The interpretation of trace element analysis in body fluids.

The clinical interpretation of trace element analysis has lagged behind the technology available to measure the elements in body fluids. Reports can be difficult to interpret and requires knowledge of toxicokinetics, the dynamics of how the trace metals accumulate and pass through the body. Trace element analysis is best used for specific applications, such as establishing levels of exposure, biological exposure indices, biomonitoring of populations, and to confirm an association following a compatible diagnosis. It is not well suited for screening individual patients. Chelation treatment may follow inappropriate trace element determinations and may carry a risk of side effects, some life-threatening. Trace element analysis should be used sparingly and with full understanding of what the results are likely to mean. The physician should only order the test with a clear idea of why he or she is doing so and what he or she will do with the result.

Mechanism and treatment of sulfide-induced coma: a rat model.

Sodium hydrosulfide and dimethylsulfide duplicate the effects of hydrogen sulfide in causing coma in Sprague-Dawley rats and are additive for lethality. Nitrite, pyruvate and dithiothreitol had no significant effect on coma or lethality but bicarbonate with and without glucose reduced duration of coma. This finding suggests an antidotal treatment.

Evaluation of scientific evidence in law, adjudication and policy: when occupational health takes the witness chair.

Health and medical knowledge are essential to the resolution of disputes in law and administrative applications (such as workers' compensation) and provide essential input into public policy decisions. There are no socially agreed-upon rules for the application of this knowledge except in the law. On a practical level, the legal system lacks the capacity to evaluate the validity of knowledge as evidence and therefore relies heavily on expert opinion. Over the last 30 years, an approach called "critical appraisal" and "evidence-based medicine" addressed a similar problem in medical practice and established norms for the acceptance of evidence in clinical medicine. A similar evidence-based framework may be possible for applying knowledge of health and medicine to dispute resolution in the law. One critical issue is how to apply scientific evidence when the standard is "more likely than not" rather than scientific certainty. Another is how the generalizations drawn from epidemiology and population-based sciences are interpreted and individualized, as they must be, for the case at hand. A related issue is how risk is interpreted for an individual after the fact, when conventional probability treats risk before the fact and conventional biostatistics applies primarily to a population. This emerging approach is called "evidence-based medical dispute resolution".

Lack of associations between air emissions from sour-gas processing plants and beef cow-calf herd health and productivity in Alberta, Canada.

This paper describes a large-scale investigation into the effects of licensed air emissions from sour-gas processing plants on the health and productivity of beef cow-calf herds in the province of Alberta, Canada. In conjunction with a geographical information system, two atmospheric-dispersion models were used to assess historical exposures at 5726 beef cow-calf farm-sites from 1987 to 1990. We did secondary analyses of health, productivity, and management data, from a government-extension survey previously administered to beef cow-calf producers across the province. Statistical models (adjusted for potential confounding and clustering within herd and over time) were used to determine associations with estimates of sour-gas emission exposure. All analyses were conducted at the herd-level. There were no significant (P>0.05) detrimental associations of exposure and the annual herd risk for culling, calf-crop delivered, calf-crop season profile, stillbirth and twinning, calfhood mortality, or calf-crop weaned.

Air emissions from sour-gas processing plants and dairy-cattle reproduction in Alberta, Canada.

