Biomedical subjects

J L Alberts

Publications and source records attributed to J L Alberts.

7 recordsLinked to original sources

PubMed2001

Multijoint movement control in Parkinson's disease.

Impairments in the performance of complex actions in Parkinson's disease (PD) patients are well documented. The aim of the present study was to investigate potential mechanisms that may be contributing to impaired movement performance in PD patients. PD patients and age-matched control subjects performed rapid pointing movements to a series of four tabletop targets. The height of the table was adjusted until the targets could be achieved with arm movements in the horizontal plane. The targets were arranged such that target 1 required elbow extension only and targets 2-4 required increasing amounts of horizontal shoulder flexion in addition to the elbow extension. While the control subjects accelerated and decelerated the elbow and shoulder joints simultaneously regardless of the target location, the PD patients decomposed motion during the acceleration phase by accelerating first the shoulder and then the elbow joint. For PD patients this decomposition of arm segments was associated with greater coactivation of the muscles about the elbow when elbow extension and shoulder flexion were simultaneously required (targets 2-4), in contrast to the single joint action. The control subjects decreased elbow joint coactivation while the patients increased it across the four targets. The resulting peak interaction torques at both the elbow and shoulder joints occurred relatively later for the PD patients. The coactivation patterns observed in PD patients may reduce the ability to take advantage of interaction torques and may also contribute to joint motion decomposition.

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PubMed2000

Disruptions in the reach-to-grasp actions of Parkinson's patients.

Previous research has shown that Parkinson's-disease (PD) patients produce irregular movement paths during a rapid arm pointing task. The aim of this study was to investigate the movement paths of PD patients during a prehensile action to objects requiring different levels of precision. Thus, we sought to determine if movement-accuracy requirements affect the control of movement path. Thirteen PD patients and 13 age-matched controls served as participants. In addition to having prolonged movement times, PD patients showed differences in the kinematic patterns of the transport and grasp components. For the transport component, relative time to maximum deceleration and relative time to maximum elbow velocity occurred earlier for the PD patients than the controls. Analyses of wrist paths indicated that, when accuracy requirements were increased, patients produced paths that appeared more segmented than controls. For PD patients, reaches to a small object resulted in wrist paths that were significantly less smooth, as reflected by higher jerk values, and were less continuous, as indicated by larger standard deviations in curvature. A temporal analysis of movement-initiation patterns in the vertical and horizontal planes indicated that control participants had a minimal offset between initial movement in the vertical plane and initial movement in the horizontal plane regardless of accuracy constraints. However, PD patients had a significantly longer interval between initial movement in the vertical plane and subsequent movement in the horizontal plane when reaching to the small object. Higher accuracy constraints also resulted in PD patients achieving relative time to maximum elbow velocity significantly earlier than controls. For the grasp component, PD patients produced movement patterns in which the amplitude of and relative time to maximum aperture were less sensitive to object size. In addition, patients exhibited greater variability in the time to maximum aperture. Additional analyses of the grasp component indicated that control participants exhibited a stable position, relative to object location, in which aperture began to close. Conversely, PD patients showed little consistency in where aperture began to close with respect to object location. Irregularities in the transport component suggest that PD patients have a reduced capability to precisely coordinate joint segments, particularly under high accuracy requirements. Variability in where aperture began to close and disruptions in transport-grasp coordination suggests that the basal-ganglia dysfunction, as exhibited in PD, affects the specification of these movement parameters used to produce a consistent pattern of coordination between prehensile components.

Adult↗

PubMed1998

The co-ordination and phasing of a bilateral prehension task. The influence of Parkinson's disease.

Parkinson's disease patients and control subjects performed a simultaneous bilateral reach-to-grasp task to two different sized objects and then pulled the two objects apart. The first phase of the task (reaching-to-grasp) allowed us to examine the issue that impairments in simultaneous movements for Parkinson's disease patients are seen in some tasks but not in others. It is suggested that the reason for this selective impairment is that Parkinson's disease compromises the ability to control multiple task-level degrees of freedom independently and concurrently (task-level degrees of freedom are defined as the number of independent parameters that require specification to perform the task). The first phase was used to test the hypothesis that Parkinson's disease results in a reduction of degrees of freedom that are independently controlled. It was predicted that Parkinson's disease patients would produce similar (homologous) movements of the two limbs (a symmetrical pattern) if the target objects have different accuracy requirements when they reach bilaterally to the two objects. For bilateral reaches for two different-size objects, only the control group showed reliably different patterns in the two limbs (asymmetrical pattern), while the Parkinson's disease group displayed a symmetrical pattern. These results provide support for the hypothesis that Parkinson's disease patients have a reduced capability to control multiple task-level degrees of freedom. The second phase of the task, which involved a transition from position control (reaching-to-grasp) to force control (stabilizing and pulling) was used to examine the ability of Parkinson's disease patients to make transitions between movement tasks and force control. In contrast to control subjects, Parkinson's disease patients produced staircase patterns for grip and load forces. Furthermore, a breakdown in the parallel co-ordination between grip and load force was observed for Parkinson's disease patients. These data suggest that Parkinson's disease disrupts the normal feedforward operations responsible for the co-ordination between grip and load forces.

