Biomedical subjects

D B Richardson

Publications and source records attributed to D B Richardson.

At least 19 recordsLinked to original sources

PubMed2006

The impact on relative risk estimates of inconsistencies between ICD-9 and ICD-10.

BACKGROUND: The 10th revision of the International Classification of Diseases (ICD) represents a major change in the ICD system. This paper investigates the impact on relative risk estimates of inconsistencies in outcome classification between ICD-9 and ICD-10, including scenarios in which occupational exposure levels are correlated with year of death (and therefore with the ICD revision in effect at death). The setting of interest is a cohort mortality study in which follow up spans the periods during which ICD-9 and ICD-10 were in effect. The relative risk estimate obtained when death certificates are coded to the ICD revision in effect at time of death is compared to the relative risk estimate that would be obtained if all death certificates were coded to a consistent ICD revision (that is, ICD-10). The ratio of these relative risks is referred to as the coefficient of bias. METHODS: Simple equations relate the coefficient of bias to the sensitivity and specificity of the classification of decedents into categories of cause of death via ICD-9 (treating classifications based upon ICD-10 as the standard). Bridge coded mortality data for 2,296,922 decedents (that is, death certificates coded to ICD-9 and ICD-10) are used to derive estimates of sensitivity and specificity by category of cause of death. Numerical examples illustrate the application of these equations. RESULTS: Estimates of the sensitivity of classification of decedents into categories of death defined by ICD-9 ranged from 0.26-1.00. Specificity was above 0.98 for all categories of cause of death. Numerical examples illustrate that inconsistencies in outcome classification between ICD-9 and ICD-10 may have substantial impact on relative risk estimates if there is a strong relation between exposure status and the proportion of deaths coded to a given ICD revision. CONCLUSIONS: For analyses of mortality outcomes that exhibit poor comparability between ICD-9 and -10, it may be prudent to recode cause of death information to a standard ICD revision in order to avoid bias that can occur when exposures are correlated with the proportion of deaths coded to a given ICD revision.

Cause of Death↗

PubMed2005

Risk of cancer after low doses of ionising radiation: retrospective cohort study in 15 countries.

OBJECTIVES: To provide direct estimates of risk of cancer after protracted low doses of ionising radiation and to strengthen the scientific basis of radiation protection standards for environmental, occupational, and medical diagnostic exposures. DESIGN: Multinational retrospective cohort study of cancer mortality. SETTING: Cohorts of workers in the nuclear industry in 15 countries. PARTICIPANTS: 407 391 workers individually monitored for external radiation with a total follow-up of 5.2 million person years. MAIN OUTCOME MEASUREMENTS: Estimates of excess relative risks per sievert (Sv) of radiation dose for mortality from cancers other than leukaemia and from leukaemia excluding chronic lymphocytic leukaemia, the main causes of death considered by radiation protection authorities. RESULTS: The excess relative risk for cancers other than leukaemia was 0.97 per Sv, 95% confidence interval 0.14 to 1.97. Analyses of causes of death related or unrelated to smoking indicate that, although confounding by smoking may be present, it is unlikely to explain all of this increased risk. The excess relative risk for leukaemia excluding chronic lymphocytic leukaemia was 1.93 per Sv (< 0 to 8.47). On the basis of these estimates, 1-2% of deaths from cancer among workers in this cohort may be attributable to radiation. CONCLUSIONS: These estimates, from the largest study of nuclear workers ever conducted, are higher than, but statistically compatible with, the risk estimates used for current radiation protection standards. The results suggest that there is a small excess risk of cancer, even at the low doses and dose rates typically received by nuclear workers in this study.

Dose-Response Relationship, Drug↗

PubMed2005

Investigating time patterns of variation in radiation cancer associations.

