring the effects of neurotoxic exposure have been developed and applied in epidemiologic studies of exposed workers. Although impairment of equilibrium is a common complaint among workers exposed to neurotoxicants, only a few studies have been published in which quantitative measurement of standing steadiness was used to assess occupational neurotoxicity. Possible reasons for limited use of these measures include inadequate evaluation and validation of testing protocols. The current project was undertaken to address some of these issues. Specifically, two studies of normal subjects were undertaken a) to compare standing steadiness measurements made with feet together or feet apart, and b) to assess the reliability of a number of potential summary measures for estimating standing steadiness. Study 1 was performed on eight subjects tested on 2 consecutive days. It demonstrated that a) a feet-together position resulted in greater systematic variance than a feet-apart position, b) sway varied systematically within 60-s trials, c) three 60-s eyes-open/eyes-closed trial pairs did not appear to provide more information than two pairs of trials. In Study 2, 30 subjects were tested on two occasions separated by 2 to 7 days using the procedure selected on the basis of the results from Study 1. Overall, the most reliable of several summary measures of standing steadiness was observed to be speed of sway.

Adult↗
PubMedDate not supplied

A comparison of standing steadiness measurements from two devices: covariates and normal values.

Quantifying standing steadiness may be a useful method of detecting neurotoxicity in epidemiological studies. Unfortunately, use of quantitative standing steadiness outcomes in epidemiologic studies has been limited by lack of standardization of methods, insufficient availability of normative data, and inadequately characterized effects of covariates. Additionally, the current gold standard method, the force platform (FP), has been expensive and unwieldy for use in field studies. A relatively inexpensive and portable head position monitor (HPM) has been introduced as an alternate method for measuring standing steadiness. In this study 211 subjects were tested with one or both devices using a common testing protocol. The correlations between measurements obtained with the FP and the HPM were high and similar to those obtained during repeated measurements with each device separately. The effects of potential covariates on outcome measures were investigated. There was significant age x sex interaction in the FP standing steadiness measurements in this population with decreased steadiness among older men but not older women. Information for estimating normal values for the outcome measures is provided. This study suggests that measures of standing steadiness obtained with the HPM are similar, but not identical, to measures obtained with a conventional FP and that the HPM may be useful in field studies of occupational exposure to neurotoxicants.

Adolescent↗
PubMedDate not supplied

Validation of the NES2 in patients with neurologic disorders.

Performance on the Neurobehavioral Evaluation System (NES) has been demonstrated to be affected by exposure to a variety of neurotoxicants. However, the relation of NES subtests to CNS function has not yet been documented in patients diagnosed with neurologic disorders known to implicate specific brain substrates. A validation study of the NES2 was carried out in patients with multiple sclerosis (MS) and Parkinson's disease (PD), disorders exhibiting neuropathology at loci (white matter in MS, basal ganglia in PD) believed to be the sites of action of several known neurotoxicants. The results indicated that performance on certain NES2 subtests was affected in expected ways in both types of patients. However, performance on many more subtests was impaired, relative to controls, in MS than in PD. The relative insensitivity to PD suggests that expansion and refinement of the battery are required if it is to serve well in detecting the effects of toxicants in subjects without frank physical symptoms. These are the goals of a new version of the instrument currently under development (NES3).

Affect↗
PubMedDate not supplied

A comparison of NES2 and traditional neuropsychological tests in a neurologic patient sample.

The Neurobehavioral Evaluation System (NES), a computer-assisted battery of behavioral tests, has been widely used to detect central nervous system dysfunction in occupational and environmental settings and has recently been adapted for testing of neurological patients. The purpose of the present study was to assess the relationship between NES tasks and the traditional neuropsychological tests from which many of the NES tests were developed. For this purpose, comparisons were made between scores on NES tests and traditional neuropsychological tests designed to measure functioning in the same cognitive domains in a sample of patients with idiopathic Parkinson's disease (PD). As has been found in prior studies with normal subjects, correlations between traditional and NES2 tests varied from low to moderate. Correlations tended to be low when the modality of stimulus presentation or responses was different in the NES tests from the traditional tasks (e.g., verbal rather than visual) or when divergent and highly specific cognitive functions were being measured by the tests.

Adult↗
PubMedDate not supplied

NES test performance in a large US Army veteran sample: relationships with both demographic factors and traditional neuropsychological measures.

