Biomedical subjects

Anne Beuter

Publications and source records attributed to Anne Beuter.

At least 19 recordsLinked to original sources

PubMed2006

Quantitative tremor assessment in workers with current low exposure to mercury vapor.

Measurement of tremor has been used in several occupational studies of workers with long-term exposure to mercury vapor (Hg(0)). Recent studies indicate an adverse effect even at relatively low exposure levels. In the present study, we used sensitive quantitative methods to assess tremor in chloralkali workers with current low exposure to Hg(0). Neurological examinations and recordings of tremor using both an accelerometer and a laser-based system were conducted in 43 mercury-exposed workers and 22 age-matched referents. The median urinary mercury concentration in exposed workers was 5.9 (1.3-25) microg/g creatinine (microg/gC), while it was 0.7 (0.2-4.1) microg/gC in referents. The mean exposure time was 15 years, and the median cumulative mercury index was 161 years x microg/gC in exposed workers. There were no differences between the exposed workers and the referents in the clinical evaluation of tremor. In the quantitative tremor tests, no associations were found with current or cumulative mercury exposure for the majority of tremor measures. There were indications that exposure to Hg(0) was associated with a lowering of tremor frequency in the non-dominant hand, and a possible interaction with smoking. The differences were small, however, and overall, this study indicates no significant adverse effects on tremor at these exposure levels.

Adult↗

PubMed2006

Individual subject sensitivity to extremely low frequency magnetic field.

It is becoming important to specify the smallest effects of extremely low frequency (ELF) magnetic fields (MF) on human physiology. One difficulty is that some people seem more sensitive and more responsive than others to MF exposure. Consequently, within- and between-subject differences have to be taken into account when evaluating these effects. As shown in previous work, human postural tremor is sensitive to MF exposure. But data about individual responses have not been examined in detail. Thus, postural tremor of 24 subjects was evaluated under ELF MF "on" and "off" conditions in a double-blind real/sham exposure protocol. The direction of the tremor changes was analyzed individually for three tremor characteristics. Results showed that subjects with high amplitude tremor seem to be more responsive to MF exposure. MF had an instantaneous effect (between "on" and "off" conditions) and also a more delayed and persistent one (between real and sham conditions), but differences were small. Moreover, due to the within- and between-subject variability, no statistical analysis could be done. However, these results do not show any potentially harmful effect of domestic or industrial 50 Hz MF on humans. They provide a starting point to orient future studies and should be taken into account in the establishment of new exposure limits.

Adult↗

PubMed2006

Transient effect of low-intensity magnetic field on human motor control.

There is no consensus with respect to how extremely low frequency (ELF) magnetic fields (MF) affect biological systems. However, this information is crucial to establishing new guidelines for: (i) the new design of electronic devices, (ii) working conditions of exposed workers (e.g. electric linepersons), and in a general manner (iii) policies for human risk management. This study evaluates the effect of a sinusoidal 50 Hz, 1000 microT MF centered at the level of the head on human postural tremor of the index finger, using the wavelet analysis method. In addition to the detection of transient events in tremor time series linked with MF, this method was used to evaluate the differences between MF "on" and "off" conditions and between real and sham exposure in a counterbalanced protocol. Results indicate that neither transient events nor "off-on" or "on-off" MF transition effects were present in the postural tremor time series. Surprisingly, an unexpected significant time dependent decrease in tremor average power was noted along the 20s recordings. Interestingly, this effect was significantly more pronounced in the presence of MF. These results suggest a relaxing effect of ELF MF on motor control resulting in an attenuation of postural tremor intensity.

Adult↗

PubMed2005

Automatic detection of movement disorders using recordings of rapid alternating movements.

The present work assesses the potential of rapid alternating movement analysis for detecting movement disorders like Parkinson's disease. Rapid alternating wrist movements were recorded by a diadochokinesimeter for patients with Parkinson's disease (n=10) and healthy controls (n=20). An index of irregularity was computed for each individual as the density of jerk singularities (i.e. zero-crossings) during the movements. Several scales of analysis (i.e. "coarseness") were used for detecting the jerk events and two methods were compared for all of these scales: (1) automatic classification by means of a threshold that optimally separates the indexes of irregularity of the patients from those of the controls, and (2) statistical decision (normal or abnormal) based upon a distribution of indexes of irregularity obtained from a large population of normal subjects. The results showed that (1) two scales of analysis were sufficient and that (2) both methods presented similar performances (e.g. sensitivity=1.00, specificity=0.85, efficiency=0.90). However, statistical decision should be preferred because of its simplicity. The possibility of automatic detection of movement disorders from alternating movements is discussed.

