Hepatitis B in the rural tropics.

The prevalence of HBSAg in a cross-sectional serosurvey of a rural Thai village was nearly 8%. The corresponding antibody prevalence was approximately 35%. The prevalence of antigenaemia was significantly higher for adult males than for adult females. Possible dynamics of hepatitis B virus transmission in this rural village are explored, but tend to rely on a differential handling of antigenaemia by males and females. A considerable proportion of the hepatitis B virus exposure appears to be associated with malaria prophylaxis programmes.

Chemosuppressive field trials in Thailand. IV. The suppression of Plasmodium falciparum and Plasmodium vivax parasitemias by mefloquine (WR 142,490, A 4-quinolinemethanol).

The effect of various dosages of mefloquine hydrochloride (WR 142,490) and sulfadoxine-pyrimethamine in the suppression of malaria infections was studied in an area of northeastern Thailand highly endemic for both chloroquine-resistant Plasmodium falciparum and for P. vivax. Both preparations, in all regimens studied, were effective in greatly reducing the incidence of falciparum infections. Mefloquine was more active in preventing vivax parasitemia than sulfadoxine-pyrimethamine; however, this combination remains the commercially available regimen of choice where both parasites occur and P. falciparum is resistant to chloroquine.

Mediastinal parathyroid cysts.

BACKGROUND: Mediastinal parathyroid cysts are a relatively rare clinical entity. The clinical presentation can be quite varied, although most are found incidentally during investigations for esophageal or respiratory symptoms. METHODS: We present a review of the literature and describe two instructive cases showing specific clinical findings. The clinical presentation, radiologic and pathologic findings, and treatment of mediastinal parathyroid cysts are discussed. RESULTS: In the first patient, the presenting symptom was increasing hoarseness resulting from paresis of the right recurrent laryngeal nerve. This case illustrates the rare association of a benign mediastinal parathyroid cyst with unilateral vocal cord palsy. The second patient presented with the more classic findings of progressive dyspnea and stridor related to tracheal compression. CONCLUSIONS: Although mediastinal parathyroid cysts are rare and can have varied presentations, thorough investigation can reveal the underlying cyst. Surgical excision is the treatment of choice and can be expected to produce excellent results.

Propranolol for the prevention of postoperative arrhythmias in general thoracic surgery.

BACKGROUND: Prevention of postoperative arrhythmias in patients undergoing general thoracic surgery is desirable to prevent morbidity. METHODS: A randomized, double-blind, placebo controlled trial of propranolol (10 mg every 6 hours) for 5 days was undertaken in patients undergoing major thoracic operations to determine whether arrhythmias requiring treatment could be reduced. Secondary outcomes included overall arrhythmia rate, adverse events, and length of stay. Arrhythmias were assessed by 72-hour Holter monitoring. Patients with a history of heart failure, asthma, advanced heart block, preexisting arrhythmias, sensitivity to propranolol, or use of antiarrhythmic drugs were excluded. RESULTS: Using the intention-to-treat principle there was a 70% relative risk reduction from 20% to 6% in the rate of treated arrhythmias with propranolol (p = 0.071, 95% confidence interval 0.6% to 27.2%). Overall arrhythmias were common but usually benign. Adverse effects were common, although generally mild with hypotension and bradycardia being reported more often in the propranolol group. Length of stay was not different. CONCLUSIONS: There was a trend to a reduction in the risk of perioperative arrhythmias with propranolol. Moreover, propranolol was well tolerated showing a slight increase in minor adverse events.

The use of a whey protein concentrate in the treatment of patients with metastatic carcinoma: a phase I-II clinical study.