AIMS: In occupational settings, carcinogenic exposures are often repeated or protracted over time. The time pattern of exposure accrual may influence subsequent temporal patterns of cancer risk. The authors present several simple models that may be used to evaluate the influence of time since exposure or age at exposure on cancer incidence or mortality in an occupational cohort. METHODS: A cohort of 40,415 nuclear industry workers was identified via the Canadian National Dose Registry. Vital status and cause of death were ascertained through 1994. Associations between ionising radiation and mortality due to lung cancer, leukaemia, and cancers other than lung and leukaemia were quantified using conditional logistic regression models with risk sets constructed by incidence density sampling. A step function, a bilinear function, and a sigmoid function were used to evaluate temporal variation in exposure effects. RESULTS: Step and sigmoid functions were used to explore latency and morbidity periods. For analyses of lung cancer, leukaemia, and other cancers the best fitting models were obtained when exposure assignment was lagged by 13, 0, and 5 years, respectively. A bilinear function was used to evaluate whether exposure effects diminished with time since exposure. In analyses of lung cancer and leukaemia, there was evidence that radiation effects attenuated with protracted time since exposure. In analyses of age at exposure, there was evidence of variation in radiation mortality associations for analyses of lung cancer and leukaemia; discounting radiation doses accrued at younger ages (for example, 15-35 years) led to significant improvements in model fit. CONCLUSIONS: This paper illustrates empirical approaches to evaluating temporal variation in the effect of a protracted exposure on disease risk.

Adolescent↗

PubMed2005

Poisson regression analysis of ungrouped data.

BACKGROUND: Poisson regression is routinely used for analysis of epidemiological data from studies of large occupational cohorts. It is typically implemented as a grouped method of data analysis in which all exposure and covariate information is categorised and person-time and events are tabulated. AIMS: To describe an alternative approach to Poisson regression analysis using single units of person-time without grouping. METHODS: Data for simulated and empirical cohorts were analysed by Poisson regression. In analyses of simulated data, effect estimates derived via Poisson regression without grouping were compared to those obtained under proportional hazards regression. Analyses of empirical data for a cohort of 138 900 electrical workers were used to illustrate how the ungrouped approach may be applied in analyses of actual occupational cohorts. RESULTS: Using simulated data, Poisson regression analyses of ungrouped person-time data yield results equivalent to those obtained via proportional hazards regression: the results of both methods gave unbiased estimates of the "true" association specified for the simulation. Analyses of empirical data confirm that grouped and ungrouped analyses provide identical results when the same models are specified. However, bias may arise when exposure-response trends are estimated via Poisson regression analyses in which exposure scores, such as category means or midpoints, are assigned to grouped data. CONCLUSIONS: Poisson regression analysis of ungrouped person-time data is a useful tool that can avoid bias associated with categorising exposure data and assigning exposure scores, and facilitate direct assessment of the consequences of exposure categorisation and score assignment on regression results.

Adolescent↗

PubMed2005

Age at exposure to ionising radiation and cancer mortality among Hanford workers: follow up through 1994.

BACKGROUND: Studies of workers at the plutonium production factory in Hanford, WA have led to conflicting conclusions about the role of age at exposure as a modifier of associations between ionising radiation and cancer. AIMS: To evaluate the influence of age at exposure on radiation risk estimates in an updated follow up of Hanford workers. METHODS: A cohort of 26 389 workers hired between 1944 and 1978 was followed through 1994 to ascertain vital status and causes of death. External radiation dose estimates were derived from personal dosimeters. Poisson regression was used to estimate associations between mortality and cumulative external radiation dose at all ages, and in specific age ranges. RESULTS: A total of 8153 deaths were identified, 2265 of which included cancer as an underlying or contributory cause. Estimates of the excess relative risk per Sievert (ERR/Sv) for cumulative radiation doses at all ages combined were negative for all cause and leukaemia and positive for all cancer and lung cancer. Cumulative doses accrued at ages below 35, 35-44, and 45-54 showed little association with mortality. For cumulative dose accrued at ages 55 and above (10 year lag), the estimated ERR/Sv for all cancers was 3.24 (90% CI: 0.80 to 6.17), primarily due to an association with lung cancer (ERR/Sv: 9.05, 90% CI: 2.96 to 17.92). CONCLUSIONS: Associations between radiation and cancer mortality in this cohort are primarily a function of doses at older ages and deaths from lung cancer. The association of older age radiation exposures and cancer mortality is similar to observations from several other occupational studies.

Adolescent↗

PubMed2004

Deindustrialisation and the long term decline in fatal occupational injuries.

