Biomedical subjects

H K Hudnell

Publications and source records attributed to H K Hudnell.

At least 19 recordsLinked to original sources

PubMed2001

Human visual function in the North Carolina clinical study on possible estuary-associated syndrome.

The U.S. Environmental Protection Agency assisted the North Carolina Department of Health and Human Services in conducting a study to investigate the potential for an association between fish kills in the North Carolina estuary system and the risk for persistent health effects. Impetus for the study was recent evidence suggesting that estuarine dinoflagellates, including members of the toxic Pfiesteria complex (TPC), P. piscicida and P. schumwayae, may release a toxin(s) that kills fish and adversely affects human health. This report describes one component of the study in which visual system function was assessed. Participants working primarily in estuaries inhabited by TPC or in off-shore waters thought not to contain TPC were studied. The potentially exposed estuary (n = 22) and unexposed offshore (n = 20) workers were matched for age, gender, and education. Visual acuity did not differ significantly between the cohorts, but visual contrast sensitivity (VCS), an indicator of visual pattern-detection ability for stimuli of various sizes, was significantly reduced by about 30% in the estuary relative to the offshore cohort. A further analysis that excluded participants having a history possibly predictive of neuropsychological impairment showed a similar VCS reduction. Additional analyses indicated that differences between the cohorts in age, education, smoking, alcohol consumption, and total time spent on any water did not account for the difference in VCS. Exploratory analyses suggested a possible association between the magnitude of VCS reduction and hours spent in contact with a fish kill. The profile of VCS deficit across stimulus sizes resembled that seen in organic solvent-exposed workers, but an assessment of occupational solvent, and other neurotoxicant, exposures did not indicate differences between the cohorts. These results suggest that factor(s) associated with the North Carolina estuaries, including the possibility of exposure to TPC toxin(s), may impair visual system function.

Analysis of Variance↗

PubMed2001

Possible estuary-associated syndrome: symptoms, vision, and treatment.

The human illness designated as possible estuarine-associated syndrome (PEAS) by the Centers for Disease Control and Prevention (CDC) has been associated with exposure to estuaries inhabited by toxin-forming dinoflagellates, including members of the fish-killing toxic Pfiesteria complex (TPC), Pfiesteria piscicida and Pfiesteria shumwayae. Humans may be exposed through direct contact with estuarine water or by inhalation of aerosolized or volatilized toxin(s). The five cases reported here demonstrate the full spectrum of symptoms experienced during acute and chronic stages of this suspected neurotoxin-mediated illness. The nonspecific symptoms most commonly reported are cough, secretory diarrhea, headache, fatigue, memory impairment, rash, difficulty in concentrating, light sensitivity, burning skin upon water contact, muscle ache, and abdominal pain. Less frequently encountered symptoms are upper airway obstruction, shortness of breath, confusion, red or tearing eyes, weakness, and vertigo. Some patients experience as few as four of these symptoms. The discovery that an indicator of visual pattern-detection ability, visual contrast sensitivity (VCS), is sharply reduced in affected individuals has provided an objective indicator that is useful in diagnosing and monitoring PEAS. VCS deficits are present in both acute and chronic PEAS, and VCS recovers during cholestyramine treatment coincident with symptom abatement. Although PEAS cannot yet be definitively associated with TPC exposure, resolution with cholestyramine treatment suggests a neurotoxin-mediated illness.

Adult↗

PubMed1997

Agonistic sensory effects of airborne chemicals in mixtures: odor, nasal pungency, and eye irritation.

Thresholds responses of odor, nasal pungency (irritation), and eye irritation were measured for single chemicals (1-propanol, 1-hexanol, ethyl acetate, heptyl acetate, 2-pentanone, 2-heptanone, toluene, ethyl benzene, and propyl benzene) and mixtures of them (two three-component mixtures, two six-component mixtures, and one nine-component mixture). Nasal pungency was measured in subjects lacking a functional sense of smell (i.e., anosmics) to avoid interference from olfaction. Various degrees of stimulus agonism (additive effects) were observed for each of the three sensory channels when testing mixtures. As the number of components and the lipophilicity of such components in the mixtures decreased, so did the degree of agonism. Synergistic stimulus agonism characterized the eye-irritation response for the most complex (the nine-component) and the most lipophilic (one of the six-component) mixtures. Physicochemical properties play a large role in the determination of sensitivity to airborne chemicals, particularly to their ability to evoke irritation. While this has revealed itself previously with respect to single chemicals, it seems to have relevance to mixtures as well.

Adult↗

PubMed1996

Frequency-domain measurement of vibrotactile driving responses in first-order afferent populations.

