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PubMed2002

Commonalities and differences in control of various drawing movements.

Characteristics of control at the shoulder and elbow during nine types of drawing movements were studied in the present work. The task was to repetitively track a template, depicted on a horizontal table, with the index finger at a cyclic frequency of 1.5 Hz. The templates were a circle, four ovals and four lines of different orientations. The wrist was immobilized and the movement consisted of rotations at the shoulder and elbow joints. The studied movements varied in a wide range with respect to the amplitude of elbow and shoulder movements and relative phase between them. Kinetic analysis included analysis of torque signs, impulses, and timing. It demonstrated that the role of muscle torque in movement production was different at the two joints. During eight out of the nine movement types, the muscle torque at the shoulder accelerated and decelerated this joint and almost completely coped with the influence of the interactive torque arising from elbow motion. Conversely, interactive torque generated by shoulder motion played a dominant role in elbow acceleration and deceleration, whereas muscle torque at the elbow adjusted passive elbow movement to the various template shapes. EMG data were in agreement with the conclusions made from the kinetic analysis. Collectively, these data support the hypothesis that the two joints have different functions in movement production. The shoulder creates a foundation for motion of the entire arm through the interactive torque, and the elbow serves as a fine-tuner of the end-point movement. Control of the shoulder was similar across the eight movement types and the differences in the end-point path were provided by variations in elbow control. The two joints exchanged roles during one movement type, namely, drawing the line tilted right. During this movement, the elbow musculature generated motion at this joint and the shoulder musculature counteracted mechanical influence of this motion on the shoulder position. The findings suggest that during drawing movements, the control strategy exploits intersegmental dynamics of the shoulder-elbow mechanical linkage.

Adolescent↗
PubMed2003

Kinematics of wrist joint flexion in overarm throws made by skilled subjects.

Previous studies of multijoint arm movements have shown that the CNS holds arm kinematics constant in different situations by predictively compensating for the effects of interaction torques. We determined whether this was also the case for wrist joint flexion in natural overarm throws performed by skilled subjects in 3D, a situation where large passive torques can occur at the wrist. Specifically, we investigated whether wrist flexion amplitudes are held constant in throws of different speeds. Joint rotations were recorded at 1,000 Hz with the search-coil technique. Contrary to a previous study on constrained 2D throwing, indirect evidence was found that in fast throws passive torques associated with forearm deceleration were exploited to increase wrist flexion velocity. This increase in wrist flexion velocity was associated with constant wrist flexion amplitudes at ball release (mean 27 degrees) for throws of different speeds. Furthermore, final wrist flexion positions after ball release were similar for a particular subject irrespective of the speed of the throw. This was associated in faster throws with increased magnitudes of wrist flexor and wrist extensor EMG activity which damped passive torques associated with forearm angular deceleration. It is concluded that wrist flexion in overarm throws of different speeds is produced by central signals which precisely control net joint torque by both exploiting and damping passive torques during different parts of the throw to keep wrist joint angular position parameters constant. As such the results show that control strategies for natural 3D throwing are different from those for constrained 2D throwing.

Arm↗
PubMed2004

Muscle activation patterns in point-to-point and reversal movements in healthy, older subjects and in subjects with Parkinson's disease.