The dispersion of air pollutants from all 231 licensed sour-gas processing plants in Alberta, Canada, was modeled on a monthly basis over a 10-year period (1985-1994). Exposure estimates for sulfur dioxide (SO(2)-used as a surrogate for exposure to combusted emissions) then were assigned to 1382 provincial dairy farms using a geographical-information system. Individual average and peak exposure for periods prior to each of 15 months of age and conception (four exposure-averaging periods for each of two dispersion models) were estimated for 163,988 primiparous female dairy-cattle between 1986 and 1994. Monthly or annual average farm-site exposure estimates likewise were assigned to associated herd-level data sets for the biologically relevant period of interest for each of three additional reproductive outcomes: monthly herd-average calving interval, stillbirth risk, and twinning risk. In one of the main-effects models, the maximum (i.e., peak) monthly sour-gas exposure experienced by individual-animals from birth to conception was associated with an increased time to first-calving in the very-highest exposure category (hazard ratio=0.86, 95% CI=0.80, 0.92). This equates to a decreased hazard (lambda) of calving (in each month subsequent to 22 months of age) for the highest-exposure animals (lambda=0.170) versus the zero-exposure animals (lambda=0.198) in a model with referent values for agro-ecological region and season of birth. The dose-response was not consistent across the full range of exposure categories. There was significant (P=0.003) interaction of emissions with agro-ecological region. After accounting for the interaction, a more-consistent dose-response was evident for some (but not all) agro-ecological regions. This suggests that any effect of emissions on dairy-heifer reproduction is subject to modification by features of soil type, vegetative cover, and/or climate. The increase in monthly herd-average calving interval on farms exposed to the very-highest levels of emissions appeared quite small and of limited practical importance within the range of expected exposures. There was no association between exposure and the risk for twinning. Herds exposed to higher emissions exhibited a slight decrease in risk for stillbirth.

Permanent respiratory impairment and upper airway symptoms despite clinical improvement in patients with reactive airways dysfunction syndrome.

We previously reported clinical findings for 19 patients who developed symptomatic airways hyperactivity following an acute exposure to an inhaled irritant and who were given the diagnosis of reactive airways dysfunction syndrome (RADS). We now report on nine of these patients who have been followed for a mean of 9 years, allowing assessment of function, symptoms, and comorbidity beyond the early phase of acute airway injury and inflammation. None of the patients have resolved their airway hyper-responsiveness and symptoms completely, although only in one subject, who had a premorbid history of asthma, has the condition progressed. A common feature has been sinusitis and other upper-airway symptoms. We conclude that in this group of patients, RADS presented in a consistent pattern regardless of the cause of airway injury, resolved only partially, even in subjects without a premorbid history of respiratory disease, and was associated with significant secondary morbidity, especially affecting the upper airway. This pattern was evident regardless of smoking status or age at time of exposure. We conclude that for these subjects, RADS was a distinct entity with a consistent natural history that conferred permanent impairment, but did generally improve somewhat over time.

Occupational epidemiology.

The epidemiological literature for assessing risk in many, if not most, modern occupations has now become sufficiently obsolete that it can no longer be depended upon to guide either prevention or adjudication of compensation. This obsolescence must be dealt with by developing new sources of information pertinent to occupational hazards and the risks associated with most occupations. Ideally, a comprehensive surveillance mechanism that would be automatically updated for the changing risk in a changing economy would be ideal and may be attainable with further developments in health information technology. The characteristics of such a system are described. However, there are many obstacles to such a system which appear insurmountable in the short term. A more eclectic plan for cooperation and data-sharing would help in the short term and would establish a pattern of collaboration that could both place adjudication on a more solid foundation and avoid allegations of collusion in business. The general outline for a practical programme of collaboration along these lines is presented.

The Fort McMurray Demonstration Project in Social Marketing: theory, design, and evaluation.

CONTEXT: The Fort McMurray Demonstration Project in Social Marketing is a multifaceted program that applies the techniques of social marketing to health and safety. This paper describes the origins of the project and the principles on which it was based. VENUE: Fort McMurray, in the province of Alberta, Canada, was selected because the community had several community initiatives already underway and the project had the opportunity to demonstrate "value added." CONCEPT: The project is distinguished from others by a model that attempts to achieve mutually reinforcing effects from social marketing in the community as a whole and from workplace safety promotion in particular. DESIGN: Specific interventions sponsored by the project include a media campaign on cable television, public activities in local schools, a community safety audit, and media appearance by a mascot that provides visual identity to the project, a dinosaur named "Safetysaurus." The project integrated its activities with other community initiatives. MAIN OUTCOME MEASURES: The evaluation component emphasizes outcome measures. A final evaluation based on injury rates and attitudinal surveys is underway. RESULTS: Baseline data from the first round of surveys have been compiled and published. In 1995, Fort McMurray became the first city in North America to be given membership in the World Health Organization's Safe Community Network.

