Search PubMed⌕ Search

Biomedical subjects

M D Attfield

Publications and source records attributed to M D Attfield.

At least 19 recordsLinked to original sources
PubMed1997

Respiratory symptoms and spirometry in experienced coal miners: effects of both distant and recent coal mine dust exposures.

The goal of this study was to determine whether respiratory symptoms were associated with the lower concentrations of respirable coal mine dust that were required by the U.S. Coal Mine Health and Safety Act (CMHSA) of 1969. The subjects were 1,866 male miners who had participated in the National Study of Coal Workers' Pneumoconiosis (NSCWP) and been tested at least twice, initially in either Round 1 (R1) (1969-71) or Round 2 (R2) (1972-75) and then finally in Round 4 (R4) (1985-88). Self-reported information elicited with a standardized questionnaire was used to determine the presence at the final round (i.e., R4) of chronic bronchitis, shortness of breath, and wheeze. Cumulative coal mine dust exposure was characterized for both the pre- and post-CMHSA periods. Controlling for age and other potential confounders, increased risks for the symptoms were associated with higher levels of both measurements of exposure. Moreover, the adverse effects of the lower, post-CMHSA exposure were evident for shortness of breath and wheeze especially among subjects who had little pre-CMHSA coal mining experience. These findings provide additional evidence of the limitations of the current 2.0 mg/m3 coal mine dust standard to prevent respiratory disease.

Adult↗
PubMed1996

Coal mine dust exposure and spirometry in experienced miners.

In a previous study of new miners from the National Study of Coal Workers' Pneumoconiosis (NSCWP), researchers examined changes in spirometry values associated with coal mine dust exposure (Br J Ind Med 1993; 50:929-937). An unusual pattern of dust-related effects was observed: initial sharp decrements in FVC and FEV1 were followed by partial recovery. In the current study, similar methods were used to analyze data from experienced miners. Each of 1,915 male subjects contributed data from two of the NSCWP field surveys: either Round 1 (1969-71) and Round 2 (1972-75) and Round 4 (1985-88). From the cross-sectional analysis at Round 1 or Round 2 (R1/R2), changes of +0.6 ml FVC and -0.5 ml FEV1 were associated with each mg/m3-yr of cumulative coal mine dust exposure, but were not statistically significant (p > 0.05). From the analysis of longitudinal change in spirometry from R1/R2 to Round 4 (R4), annual declines in FVC (-0.10 ml/yr per mg/m3-yr, p = 0.003) and FEV1 (-0.07 ml/yr per mg/m3-yr, p = 0.006) were associated with pre-R1/R2 exposure. Both the pattern and the magnitude of the exposure-response relationship were different for experienced versus new miners. Possible reasons for these contrasts include differences in cumulative exposure between the two groups and the healthy worker effect among experienced miners.

Coal↗
PubMed1996

Radiographic and pathologic correlation of coal workers' pneumoconiosis.

The relationships between chest radiographs (CXR) and corresponding pathology were investigated in 430 autopsied coal miners from West Virginia. Whole-lung sections were reviewed and graded on four-point severity scales for the following lesions of coal workers' pneumoconiosis (CWP): macules, micro- and macronodules (small and large fibrotic nodules), and progressive massive fibrosis (PMF). Antemortem CXR were classified by three B readers using the 1971 International Labor Office (ILO) U/C classification (6). On pathologic examination, 96% of miners had macules, 70% micronodules, 45% macronodules, 15% silicosis, and 28% PMF. By CXR, 69% of the miners had small, rounded opacity profusions of category > or = 0/1. Data analysis revealed increasing odds that small opacities of category > or = 0/1 would be detected with increasing grade of nodules. Profusion category 0/0 was often reported for cases with macules of mild to moderate grade and mild levels of micronodules. Overall, q-type opacities were associated with macules and micronodules, whereas the large r-type opacities were associated with macronodules. By CXR, large opacities showed good correlation with pathologic PMF. However, about one-third of cases identified as having large opacities by CXR were not substantiated as PMF by pathology. One-fourth of these cases could be explained by lung lesions such as Caplan's nodules, tuberculosis scars, and tumors. Similarly, 22% of cases classified as PMF on pathology had no large opacities by CXR. In half of these cases, the radiologists had noted other abnormalities (cancer, tuberculosis) by CXR as large opacities. Overall, the study showed good agreement (Somer's d = 0.64) between the predicted probabilities and observed responses of a profusion category > or = 0/1 for pathologic CWP lesions. However, the study also showed that CXR were insensitive for detecting minimal CWP lesions, and were unreliable indicators in the presence of concomitant pulmonary pathology.