When young, healthy subjects perform rapid point-to-point and reversal movements over a range of distances, the patterns of muscle activation associated with accelerating the limb toward the target are modulated in the same way for both movement tasks. Differences in patterns of muscle activation for these two movement types are not observed until the deceleration phase of the movements. In this study, we first test the hypothesis that healthy, older subjects and subjects with Parkinson's disease will modulate the pattern of muscle activation in the same way during the acceleration phase of point-to-point and reversal elbow movements. Second, we test the hypothesis that healthy, older subjects and subjects with Parkinson's disease exhibit the same relationship in muscle activation patterns between the two movement types that have been observed for the young in the deceleration phase of the movements. Subjects performed point-to-point and reversal movements initiated in the direction of flexion over three distances (36, 54 and 72 degrees) "as fast as possible". Angle, velocity, acceleration and surface EMGs from biceps and triceps were recorded. With respect to the first hypothesis, the EMG, kinetic, and kinematic measures related to the acceleration phase of the movements were modulated in the same way for both movement types in the healthy older subjects. In the Parkinson's disease group, the kinematic and kinetic measures during the acceleration phase of the movements were the same in both movement types; however, the flexor and extensor EMG activation was smaller during reversal movements than during point-to-point movements. With respect to the second hypothesis, in contrast to that found in young subjects, in healthy older subjects, there was no significant difference between the movement types in the flexor EMG activity immediately after the time of peak velocity. This difference between younger and older subjects may be attributed to the fact that older subjects perform both movement types more slowly than do younger subjects. Although subjects with Parkinson's disease also move slowly, the flexor EMG shuts off more abruptly and more completely just after the time of peak velocity during reversal movements than during point-to-point movements. These results show that (1) for healthy subjects, when the task requirements are the same for the two movement types (acceleration phase), muscle activation patterns are modulated in the same way, and (2) both age and disease alter the relationship of muscle activation, kinetics and kinematics between point-to-point and reversal movements.

Aged↗
PubMed2004

Saccades to stationary and moving targets differ in the monkey.

Saccade characteristics in response to moving and stationary targets were studied in three monkeys (Macaca mulatta) that had been trained to look at a target, which after an initial jump either remained in place or moved forward or backward with constant velocity (10 degrees /s). Eye movements were recorded using a search coil. The contribution of smooth pursuit to the saccade amplitude was small (<0.25 degrees ). Saccades having the same amplitude (5.67-6.83 degrees for different monkeys) to forward and backward moving targets were compared. Peak velocity was higher (37-42 degrees /s on average for different monkeys) and saccade duration was shorter (8-10 ms on average) for backward saccades than for forward saccades These differences were highly significant (t-test: P<0.001). Thus, forward and backward saccades are not on the same main sequence. This suggests that saccade dynamics are affected not only by the retinal position error but also by target motion. Further analysis revealed that saccade peak velocity mainly depends on the retinal position error, but saccade amplitude also depends on a stimulus-related velocity factor, which affects the saccade mainly during deceleration. This velocity factor could be retinal slip or target velocity, which was the same under our conditions. Our results experimentally support recent models that propose that the saccade acceleration in response to moving targets might be controlled by the superior colliculus, whereas the deceleration changes are fine-tuned by the cerebellum. This prediction must still be tested on a neuronal level.

Algorithms↗
PubMed2001

Time course and temporal order of changes in movement kinematics during motor learning: effect of joint and instruction.

Learning a motor task is associated with specific changes in movement kinematics. Recently, it has been shown that changes in different kinematic parameters occurred with different time courses for subjects who practiced simple, single-joint elbow movements. For example, movement time was seen to decrease and level off in a shorter time than peak velocity, which increased and plateaued later. What is not known, however, is whether the time course and temporal order of these learning-related changes seen at the elbow are similar for movements learned at other joints and with different instructions. In this study, neurologically normal subjects practiced 50 degrees -flexion movements made at the wrist, with the instruction to be both "fast and accurate" (same instruction used in the earlier elbow study). A different group of subjects practiced wrist movements of the same amplitude, but with instructions to make movements that were "always accurate;" only as movement skill developed could subjects increase their speed (but without ever sacrificing accuracy). We measured time-related parameters (duration of acceleration, duration of deceleration, and total movement duration) and magnitude-related parameters (peak velocity, peak acceleration, and peak deceleration). We found that the time course of changes in kinematic parameters for subjects instructed to be "fast and accurate" was similar to that reported at the elbow. When the instruction was changed to be "always accurate," the time for changes in kinematic parameters to level off was found to be longer. However, regardless of instruction, time-related parameters plateaued before magnitude-related parameters. Thus, our results indicate that motor learning mechanisms may operate in a similar way at different joints.