Adult↗

PubMed2005

Neuromotor functions in Inuit preschool children exposed to Pb, PCBs, and Hg.

The aim of this study was to examine the effects of prenatal and postnatal chronic exposure to mercury (Hg), polychlorinated biphenyls (PCBs) and lead (Pb) on the neuromotor development of preschool children. The study population consisted of 110 preschool Inuit children from Nunavik (Canada). Blood Hg, PCBs and Pb concentrations were measured at birth (cord blood) and at the time of testing. Gross motor functions were evaluated and a neurological examination was performed. Fine neuromotor performance was assessed using quantitative measures of postural hand tremor, reaction time, sway oscillations, as well as alternating and pointing movements. Potential covariates were documented including demographic and familial characteristics, other prenatal neurotoxicants (alcohol, tobacco) and nutrients (selenium (Se), Omega-3 polyunsaturated fatty acids (n-3 PUFA)). Hierarchical multivariate regression analyses were performed, controlling for significant covariates. Gross motor development was not linked to prenatal exposures. However, significant associations were observed between blood Pb concentration at testing time and changes in reaction time, sway oscillations, alternating arm movements and action tremor. For some of these outcomes, neuromotor effects of Pb exposure are observed at blood concentrations below 10 microg/dl. Negative effects of PCBs on neuromotor development were not clearly observed, neither were the potential beneficial effects of n-3 PUFA and selenium. Tremor amplitude was related to blood Hg concentrations at testing time, which corroborate an effect already reported among adults.

Child, Preschool↗

PubMed2005

Effect of a low intensity magnetic field on human motor behavior.

Extremely low frequency (ELF) magnetic fields (MF) are omnipresent in our modern daily environment, but their effects on humans are still not clearly established. The aim of this study was to determine the effect of a 50 Hz, 1,000 microT MF centered at the level of the head on human index finger micro-displacements. Twenty-four men recruited among the personnel of the French company, Electricité de France (EDF), completed the experiment. Their postural and kinetic tremors were recorded under four "field-on" and four "field-off" conditions, each tested during a real and a sham sequence. Eight postural and four kinetic tremor characteristics were calculated on recorded time series and were used for statistical analysis. No effect of the MF was found for kinetic tremor. Concerning postural tremor, the proportion of oscillations at low frequencies (between 2 and 4 Hz) was higher during the real than during the sham exposure sequence (P<.05). It suggests that MF could have a subtle delayed effect on human behavior, which is clearly not pathological. These results should be taken into account for the establishment of new exposure limits.

Adult↗

PubMed2005

Characterization of subclinical tremor in Parkinson's disease.

The physiological or pathological nature of subclinical tremor amplitude in Parkinson's disease (PD) is not well established. We analyzed characteristics of resting and postural tremors of subclinical amplitude in 17 patients with idiopathic PD without visible resting tremor, having a postural tremor in their least-affected hand rated 0 (12 subjects) or 1 (5 subjects) on Item 21 of the Unified Parkinson's Disease Rating Scale, compared to 17 control subjects matched for age, sex, and handedness. Tremor was recorded at the tip of the index finger using a displacement laser transducer. Overall results show that subclinical resting tremor in PD is significantly different from physiological tremor in terms of amplitude fluctuation, frequency dispersion, harmonic index, and proportional power in 4 to 6 Hz. No significant differences were found for postural tremor. These differences appear to originate mainly from patients with the mixed form of the disease. This study also confirms the preservation of physiological tremor likely originating from a distinct central oscillator in PD. The use of this method in the early and detailed characterization of PD tremors when amplitude is still within normal limits is proposed.

Adult↗

PubMed2005

Standardization of quantitative tests for preclinical detection of neuromotor dysfunctions in pediatric neurotoxicology.