Surface recordings made at the wrist during moderate vibrotactile stimulation of a digit display rhythmic activity at the frequency of the driving stimulus. This activity is abolished by local anesthesia of the stimulated digit and by substitution of the corresponding digit of the opposite hand with the recording geometry and the load on the stimulator unchanged. Several additional features of the response are similarly incompatible with an artifactual origin in properties of the stimulus motion or the associated electromagnetic field, but consistent with previous neurophysiological observations. The frequency-domain analysis extends readily to the single-trial level, making the technique potentially useful for a variety of basic research and clinical purposes.

Adult↗

PubMed1995

Work-site clinical and neurobehavioral assessment of solvent-exposed microelectronics workers.

Twenty-five workers, five currently and 20 formerly involved in the manufacture of hybrid microcircuits, underwent clinical evaluations at the request of a management-union committee concerned about chronic solvent exposures in a research and development laboratory. A battery of neurobehavioral tests was administered to compare the solvent-exposed group with 32 age-, gender-, ethnicity-, and education-matched controls. The tests included: MMPI-I, hand grip strength, tactile sensitivity, dexterity, color discrimination, visual acuity and contrast sensitivity, and tests selected from the computerized Neurobehavioral Evaluation System (NES2). Clinical narratives and retrospective exposure assessments in the study group suggested chronic low-level exposure to solvents, with intermittent acute excursions. Work-related diagnoses included upper respiratory mucosal irritation and sinusitis (44%), lower respiratory reactive airway disease (12%), and dermatitis (5%). Three workers (12%) had findings consistent with a solvent-induced encephalopathy. Significant differences (after Bonferroni correction) were found between the two groups on 5 of 11 NES subtests: symptom scale, mood scale, finger tapping, simple reaction time, and symbol-digit substitution. Differences also reached significance for overall vibration sensitivity thresholds, visual contrast sensitivity, and grip strength. The MMPI average clinical scale elevation was significantly higher in the exposed group than controls. These results support an association between chronic low-dose solvent exposure and measurable neurobehavioral changes.

Adult↗

PubMed1993

The use of visual and chemosensory evoked potentials in environmental and occupational health.

The application of visual (VEP) and chemosensory evoked potentials (CSEP) in occupational and environmental health is briefly reviewed. VEPs have been used extensively in experimental neurotoxicity and play an increasingly important role in human neurotoxicity testing. The similarity of VEP waveforms in different species renders them useful for cross-species extrapolation. CSEPs, used in conjunction with traditional psychophysical tests and rating scales, offer a promising new approach to the study of indoor air pollution.

Animals↗

PubMed1991

The comparability of rat and human visual-evoked potentials.

A series of experiments addressed the issue of comparability among neurological processes in pigmented rat and human visual systems. In the first set of experiments, transient visual-evoked potentials (VEPs) were elicited by the onset of sine-wave gratings of various spatial frequencies. The spatial frequency-response profiles of the first positive and immediately succeeding negative components differed from one another, but were similar in the two species. In addition, amplitude of the negative, but not the positive, component was strongly attenuated in both species following stationary pattern adaptation. In the second set of experiments, steady-state VEPs were elicited by the onset and offset of the gratings. The spatial frequency profiles of the 1F (response amplitude at the frequency of stimulus onset-offset) and 2F response components differed from one another, but were similar in both species. The final set of experiments indicated that diazepam, a GABA agonist, reduced amplitude of 2F, but not 1F, in both species. These results suggested that at least some functional subsystems mediating spatial vision in humans may have qualitatively similar counterparts in rats.

Adaptation, Ocular↗

PubMed1991

Quantitative methods for cross-species mapping (CSM).

Cross-species extrapolation will be defined as prediction from one species to another without empirical vetification. Cross-species mapping (CSM) is the same except empirical vetification is performed. CSM may be viewed as validation of methods for extrapolation. Algorithms for CSM may originate from theory, from empirical observations or a combination of the two. Regardless of their origins, CSM algorithms must be explicated and confidence intervals given around their predictions. This paper offers a quantitative method for constructing CSM equations which is useful in evaluation of the CSM and as an aid in the design of new experiments in CSM and extrapolation. The method requires fitting mathematical models for the physiological or behavioral phenomena to be mapped across species. A CSM equation can then be derived from the models in each species and approximate confidence limits may be obtained for predictions from the equation. The method is useful even when the models in the two species differ in form, implying differences in physiology or behavioral principles between species. The method proposed has a number of remaining uncertainties and possible problems.

Animals↗

PubMedDate not supplied

Stationary pattern adaptation and the early components in human visual evoked potentials.