Adult↗
PubMed1997

The functional effectiveness of neck muscle reflexes for head-righting in response to sudden fall.

Reflex head-righting in normal and labyrinthine-defective (LD) subjects was compared to identify the relative functional effectiveness of vestibular-collic and cervico-collic myotactic reflexes. To restrict stimuli largely to the head and neck, subjects lay supine, supported up to the shoulders on a horizontal bed with their head supported in a sling over the edge. The head fell freely as the sling was released with an electromagnetic catch. Head drops were delivered with the subjects instructed to relax and accept the fall passively or to actively right the head as fast as possible. With both instructions, righting responses in normal subjects commenced with electromyographic (EMG) bursts in the sternocleidomastoid (SCM) at 24.5 ms latency, which was reflected in a deceleration of the downwards head velocity. The latency of the earliest EMG responses in LD subjects was 67.4 ms, accompanied by similar deceleration. It is assumed that the earliest response in normal subjects is vestibular, whereas in LDs the SCM stretch reflex is the earliest response. These reflexes are followed at circa 100 ms by more intense EMG activity due to voluntary movement, but braking of head fall is evident before voluntary activity takes effect. Righting was more effective in normal subjects than in LDs, and when "active" normal subjects made more vigorous righting responses than when "passive"; whereas active righting in LDs was no better than passive. The results demonstrate that reflex responses contribute significantly to head-righting. The vestibular contribution gives an advantage over stretch reflexes alone and also assists in voluntary enhancement of reflex responses.

Acceleration↗
PubMed1998

The representation of gravitational force during drawing movements of the arm.

The purpose of the present experiment was to study the way in which the central nervous system (CNS) represents gravitational force (GF) during vertical drawing movements of the arm. Movements in four different directions: (a) upward vertical (0 degrees), (b) upward oblique (45 degrees), (c) downward vertical (180 degrees) and (d) downward oblique (135 degrees), and at two different speeds, normal and fast, were executed by nine subjects. Data analysis focused upon arm movement kinematics in the frontal plane and gravitational torques (GTs) exerted around the shoulder joint. Regardless of movement direction, subjects showed straight-line paths for both speed conditions. In addition, movement time and peak velocity were not affected by movement direction and consequently changes in GT, for both speeds tested. Movement timing (evaluated through the ratio of acceleration time to total time) changed significantly, however, as a function of movement direction and speed. Upward movements showed shorter acceleration times when compared with downward movements. Concerning the four directions, movements made at 0 degrees and 45 degrees differed significantly from those made at 135 degrees and 180 degrees. Drawing movements executed at rapid speed presented similar acceleration and deceleration times compared with movements executed at normal speed, which showed greater acceleration than deceleration times. In addition, the form of velocity profiles (assessed through the ratio of maximum to mean velocities), was significantly modified only with movement speed. Results from the present study suggest that GF is efficiently incorporated into internal dynamic models that the brain builds up for the execution of arm movements. Furthermore, it seems that GF not only is a mechanical parameter to be overcome by the motor system but also constitutes a reference (vertical direction), both of which are represented by the CNS during inverse kinematic and dynamic processes.

Adult↗
PubMed1999

Time course and temporal order of changes in movement kinematics during learning of fast and accurate elbow flexions.