Support groups for injured workers: process and outcomes.

We evaluated the efficacy of a support group for injured workers as a low-cost intervention that might modify chronicity and improve outcome among workers' compensation claimants with chronic musculoskeletal disorders. This study examined the impact of support groups on injured workers with musculoskeletal injuries in relation to four health indicators: pain, somatization, depression, and pain-locus-of-control. We held nine support groups between October 1992 and March 1994. A total of 62 subjects completed the groups. The evaluation of the support group program employed a type of quasi-experimental design, a nonequivalent control group design. A comparison group was created for purposes of evaluation from Workers' Compensation Board of Alberta claimants who did not participate in the groups. We found that participation in the support groups did not seem to affect the well-being of injured workers by reducing their levels of pain, somatization, and depression, and/or by altering their pain-locus-of-control. The results do not necessarily rule out any beneficial effects of participating in support groups. However, these methods applied to this type of support group showed no demonstrable effect.

Differential sensitivity of lung and brain to sulfide exposure: a peripheral mechanism for apnea.

Acute exposure to hydrogen sulfide (H2S) causes 4 dose-dependent responses: hyperpnea, unconsciousness or knockdown, apnea, and death. At present, scientific mechanisms for these effects are unknown, but inhibition of cytochrome oxidase in the central nervous system (CNS) by sulfide has been suggested. In this study, the premise of brain as target is examined by comparing peripheral with direct delivery of sulfide to brain. NaHS was administered to anesthetized Sprague-Dawley male rats, by femoral intravenous, or carotid intra-arterial injection. With apnea as the test, ED100 values of 0.6 and 3.0 mg kg(-1) were found for peripheral and direct delivery to brain, respectively. Peripheral delivery is 5 times as effective as direct delivery to the brain, and greater if the relative dilution factors are considered. Lidocaine, applied to the vagus, prevented apnea, so lung-brain transmission was essential. It was therefore concluded that the lung is the peripheral site of action. Hyperpnea increased in duration with dose. The carotid body, located distal to the arterial catheter, sensed the high doses of NaHS but did not trigger apnea. Intravenous infusion or intraperitoneal injection with NaHCO3 prevented hyperpnea, apnea, and death. The following conclusions are drawn: the carotid body is not implicated in NaHS-induced apnea, the lung and not brain harbors the primary site of action of H2S, and an afferent neural signal from the lung via the vagus induces the apnea. Finally, NaHCO3 appears to prevent toxicity from sulfide, and therefore H2S, by some unexplained mechanism. Practical emergency treatment for acute toxicity in the field may be possible.

Zinc exposure in Chinese foundry workers.

BACKGROUND: Inhalational exposure to zinc oxide fumes is associated with metal fume fever, a self-limited but very uncomfortable condition closely resembling influenza. Very little is known regarding the toxicokinetics of inhaled zinc, making the interpretation of zinc measurements in serum and urine problematic. METHODS: Twenty workers in a zinc foundry in Baiyin, Peoples' Republic of China, were investigated with serial examinations by a physician, chest radiographs, and spirometry. Exposure assessment consisted of the measurement of zinc in serum, urine, and personal air samples. RESULTS: No cases of metal fume fever were observed during the study period despite exposures to as high as 36.3 mg/m3 over less than 4 hr. In addition, no radiographic or functional changes were noted. Serum zinc levels of all workers were within the reference range and did not correlate with external exposure measurements. However, elevations were noted in urinary zinc levels, which showed a significant association (Spearman's correlation coefficient = 0.47, P = 0.04) between exposure to zinc and urine zinc. CONCLUSIONS: These results provide exposure measurements for zinc at which workers demonstrate tolerance to the development of metal fume fever. Furthermore, they suggest that urine may be the preferred biological medium for the assessment of zinc exposure.

Indicators of cardiovascular risk among workers exposed to high intermittent levels of carbon disulphide.

