Fredric Gerr

Background: Occupational and environmental exposure to lead has been examined for its effect on blood pressure (BP) in adults with varying results. The present analyses assessed the association between bone lead concentration and BP in early adult life in persons exposed during childhood.Methods: Study participants included young adult members of two cohorts with different past histories of lead exposure. Lead exposure was assessed using noninvasive K‐X‐ray fluorescence spectroscopy to quantify bone lead concentration, an index of long‐term lead exposure superior to current blood lead concentration. Systolic and diastolic BP measurements were obtained using conventional clinical methods. Multiple linear regression models were constructed to allow for control of covariates of BP identified a priori.Results: Analyses were performed on 508 participants. While controlling for potential confounders, systolic BP was 4.3 mm Hg greater among members of the highest of four bone lead concentration groups (> 10 μgPb/g bone) when compared with the lowest bone lead concentration group (< 1 μgPb/g bone; P = 0.004), and diastolic BP was 2.8 mm Hg greater among members of the highest bone lead concentration group when compared with the lowest bone lead concentration group (P = 0.03).Conclusions: These results suggest that substantial lead exposure during childhood can increase BP during young adulthood. Am. J. Ind. Med. 42:98–106, 2002.

Background: A prospective study of computer users was performed to determine the occurrence of and evaluate risk factors for neck or shoulder (N/S) and hand or arm (H/A) musculoskeletal symptoms (MSS) and disorders (MSD).Methods: Individuals (n = 632) newly hired into jobs requiring ≥ 15 hr/week of computer use were followed for up to 3 years. At study entry, workstation dimensions and worker postures were measured and medical and psychosocial risk factors were assessed. Daily diaries were used to document work practices and incident MSS. Those reporting MSS were examined for specific MSD. Incidence rates of MSS and MSD were estimated with survival analysis. Cox regression models were used to evaluate associations between participant characteristics at entry and MSS and MSD.Results: The annual incidence of N/S MSS was 58 cases/100 person‐years and of N/S MSD was 35 cases/100 person‐years. The most common N/S MSD was somatic pain syndrome. The annual incidence of H/A MSS was 39 cases/100 person‐years and of H/A MSD was 21 cases/100 person‐years. The most common H/A disorder was deQuervain's tendonitis. Forty‐six percent of N/S and 32% of H/A MSS occurred during the first month of follow‐up. Gender, age, ethnicity, and prior history of N/S pain were associated with N/S MSS and MSD. Gender, prior history of H/A pain, prior computer use, and children at home were associated with either H/A MSS or MSD.Conclusions: H/A and N/S MSS and MSD were common among computer users. More than 50% of computer users reported MSS during the first year after starting a new job. Am. J. Ind. Med. 41:221–235, 2002.

Many summary measures of data obtained from tremor measurement procedures are commonly reported. The reliability of many of these summary measures of tremor measurements made in field testing situations is unknown. The purpose of the present investigation was to assess the reliability of a number of summary measures produced by the software of a widely used, commercially available tremor measurement instrument using data collected in three field epidemiologic studies. Tremor data were obtained from 689 participants in 3 previously conducted studies of groups exposed to elemental mercury or arsenic. A widely used, commercially available tremor measurement instrument was used. Two-axis accelerometer measurements were obtained on 2 or more trials from each hand for each participant. Estimates of trial-to-trial and internal consistency reliability were calculated for 5 summary measures calculated by instrument manufacturer's software and 5 additional summary measures calculated from data output by the software. An RMS acceleration measure had the highest reliability in all 3 studies. The average over 4 trials of RMS acceleration and its logarithm had high reliability (>0.9). Recalculation of a tremor summary index and a harmonicity index as suggested by Edwards and Beuter (1999) resulted in measures with higher reliability and better distributional shape than the corresponding measures provided by the instrument manufacturer's software. The results in all three studies were similar. For the tremor measurement instrument and testing procedure that we employed, we recommend using the common logarithm of the RMS accelerations and recalculated tremor index as summary measures. We also recommend employing multiple trials of each type (e.g., with each hand) and averaging summary measures from those trials to derive outcome measures of tremor for use in epidemiologic studies. We recommend at least 2 trials for RMS acceleration measures and more for less reliable measures, particularly for designs employing repeated measurements of individuals. Summary measures averaged over at least 4 trials for mean frequency, dispersion of frequency, and power in the 3-6.5 and 6.6-10 Hz frequency ranges have sufficiently high reliability for use in epidemiologic studies.

The purpose of the present investigation was to 1) compare a neurologist's physical examination (NPx) rating of severity of postural tremor to several summary measures derived from quantitative measurements of tremor and 2) compare a NPx rating of standing steadiness and related clinical findings to quantitative sway speed measurements. Comparisons were performed on data obtained from two epidemiological field studies: 1) retired heavy industrial workers (n= 198, approximately half previously exposed to elemental mercury), and 2) small town residents (n=234, approximately 40% with environmental exposure to arsenic). A commercially available tremor measurement instrument was used in both studies. To obtain standing steadiness measures, a head position monitoring device was used in the mercury study, and a force platform was used in the arsenic study. The NPx included assessment of postural tremor, as well as evaluation of vibration perception and proprioception of the great toe, Achilles tendon reflex activity, Romberg test status, and tandem gait. One neurologist performed all the NPx in both studies and results were graded as normal, equivocal, or abnormal. The square root of the proportion of variance accounted for by a linear trend term in ANOVA models was used as an estimate of association between quantitative tests and clinical examination grade. An estimate of agreement, kappa, was also calculated after both NPx and quantitative test results were dichotomized. Most tremor summary measures varied monotonically with NPx tremor severity grade. Moderately good associations were observed between the tremor acceleration measure and NPx postural tremor grade (correlations up to approximately 0.5). Sway speed with eyes open and with eyes closed increased monotonically with NPx grade for most of the clinical signs. The NPx signs showing the strongest relationships with sway speed were Romberg test performance, tandem gait, and proprioception and vibration sensation of the great toe (correlations up to approximately 0.5). Quantitative tremor measurements were related to a neurologist's grading of postural tremor. Sway speed was associated with several NPx findings related to standing stability. Quantitative measurements of tremor and standing stability may provide more precise and objective measures of neurological function than NPx by a neurologist and are likely to be more consistent across times and examiners.