Learning of a motor task, such as making accurate goal-directed movements, is associated with a number of changes in limb kinematics and in the EMG activity that produces the movement. Some of these changes include increases in movement velocity, improvements in end-point accuracy, and the development of a biphasic/triphasic EMG pattern for fast movements. One question that has remained unanswered is whether the time course of the learning-related changes in movement parameters is similar for all parameters. The present paper focuses on this question and presents evidence that different parameters evolve with a specific temporal order. Neurologically normal subjects were trained to make horizontal, planar movements of the elbow that were both fast and accurate. The performance of the subjects was monitored over the course of 400 movements made during experiments lasting approximately 1.5 h. We measured time-related parameters (duration of acceleration, duration of deceleration, and movement duration) and amplitude-related parameters (peak acceleration, peak deceleration, peak velocity), as well as movement distance. In addition, each subject's reaction time and EMG activity was monitored. We found that reaction time was the parameter that changed the fastest and that reached a steady baseline earliest. Time-related parameters decreased at a somewhat slower rate and plateaued next. Amplitude-related parameters were slowest in reaching steady-state values. In subjects making the fastest movements, a triphasic EMG patterns was observed to develop. Our findings reveal that movement parameters change with different time courses during the process of motor learning. The results are discussed in terms of the neural substrates that may be responsible for the differences in this aspect of motor learning and skill acquisition.

Adult↗
PubMed1999

The kinematics of eating with a spoon: bringing the food to the mouth, or the mouth to the food?

In traditional reach-to-point and reach-to-grasp studies an increase in accuracy demands typically results in a lengthening of the deceleration phase of the reach and a freezing of the more distal joints. The purpose of the present experiment was to examine whether similar changes in the reach kinematics could be observed during a tool-using skill, as would be predicted from an effector independence perspective. Five subjects were required to eat two substances (i.e. a solid and a liquid one) that imposed different requirements on the accuracy of the movement. The subjects transported the substances from the plate into the mouth. A prolonged movement duration was found for the liquid as compared to the solid substance. However, rather than being exclusively due to a lengthening of deceleration phase, the larger movement duration resulted from a slowing down of the whole movement. Therefore, the skewed velocity profiles found in the traditional reach-to-grasp studies may well be the result of the accuracy demands only impinging on the final part of the movement trajectory, rather than being a consequence of central, effector-independent, organising principles. In addition, under increased accuracy demands subjects were shown to redistribute their movement in a proximodistal direction. Movements of the distal components were reduced to a minimum and the involvement of trunk and head movement increased.

Adult↗
PubMedDate not supplied

Pressure-regulated volume control vs volume control ventilation in infants after surgery for congenital heart disease.

The objective of this investigation was to compare how two modes of positive pressure ventilation affect cardiac output, airway pressures, oxygenation, and carbon dioxide removal in children with congenital heart disease in the immediate postoperative period. The investigation used a one group pretest-post-test study design and was performed in the pediatric cardiac intensive care unit in a university-affiliated children's hospital. Nine infants were enrolled immediately after repair of tetralogy of Fallot (2) or atrioventricular septal defects (7) with mean weight = 5.5 kg (4.2-7.3 kg). Children were admitted to the pediatric cardiothoracic intensive care unit after complete surgical repair of their cardiac defect and stabilized on a Siemen's Servo 300 ventilator in volume control mode (VCV1) (volume-targeted ventilation with a square flow wave pattern). Tidal volume was set at 15 cc/kg (total). Hemodynamic parameters, airway pressures and ventilator settings, and an arterial blood gas were measured. Patients were then changed to pressure-regulated volume control mode (PRVC) (volume-targeted ventilation with decelerating flow wave pattern) with the tidal volume set as before. Measurements were repeated after 30 minutes. Patients were then returned to volume control mode (VCV2) and final measurements made after 30 minutes. The measurements and results are as follows: After correction of congenital heart defects in infants, mechanical ventilation using a decelerating flow wave pattern resulted in a 19% decrease in peak inspiratory pressure without affecting hemodynamics, arterial oxygenation, or carbon dioxide removal.

Analysis of Variance↗
PubMedDate not supplied

Frequent embolization in peripheral angioplasty: detection with an embolism protection device (AngioGuard) and electron microscopy.