The effects of exposure to carbon disulphide have been studied mostly among workers in the viscous rayon industry, where the usual exposure profile has been relatively steady exposure over work shifts. We investigated 13 workers in a small chemical company who were exposed to low levels, peaking intermittently to relatively high levels in the range of 100-200 ppm at the end of the work shift, a pattern that may change the risk profile. Our investigation was part of a compliance order that was fought by the company and our access and follow-up was limited. Two workers had burns on their bodies associated with exposure to caustic. Four had elevations in total serum cholesterol, one had elevated serum triglycerides and three had elevations in fasting blood glucose--two of them were known to be diabetics before employment and one had a history of unexplained peripheral neuropathy. No consistent pattern suggestive of a defined lipoprotein abnormality was obvious but several atherogenic profiles were observed. Five had abnormalities on electrocardiogram, four of whom appeared to be among the most heavily exposed. The presence of these changes taken together in this context may suggest accelerated atherosclerotic changes. Tests of liver and kidney function were within the normal range for all workers, as was a complete blood count. Four of the workers had evidence of a bilateral reduction in hearing threshold at 4,000 Hz. A complete set of recommendations was forwarded to the employer, emphasizing further control of exposure to carbon disulphide, personal protection requirements and a cardiovascular risk reduction programme. Conditions improved in the plant following modifications introduced in response to a stop work order from the provincial government's occupational health and safety agency. However, a fire in 1998 put the company out of business and ended further follow-up or interventions. We conclude that these findings, while difficult to interpret because of the circumstances of the investigation, are compatible with an atherogenic effect of exposure to peaking levels of carbon disulphide. The observation should be tested in a larger population with fewer confounding factors and greater control over the investigation.

Evidence-based medical dispute resolution in workers' compensation.

There is a trend toward insisting on empirical evidence, rather than relying on expert judgement, in both health care and law. Medical knowledge is applied in law to provide solid logic for the physician's opinion and to place the opinion in a context that assists the adjudicator. Dr. Guidotti examines workers' compensation disputes in the light of hypothesis development and application of scientific theory.

Applying epidemiology to adjudication.

Dr. Guidotti describes an epidemiologic study of firefighters, conducted by the University of Alberta, to underscore the difficulties of obtaining data and the years that can pass before analysis can even begin. He then delineates problems encountered when interpreting data in any epidemiologic study.

Evaluation of the worker with suspected occupational lung disease.

A systematic approach to evaluation of suspected occupational lung disorders is presented to assist the health care professional with diagnosis, treatment, and prognosis, as well as management of the disease in the workplace.

Effective intervention to reduce occupational injuries in Alberta: a case study of financial incentives.

High injury rates in particular industries in Alberta, Canada were the impetus for government initiatives to control injury frequency and severity. Safety associations, a financial incentives program, research projects, and safety demonstrations substantially decreased injury rates within 5 years. Since then, companies manage their own performance, but undergo periodic audits.

Variability in the classification of radiographs using the 1980 International Labor Organization Classification for Pneumoconioses.

This study describes the extent of agreement in classification of chest radiographs using the International Labor Organization (ILO) classification among six readers from the United States and Canada. A set of 119 radiographs was created and read by three Canadian and three US readers. The two ratings of interest were profusion (scored from 0/- to 3/+) and pleural abnormalities consistent with pneumoconiosis (scored with the ILO system, then collapsed into a yes/no). We used a number of approaches to evaluate interreader agreement on profusion and pleural changes, determining concordance, observed agreement, kappa statistic, and a new measure to approximate sensitivity and specificity. This study found that five of six readers had good fair to good agreement for pleural findings and for profusion as a dichotomous variable (> or = 1/0 vs < or = 0/1) using the kappa statistic, while a sixth reader had poor agreement. We found that concordance, expressed as percent agreement, was higher for normal radiographs than for ones that showed disease, and describe the use of the kappa statistic to control for this finding. This analysis adds to the existing literature with the use of the kappa statistic, and by presenting a new measure for "underreading" and "overreading" tendencies.