In the neurotoxicology pediatric domain, few neuromotor tests are specifically designed to be sensitive enough for the early detection of subtle deficits in voluntary and involuntary movements. In research and clinical domains, an effort is done to objectify or quantify the qualitative aspects of a movement (pattern of movement) in predicting neurological problems. This study aimed to standardize quantitative motor measures initially developed for adults and adapted to the evaluation of preschoolers. The sample consisted of 110 healthy children aged 4-6. The following quantitative neuromotor tests were selected: alternating movements and pointing movements (DOCO Microsystèmes Inc., Montréal, Canada), postural tremor, postural sway and simple reaction time (Danish Product Development Ltd., Snekkersten, Denmark). Validation measures included global motor tasks and a neurological examination. Results indicate adequate test-retest reliability and complementarities amongst the selected voluntary and involuntary measures. Both the feasibility and relevance of quantitative neuromotor tests in preschool aged children were established. Results also provide a representation of intra-individual and inter-individual variability within this population. Lastly, the results highlight the importance of developmental factors, behavioral factors and testing conditions in the neuromotor evaluation of young children. The proposed tests could help in the early detection of children at risk for motor dysfunctions following neurotoxic exposure. The tests can also be used for the follow up of various conditions relating to motor functions (cerebral palsy, muscular dystrophy, preterm infants) and in the evaluation of the effects of medication.

Attention↗

PubMed2004

Quantifying postural tremor in workers exposed to low levels of manganese.

The aim of this study was: (1) To determine the minimum number of characteristics necessary to discriminate between postural tremor recorded in control subjects (CO), in subjects exposed to manganese (MN), and in patients with Parkinson's disease (PD), and (2) to examine the continuum of changes between the three groups examined. Workers previously exposed to Mn (n = 10), patients with PD (n = 10), and control subjects (CO) (n = 11) underwent a clinical examination. Blood Mn was measured at the end of exposure time for the MN group and 12 months later at the beginning of the experiment for all groups. Postural tremor with visual feedback was recorded in the index finger with a laser system. Statistical criteria were used to reduce computed tremor characteristics to a minimal set of reliable discriminating variables. Two variables were retained namely corrected wobble (CW), describing the morphology of the tremor oscillations, and variability ratio (VR), describing proportional power of tremor. Both variables had an overall correct classification rate of 77.4%. Blood Mn levels at the time of the experiment were similar for all groups and had insignificant correlation with tremor variables. However, blood Mn levels in workers which were also measured at the end of exposure time (i.e., 12 months before) showed significant correlation (Spearman's rank coefficient) with both harmonic index (rho = 0.70, P = 0.03) and first maximum of the autocorrelation function (rho = 0.89, P = 0.001). We conclude that (1) the tremor of workers exposed to Mn could be adequately described with only two variables; (2) a continuum of changes between tremor recorded in control subjects, in subjects exposed to Mn and in patients with PD was observed, with the MN group always found in between the control (CO) and the PD groups; (3) while blood Mn levels in workers were back at control levels at the time of the experiment, the effect of Mn on postural tremor was still detected. Thus our method has the potential to detect the effect of Mn on tremor with only two variables even after Mn level in the blood is back to normal values.

Chemical Industry↗

PubMed2004

Lack of efficacy of a nicotine transdermal treatment on motor and cognitive deficits in Parkinson's disease.

UNLABELLED: Studies assessing the efficacy of nicotine in Parkinson's disease (PD) have generated contradictory results. The controversy seems to stem from uncontrolled factors including the lack of objective measures, the practice effect in a test-retest design, and the absence of plasmatic dosage. This study aimed at further controlling these factors using transdermal nicotine in PD. METHODS: Twenty-two nonsmoking PD patients received a transdermal nicotine treatment over 25 days in increasing titrated doses. Motor and cognitive assessments were carried out on days 11 and 25 (low-dose and high-dose assessments, respectively) and after a 14-day washout period. RESULTS: Patients tolerated nicotine poorly. Thirteen (59%) withdrew, mostly because of acute side effects. In the remaining nine patients, nicotine neither improved nor worsened motor or cognitive functioning in comparison with 10 age, gender and education matched controls. CONCLUSIONS: Transdermal nicotine is not effective in treating motor and cognitive deficits in PD. The results obtained with our objective measures confirm a recent double-blind, placebo-controlled study that used clinical measures. It is possible that nicotine lacks specificity in targeting critical nicotinic receptors that might be involved in PD pathophysiology. The low tolerability may be related to such a lack of specificity of nicotine, which would directly stimulate the autonomic nervous system.

Administration, Cutaneous↗

PubMed2003

Effect of chronic exposure to methylmercury on eye movements in Cree subjects.