Pattern-onset visual evoked potentials were elicited from humans by sinusoidal gratings of 0.5, 1, 2 and 4 cpd (cycles/degree) following adaptation to a blank field or one of the gratings. The wave forms recorded after blank field adaptation showed an early positive component, P0, which decreased in amplitude with spatial frequency, whereas the immediately succeeding negative component, N1, increased in amplitude with spatial frequency. P0 and N1 components of comparable size were recorded at 1 cpd. Stationary pattern adaptation to a grating of the same spatial frequency as the test grating significantly reduced N1 amplitude at 4, 2 and 1 cpd. The N1 component elicited at 4 cpd was attenuated in log-linear fashion as the spatial frequency of the adaptation grating increased. P0, on the other hand, was unaffected by stationary pattern adaptation at all combinations of test and adapting spatial frequencies, although P0 amplitude is known to be attenuated by adaptation to a drifting grating. Since N1, but not P0, was significantly attenuated following adaptation and testing at 1 cpd, it was concluded that the neurons generating these components are functionally distinct. The use of a common adaptation grating discounted the possibility that N1, but not P0, was affected due to a difference in the rates of retinal image modulation caused by eye movements made while viewing adaptation gratings of different spatial frequencies. The neurons generating N1 were adapted at a lower rate of retinal image modulation than that apparently required for adaptation of the neurons generating P0, which suggests a difference between these neurons in the rate of stimulus modulation necessary for activation.

Adaptation, Ocular↗

PubMedDate not supplied

Carbon monoxide exposure and human visual detection thresholds.

In order to test for CO exposure effects on vision, a battery of visual tests was administered to male college students. All subjects completed the battery of tests both before and during an exposure period in a double-blind study. Experimental subjects received CO during the exposure period, whereas control subjects received only room air. The battery of visual tests was designed for the assessment of scotopic (dark adapted, rod mediated) detection, photopic (light adapted, cone mediated) detection, the pattern detection process and the motion detection process. Contrast thresholds for the detection of stimulus pattern and for the detection of stimulus motion were measured under both photopic and scotopic viewing conditions, and sensitivity was monitored throughout the course of dark adaptation by measuring luminance thresholds. The results indicated that visual function in healthy, young-adult males was not affected by a COHb level of about 17% which was maintained for over 2 hours.

Adaptation, Physiological↗

PubMedDate not supplied

Rat and human visual-evoked potentials recorded under comparable conditions: a preliminary analysis to address the issue of predicting human neurotoxic effects from rat data.

Pattern-onset visual-evoked potentials (VEPs) were recorded from rats and humans in order to perform cross-species comparison of neuronal functional properties reflected by the early VEP components. The spatial frequency of a sinusoidal test grating was varied in Experiment 1. For both species, amplitude of the first positive VEP component was larger at low spatial frequency and decreased as spatial frequency increased. The immediately succeeding negative component was small at low spatial frequency and was of maximal amplitude at moderate spatial frequency. The effects of stationary pattern adaptation on these components were investigated in Experiment 2. Subjects viewed either a blank field or the test grating prior to recording VEPs. For both species, adaptation had no effect on the positive component but strongly attenuated the negative component. Experiment 3, in which only humans were tested, indicated that the negative component was of cortical origin. Only cortical neurons are known to be orientation selective, and the effect of adaptation diminished as the orientation difference between the adaptation and test gratings increased. These results suggest that the early positive and negative components arise from parallel visual pathways, and that the rat components may reflect visual processes qualitatively similar to those of humans.

Adaptation, Physiological↗

PubMedDate not supplied

Neurobehavioral and sensory irritant effects of controlled exposure to a complex mixture of volatile organic compounds.

Subjective reactions of discomfort, impaired air quality, irritation of mucosal membranes, and impaired memory have been reported in chemically sensitive subjects during exposure to volatile organic compounds (VOCs) found in new buildings. Sixty-six normal healthy male subjects aged 18-39 were exposed for 2.75 hr to a complex VOC mixture at 0 and 25 mg/m3. Each subject completed control and exposure sessions at one-week intervals in counterbalanced order. Measurements included comfort ratings of eye, nose and throat irritation, symptom questionnaire and computerized behavioral tests. Subjects found the odor of VOCs unpleasantly strong and reported that VOC exposure degraded air quality, increased headache and produced general discomfort. VOC exposure did not affect performance on any behavioral tests.

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

Neurobehavioral Evaluation System (NES): comparative performance of 2nd-, 4th-, and 8th-grade Czech children.