Glutathione (GSH) concentration is high in most tumour cells and this may be an important factor in resistance to chemotherapy. Previous in-vitro and animal experiments have shown a differential response of tumour versus normal cells to various cysteine delivery systems. More specifically, an in-vitro assay showed that at concentrations that induce GSH synthesis in normal human cells, a specially prepared whey protein concentrate, Immunocal, caused GSH depletion and inhibition of proliferation in human breast cancer cells. On the basis of this information five patients with metastatic carcinoma of the breast, one of the pancreas and one of the liver were fed 30 grams of this whey protein concentrate daily for six months. In six patients the blood lymphocyte GSH levels were substantially above normal at the outset, reflecting high tumour GSH levels. Two patients (#1, #3) exhibited signs of tumour regression, normalization of haemoglobin and peripheral lymphocyte counts and a sustained drop of lymphocyte GSH levels towards normal. Two patients (#2, #7) showed stabilisation of the tumour, increased haemoglobin levels. In three patients (#4, #5, #6,) the disease progressed with a trend toward higher lymphocyte GSH levels. These results indicate that whey protein concentrate might deplete tumour cells of GSH and render them more vulnerable to chemotherapy.

The use of dose equivalency as a risk assessment index in behavioral neurotoxicology.

This article reports changes with graduated dosage of alcohol on a standardized set of cognitive and psychomotor performance tests and refers to the approach as dose equivalency. Subjects (N = 20) were tested until their performance was stable on 10 tests from a microcomputer test battery. After administration of sufficient alcohol to achieve .15 blood alcohol level (BAL), using breath as the independent variable, the descending branch of the BAL curve was followed by measuring performance at set levels of alcohol. A dose-response relationship was confirmed in all performance tests (p less than .01), and multiple regression was used to select performance subtests that maximally predicted alcohol level. Four subtests were combined into a linear composite that related well to alcohol levels above 0.05 BAL (shrunken R = .75), which was used in a power function to approximate the roughly linear relation above 0.05, as well as the clearly nonlinear function between 0.05 and zero. It is suggested that alcohol, a powerful central nervous system depressant, can be a useful metric in communicating risk in neurotoxicological research.

Eye movement indices of mental workload.

Four investigations were carried out to assess the feasibility of using eye movement measures as indices of mental workload. In the first experiment, saccadic extent was measured during free viewing while subjects performed low, moderate and high complexity, auditory tone counting as the workload tasks. The range of saccadic extent decreased significantly as tone counting complexity (workload) was increased. In the second experiment the range of spontaneous saccades was measured under three levels of counting complexity with a visual task that did not require fixation or tracking. The results indicated that the extent of saccadic eye movements was significantly restricted as counting complexity increased. In the third experiment, the effects of practice were examined and decreased saccadic range under high tone counting complexity was observed even when significant increases in performance occurred with practice. Finally, in experiment 4, the first experiment was repeated with additional optokinetic stimulation and the saccadic range was again observed to decrease with tone counting complexity. The results indicated that the extent of spontaneous and elicited eye movements was significantly restricted as counting complexity increased. We conclude that this measure may provide a valuable index of mental workload.

A method for understanding admission decision making in a psychiatric emergency room.

OBJECTIVE: To increase understanding of decisions about inpatient admission, a four-step algorithm was used to examine 2,073 consecutive visits to a public hospital psychiatric emergency room, 684 of which resulted in admission. METHODS: Admission decision outcomes and patient data were cross-tabulated to identify conditions, or rules, under which outcome was almost certain. Discriminant function models were then made of individual clinicians' decision-making process and of individual diagnostic groups. To understand cases not covered in previous steps, a third discriminant function model was constructed. RESULTS: The four-step method successfully predicted outcomes in 85 percent of cases at a minimum of an 80 percent confidence level. The variables of psychosis and violence combined into the most powerful predictor of admission. Twelve rules that applied to 41.4 percent of all cases were found. Eleven models of individual clinicians' decision policies applied to slightly more half of all cases and successfully classified about 95 percent of them. Eleven models of diagnostic groups applied to 93.2 percent of all cases and correctly predicted about 75 percent. The final discriminant model for the 171 cases not covered by the by the first three steps correctly classified about 90 percent of residual cass. CONCLUSIONS: Psychiatric admission decisions are influenced by multiple variables that should be studied by examining general admission criteria and differences between clinicians.

Indexing cognitive tests to alcohol dosage and comparison to standardized field sobriety tests.

