Postural stability of workers exposed to lead

Relationship between Postural Stability, Lead Content, and Selected Parameters of Oxidative Stress

This study attempts to determine whether the increased blood lead concentration affects the posturographic test and to determine the relationship between the parameters of posture stability and selected parameters of oxidative stress. The study population consisted of 268 male employees and was divided into two equal subgroups, depending on the lead content in the blood. A posturographic examination was performed. Concentrations of lead, cadmium, zinc protoporphyrin, selected essential elements, and selected markers of oxidative stress in the blood were tested. Higher blood lead concentrations positively affected the values of the sway results: the field and the mean velocity of the center of the feet pressure in posturography. The absolute value of the proprioception ratio was similar in both subgroups. The content of malondialdehyde shows a statistically significantly higher value in a subgroup with high blood lead concentration and exhibits significant correlations only with some of the posturography parameters. The lipofuscin content in erythrocytes correlates with the results of the posturography test. Zinc protoporphyrin, total oxidant status, total antioxidant capacity, selected minerals, and metals did not correlate with the results of the posturography test. In conclusion, posturographic results correlate only with selected markers of oxidative stress, so it can be assumed that the effect on the body balance is only partial.

Study Correlating Lead (Pb) Level Exposure and Bone Shock Absorption Capacity Based on Damping Associated With Higher Modes of Vibration

Noninvasive vibration testing is one of the tools for characterizing the biomechanical properties of bones and muscle groups in humans and animals. They present alternatives for evaluating bone health quality and may serve as early indicators for bone fragility and bone-related diseases. In recent years, a vibration-based bone shock absorption (BSA) method has shown potential to relate the damping capacity associated with the fundamental (first) vibration modes for developing dynamic bone quality indicators for osteoporosis patients. This research presents a study of early life (birth to age 78 months) lead (Pb) exposure on the damping capacity (bone fragility measures) with the bone shock absorption method. The damping ratio corresponding to few vibration modes is extracted and analyzed using clinical bone shock absorption data of patients with different Pb exposure levels. A method is developed for clustering and identifying three dominant vibration modes and their corresponding damping ratio. The statistical correlation between the damping parameters associated with higher vibration modes and Pb exposure level is presented here. This study highlights the importance of analyzing higher vibration modes and their damping capacity, which could be used to predict early diagnostics precursors of the bone- and/or muscle-related conditions or disorders.

Acute diesel exhaust exposure and postural stability: a controlled crossover experiment

Recent epidemiological evidence connects ambient air pollutants to adverse neurobehavioural effects in adults. In animal models, subchronic controlled exposures to diesel exhaust (DE) have also showed evidence of neuroinflammation. Evidence suggests that DE not only affects outcomes commonly associated with cognitive dysfunction, but also balance impairment. We conducted a controlled human exposure experiment with 28 healthy subjects (average age = 28 years (SD = 7.1; range = 21-49); and 40% female) who were exposed to two conditions, filtered air (FA) and DE (300 μg PM2.5/m3) for 120 min, in a double-blinded crossover study with randomized exposures separated by four weeks. Postural stability was assessed by the Balance Error Scoring System (BESS), a brief, easily-administered test of static balance. The BESS consists of a sequence of three stances performed on two surfaces. With hands on hips and eyes closed, each stance is held for 20 s. "Error" points are awarded for deviations from those stances. Pre- and immediately post-exposure BESS "error" point totals were calculated and the difference between the two timepoints were compared for each of the two exposure conditions. A mixed effect model assessed the significance of the association. While our data demonstrates a trend of reduced postural stability in response to exposure to DE, exposure was not significantly associated with BESS value. This is the first study to investigate changes in postural stability as a result of exposure to DE in human subjects.

Lead and cadmium levels and balance and vestibular dysfunction among adult participants in the National Health and Nutrition Examination Survey (NHANES) 1999-2004

BACKGROUND

Few studies have been conducted to identify risk factors for balance and vestibular dysfunction in general populations, but previous studies have reported evidence of adverse effects of lead and cadmium on balance control in high-risk groups.

OBJECTIVE

We evaluated the relationship between blood lead and cadmium levels and balance and vestibular dysfunction in a general population study.

METHODS

We analyzed data from the 1999-2004 National Health and Nutrition Examination Survey (NHANES) of 5,574 adults ≥ 40 years of age. Balance dysfunction was evaluated by the Romberg Test of Standing Balance on Firm and Compliant Support Surfaces, which examines the ability to stand unassisted using four test conditions to evaluate vestibular system, vision, and proprioception inputs that contribute to balance. Blood levels of lead and cadmium were measured by atomic absorption spectrometry. Associations were estimated using logistic regression models adjusted for potential confounders. Associations with time to loss of balance were estimated using adjusted Cox proportional hazard models.