AIMS: To examine the extent to which deindustrialisation accounts for long term trends in occupational injury risk in the United States. METHODS: Rates of fatal unintentional occupational injury were computed using data from death certificates and the population census. Trends were estimated using Poisson regression. Standardisation and regression methods were used to adjust for the potential effect of structural change in the labour market. RESULTS: The fatal occupational injury rate for all industries declined 45% from 1980 to 1996 (RR (rate ratio) 0.55, 95% CI 0.52 to 0.57). Adjustment for structural changes in the workforce shifted the RR to 0.62 (95% CI 0.60 to 0.65). Expanding industries enjoyed more rapid reduction in risk (-3.43% per year, 95% CI -3.62 to -3.24) than those that contracted (-2.65% per year, 95% CI -2.88 to -2.42). CONCLUSIONS: Deindustrialisation contributed to the decline of fatal occupational injury rates in the United States, but explained only 10-15% of the total change.

Accidents, Occupational↗

PubMed2004

The impact of exposure categorisation for grouped analyses of cohort data.

BACKGROUND: Poisson regression is routinely used in occupational and environmental epidemiology. For typical Poisson regression analyses, person-time and events are tabulated by categorising predictor variables that were originally measured on a continuous scale. In order to estimate a dose-response trend, a researcher must decide how to categorise exposures and how to assign scores to exposure groups. AIMS: To investigate the impact on regression results of decisions about exposure categorisation and score assignment. METHODS: Cohort data were generated by Monte Carlo simulation methods. Exposure categories were defined by quintiles or deciles of the exposure distribution. Scores were assigned to exposure groups based on category midpoint and mean exposure levels. Estimated exposure-disease trends derived via Poisson regression were compared to the "true" association specified for the simulation. RESULTS: Under the assumption that exposures conform to a lognormal or exponential distribution, trend estimates tend to be negatively biased when scores are assigned based on category midpoints and positively biased when scores are assigned based on cell specific mean values. The degree of bias was greater when exposure categories were defined by quintiles of the exposure distribution than when categories were defined by deciles of the exposure distribution. CONCLUSIONS: The routine practice of exposure categorisation and score assignment introduces exposure misclassification that may be differential with respect to disease status and, consequently, lead to biased exposure-disease trend estimates. When using the Poisson regression method to evaluate exposure-disease trends, such problems can be minimised (but not necessarily eliminated) by forming relatively refined exposure categories based on percentiles of the exposure distribution among cases, and by assigning scores to exposure categories that reflect person-time weighted mean exposure levels.

Cohort Studies↗

PubMed2004

An incidence density sampling program for nested case-control analyses.

BACKGROUND: The nested case-control design can be a very efficient approach to an epidemiological investigation. In order to obtain unbiased estimates of relative risk, controls should be selected by incidence density sampling, which involves matching each case to a sample of those who are at risk at the time of case occurrence. METHODS: This paper presents a simple computer program for incidence density sampling. This program was evaluated using data derived from a cohort study of mortality among workers employed in the nuclear weapons industry. Controls were selected for cases via incidence density sampling; an estimate of the exposure-mortality association was obtained via conditional logistic regression. After 100 iterations of this procedure, the average effect estimate was compared to the risk estimate obtained via proportional hazards regression. The same methods were used to evaluate a program for incidence density sampling that was proposed previously by Pearce in 1989. RESULTS: Relative risk estimates obtained from nested case-control analyses conducted using the incidence density sampling program reported in this paper are unbiased. In contrast, the program for incidence density sampling proposed by Pearce tended to produce biased relative risk estimates; the magnitude of bias increased with increasing numbers of controls selected per case. CONCLUSIONS: The computer program described in this paper offers a simple approach to incidence density sampling for nested case-control analyses with exact matching on attained age and appropriate enumeration of the pool of eligible controls for each case. This method overcomes problems of bias inherent in a previously proposed program for incidence density sampling.

Bias↗

PubMed1999

Greater sensitivity to ionizing radiation at older age: follow-up of workers at Oak Ridge National Laboratory through 1990.