Cognitive tests from a computerized battery of mental tests and standardized roadside field sobriety tests (FST) were administered in three experiments involving graded dosages of alcohol but different administration schedules. In the first experiment, subjects were raised to one of four levels of alcohol dosage in four sessions 1 week apart. In the second experiment, the descending branch of the blood alcohol concentration (BAC) curve was monitored from 150 mg/dl BAC in a single session. In the third experiment, the ascending and descending limbs of the alcohol dosage curve were followed over a single session. Dose response relationships were observed for all tests, and the changes were statistically significant (p < .001) in all three studies for all tests when evaluated singly, except for grammatical reasoning. When cognitive and FST tests were combined into a single multiple regression analysis, Gaze Nystagmus consistently accounted for the most variance in BAC, followed by code substitution. While multiple regression analyses reveal that tests from the two batteries can be combined to improve overall prediction of alcohol concentration, it is also true that the two batteries share considerable variance (i.e., > 30%). This suggests that, while the two batteries may not be substitutable, they are measuring different aspects of the same thing.

Psychophysical scaling of circular vection (CV) produced by optokinetic (OKN) motion: individual differences and effects of practice.

Vection (V) refers to the compelling visual illusion of self-motion experienced by stationary individuals when viewing moving visual surrounds. The phenomenon is of theoretical interest because of its relevance for understanding the neural basis of ordinary self-motion perception, and of practical importance because it is the experience that makes simulation, virtual reality displays, and entertainment devices more vicarious. This experiment was performed to address whether an optokinetically induced vection illusion exhibits monotonic and stable psychometric properties and whether individuals differ reliably in these (V) perceptions. Subjects were exposed to varying velocities of the circular vection (CV) display in an optokinetic (OKN) drum 2 meters in diameter in 5 one-hour daily sessions extending over a 1 week period. For grouped data, psychophysical scalings of velocity estimates showed that exponents in a Stevens' type power function were essentially linear (slope = 0.95) and largely stable over sessions. Latencies were slightly longer for the slowest and fastest induction stimuli, and the trend over sessions for average latency was longer as a function of practice implying time course adaptation effects. Test-retest reliabilities for individual slope and intercept measures were moderately strong (r = 0.45) and showed no evidence of superdiagonal form. This implies stability of the individual circularvection (CV) sensitivities. Because the individual CV scores were stable, reliabilities were improved by averaging 4 sessions in order to provide a stronger retest reliability (r = 0.80). Individual latency responses were highly reliable (r = 0.80). Mean CV latency and motion sickness symptoms were greater in males than in females. These individual differences in CV could be predictive of other outcomes, such as susceptibility to disorientation or motion sickness, and for CNS localization of visual-vestibular interactions in the experience of self-motion.

Motion sickness questionnaire and field independence scores as predictors of success in naval aviation training.

The present report has shown that a motion sickness questionnaire can be used to predict susceptibility to motion sickness or flight training success, depending on the items scored. There is a discussion of the theory that motion sickness results from conflicting perceptual inputs. This theory is related to aircraft operating conditions. Scores on a personality test which appear to be related to similar perceptual phenomena are related to aviation success. One phenotype, field independence, seems to be promising in this regard. In addition to use of this finding in aviator selection, it is felt that studies of this trait, as it relates to an ability to reconcile conflict and to motion sickness insusceptibility, should be conducted.

Incidence of vestibular symptomatology in 2,500 U.S. Navy diving accidents (1933-1970).

The U.S. Navy diving accident records of 2,500 cases for the years 1933 to 1970 were analyzed and sorted into Type I and Type II decompression sickness. Type II was further sorted into "vestibular" and "other" categories. It was concluded that Type II symptoms accounted for 30% of the decompression accidents and it was estimated that the overall incidence of vestibular symptomatology was between 10 and 20%. Nearly 30% of the Type II cases were diagnosed as having vestibular involvement, although almost 60% of the cases contained a report of a symptom typically associated with the vestibular system complex, e.g., dizziness and nausea.