RESULTS

The adjusted odds ratio (OR) for balance dysfunction in association with the highest quintile (3.3-48 µg/dL) versus the lowest quintile (< 1.2 µg/dL) of lead was 1.42 [95% confidence interval (CI): 1.07, 1.89]. The corresponding OR for cadmium (0.9-7.4 µg/L vs. < 0.2 µg/L) was 1.27 (95% CI: 1.01, 1.60). The adjusted hazard ratio for time to failure for the most physiologically challenging balance test among subjects with the highest vs. lowest quintiles of blood lead was 1.24 (95% CI: 1.04, 1.48). Cadmium levels were not associated with time to failure.

CONCLUSIONS

Our findings suggest that blood lead and cadmium levels may be associated with balance and vestibular dysfunction in a general sample of U.S. adults.

Neurotoxic effect of occupational exposure to mixed organic solvents in Korea: Posturographic study

BACKGROUND

This study used static posturography to investigate the neurotoxic effects on workers exposed to mixed organic solvents at low concentrations under the levels of the threshold limit values (TLV).

METHODS

Forty-one workers from four plants exposed to mixed solvents and 90 non-exposed referents were examined. The lifetime cumulative biological exposure (CE) was estimated according to subject's occupational history and biological monitoring results. Static posturography and questionnaire were the basis of data collection.

RESULTS

The mean exposure index of mixed organic solvents of four plants was 0.47 (SD: 0.33, range: 0.08-1.39). The exposed group showed a larger sway area and length under the eye open condition than did the non-exposed group. In a multiple linear regression, a significant positive association was demonstrated between postural sway area and CE.

CONCLUSIONS

This study results suggest that the exposure to organic solvents under TLV levels may cause disturbance in postural stability.

Critical dose of lead affecting postural balance in workers

BACKGROUND

The threshold blood lead (BPb) level for nervous system dysfunction in adults has been estimated to be 30-40 microg/dl. This study was carried out to estimate the critical dose of lead affecting the neuromotor function in workers by introducing the benchmark dose (BMD) approach, as well as to identify the specific postural sway to lead exposure.

METHODS

Postural sway parameters with spectral analysis were compared between 121 lead workers with BPb levels of 6-89 (mean 40) microg/dl and 60 unexposed controls.

RESULTS

All sway parameters, except for sagittal sways with eyes open, were significantly larger in the lead workers than in the controls; also, the Romberg quotient for sagittal sway was significantly higher in the lead workers. The BPb level in the lead workers was significantly related to sagittal sways at 1-2 Hz and 2-4 Hz with eyes open, and sagittal and transversal sways at 1-2 Hz and 2-4 Hz with eyes closed. The BMD levels of BPb (i.e., lower 95% confidence limits of BMD) were estimated to be 12.1-17.3 (mean 14.4) microg/dl for postural sway.

CONCLUSIONS

Neuromotor dysfunction in lead workers may be initiated at BPbs below the level previously accepted as effectless, and be characterized mainly by an increased sway of high frequency (1-4 Hz) in the sagittal direction with eyes closed (high Romberg quotient).

Postural stability and neurobehavioural effects of heat exhaustion among adult men

The medical complications of heat disorders, including haematological, cardiovascular and renal damage, have been well documented. However, very little has been written on its neurological complications. The objective of this study was to assess the effects of heat exhaustion on postural stability and neurobehavioral functions of men. The study is prospective in design and spans a 3-year period. All soldiers who were diagnosed to have heat exhaustion (cases) from 1 March 1998 to 31 August 1998 were included in the study. For each case, a healthy soldier (matched for age, ethnicity, years of education and military vocation) was recruited to serve as control. Each subject had a neurobehavioral assessment by using the Swedish Performance Evaluation System (SPES), a computerized test battery. The postural stability of the subjects was assessed using a computerized postural sway system. Findings for 37 heat exhaustion cases and 37 controls revealed that cases had a significantly higher prevalence of neurasthenia symptoms compared to the controls. There were significant (small) differences between the cases and controls in the neurobehavioral tests of choice reaction time, digit span and some parts of colour word stress and logical series measures. Postural stability in the cases was significantly poorer when in the "eyes-closed" condition, compared with the controls. Men with heat exhaustion, studied 2 weeks after the acute episode, had significantly more symptoms of neurasthenia, poorer performance in short-term memory and slower reaction time. The cases (as a group) had significantly poorer postural stability.

Effect of exposure to lead on postural control in workers

OBJECTIVES

To examine the effect of lead on postural control of workers who have been exposed to lead.