A large sample of Vietnam-era US Army veterans completed a set of 16 neuropsychological tests, including six computer-based tests from the Neurobehavioral Evaluation System (NES), during medical examinations supervised by the US Centers for Disease Control (CDC). Data for 881 participants of the Agent Orange Validation Study (AOV) and Vietnam Experience Study (VES) were available for analysis from public access data tapes provided by CDC. Information was available for several potential covariates from demographic questionnaires, a medical examination, and a medical history. Explorator, principal components factor analysis of 16 test variables yielded four factors, including one on which most of the NES tests loaded. The single best predictor of most neuropsychological performance variables was an index of general intellectual level as measured at entry into the Army almost 20 years before the neuropsychological examinations. Alcohol drinking variables were not related to neuropsychological performance. Several measures of general intelligence were compared for use as covariates of neuropsychological test performance. All were superior to years of education in statistically controlling for general intellectual level.

Adult↗
PubMedDate not supplied

Feasibility and validity of three computer-assisted neurobehavioral tests in 7-year-old children.

Three tests from the computerized Neurobehavioral Examination System (NES) were administered to a group of 917 Faroese children at approximately 7 years of age. The NES Continuous Performance Test (CPT) was modified to use animal silhouettes as stimuli instead of letters. Almost all children completed Finger Tapping (FT), the modified CPT, and Hand-Eye Coordination (HE). However, 18% of the children missed at least 25% of the stimuli on the CPT (full test period), and 37% of the children did not improve their HE performance by at least 10%, as compared to the first trial. Boys obtained better results than girls, and older children performed better than younger ones. However, both factors were confounded by acquaintance with computer games. Children who used glasses, who had strabismus, or who had decreased contrast sensitivity obtained less satisfactory scores, especially on CPT and HE. The NES performance was significantly associated with functional neurological performance, including catching a ball, diadochokinesia, and finger agnosia. Slight, though statistically significant, decrements were seen with increased levels of prenatal exposure to neurotoxicants, as indicated by the mercury concentrations in cord blood obtained at the time of birth. In conclusion, the tests were feasible in this age group after slight modifications, and the test results showed meaningful associations with major predictors, thus supporting the validity of the data.

Adolescent↗
PubMedDate not supplied

Development of a computer-based battery designed to screen adults for neuropsychological impairment.

The initial step in the development of a new computer-based neuropsychological testing system is described. A new hardware-software system and a screening battery consisting of an orientation task and five cognitive tests has been implemented. This novel screening battery is designed for use in identifying individuals among exposed groups who may require more extensive follow-up neuropsychological evaluation. Sophisticated, but currently available, and relatively inexpensive hardware and software technology are employed, introducing an improvement over existing computer-based batteries. Use of a digitized speech production device for producing instructions facilitates testing of illiterate subjects, use of auditory stimulus materials, and relatively easy translation of the testing instructions to other languages. Use of a pen-based notebook computer enables responding by the subject in a manner that is both natural and analogous to that used in existing paper-and-pencil testing instruments. Five neuropsychological tests were developed to cover a range of cognitive domains: 1) verbal list learning and recognition memory, 2) visual memory span, 3) conceptual and motor tracking, 4) psychomotor speed and accuracy, and 5) delayed verbal recognition. The screening instrument has been pilot-tested for feasibility of use among outpatients at an occupational medicine clinic and among community-dwelling older adults. This instrument is intended to provide a standardized efficient, cost-effective method for widespread use in occupational medicine and public health to detect and track subclinical neurotoxic effects and to prevent additional harmful exposure. Additional aspects of development of the computer-based testing system are discussed.

Adult↗
PubMedDate not supplied

Symposium on computerized behavioral testing of humans in neurotoxicology research: overview of the proceedings.

The Symposium on Computerized Behavioral Testing of Humans in Neurotoxicology Research, held in Portland, OR (USA), on June 21-23, 1995, is the subject of the 23 articles in this issue of Neurotoxicology and Teratology. It is the first open forum to focus exclusively on computer-implemented behavioral test methods for neurotoxicology. Both the Symposium and this proceedings have been organized around the topics: new technologies and new batteries, confounders and methodologic factors, special populations (children), sensory and motor testing, clinical applications, and neurotoxicology research. The Symposium emphasized common approaches to computerized testing, highlighted fundamental differences in strategies for the selection of tests, and produced tangible evidence that the NES2 test battery has become a pervasively used instrument for presenting valid tests in human neurotoxicology research. However, the dominant impression drawn from the Symposium is that there is a methodologic vigor in the field of computerized behavioral testing. This is revealed by the appearance of new test batteries, criticism of existing procedures, challenges to the existing order of test selection, and the identification of analytic covariates for commonly used tests.

Behavior↗