Objective. The purpose of this investigation was to develop and apply case definitions of peripheral neuropathy (PN) derived from a set of individual measures of peripheral nerve function obtained in two epidemiological studies. Methods. In the first study, retired workers of an industrial plant who were either previously exposed to mercury or not underwent a set of peripheral neurological tests. In the second study, persons living in an arsenic contaminated community in rural Georgia, USA, and unexposed comparison subjects were tested. In both studies all participants received a neurological physical examination, functional quantitative tests of vibrotactile thresholds and standing stability, and nerve conduction measurements. Two types of analyses were performed First, the effect of exposure group status was examined for each individual test. For tests with continuous outcomes, the effect of exposure group was estimated while controlling for covariates. For tests with categorical outcomes (all of the neurological examination outcomes), exposure group effects were estimated by comparison of the proportion of abnormal test results among the exposed and unexposed groups. Second, case definitions of PN were constructed using combinations of results of the tests performed. Each of the continuous measures was categorized as normal, equivocal, or abnormal on the basis of adjusted standardized scores. Separate "abnormality scores" were constructed for I) the nerve conduction tests and 2) the functional quantitative tests and physical examination findings. Five case definitions for PN were constructed based on combinations of these two abnormality scores. Results. Generally, small differences were observed between exposed (n=79 arsenic exposed and 85 mercury exposed) and unexposed (n=84 arsenic unexposed and 718 mercury unexposed) groups when results of each clinical, functional or electrophysiological test were examined separately. Clearer group differences were observed in the proportions of each group who met case definitions for PN, however. For example, for both studies, the largest difference in nerve conduction measures between exposed and unexposed groups was approximately 0.33 SD, while the composite case definition showed an odds ratio of more than 3.1 for the mercury study and 5.1 for the arsenic study. Conclusions. These results suggest improved efficiency (and avoidance of the multiplecomparisons problem) for detecting peripheral nerve effects when case definitions of PN are constructed rather when results of individual tests of PN function are compared. (C) 2000 Inter Press, Inc.

Persons living in a small town in Georgia, USA, were studied because of known environmental exposure to arsenic-containing dust. To assess the effects of this exposure on the nervous system, a cross-sectional epidemiological study was performed. The health outcome assessments of the study were based on a priori selected clinical examination results and quantitative electrophysiologic and behavioral outcome measures. Because the primary goal was to identify cases of peripheral neuropathy, a clinically relevant case definition, based on results of these outcomes was created. Historical exposure reconstructions were performed on a subset of the exposed subjects for whom such information was available. Of the 238 persons enrolled in the study, 133 were classified as non-exposed (i.e., did not reside in the area of known exposure) and 105 were classified as exposed (i.e., did reside in the area of known exposure). Following exclusions of persons with occupational exposure to neurotoxicants, pre-existing conditions associated with peripheral nerve impairment, or age below 18 years, 118 unexposed subjects and 85 exposed subjects were available for inclusion in the analyses of peripheral nerve outcomes. A total of 4 (3.4%) of the unexposed subjects and 13 (15.3%) of the exposed subjects met the case definitions for peripheral neuropathy (OR=5.1; p=0.004). Comparison of three exposure groups (none, low, high) did not yield statistically significant differences. Statistically significant exposure group differences were observed on quantitative tests of standing steadiness, vibrotactile threshold and tremor intensity but not for nerve conduction measures. These results demonstrate a strong association between community arsenic containing dust exposure and peripheral neuropathy among participants in this investigation.

This investigation tested the hypotheses that (1) physical workstation dimensions are important determinants of operator posture, (2) specific workstation characteristics systematically affect worker posture, and (3) computer operators assume “neutral” upper limb postures while keying. Operator head, neck, and upper extremity posture and selected workstation dimensions and characteristics were measured among 379 computer users. Operator postures were measured with manual goniometers, workstation characteristics were evaluated by observation, and workstation dimensions by direct measurement. Considerably greater variability in all postures was observed than was expected from application of basic geometric principles to measured workstation dimensions. Few strong correlations were observed between worker posture and workstation physical dimensions; findings suggest that preference is given to keyboard placement with respect to the eyes (r = 0.60 for association between keyboard height and seated elbow height) compared with monitor placement with respect to the eyes (r = 0.18 for association between monitor height and seated eye height). Wrist extension was weakly correlated with keyboard height (r = −0.24) and virtually not at all with keyboard thickness (r = 0.07). Use of a wrist rest was associated with decreased wrist flexion (21.9 versus 25.1°, p < 0.01). Participants who had easily adjustable chairs had essentially the same neck and upper limb postures as did those with nonadjustable chairs. Sixty-one percent of computer operators were observed in nonneutral shoulder postures and 41% in nonneutral wrist postures. Findings suggest that (1) workstation dimensions are not strong determinants of at least several neck and upper extremity postures among computer operators, (2) only some workstation characteristics affect posture, and (3) contrary to common recommendations, a large proportion of computer users do not work in so-called neutral postures.