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Biomedical subjects

R Letz

Publications and source records attributed to R Letz.

At least 19 recordsLinked to original sources
PubMed1994

Heterogeneity of effects of ethanol ingestion on postural stability as measured by two devices.

Measurement of postural stability has been used to assess effects of exposure to selected neurotoxicants. Its widespread application has been limited by several factors, including the use of cumbersome, expensive measurement systems and limited demonstration of sensitivity for detecting neurotoxicity. Recently, a less expensive, portable device for assessing postural stability via measurement of head position has been developed and used in some field studies. Although this head position monitor (HPM) is commercially available, no validation information for it has been published. To evaluate the HPM's utility, it was compared to a force platform (FP) system in an ethanol experiment. Ten adult male subjects were given 0.5 ml/kg ethanol and placebo using a counterbalanced, cross-over design. Stability measurements were made immediately prior to administration of alcohol or placebo and at fifteen minute intervals for two hours following administration. At each time interval, stability was monitored during two eyes-open trials alternated with two eyes-closed trials, each of 60-second duration. On a group basis, marginally significant effects of alcohol consumption consistent with results of other published studies were observed with both devices. The maximum increase in speed of sway occurred at 15 minutes post-ethanol ingestion for the eyes-closed condition. Specifically, sway speed increased from 1.11 cm/sec pre-ingestion to 1.50 cm/sec 15 minutes post-ingestion for the HPM, and from 1.81 m/sec to 2.13 cm/sec for the FP. No significant increase in sway speed was observed for the eyes-open condition. These groups differences obscured substantial heterogeneity of response to ethanol among the ten subjects, i.e., only two of the 10 subjects showed an observable increase in sway speed following ethanol ingestion.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

A cross sectional epidemiological survey of shipyard workers exposed to hand-arm vibration.

The hand-arm vibration syndrome, widely known as vibration white finger, is a disorder of nerves and blood vessels that occurs in workers exposed to segmental vibration. A cross sectional symptom survey was performed on a sample of workers employed by a large shipyard in the north eastern United States. Random samples were drawn from departments composed of full time dedicated pneumatic grinders, workers with part time exposure to vibration, and other workers not exposed to vibratory tools. Of the 375 workers sampled, 79% responded. The prevalence of white finger symptoms was 71%, 33%, and 6% among the three exposure groups respectively. Similarly, the prevalence of numbness and tingling in the hands and fingers in the three exposure groups was 84%, 50%, and 17%. Workers were classified according to the Stockholm Workshop staging systems for vascular and sensorineural symptom severity. Exposure-response analyses of both vascular and sensorineural stage showed monotonically increasing prevalence of higher disease stages with increasing duration of exposure. Logistic regression analysis, performed to control for potential confounding factors including age and current smoking state, produced highly significant (p less than 0.001) associations between cumulative duration of exposure and prevalence of symptoms. In these analyses smoking state was significantly related to vascular and sensorineural symptoms and age was not. Average latency to onset of symptoms was less than five years of full time equivalent work with vibratory tools. Logistic regression analyses were performed to assess the effect of use of particular work practices on reported symptoms. Further study of this workforce with objective, quantitative measures of peripheral neurological and vascular function is required to characterise the clinical and subclinical effects of vibration exposure.

Cross-Sectional Studies↗
PubMed1991

Quantitative neurologic and neurobehavioral testing of persons infected with human immunodeficiency virus type 1.

Assessment of neurobehavioral and peripheral neurologic performance among homosexual men was made on two occasions, using a computer-administered neurobehavioral instrument and quantitative vibration threshold testing, respectively. Persons studied included high-risk human immunodeficiency virus (HIV)-negative men (n = 13), asymptomatic HIV-positive men (n = 30), and patients with acquired immunodeficiency syndrome (AIDS)-related complex of AIDS (n = 17). In addition, subjects were characterized immunologically at the time of neurologic and neuropsychologic assessment via determination of circulating lymphocyte counts (total lymphocytes, helper T cells, suppressor T cells, total T cells, activated T cells) and markers of HIV type 1 (HIV-1) infection. At the first cycle of testing, the results of asymptomatic HIV-positive men were indistinguishable from those of HIV-negative men, while persons with AIDS-related complex or AIDS tended to have lower mean performance. These differences did not achieve statistical significance on any single test, but the group with AIDS-related complex or AIDS had the worst mean performance on 12 of 13 individual performance tests. Thirty-seven men underwent repeated testing after a mean interval of approximately 4.5 months. There was little change in mean neurobehavioral performance and vibratory thresholds among all three groups. Measures of neurobehavioral performance and vibrotactile thresholds were not correlated with measures of immunological status. These results are consistent with the concept that asymptomatic infection with HIV-1 does not imply the presence of measurable or significant neurologic or neurobehavioral impairment.