OBJECTIVES: To examine the effect of chronic exposure to methylmercury on eye movements (pursuit, fixation and dynamic saccades) in Cree subjects from Northern Quebec. METHODS: Eye movements were recorded in a group of Cree subjects ( n=36) exposed chronically to methylmercury, a group of patients with Parkinson's disease (PD) ( n=21), and a group of control subjects ( n=30) by use of an infrared eye-movement recording system. Pursuit, fixation, and prompted and remembered saccades were recorded twice for both eyes in the horizontal and vertical axes. Blinks were removed, and data were calibrated. RESULTS: Analyses of variance revealed significant differences for all characteristics examined for fixation and pursuit, and for some characteristics in dynamic saccades. These differences arose sometimes from the Cree group, sometimes from the PD group and sometimes from both groups. CONCLUSIONS: The results suggest that eye movements of Cree subjects exposed to methylmercury are qualitatively different from those of both control subjects and patients with PD. Comparisons between more-exposed and less-exposed Cree subjects matched for age with control subjects also showed significant differences for fixation, pursuit and dynamic saccades. The average scores of the more-exposed group were clearly separated from those of the less-exposed and control groups for characteristics of fixation and pursuit, and for accuracy and sharpness of prompted saccades. This trend was less clear in other results where a possible effect of mercury exposure could not be distinguished from a possible cultural effect. Further studies should focus on the most discriminating characteristics for the Cree group, such as measures of accuracy and coherence in all tests and sharpness of saccades.

Adult↗

PubMed2003

Modulation of tremor amplitude during deep brain stimulation at different frequencies.

Rest tremor was quantified in the index finger tip of 16 patients with Parkinson's disease (PD) receiving deep brain stimulation (DBS) of the ventro-intermediate nucleus (Vim) of the thalamus, the subthalamic nucleus (STN), or the internal part of the globus pallidus (GPi) while being off L-dopa for 12h. Clinically, without DBS, tremor amplitude varied from absent to high. Tremor was recorded continuously for about 5 min under three conditions of DBS repeated twice, namely, effective frequency (E), ineffective frequency (I), and no DBS (O). No changes in tremor were observed across conditions in subjects with little or no tremor. However, in subjects with moderate to large amplitude tremor, DBS decreased tremor amplitude to near normal values within a few seconds. Generally, transitions were progressive and occurred with a varying time delay. Occasionally, tremor escaped from control regardless of the stimulation condition considered. In some cases tremor amplitude in one condition appeared to depend on the preceding condition. Finally, the results were reproducible on two consecutive days. We conclude that tremor control with DBS follows specific dynamical rules, which must be compatible with the hypotheses proposed regarding the underlying mechanisms of DBS.

Aged↗

PubMed2003

Event identification in movement recordings by means of qualitative patterns.

We present a pattern-matching technique for detecting events in movement recordings. The events are defined as sequences of qualitative changes in the speed and/or the higher order derivatives (e.g., in a speed peak, the acceleration changes from positive to negative). The technique uses qualitative patterns that are sequences of qualitative states (e.g., negative, infinitesimal, positive...) of the speed and the higher order derivatives. A fast pattern-matching algorithm is presented. Its sensitivity can be tuned by means of a filtering parameter, and a multiscale analysis method is proposed for detecting events of different amplitudes and durations. An application to the assessment of the irregularity of rapid movement in Parkinson's disease is presented.

Acceleration↗

PubMed2003

Neuromotor effects of acute ethanol inhalation exposure in humans: a preliminary study.

Ethanol (ETOH) is added to unleaded gasoline to decrease environmental levels of carbon monoxide from automobiles emissions. Therefore, addition of ETOH in reformulated fuel will most likely increase and the involuntarily human exposure to this chemical will also increase. This preliminary study was undertaken to evaluate the possible neuromotor effects resulting from acute ETOH exposure by inhalation in humans. Five healthy non-smoking adult males, with no history of alcohol abuse, were exposed by inhalation, in a dynamic, controlled-environment exposure chamber, to various concentrations of ETOH (0, 250, 500 and 1,000 ppm in air) for six hours. Reaction time, body sway, hand tremor and rapid alternating movements were measured before and after each exposure session by using the CATSYS 7.0 system and a diadochokinesimeter. The concentrations of ETOH in blood and in alveolar air were also measured. ETOH was not detected in blood nor in alveolar air when volunteers were exposed to 250 and 500 ppm, but at the end of exposure to 1,000 ppm, blood and alveolar air concentrations were 0.443 mg/100ml and 253.1 ppm, respectively. The neuromotor tests did not show conclusively significant differences between the exposed and non-exposed conditions. In conclusion, this study suggests that acute exposure to ethanol at 1,000 ppm or lower or to concentrations that could be encountered upon refueling is not likely to cause any significant neuromotor alterations in healthy males.