Adult↗
PubMed1995

Prevalence of pneumoconiosis and its relationship to dust exposure in a cohort of U.S. bituminous coal miners and ex-miners.

Information on radiographic evidence of coal workers' pneumoconiosis (CWP) is presented for a group of 3,194 underground bituminous coal miners and ex-miners examined between 1985 and 1988. Prevalence of CWP was related to estimated cumulative dust exposure, age, and rank of coal. On the basis of these data, miners of medium to low rank coal, who work for 40 years at the current federal dust limit of 2 mg/m3, are predicted to have a 1.4% risk of having progressive massive fibrosis on retirement. Higher prevalences are predicted for less severe categories of CWP. Miners in high rank coal areas appear to be at greater risk than those mining medium and low rank coals. Ex-miners who said that they left mining for health-related reasons had higher levels of abnormality compared to current miners.

Adult↗
PubMed1995

Does regression analysis of lung function data obtained from occupational epidemiologic studies lead to misleading inferences regarding the true effect of smoking?

Exposure-response studies of the relationship between ventilatory function and dust exposure in workers are often quantified using linear regression methods. In coal miners, this technique has indicated that average effects of smoking and moderate dust exposure are roughly equivalent. However, the validity of direct comparison of the average effects of smoking and dust exposure has been questioned, the argument being that smoking causes severe effects in a minority, but leaves the remainder largely unaffected. This hypothesis was studied by examining distributions of FEV1 in a group of working coal miners where mean effects associated with both smoking and dust exposure have been detected. Overall, the results suggest that comparison of average effects of smoking and dust exposure derived from linear regression analysis is valid and not misleading.

Adult↗
PubMed1995

Exposure-response analysis of mortality among coal miners in the United States.

The quantitative relationship between exposure to respirable coal mine dust and mortality from nonmalignant respiratory diseases was investigated in a study of 8,878 working male coal miners who were medically examined from 1969 to 1971 and followed to 1979. Exposure-related mortality was evaluated using Cox proportional hazards modeling for underlying or contributing causes of death and modified lifetable methods for underlying causes. For pneumoconiosis mortality, the lifetable analyses showed increasing standardized mortality ratios (SMRs) with increasing cumulative exposure category. Significant exposure-response relationships for mortality from pneumoconiosis (p < 0.001) and from chronic bronchitis or emphysema (p < 0.05) were observed in the proportional hazards models after controlling for age and smoking. No exposure-related increases in lung cancer or stomach cancer were observed. Pneumoconiosis mortality was found to vary significantly by the rank of coal dust to which miners were exposed. Miners exposed at or below the current U.S. coal dust standard of 2 mg/m3 over a working lifetime, based on these analyses, have an elevated risk of dying from pneumoconiosis or from chronic bronchitis or emphysema.

Coal Mining↗
PubMed1993

Longitudinal and cross sectional analyses of exposure to coal mine dust and pulmonary function in new miners.

The association between exposure to dust and pulmonary function was studied by longitudinal and cross sectional analyses in a group of United States underground coal miners beginning work in or after 1970. Quantitative estimates of exposure to respirable coal mine dust were derived from air samples taken periodically over the entire study period. The cohort included 977 miners examined both in round 2 (R2) (1972-5) and round 4 (R4) (1985-8) of the National Study of Coal Workers' Pneumoconiosis. Multiple linear regression models were developed for both cross sectional (pulmonary function at R2 and R4) and longitudinal (change in pulmonary function between R2 and R4) analyses with exposure partitioned into pre-R2 and post-R2 periods and controlled for covariates including smoking history. The results indicate a rapid initial (at R2) loss of FVC and FEV1 in association with cumulative exposure of the order of 30 ml per mg/m3-years. Between R2 and R4 (about 13 years) no additional loss of function related to dust exposure was detected although the percentage of predicted FVC and FEV1 did decline over the period. After some 15 years since first exposure (at R4), a statistically significant association of cumulative exposure with FEV1 of about -5.9 ml per mg/m3-years was found. These results indicate a significant non-linear effect of exposure to dust on pulmonary function at dust concentrations present after regulations took effect. The initial responses in both the FVC and FEV1 are consistent with inflammation of the small airways in response to exposure to dust.