AIDS-Related Complex↗
PubMed1991

Comparison of vibrotactile thresholds with physical examination and electrophysiological assessment.

Measurement of cutaneous vibrotactile thresholds may be useful for assessment of the functional integrity of the somatosensory system. To validate a rapid method of determining vibrotactile thresholds that uses a commercially available electromechanical device, vibrotactile thresholds were compared with standardized physical examination findings of sensory function and electrophysiological parameters in 79 patients referred to the Mount Sinai Hospital Neurophysiology Laboratory for clinical electrophysiological evaluation. A statistically significant monotonic association between graded physical examination of vibration perception and vibrotactile threshold was observed for all digits tested in the upper and lower extremities. Statistically significant associations were also observed between vibrotactile thresholds and a variety of electrophysiological measures of the median, ulnar, tibial, peroneal, and sural nerves. The strongest associations were observed between great toe vibrotactile thresholds and late response latencies measured in nerves in the lower extremities. Determination of vibrotactile thresholds may be useful in settings where quantitative measures of large fiber nerve function are desirable and electrophysiological study is not feasible.

Action Potentials↗
PubMed1991

Neurobehavioral effects of the on-call experience in housestaff physicians.

Sixty-tree medical residents were tested on a battery of computer-based, self-administered neurobehavioral tests before and after a 36-hour in-hospital call plus postcall day to assess the central nervous system effects of the call experience and its accompanying sleep deprivation. Statistically significant decreases in performance were found postcall on tests of sustained visual attention (P less than 0.0001), speed and coding ability (P less than 0.0001) and short-term recall (P less than 0.0001). Hand-eye coordination improved (P less than 0.02).

Humans↗
PubMed1991

Upper-extremity musculoskeletal disorders of occupational origin.

Sufficient evidence is available at this time to conclude that several well-defined soft-tissue disorders of the upper extremities are etiologically related to occupational factors. These disorders include tendinitis of the hand and wrist, CTS, and hand-arm vibration syndrome. Force, repetition, and vibration have been established as risk factors in the etiology of these disorders. Evidence exists that other, poorly understood factors also may contribute to etiology. At this time no firm guidelines can be established regarding maximum no-effect exposure levels. We agree, however, with Armstrong (3): "Although there are no standards for excessively repetitive or forceful work, common sense dictates that these tasks be minimized to the extent possible." Tool and job redesign may be required in many situations to accomplish these goals. In addition to appropriate reductions in risk factors, medical surveillance is required and will allow greater appreciation of the extent of this growing problem, as well as ongoing assessment of the efficacy of preventive intervention.

Arm↗
PubMed1991

Use of computerized test batteries for quantifying neurobehavioral outcomes.

Neurobehavioral testing provides for noninvasive assessment of the functional integrity of the nervous system. Neurobehavioral tests have been used as quantitative outcome measures in a number of epidemiologic investigations of the potential effects on the nervous system from exposure to organic solvents, heavy metals, and pesticides. Because of the functional complexity of the nervous system, sets of tests assessing a range of functions have been used, with inconsistency from one study to another. Although there has been recent progress in standardizing a core set of tests for use in occupational epidemiology, major consensus on testing methods has not emerged. Standardization of test methods is essential to provide a consistent database for risk analysis. Automation of data collection provides not only standardization, but also improved time efficiency, of data collection and analysis. The computerized Neurobehavioral Evaluation System (NES) has been developed to address the need for standardized, efficient data acquisition of a range of neurobehavioral variables. Examples of application of NES in epidemiologic studies of workers exposed to solvents are summarized. The need for use of NES as a tool for surveillance and in prospective epidemiologic investigations is emphasized.

Behavior↗
PubMed1990

Sister-chromatid exchanges in lymphocytes from styrene-exposed boat builders.

