Annals of Occupational and Environmental Medicine

Original Article

Significance of Time-dependent Exposure Variable in Occupational Disease Study: Jai Dong Moon; Korean Journal of Occupational and Environmental Medicine 1997;9(2):201-207. Published online June 30, 1997; DOI: https://doi.org/10.35371/kjoem.1997.9.2.201

Abstract PDF: Although the final cumulative exposure has been used as a exposure variable on the cohort study for the relation between exposure and disease, the bias from the use of fixed exposure can be developed because the exposure amount changes across the time. We developed the program to handle the Cox model with irregularly changing time-dependent exposure variable and covariates, and the validity about the application of time-dependent exposure variable and lagged interval was practically evaluated by analyzing the data collected for typical retrospective cohort study with that program. The results were as follows : The exposure-response relations between the deaths from lung cancer and exposures (fixed or time-dependent) were not clear when 0 year lagged interval was applied. When 15 years lagged interval was applied, the exposure-response relations between the deaths from lung cancer and the time-dependent exposures to crystalline silica were observed and relative risky increased like 1.00, 1.17, 1.30 and 2.45 across the exposure levels. The relative risk estimates for lung cancer with time-dependent exposure variable were higher than those with fixed exposure variable without regard to the application of lagged interval. The exposure-response relations between the deaths from non-malignant respiratory disease (NMRD) and exposures (fixed or time-dependent) were observed across exposure levels when 0 year lagged interval was applied. When 15 years lagged interval wag applied, the exposure-response relations between the deaths from NMRD and the time-dependent exposures to crystalline silica were observed, but were not with fixed exposure variable. The relative risk estimates for NMRD mortality with time-dependent exposure variable were higher than those with fixed exposure variable, and the application of lagged interval on the evaluation of NMRD mortality was meaningless. The results suggests that the application of time-dependent exposure variable on the study of exposure-effect relation should be considered and the application of lagged interval should be decided according to the time needed from disease detection to death.

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Original Article

Changes in Cadmium Deposit and Histopathologic Finding of Testis, Liver and Kidney in Cadmium Exposed Rats: Young Goo Lee, Jung Duck Park, Byung Sun Choi, Yeon Pyo Hong, Im Won Chang; Korean Journal of Occupational and Environmental Medicine 1994;6(1):56-68. Published online February 28, 1994; DOI: https://doi.org/10.35371/kjoem.1994.6.1.56

Abstract PDF: To assess the changes of cadmium deposit and histopathologic finding of testis, liver and kidney, different dose of cadmium (Cd) was administered into male Sprague-Dawley rat(purchased from KIST, Korea Institute of Science and Technology) by single intravenous injection. At 12, 24, 48, 168 and 672 hours after Cd injection, tissue cadmium concentration and histopathological change were examined. Cd exposed group showed lesser weight gain than the control. Renal Cd content tended to increase in time-dependent pattern, while hepatic and testicular Cd content tended to decrease. Mean of renal Cd content to hepatic Cd content (Cd K/Cd L) also progressively increased. These results suggest that Cd might be gradually transported to kidney fro other organs. In testis and liver, degenerative changes appeared relatively in acute phase. These changes became more pronounced in testis, while less prominent in liver. In kidney, swelling of proximal tubluar cells and thickening of glomerular basement membrane appeared relatively later and these changes were progressively aggravated.

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