Adult↗

PubMed2002

Optokinetic stimulation and the egocentred midsagittal plane: an fMRI study.

Animal studies and observations of neglect patients suggest that the posterior parietal cortex is part of a system that codes ego-centred space. Few studies show the existence of areas involved in the representation of egocentred space in healthy humans. We investigated with fMRI and a conjunction protocol, the overlap of activity between optokinetic stimulation and a task of midline computation. Results showed that the right posterior parietal and frontal cortices were involved in both tasks (p < 0.0001). The evidence presented in this study provides the neuroanatomical substrate involved in the recovery of neglect during vestibular stimulation. This last point is of clinical interest for the rehabilitation of hemineglect.

Adult↗

PubMed2002

Kinetic tremor during tracking movements in patients with Parkinson's disease.

This study was undertaken to analyse kinetic tremor during a compensatory tracking task performed with the index fingers. Patients with Parkinson's disease (PD) (n=21) and control subjects (n=30) were tested using a laser system transducing displacement. All participants underwent a clinical examination. Nine characteristics quantifying the tracking task and tremor were applied to the processed displacement or velocity signal. The discriminating power of each characteristic was evaluated using differences between group means (p values), maximum percentage discrimination, and number of outliers in the patient group. All nine characteristics showed significant differences between means of the two groups using Welch-modified t-tests for unequal variances. The most discriminating characteristics reflected differences in the frequency distribution of the movement (proportional power in the 3-4Hz range, harmonicity and median frequency). These differences were rarely visible and did not correlate highly with tremor amplitude or with clinical ratings of tremor. Control subjects had residual spectral power from the tracking oscillations leaking above 3Hz, while most patients had a small 'kinetic tremor' in the 7-12Hz range. The maximum discrimination was moderate, 63% in the best case. Combining representative information about proportional power during posture (recorded in the same subjects) and tracking gave a much higher discrimination (90%) with respect to the 96.7th percentile of the control group. These results suggest that information coming from postural and kinetic tremors can be combined to isolate a subclinical feature of PD symptomatology. This feature could be used to re-evaluate the classic distinction made between the akineto-rigid and tremulous forms of PD and is independent of tremor amplitude.

Aged↗

PubMed2001

Dynamics of Parkinsonian tremor during deep brain stimulation.

The mechanism by which chronic, high frequency, electrical deep brain stimulation (HF-DBS) suppresses tremor in Parkinson's disease is unknown. Rest tremor in subjects with Parkinson's disease receiving HF-DBS was recorded continuously throughout switching the deep brain stimulator on (at an effective frequency) and off. These data suggest that the stimulation induces a qualitative change in the dynamics, called a Hopf bifurcation, so that the stable oscillations are destabilized. We hypothesize that the periodic stimulation modifies a parameter affecting the oscillation in a time dependent way and thereby induces a Hopf bifurcation. We explore this hypothesis using a schematic network model of an oscillator interacting with periodic stimulation. The mechanism of time-dependent change of a control parameter in the model captures two aspects of the dynamics observed in the data: (1) a gradual increase in tremor amplitude when the stimulation is switched off and a gradual decrease in tremor amplitude when the stimulation is switched on and (2) a time delay in the onset and offset of the oscillations. This mechanism is consistent with these rest tremor transition data and with the idea that HF-DBS acts via the gradual change of a network property. (c) 2001 American Institute of Physics.

Journal Article↗

PubMed1995

Tremor: Is Parkinson's disease a dynamical disease?

Experimental evidence has shown a plethora of short-term fluctuations in patients with Parkinson's disease. We investigate these transitory events using the concept of dynamical disease. Several examples of short-term fluctuations in tremor are analyzed, and in two cases, other systemic variables (i.e., respiration and blood pressure) are examined as well. A model for tremor, based on negative feedback with delays is proposed, and the transient events are simulated. The theoretical implications of the model suggest that interactions between the central and peripheral loops, as well as interactions between the control loops and other systemic signals, can give rise to transitory events in tremor, both in the pathological and in the normal case. (c) 1995 American Institute of Physics.

Journal Article↗