Sister-chromatid exchanges (SCE) were measured in peripheral blood lymphocytes from 40 workers in the boat-building trade. Twenty of these workers were exposed to significant amounts of styrene. The mean air concentration of styrene in the breathing zone of the boat builders was 209 mg/m3 in the 7 exposed current smokers and 230 mg/m3 in the 13 exposed non-smokers. Urinary styrene metabolites were also measured and the mean mandelic acid/creatinine ratios in the exposed, smokers was 275 mg/g, and in the exposed, non-smokers 323 mg/g. The SCE frequency in lymphocytes from the styrene-exposed group did not differ from that in the controls, although smoking significantly induced SCE in these workers.

Adult↗
PubMed1990

Detailed clinical assessment of neurological function in symptomatic shipyard workers.

Forty eight patients with extensive occupational exposure to pneumatic grinding tools were evaluated at a university sponsored occupational health clinic. All patients were interviewed and examined by a physician and assessed neurologically with standard clinical, functional motor, quantitative vibrotactile, and electrodiagnostic tests. Sensorineural symptoms were nearly universal; 47 patients (98%) reported numbness and tingling of the hands and fingers. Among clinical tests, two point discrimination and 30 Hz vibration perception were most frequently abnormal. In order to evaluate associations between quantitative test results and sensorineural symptoms, patients were stratified into two groups of symptom severity according to a consensus sensorineural staging system. The tests that discriminated best between the groups of more and less symptomatic patients were hand strength dynamometry, and vibrotactile thresholds. Age standardised 120 Hz vibrotactile thresholds were significantly raised in digit II in 41% of hand measurements. Nerve conduction studies were neither significantly different between more and less symptomatic groups nor correlated with clinical and quantitative sensory tests. Twenty five per cent of the patients had slowing of sensory conduction velocities in the median nerve at the wrist (less than 48 m/s). Of this subset of patients only two showed abnormal slowing of the median nerve distal to the wrist, but half also showed ulnar nerve slowing (less than 47 m/s). This observation highlights the difficulty of differentiating median nerve entrapment from diffuse distal neuropathy in workers exposed to vibration and points to the need for concomitant quantitative sensory and functional motor assessment.

Adult↗
PubMed1989

Sensory thresholds among construction trade painters: a cross-sectional study using new methods for measuring temperature and vibration sensitivity.

Instruments that measure quantitatively sensory threshold to vibration and temperature difference were used to test 93 construction trade painters and a reference group of 105 healthy construction and industrial workers who were not painters. A "forced-choice" testing procedure, and an algorithm for threshold estimation (the "Best PEST"), was used for the Temperature Sensitivity Tester and the Vibratron. The method of limits procedure was used for the Biothesiometer. When measured with the Vibratron, painters in the older age stratum were found to have significantly higher vibration thresholds than the reference group. Painters had significantly more temperature sensitivity thresholds classified as "high" than the reference group. Among painters, exposure intensity and cumulative exposure over the past year was positively associated with vibration thresholds estimated using the Vibratron. Lifetime cumulative exposure, cumulative exposure over the previous month, and exposure intensity were positively associated with vibration thresholds estimated using the Biothesiometer.

Adult↗
PubMed1988

Occupational screening for neurotoxicity: computerized techniques.

Computer-administered testing systems for assessing the functional consequences of neurotoxicant exposure in the workplace have recently been developed. Mainly, they have been applied in laboratory studies of acute exposures, quasi-experimental field studies of acute and sub-acute exposures, and cross-sectional epidemiologic investigations of chronic exposures. Some automated tests appear quite sensitive and reliable in these situations where group comparisons are made. However, testing methods suitable for the purpose of clinical evaluation are not yet well developed. Programs of neurobehavioral surveillance in industry are necessary to provide reference data for clinical, screening and epidemiologic purposes and to provide essential baseline data for individuals at risk.

Electronic Data Processing↗
PubMed1988

Experimental nitrous oxide exposure as a model system for evaluating neurobehavioral tests.