Adult↗
PubMed1992

Exposure-response relationships for coal mine dust and obstructive lung disease following enactment of the Federal Coal Mine Health and Safety Act of 1969.

Underground U.S. coal miners were studied cross-sectionally for the association of respirable coal mine dust exposure with pulmonary function and symptoms of airways obstruction. The study group included 1,185 miners participating in Round 4 of the National Study of Coal Workers' Pneumoconiosis who had started mining in or after 1970 when comprehensive exposure regulations first came into effect. Quantitative estimates of cumulative exposure, derived using respirable dust measurements taken by the Mine Safety and Health Administration over the entire study period, were used in linear and logistic regression models on indicators of pulmonary function and chest symptoms while controlling for smoking status, pack-years, and other potential confounders. Statistically significant associations between log cumulative exposure and decrements in FVC, FEV1, and FEV1/FVC were observed. In logistic models, statistically significant associations of cumulative exposure with increasing prevalence of FEV1 and FEV1/FVC less than 80% predicted and symptoms including chronic phlegm, chronic bronchitis, breathlessness, wheeze, and wheeze with shortness of breath were found. It is concluded that exposures to respirable coal mine dust present in U.S. mines since 1970 continue to affect respiratory health in underground miners.

Adult↗
PubMed1992

Some observations on the variation in height coefficients in prediction equations for forced vital capacity.

Intercept and height coefficients in prediction equations for forced vital capacity (FVC) are highly correlated and highly variable, due in part to the small coefficient of variation of height (4%). This degree of imprecision and relationship was observed among the coefficients of a set of 26 unrelated published prediction equations, and appeared to dominate any systematic differences between them in methodology and technique. The findings indicate that care needs to be taken when using equations for predicting the FVC of people at the extremes of height. They also demonstrate the need for careful planning in the design of studies intended for the compilation of prediction equations, including provision for sufficient numbers of observations. Support is also given to the use of a composite formula based on the averaging of many individual prediction equations. The results are applicable to other similar and commonly used lung function equations (e.g. that for forced expiratory volume in 1 second, FEV1) that employ height as a predictor variable.

Adult↗
PubMed1992

The derivation of estimated dust exposures for U.S. coal miners working before 1970.

A number of reports on the prevalence of coal workers' pneumoconiosis in U.S. coal miners have been published, yet very little is known about the relationship between dust exposure and pneumoconiosis levels in the U.S. This report describes the derivation of cumulative dust exposure estimates by back-extrapolation of data processed by the Mine Safety and Health Administration after 1970 by using a ratio of dust concentrations based on information collected during environmental surveys at certain U.S. mines by the Bureau of Mines between 1968 and 1969. Cumulative personal dust exposure estimates were calculated by using occupational histories obtained from the miners and job-specific estimates of dust concentration. In other reports, the resulting estimated exposures have been shown to correlate well with various measures of respiratory morbidity.

Adult↗
PubMed1992

Exact expressions for the bias and variance of estimators of the mean of a lognormal distribution.

Exact mathematical expressions are given for the bias and variance of the arithmetic and maximum likelihood estimators of the first moment (mean) of a lognormal distribution. On the basis of these exact expressions, and without the need for simulation, statistics on the bias and variance have been computed for a range of sample sizes and geometric standard deviations. The results reaffirm that an unbiased maximum likelihood estimator exists that has minimum variance. Contrary to some recent recommendations, this is the preferred estimator if the data truly come from a lognormal distribution.

Analysis of Variance↗
PubMed1992

An investigation into the relationship between coal workers' pneumoconiosis and dust exposure in U.S. coal miners.

The National Study of Coal Workers' Pneumoconiosis (NSCWP) is a large, continuing epidemiologic study of the respiratory health of U.S. coal miners. By using information from the study, prevalence of coal workers' pneumoconiosis (CWP) was related to indexes of dust exposure obtained from research and compliance sampling data. Clear relationships between prevalences of both simple CWP and progressive massive fibrosis (PMF) and estimated dust exposure were seen. Additional effects independently associated with coal rank (% carbon) and age were also seen. Logistic model fitting indicated that between 2% and 12% of miners exposed to a 2-mg/m3 dust environment in bituminous coal mines would be expected to have Category 2 or greater CWP after a 40-yr working life; PMF would be expected for between 1.3% and 6.7%. The risks for anthracite miners appeared to be greater. There was a suggestion of a background level of abnormality, not associated with dust exposure, but increasing with age. Although there are certain weaknesses in the data used to derive these exposure estimates, the results are in general agreement with, but somewhat greater than, some recent findings for British coal miners.