BACKGROUND: Workers at Oak Ridge National Laboratory (ORNL) were individually monitored for whole body exposure to ionizing radiation. Studies of these workers may provide valuable information about the long-term effects of occupational exposure to ionizing radiation. Since biological changes occur as adults age, a potentially important question in these investigations is whether sensitivity to the carcinogenic effects of ionizing radiation changes with age at exposure. METHODS: Vital status and cause of death were ascertained through 1990 for 8307 white males hired at ORNL from 1943 through 1972. Associations between whole body ionizing radiation dose and all-cancer mortality were quantified using life table regression methods for time dependent exposures. Analyses focused of differences in radiation-cancer associations with age at exposure. Length of follow-up, period of hire, and age at risk were considered as alternative explanations for effects of age at exposure. RESULTS: Cumulative radiation dose was associated with a 1.8% (SE = 0.9) increase in all-cancer mortality per 10 mSv, assuming a 10-year lag between exposure and mortality. However, radiation doses received at older ages exhibited larger associations with cancer mortality than doses received at younger ages. Doses received after age 45 were associated with a 5.9% (SE = 1.7) increase in cancer mortality per 10 mSv, adjusted for doses received before age 45. Dose-response associations between cancer mortality and doses received after age 45 appeared consistent across periods of follow-up, periods of hire, and ages at risk. CONCLUSIONS: Findings suggest that sensitivity to the carcinogenic effects of ionizing radiation may increase with older ages at exposure. More attention should be given to the role of age at exposure in studies of the health effects of low-level exposure to ionizing radiation, and to efforts to limit exposure to ionizing radiation.

Adult↗

PubMed1999

Radiation and mortality of workers at Oak Ridge National Laboratory: positive associations for doses received at older ages.

We examined associations between low-level exposure to ionizing radiation and mortality among 14,095 workers hired at the Oak Ridge National Laboratory between 1943 and 1972. Workers at the facility were individually monitored for external exposure to ionizing radiation and have been followed through 1990 to ascertain cause of death information. Positive associations were observed between low-level exposure to external ionizing radiation and mortality. These associations were larger for doses received after 45 years of age, larger under longer lag assumptions, and primarily due to cancer causes of death. All cancer mortality was estimated to increase 4.98% [standard error (SE) = 1.5] per 10-mSv cumulative dose received after age 45 under a 10-year lag, and 7.31% (SE = 2.2) per 10-mSv cumulative dose received after age 45 under a 20-year lag. Associations between radiation dose and lung cancer were of similar magnitude to associations between radiation dose and all cancers except lung cancer. Nonmalignant respiratory disease exhibited a positive association with cumulative radiation dose received after age 45, whereas ischemic heart disease exhibited no association with radiation dose. These findings suggest increases in cancer mortality associated with low-level external exposure to ionizing radiation and potentially greater sensitivity to the carcinogenic effects of ionizing radiation with older ages at exposure.

Adult↗

PubMed1998

Methods for investigating age differences in the effects of prolonged exposures.

People experience physiological changes with age which may lead to changes in sensitivity to many kinds of exposure. In situations of prolonged, low level exposure, differences in the effects of exposures received at different ages may be difficult to evaluate, since study members receive low level exposures over a range of ages. Such investigations require examination of the effects of different age-patterns of exposure. Three approaches to investigating age-related variability in the effects of prolonged exposures are described: subcohort analyses; the use of smooth weighting functions; and the evaluation of separate effects of cumulative exposures received at different age ranges. Each method can contribute to the overall evaluation of age-specific exposure effects. These methods are illustrated with occupational cohort data for employees of Oak Ridge National Laboratory. The methods presented in this paper should facilitate examination of the effects of aging on sensitivity to prolonged exposures.

Adult↗

PubMed1997

Fatal occupational injuries in a southern state.