A recent study reported that a minimally suprathreshold dose of 20% nitrous oxide significantly affected performance on 3 of 9 computer-administered neurobehavioral tests. Performance decrements were observed in that study on 3 tests of psychomotor speed while other neurobehavioral functions such as visuospatial ability, verbal learning and mood were not significantly affected. The current study was undertaken to assess the reproducibility of these earlier results. Its experimental design was expanded to include an additional dose of the anesthetic and a more complex reaction time task implemented by the authors since the earlier study. Fifteen males aged 24-34 years were tested with the Neurobehavioral Evaluation System (NES) test battery on 4 separate occasions. An initial training session was followed by randomly presented control, 20%, and 40% drug sessions. Drug-induced decrements in performance were observed in the current study at the 20% dose for 2 of the 3 tests of psychomotor speed which had shown effects in the earlier study, and average decrement in performance on the third approached statistical significance in the current study (P = 0.055). Performance on a complex reaction time task was significantly affected at the low dose. The higher dose of nitrous oxide impaired performance on 8 of the 9 tests administered, and impairment on the ninth test was nearly significant (P = 0.055). Overall, these data are consistent with those in the previous study and with other reports that higher doses of nitrous oxide produce impairments in more cognitive CNS functions. Owing to its relative safety at low dosages, ease of administration, and ready acceptance by experimental subjects, nitrous oxide appears to be a useful model for evaluating the validity of neurobehavioral tests.

Adult↗
PubMed1988

The P-300 event-related potential in experimental nitrous oxide exposure.

Without the availability of objective measures of central neurologic dysfunction, neuroepidemiologic investigations of individuals exposed to psychoactive drugs and potential environmental and occupational neurotoxins are extraordinarily difficult, particularly when the central nervous system manifestations are subtle, diffuse, and limited to cognitive deficits. In an attempt to assess and quantitate psychomotor dysfunction, P-300 event-related potentials, Symbol Digit Test, Continuous Performance Test, and Finger Tapping Test were obtained from six subjects sequentially exposed to nitrous oxide at 0%, 10%, 20%, and 40%. With increasing concentration of N2O, there was prolongation of P-300 latency and worsening of Continuous Performance Test and Symbol Digit Test performance; P-300 amplitude and Finger Tapping Test performance were decreased by exposure to N2O. This study demonstrates a dose-dependent reduction in P-300 amplitude and prolongation of P-300 latency in subjects in whom psychomotor impairment was induced by the acute administration of N2O.

Adult↗
PubMed1988

Reliability of a widely used test of peripheral cutaneous vibration sensitivity and a comparison of two testing protocols.

Quantitative, non-invasive instruments for assessing peripheral sensory function are being used in many epidemiological investigations of workplace hazards. To be useful in this context such tests should have high reliability and short administration time. The reliability and time efficiency of two testing protocols for determining cutaneous vibration sensitivity (vibration threshold) were compared in 22 healthy volunteers. Both methods were administered using a widely used testing device (Vibratron II). The first testing protocol was a two alternative "forced choice" method recommended by the instrument manufacturer. The second protocol was a "yes-no" method of limits procedure. Each subject's dominant index finger was tested with both methods on two occasions to compare their reliability. In these well educated subjects the method of limits procedure was found to be substantially more reliable and was much less time consuming than the recommended forced choice procedure. The simpler method of limits procedure may be preferable to the forced choice method in certain test conditions.

Clinical Protocols↗
PubMed1988

Effects of scopolamine and dextroamphetamine on human performance.

The effects of two drugs used to prevent symptoms of motion sickness in the operational environment were examined in this study of human performance as measured by computer-based tests of cognitive and psychomotor skills. Each subject was exposed repetitively to five tests: Symbol-Digit Substitution, Simple Reaction Time, Pattern Recognition, Digit Span Memory, and Pattern Memory. Although there have been previous reports of decreases in human performance in similar testing with higher dosages of scopolamine or dextroamphetamine, no significant decrements were observed with the operational-level combined dose used in this study (0.4 mg oral scopolamine and 5.0 mg oral dextroamphetamine.) The controversy over the use of combination drug therapy in this environment is discussed along with the indications for further research based on the findings.

Attention↗
PubMed1986

Neurobehavioral testing in monitoring hazardous workplace exposures.

Exposure to workplace toxins, particularly organic solvents, lead, and pesticides, has been shown to cause both transient and persistent derangements of CNS function. Neurobehavioral testing is described as a means of evaluating the health effects of exposure to toxic chemicals. The use of neurobehavioral testing is most appropriate where an exposure has been characterized and the diseases of interest specified. Most investigators use batteries of tests to evaluate psychomotor function, memory, verbal ability, mood, and visual/spatial abilities. Because of the shortcoming of the interviewer-administered test batteries, existing neurobehavioral tests have been adapted to a computer-administered format. This tool offers promise for future efforts to monitor CNS function in exposed workers.

Central Nervous System Diseases↗