Adult↗
PubMed1992

Pulmonary function of U.S. coal miners related to dust exposure estimates.

This study of 7,139 U.S. coal miners used linear regression analysis to relate estimates of cumulative dust exposure to several pulmonary function variables measured during medical examinations undertaken between 1969 and 1971. The exposure data included newly derived cumulative dust exposure estimates for the period up to time of examination based on large data bases of underground airborne dust sampling measurements. Negative associations were found between measures of cumulative exposure and FEV1, FVC, and the FEV1/FVC ratio (p less than 0.001). In general, the relationships were similar to those reported for British coal miners. Overall, the results demonstrate an adverse effect of coal mine dust exposure on pulmonary function that occurs even in the absence of radiographically detected pneumoconiosis.

Adult↗
PubMed1992

Epidemiological data on US coal miners' pneumoconiosis, 1960 to 1988.

OBJECTIVES: Statistics on prevalence of pneumoconiosis among working underground coal miners based on epidemiologic data collected between 1960 and 1988 are presented. The main intent was to examine the time-related trend in prevalence, particularly after 1969, when substantially lower dust levels were mandated by federal act. METHODS: Data from studies undertaken between 1960 and 1968 were collected and compared. Information for the period 1969 to 1988 was extracted from a large ongoing national epidemiologic study. Tenure-specific prevalence rates and summary statistics derived from the latter data for four consecutive time intervals within the 19-year period were calculated and compared. RESULTS: The results indicate a reduction in pneumoconiosis over time. The trend is similar to that seen in a large radiologic surveillance program of underground miners operated concurrently. CONCLUSIONS: Although such factors as x-ray reader variation, changes in x-ray standards, and worker self-selection for examination may have influenced the findings to some extent, adjusted summary rates reveal a reduction in prevalence concurrent with reductions in coal mine dust levels mandated by federal act in 1969.

Adult↗
PubMed1992

Surveillance data on US coal miners' pneumoconiosis, 1970 to 1986.

OBJECTIVES: Statistics on prevalence of pneumoconiosis among working underground coal miners from data collected as part of a large national radiographic surveillance program between 1970 and 1986 are presented. The main intent was to examine the time-related trend in prevalence over this period, which coincides with historically low dust levels mandated by federal act. METHODS: Tenure-specific prevalence rates and summary statistics derived from them for four consecutive time intervals within the 16-year period were calculated and compared. RESULTS: The results indicate a reduction in pneumoconiosis over the life of the program. This trend is similar to that seen in epidemiologic studies undertaken concurrently. CONCLUSIONS: Although low participation in the surveillance program and other problems complicate the findings, it appears that reductions in dust exposure mandated by federal act in 1969 have led to lower prevalence of pneumoconiosis among underground coal miners.

Bias↗
PubMed1992

British data on coal miners' pneumoconiosis and relevance to US conditions.

OBJECTIVES: The current primary federal dust standard for US underground coal miners of 2 mg/m3 respirable dust is based on British epidemiological information on exposure-response derived in 1969. Since then, much new information has become available. This paper reviews and compares the available information as it relates to the US mining situation. METHODS: Recent exposure-response information on pneumoconiosis and dust exposure derived by British researchers was employed to estimate working-life risks of pneumoconiosis for miners exposed to 2 mg/m3. RESULTS: It is estimated that close to 9% of underground coal miners who work for 40 years in a 2 mg/m3 environment would develop pneumoconiosis (category 1 or greater). Progressive massive fibrosis would develop in 0.7%. CONCLUSIONS: There are unresolved questions relating to the validity of extrapolating findings on British mines and miners to the US and also in predicting disease levels at the low end of the dust exposure spectrum. Given the data available, current information suggests miners who are employed for a working life-time at the current federal dust limit of 2 mg/m3 are still at risk of developing pneumoconiosis.

Bias↗