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PubMed1997

The influence of movement segment difficulty on movements with two-stroke sequence.

Arm movements in the horizontal plane consisting of two segments were examined to determine whether the difficulty of the second segment influenced the kinematic characteristics of the first segment. The direction of the first segment was an elbow extension movement away from the trunk and remained constant throughout the experiment. The direction of the second segment varied between forearm extension and flexion movements. Based on Fitts' law, two different indexes of difficulty (ID) of the second segment were utilized by changing target size and movement amplitude. The effects of changing ID were examined for two different movement amplitudes. All movements were single-joint movements employing elbow flexion/extension and were recorded by an x-y digitizer. Variations in the ID of the second segment produced context-dependent kinematic changes in the performance of the initial segment. Movement duration increased when the ID was increased by reducing target size for both extension-extension sequence and extension-flexion sequences. Peak velocity also decreased for higher ID targets in the extension-flexion sequence. However, there was an interaction between the ID and movement amplitude in the extension-flexion sequence. In this sequence the duration of movement for the high ID/large movement amplitude condition increased substantially compared with the low ID/small movement amplitude condition. In addition, changing ID of the second segment influenced the time between the two segments (intersegment interval) in the extension-flexion sequence. Collectively, these data suggest that the planning of complex movements is based in part on the accuracy demands of multiple segments of the sequence.

Adult↗

PubMed1997

One-year, low-dose neuroleptic study of in-patients with chronic schizophrenia characterised by persistent negative symptoms. Amisulpride v. haloperidol.

BACKGROUND: Amisulpride is a potent substituted benzamide antipsychotic drug claimed to improve the negative symptoms of schizophrenia, particularly at low dosage. METHOD: Sixty long-term in-patients with schizophrenia and selected for predominant negative symptoms were randomised to receive either haloperidol or amisulpride. Over a year there was systematic dose reduction, as symptoms allowed. RESULTS: There were no significant differences between the treatment groups in the proportion receiving low-dose treatment, the control of positive symptoms, or ratings of social behaviour, side-effects or tardive dyskinesia. For negative symptoms, there were consistent but non-significant trends in favour of amisulpride. The amisulpride patients required significantly less anticholinergic medication. CONCLUSIONS: In chronically-hospitalised in-patients with schizophrenia characterised by persistent negative symptoms, amisulpride was a well-tolerated maintenance antipsychotic medication. The drug had only a limited effect in reducing negative symptoms, which were relatively stable, enduring phenomena in this sample, despite dosage reduction.

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PubMed1994

Tiapride in the prevention of relapse in recently detoxified alcoholics.

BACKGROUND: The aim was to investigate the effect of tiapride (100 mg three times a day for at least one month) on outcome following detoxification. METHOD: The setting was a tertiary referral centre. The study design was randomised, double-blind, and placebo-controlled. One hundred routinely admitted alcohol-dependent patients were entered, and 54 completed the trial. Outcome was assessed by considering drinking status at three months and six months follow-up, and by comparing psychological status at intake and follow-up using the Crown-Crisp Experiential index, the Litman Self-esteem scale and a Satisfaction with Life Situations scale. We also compared performance over the six months before admission with the three and six months of follow-up on measures of health, social and drinking variables. RESULTS: Tiapride proved better (usually at statistically highly significant levels) than placebo at promoting: abstinence, self-esteem, and satisfaction with life situations; and at reducing: alcohol consumption, use of health service resources, and levels of neuroticism. CONCLUSIONS: Tiapride merits serious consideration in the longer-term treatment of alcoholic patients.

Alcohol Drinking↗

PubMedDate not supplied

Short-term effects of propranolol on portal venous pressure.

The present study was designed to investigate the effect of propranolol on portal pressure of patients with alcoholic cirrhosis and portal hypertension and to correlate these effects with clinical and laboratory parameters. The mean baseline hepatic venous pressure gradient in the 50 patients studied was of 18.2 +/- 4.1 mm Hg. It decreased significantly 2 hr after the oral administration of 40 mg of propranolol to 15.7 +/- 4.2 mm Hg (a mean reduction of 13.4 +/- 17%). This reduction in hepatic venous pressure gradient resulted mainly from a decrease in mean wedged hepatic venous pressure. There was no correlation between the decrease in hepatic venous pressure gradient and the decrease in heart rate. When results were analyzed individually, only 15 (30%) showed a large decrease in hepatic venous pressure gradient (greater than 20%), 15 (30%) showed a moderate decrease (10 to 19%), and in 20 patients (40%) there was no reduction or an increase in hepatic venous pressure gradient. Comparison of "responders" (those that reduced hepatic venous pressure gradient greater than 10%) and "nonresponders" (hepatic venous pressure gradient reduction less than 10%) showed no significant differences in baseline laboratory and hemodynamic parameters, in the severity of the liver disease, in the heart rate and blood pressure response to propranolol, nor in the propranolol plasma levels achieved 2 hr after propranolol administration. Propranolol plasma levels correlated with the reduction in heart rate but not with the reduction in hepatic venous pressure gradient. Of 14 nonresponders to 40 mg of propranolol who received additional doses, six showed a reduction in hepatic venous pressure gradient.(ABSTRACT TRUNCATED AT 250 WORDS)

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