Fatal occupational injuries were studied using data from medical examiners' reports in North Carolina for the years 1977-1991. Cases were defined as deaths due to accidents or homicide at the workplace, and populations at risk were estimated from the 1980 and 1990 US Censuses. Mortality rate ratios and proportionate mortality ratios were used as measures of association, and the population attributable risk percentage was used as an indicator of the burden of injury. Standard weights for direct age-adjustment of rates were obtained from the total state workforce. There were 2,524 eligible deaths-83 percent from unintentional traumatic injuries, 14 percent from homicide, and the remainder from other causes. This report focuses on unintentional trauma deaths, which were strongly associated with the wood production, fishing, and transportation industries. Elderly, African-American, and self-employed workers had higher fatality rates than members of other groups. Among male workers, motor vehicle crashes were the principal cause of death on the job, followed by falling objects, machinery, and falls. The industries contributing the largest proportions of these deaths were construction, trucking, agriculture, and logging (population attributable risk percentages were 16.8%, 8.8%, 7.9%, and 6.9%, respectively). The fatality patterns of female workers were different: Numbers of deaths from homicide and unintentional trauma were equal, and 27% of the latter deaths occurred in one catastrophic fire. Decentralized and rural industries were the most hazardous, but many deaths were outside the current jurisdiction of occupational safety and health agencies. These patterns suggest that greater scrutiny of such industries, through both research and intervention, is warranted.

Accidents, Occupational↗

PubMed1995

Respiratory effects of chronic hydrogen sulfide exposure.

A cross-sectional study investigated whether the exposure of sewer workers to hydrogen sulfide (H2S) was associated with reduced lung function. Sixty-eight sewer workers and 60 water treatment workers performed spirometric tests. Job titles were used to classify the sewer workers according to presumed H2S exposure, and water treatment workers served as a comparison population presumed to have no occupational exposure to H2S. There was a statistically significant difference in mean FEV1/FVC values between sewer and water treatment workers of similar age, height, race, and smoking habits (-3.1, s.e. = 1.4). This deficit was greatest (-5.7, s.e. = 2.0) for sewer workers presumed to have high H2S exposure. Nonsmoking sewer workers presumed to have high H2S exposure achieved only 89% of their predicted FEV1/FVC value, whereas nonsmoking water treatment workers achieved nearly 98% of their predicted FEV1/FVC value. In conclusion, this study found evidence that chronic low level exposure to H2S may be associated with reduced lung function.

Adult↗

PubMed1992

Elderly patients in the emergency department: a prospective study of characteristics and outcome.

OBJECTIVE: To describe the characteristics of elderly patients presenting to an emergency department and the outcome for these patients at 90 days. DESIGN: Prospective, descriptive study of all patients over 75 years of age presenting in a four week period. Follow-up data were obtained from the case notes, the Registry of Deaths, the Geriatric Assessment Team and, where necessary, contact with the family doctor. SETTING: The Department of Emergency Medicine at the Royal Hobart Hospital, Tasmania, in late 1989. MAIN OUTCOME MEASURES: Death or increased dependence as defined by permanent institutionalisation, moving in with family, or more than 90 days inpatient care. RESULTS: There were 210 presentations by 191 different patients; 116 were admitted to our hospital (55.2%), and three (1.4%) to other hospitals. Follow-up data were obtained for all but five patients. At 90 days from first presentation 23 had died (12.4%) and in a further 19 (10.2%) their dependence had increased. Risk factors for death were fractured neck of femur or cardiac failure. Risk factors for either death or increased dependence were referral by someone outside the immediate family, neurological disease, cardiac failure, an apparent social/placement problem, and being assessed as needing admission. The strongest predictor was a social problem. Age was not a risk factor. CONCLUSIONS: A predictive formula for poor outcome in this group can be derived. However, outcome may not be altered by admission, or intervention. In the elderly, it is quality rather than duration of life which should be paramount in considering the benefits of therapy.

Aged↗

PubMed1992

Blood flow imaging through detection of temporal variations in magnetization.

Two hypotheses were tested: (a) that view-to-view variations in bulk phase and modulus of magnetization in vascular volume elements can indicate the presence of disordered blood flow, and (b) that a substantial loss of signal intensity on magnetic resonance (MR) angiograms of poststenotic regions is due to view-to-view changes in magnetization. To test these hypotheses, a technique was developed in which view-to-view variations in transverse magnetization were used to create angiographic projection images, which showed only disordered flow (disordered flow maps) in vitro and in vivo. In phantom studies, this technique recovered signal intensity downstream from stenoses. A combination of disordered flow maps with morphologic images improved visualization of stenotic regions and provided information on characteristics of local flow. These results show that view-to-view variations in transverse magnetization occur in regions of disordered flow and are an important cause of loss of signal intensity. This technique can provide information about dynamic blood flow and improve depiction of anatomic structures on MR angiograms.