METHODS

63 Male, lead battery workers mean (SD) age 41.0 (7.4) were compared with 48 age matched male controls after excluding those with acute or chronic diseases. Exposed workers had mean (SD) past blood lead concentrations of 37.5 (9.2) micrograms/dl and 11.2 (5.7) years of employment. Postural control was measured with a computerised postural sway measurement system which measured both sway and total movements.

RESULTS

Workers standing straight with eyes open on the bare plates had sway and total movements which were not notably different from controls. On the other hand increased movements were needed in the exposed workers to maintain stability (the general stability quotient 18.2 (5.4) v 15.4 (4.4) in controls, p < 0.01) when standing directly on the foot-plates with closed eyes,, and with the head tilted (15.0 (3.8) v 11.5 (3.0) in controls, p < 0.001). Exposed workers also had a trend for less ability to synchronize anterior posterior and lateral sway in the stress positions (0.0625) than had non-exposed workers. Significant but low correlations were found between the estimate of the chronic internal dose of lead and three of 10 of the postural control measurements, and present lead blood concentrations and only one of the 10 measurements and (r values ranged from 0.21 to 0.31, p < or = 0.03).

CONCLUSIONS

These findings suggest that lead affects postural control in asymptomatic workers. Further studies are warranted to find whether workers with decreased postural control are at increased risk of accidents and the relation, if any, of these measurements with subsequent morbidity.

Subclinical neurophysiological effects of lead: A review on peripheral, central, and autonomic nervous system effects in lead workers

BACKGROUND

The peripheral nerve conduction velocity (NCV), distribution of nerve conduction velocities (DCV), somatosensory, visual, and brainstem auditory evoked potentials (SEP, VEP, and BAEP, respectively), event-related potential (P300), computerized static posturography with spectral analysis (postural balance), and electrocardiographic R-R interval variability (CV(RR)) with spectral analysis appear to be promising techniques for assessing subclinical effects of lead on the peripheral, central and autonomic nervous systems. This article presents an overview of research addressing subclinical neurophysiological effects of lead in workers exposed to lead.

METHODS

We reviewed 102 articles to examine the effects and dose-effects relationships of lead on peripheral, central, and autonomic nervous system function together with reversibility of the effects, interaction between lead and other metals, and relative sensitivity and specificity of each technique. Background and methodology were also reviewed.

RESULTS AND CONCLUSION

Available data suggest that, on a group basis, the reduction in the NCV, together with the effects on the P300 latency, postural balance, and CV(RR), occurs at a mean blood lead concentration (BPb) as low as 30-40 microg/dL; the effects on the latencies of the short-latency SEP, VEP, and BAEP, as well as the DCV, start at a BPb as low as 40-50 microg/dL. Further cross-sectional and preferably prospective studies by using each of those methods are needed to establish more precise dose-effects (and response) relationships of lead.

Cumulative concentrations of blood lead and postural stability

OBJECTIVE

To study the association in a group of battery manufacturing workers between computerised postural sway parameters and present concentrations of blood lead (PPb), index of cumulative blood lead years (CBI), and cumulative blood lead at different years of exposure (CPbYs).

METHODS

Postural stability was investigated with a computerised postural sway measurement system in 60 workers exposed to lead with exposure duration of 84 (range 3-366) months and in 60 control subjects. An index of CBIs in 55 workers (previous blood lead results of five workers were not available) and CPbYs were computed for each worker by calculating the area under the curve of concentrations of blood lead against time.

RESULTS

The mean (SD) PPb was 36.0 (11.7) (range 6.4 to 64.5) micrograms/dl for the exposed workers and 6.3 (2.4) (range 3.1-10.9) micrograms/dl for the 14 randomly selected control subjects. Significant differences between groups for the postural sway parameters obtained when the eyes were closed were found for length of sway path (L); mean velocity of the centre of pressure along its path (Vel); area included within the path of the centre of pressure (Ao); 95% confidence elliptical area (Ae). The Romberg ratio (the relation between eyes closed and open) for the Vel, L, Ao, and Ae of the exposed group were also significantly different from those of the controls. The postural sway parameters (eyes closed) were not significantly correlated with PPb or CBI. However, the cumulative blood lead for the past two years before the postural sway assessment, CPbY2, was significantly correlated with all the postural sway parameters.

CONCLUSION

The study showed that workers exposed to lead had significantly poorer postural stability than a control group. Lead may affect certain parts of the somatosensory system resulting in postural instability when the visual input is cut off. The CPbY2 was significantly positively correlated with most of the postural sway parameters. Effects of lead on postural stability may be related to recent increases in blood lead concentration among the exposed workers rather than to cumulative body burden.