Development of performance evaluation tests for environmental research (PETER): complex counting test.

This study is the first in a program to develop a battery of Performance Evaluation Tests for Environmental Research (PETER). Nineteen volunteer subjects were tested daily for 3 weeks on a complex task requiring the operator to keep simultaneous track of several things with changing states. Average daily performances are reported as well as reliabilities of three main types: 1) internal consistency of the test; 2) sensitivity--the ability to differentiate subjects, and 3) stability--consistency of measurement over repeated sessions. The results showed that, on this task, learning was accomplished quickly, and performance stayed level for 3 weeks. The cross-tidal reliability for this test was found relatively stable after 3 d of practice, with a decline of only r=.94 to r=.79 over 11 d. This task is further noted as having several characteristics which make it particularly suitable for use in environmental research. It is concluded that the complex counting test can be recommended for use in environmental and other time-course research.

Postural and performance changes following exposures to flight simulators.

Flight simulators are cost-effective, safe, and flexible training tools for aviators. However, their advantages may be offset by the occurrence of motion sickness-like symptoms which have been reported during and following simulator training. Although symptoms have been well documented in simulators, their time course, causes, and implications for training are not yet fully understood. Tests of standing and walking steadiness were administered along with cognitive and motor performance tests to Navy and Marine Corps aviators before and after their regular simulator training, resulting in records of 726 pilot exposure observations. When exposed pilots were compared to a control group who did not fly in a simulator, statistically significant decrements in postural equilibrium test scores were found for all of the moving base simulators, but for only one of the three fixed-base simulators. The size of these losses was approximately 15% of baseline. Cognitive and motor changes, while statistically significant, were complicated by learning effects in all groups for all tests. When compared to the control group, improvement in cognitive scores was always less in the simulator groups, but greater improvement occurred in the simulator groups for motor speed scores, although this latter difference was small (< 1% of baseline). Further study of performance changes is recommended. In those simulators where significant effects occurred, the ataxia and the time-course of the disequilibrium should be followed.

Disorientation and postural ataxia following flight simulation.

BACKGROUND: Motion sickness-like symptoms can afflict pilots training in military simulators. This simulator sickness involves symptoms of gastrointestinal distress, eyestrain and disorientation. A simulator sickness Questionnaire (SSQ) with subscales available for each of these dimensions has been developed to assess the problem. HYPOTHESIS: This study examined the hypothesis that there is a strong correlation between the SSQ subscale which summarized self report of disorientation symptoms and an objective measure of post-simulation postural instability. METHODS: Data from two Navy simulators were analyzed: Device 2F114, a Weapon System Trainer for the A-6E Intruder, and Device 2F143, an Operational Flight Trainer for the EA-6B. Tests of standing and walking unsteadiness were administered along with the Simulator Sickness Questionnaire (SSQ). RESULTS: Significant correlations were found between scores on postural stability tests and the SSQ disorientation subscale scores, but correlations between scores on postural stability tests and the SSQ nausea and oculomotor subscale scores were much weaker and not statistically significant. CONCLUSIONS: These results provide some evidence for the validity of the disorientation subscale of the SSQ and suggest that the postural instability observed after simulator exposure may, in fact, result from disorientation.

Development of performance evaluation tests for environmental research (PETER): navigation plotting.

A navigation plotting task, modeled after actual shipboard navigation and plotting practices, was evaluated for inclusion in the Performance Evaluation Tests for Environmental Research (PETER) task battery. The differential stability of the 9-min self-paced task was examined independently in the laboratory and during a field study conducted at sea aboard three seagoing vessels. Repeated testing in both laboratory and field conditions showed that the percent correct metric was not reliable. After 10-15 practice trials, the total completion and total correct scores were found to meet minimum statistical stability and reliability criteria. Inclusion of the Navigation Plotting task in the PETER test battery is recommended given the task's direct operational validity, its demonstrated sensitivity to vessel motion and motion sickness, and the degree of statistical stability and reliability found with the total completion and total correct metrics.

Television computer games: a 'new look' in performance testing.