Blood Circulation↗

PubMed1981

Water intake elicited by injections of angiotensin II into preoptic area of rats.

Drinking in response to unilateral injections of angiotensin II (AII) into the preoptic area is relatively weak and a relatively high dose of AII is required. A comparison was made of the drinking elicited by bilateral and unilateral injections of AII. Reliable drinking was observed when 5 X 10(-12) mol of AII in 0.2 microliter was injected bilaterally into the preoptic area, and in some animals when the dose of AII was 0.5 X 10(-12) mol in 0.2 microliter. The volumes of water intake were significantly larger with bilateral injections compared to unilateral injections. By injection of tritiated AII to elicit drinking and subsequent autoradiographic analysis of brain sections, it was shown that the injections were confined to the preoptic region and did not reach the cerebral ventricles. The results suggest that 1) bilateral injections may be more appropriate for comparing the preoptic region with other putative angiotensin receptive sites, 2) there is a greater responsiveness of the preoptic region to bilateral as compared with unilateral injections, and 3) the AII receptive area is diffusely represented in the region of the medial preoptic nucleus.

Angiotensin II↗

PubMedDate not supplied

Magnetization-prepared MR angiography with fat suppression and venous saturation.

Magnetization-prepared magnetic resonance (MR) angiography (MPMRA) is an inflow-based two-dimensional (2D) imaging sequence in which a preparation phase precedes rapid image acquisition. For maximal blood/tissue contrast, an inversion-recovery preparation nulls signal from static tissue. If needed, a second inversion suppresses signal from fat. Fully magnetized blood flows in after the inversion pulse(s), providing high signal intensity. The centric phase-encoding order, which ensures that the initial contrast is reflected in the image set, requires the use of a modified venous saturation technique. The sequence is described and its performance assessed with regard to (a) depiction of in-plane flow, (b) fat suppression, and (c) venous saturation. Phantom and volunteer studies showed good performance in all three areas. MPMRA images, acquired in just 2-4 seconds per image, had a blood/tissue contrast-to-noise ratio nearly twice that of standard 2D time-of-flight MR angiograms, acquired in 5-7 seconds. The technique is promising for restless patients and in anatomic areas plagued by motion degradation.

Adipose Tissue↗

PubMedDate not supplied

Asymmetric-echo, short TE, retrospectively gated MR imaging of the heart and pulmonary vessels.

Although retrospectively cardiac-gated (cine) magnetic resonance imaging has shown promise for large-vessel pulmonary vascular imaging, it has not been able to depict the peripheral pulmonary vasculature, where signal is dephased because of susceptibility and/or motion artifacts. The authors developed a cine pulse sequence that uses asymmetric echoes and radio-frequency envelopes to achieve reduced gradient moments and a short TE, thereby reducing signal losses due to disordered flow and susceptibility effects. The effects of TE (2.8-12 msec) and the degree of echo symmetry as measured by the echo symmetry fraction (ESF) (0.6-1.0) are considered in the pulmonary vasculature and the heart. In pulmonary vessels, the signal-to-noise ratio nearly doubled as TE was decreased from 12 to 2.8 msec, but there was only about a 15% difference as the ESF decreased from 1.0 to 0.6, consistent with T2* losses dominating gradient moment dephasing. At a TE of 2.8 msec, the sequence improves visualization of pulmonary vessels and may be helpful for diagnosing pulmonary emboli. In the heart, however, the contrast-to-noise ratio between blood and cardiac tissue decreased by 30% as TE decreased from 12 to 2.8 msec and was not affected by changes in ESF. Flow artifacts in the cardiac blood pool, including those that can aid in diagnosis (eg, signal loss due to "jet" flow), are much less pronounced when a small ESF and short TE are used, making this sequence less attractive for investigation of cardiac flow irregularities. The reduced flow artifacts in this case, however, permit excellent depiction of gross cardiac anatomy.

Arteriovenous Malformations↗