The Neurobehavioral Evaluation System was designed for field studies of workers, but many NES tests can be performed satisfactorily by children as young as 7 or 8 years old and a few tests, such as simple reaction time, can be performed by preschool children. However, little comparative data from children of different ages or grade levels are available. Studies of school children in the Czech Republic indicate that 2nd-grade children could perform the following NES tests satisfactorily: Finger Tapping, Visual Digit Span. Continuous Performance, Symbol-Digit Substitution, Pattern Comparison, and simpler conditions of Switching Attention. Comparative scores of boys and girls from the 2nd, 4th, and 8th grades and power analyses to estimate appropriate sample size were presented. Performance varied systematically with grade level and gender. Larger samples were needed with younger children to achieve comparable levels of statistical power. Gender comparisons indicated that boys responded faster, but made more errors than girls.

Adolescent↗

PubMedDate not supplied

The influence of vision on computerized neurobehavioral test scores: a proposal for improving test protocols.

Computerized tests of neurobehavioral function are frequently administered in neurotoxicological studies with little attention given to the optical properties of test stimuli or to the vision of subjects. Yet many test stimuli are small or briefly presented, and test endpoints often involve short reaction times. Stimulus detection and reaction time are known to be strongly dependent upon stimulus luminance, contrast, and size, as well as on the subject's visual abilities. The current study assessed the influence of visual contrast sensitivity on Neurobehavioral Evaluation System 2 (NES2) test results in three data sets. Analyses indicated that vision was associated with up to 24% of the variance (Hand Eye Coordination test) in NES2 scores, even when visual acuity was normal, and that vision often influenced the significance of group differences. It is suggested that researchers measure the luminance, contrast, and size of test stimuli, the distance from the subject's eyes to the monitor, and the subject's visual contrast sensitivity. The measurement and control of stimulus parameters and the inclusion of visual function scores in analysis models could reduce the variability among computerized test scores both within and between studies. Models that assess the influence of vision on computerized test results may help to identify the CNS domains and specialized functions adversely affected by neurotoxicant exposures.

Adolescent↗

PubMedDate not supplied

Critical issues in the use and analysis of the Lanthony Desaturate Color Vision test.

The Lanthony Desaturate Color Vision test (D-15d) has been used to demonstrate the incidence of acquired color vision defects resulting from toxic exposure. The D-15d is a sensitive test designed to grade color deficiencies, but results can be difficult to interpret beyond the qualitative level, and the high incidence of errors reported for controls in some toxicology studies raises questions about how to effectively use this test. This article reviews standard administration of the test, physical determinants of performance, classification of acquired color vision defects, and methods of analysis that have been used to quantify results. The basis for a new method of analysis is discussed, illustrating the source of some characteristic errors, and recommendations are made for test protocols to attempt to more closely identify the type of color vision loss with the goal of identifying the site of toxicological insult.

Color Perception↗

PubMedDate not supplied

Exposure of humans to a volatile organic mixture. I. Behavioral assessment.

Exposure to a low-level mixture of volatile organic compounds, typical of those found in new buildings, has been reported to impair neurobehavioral function in persons who have experienced sick building syndrome (SBS). Sixty-six healthy young males who had no history of chemical sensitivity were exposed for 2.75 h to a complex mixture of volatile organic compounds at 0 and 25 mg/m3. Even though subjects reported more fatigue and more mental confusion following exposure to volatile organic compounds than to clean air, performance on 13 neurobehavioral tests was not affected. Practice or learning effects were observed if administration of many behavioral tests were repeated. Further studies are needed to clarify the relationship of exposure to volatile organic chemicals, neurobehavioral performance, and subject characteristics, e.g., age, gender, and chemical sensitivity.

Adolescent↗

PubMedDate not supplied

Exposure of humans to a volatile organic mixture. II. Sensory.

Time-course functions for symptoms of the sick building syndrome were derived from 66 healthy males who, during separate sessions, were exposed to clean air and to a volatile organic compound (VOC) mixture. The mixture contained 22 VOCs (25 mg/m3 total concentration) commonly found airborne in new or recently renovated buildings. Subjects rated the intensity of perceived irritation, odor, and other variables before, and twice during, 2.75-h exposure periods. Eye and throat irritation, headache, and drowsiness increased or showed no evidence of adaptation during exposure, whereas odor intensity decreased by 30%. These results indicate that irritation intensity and other symptoms are not related in any simple way to odor intensity, which suggests that the symptoms may not be a psychosomatic response to the detection of an aversive odor. Instead, subthreshold levels of VOCs may interact additively or hyperadditively and stimulate trigeminal nerve receptors. Also, air quality ratings improved by 18% during exposure, which suggests that both odor and irritation intensity may influence assessments of air quality.

Adolescent↗