Work at the Naval Biodynamics Laboratory aims at developing a battery of performance evaluation tests for environmental research (PETER). Because repeated-measures designs are virtually universal in environmental studies, the paradigm focuses on stabilisation with practice; thus far, over 50 tasks have been studied. The present report describes how five computerized video games fare as performance tests. The tasks were performed for 3 weeks each, in the same order, by the same subjects. The results show that four out of the five games meet all criteria satisfactorily and one does not, a favorable showing for the video games in comparison with conventional tests of either the paper-and-pencil or apparatus types. In terms of availability, equipment reliability, expense, and other practical considerations, the video games have many advantages. It is concluded that video games have considerable promise for performance testing and other applied contexts.

Differential effects of scopolamine and amphetamine on microcomputer-based performance tests.

Scopolamine (1.0 mg) and d-amphetamine (10 mg) were administered alone and in combination to 16 subjects (medical students), randomly assigned to testing sessions in a fully crossed-over (Latin square) within-subjects design. After being practiced to stability, 9 performance tests from a menu of portable microcomputer-based tests were administered double-blind over 4 weekly treatments (including a placebo). Differential effects of drugs on performance were found. Motor and perceptual speed tests appeared enhanced by d-amphetamine and not degraded by scopolamine. Two of the five cognitive tests showed reductions with scopolamine. The findings are discussed in connection with using a menu of performance tests that can have diagnostic significance for assessment of drug treatments. The effects of scopolamine in this study and others are considered in terms of a model which implies that magnitude of performance deficit depends on performance type (cognitive, motor, self-report) and dosage level. Applying the model, we offer the following summary: below 0.15 mg scopolamine is without any effect; below 0.50 mg, the effect is limited, but can be revealed by some sensitive, complex performance tests and self-report; above 1.0 mg, the effect is likely to impact on operational efficiency.

Relating alcohol-induced performance deficits to mental capacity: a suggested methodology.

Performance tests are generally more reliable and more easily administered than on-the-job measures of performance, and in this way are preferable for studying the adverse consequences of environmental stressors. However, a linkage or context would be useful in interpretation of these laboratory measures. This paper reports findings with two indexing methods using multiple regression. In the first study, we illustrate "dose equivalency" where deficits on microcomputer performance tests were related to graded dosages of alcohol, and prediction equations of blood alcohol level were established. In the second experiment, "surrogate criteria" are demonstrated where cognitive mental tests of military aptitude, known to be predictive of operational performances, were administered to a sample who were tested repeatedly on the same microcomputer performance test. Multiple regression analyses of the computerized tests with the amplitude tests were significant (p < 0.01) and ranged from R = 0.50 to 0.94. Finally, the loss in performance owing to alcohol was indexed to loss on the microcomputer tests through the relationship of the tests to the Armed Services Vocational Aptitude Battery (ASVAB). Since the latter is strongly predictive of all forms of military operational performance, we suggest that alcohol-related losses in microcomputer performance test scores can serve as a useful intermediary, permitting meaningful linkage to these real-world performances.

Changes in the dark focus of accommodation associated with simulator sickness.

The relationship between the dark focus of accommodation and simulator sickness, a form of motion sickness, was examined in three experiments. In Experiment 1, dark focus was measured in 18 college students in a laboratory setting before and after they viewed a projected motion scene depicting low altitude helicopter flight. In Experiments 2 and 3, dark focus was measured in pilots (N = 16 and 23, respectively) before and after they "flew" in moving-base helicopter flight simulators with optical infinity CRT visual systems. The results showed that individuals who experienced simulator sickness had either an inward (myopic) change in dark focus (Experiments 1 and 3) or attenuated outward shifts in dark focus (Experiment 2) relative to participants who did not get sick. These results are consonant with the hypothesis that parasympathetic activity, which may be associated with simulator sickness, should result in changes in dark focus that are in a myopic direction. Night vision goggles, virtual environments, extended periods in microgravity, and heads-up displays all produce related visual symptomatology. Changes in dark focus may occur in these conditions, as well, and should be measured.