PURPOSE: To evaluate the deliverability and protection capabilities of an embolism protection filter in angioplasty of peripheral arteries. METHODS: The Angioguard emboli capture guidewire system was applied in 11 patients with femoropopliteal lesions (6 stenoses, 3 occlusions, 2 controls). Data on lesion crossing, flow deceleration and macroembolization were recorded. Filter membranes were evaluated with scanning electron microscopy (SEM). RESULTS: System delivery was successful in all patients. Primary lesion crossing was feasible in four of six stenoses; predilatation was required in two of six. Marked flow deceleration was recorded in six patients. Emboli next to the filter were detected in each patient with concentric plaques, but could not reliably be removed with the filter. Downstream macroembolization was also present in all patients with concentric stenoses, but in none with chronic occlusion. None of the patients had clinical signs of ischemia. SEM analysis demonstrated only small particles on control group filters and non-obliterating fibrinous conglomerates on filters used in chronic occlusion. Substantial obliteration was seen on several filters used in stenotic lesions. CONCLUSION: Microembolization of fibrin aggregates is a common incident in balloon angioplasty of femoropopliteal stenoses. Macroembolization occurred more frequently than previously reported. The use of embolism protection filters aided in the detection but not in the removal of larger emboli.

Aged↗
PubMed2004

Effects of interferon-alpha therapy on cardiac function in patients with chronic hepatitis B infection.

Various types of cardiovascular complications, such as myocardial infarction, cardiac arrhythmias, cardiomyopathy, and myocarditis attributed to interferon therapy have been reported. The aim of this study was to evaluate the cardiac effects of interferon-alpha (IFN-alpha) in patients with chronic hepatitis B infection. Forty-five patients with chronic hepatitis B infection (41 men and 3 women; mean age 34.2 +/- 11.5 years) were included in the study, and 10MU IFN-alpha 2b was administered three times a week for 6 months to the patients. Cardiac evaluation (detailed medical history, physical examination, electrocardiography, systolic and diastolic function parameters by echocardiography) was performed at the beginning, and at the 1st, 3rd, and 6th months of therapy. No patients had any cardiac symptoms during interferon therapy, and systolic and diastolic blood pressure and heart rate were not significantly affected (P > 0.05). None of the patients revealed cardiac rhythm disturbance on electrocardiography before or during the therapy period. No significant changes were detected in systolic (ejection fraction, fractional shortening, pre-ejection period, left ventricular ejection time, the ratio of pre-ejection period/ejection time, Q-V peak) and diastolic (E peak, A peak of transmitral flow velocity, E/A ratio, deceleration time, isovolumic relaxation time by conventional echocardiography, and E peak, A peak, deceleration time of E wave at the medial and lateral corners of the mitral annulus by tissue Doppler echocardiography) left ventricular function parameters between the beginning and the 1st, 3rd, and 6th months of therapy. The results of this study suggest that IFN-alpha therapy does not cause a significant deterioration in cardiac function in patients with chronic hepatitis B infection, and it may be used safely in patients without cardiac disease.

Adult↗
PubMed2002

Compression and expansion wavefront travel in canine ascending aortic flow: wave intensity analysis.

The forces underlying left ventricular ejection were investigated by applying a wavefront analysis to blood pressure (P) and velocity (U) waveforms measured in the ascending aorta of anesthetized dogs (n = 13). Wavefronts travel forward (to the periphery) and/or backward (to the heart) after peripheral reflection. They are characterized by the rate of pressure change they cause, i.e., the time derivative of pressure (dP/dt): compression wavefronts have dP/dt > 0: expansion wavefronts have dP/dt < 0. Wave intensity is defined as (dP/dt)(dU/dt), where dU/dt is the time derivative of U. Forward wavefronts contribute positively to wave intensity and backward wavefronts contribute negatively. Therefore, wave intensity indicates whether the effects of forward wavefronts are predominant or whether those of backward wavefronts predominate in the formation of pressure and velocity waveforms. Under control conditions, wave intensity was positive in early and late systole, indicating that forward compression and expansion wavefronts dominate aortic acceleration and deceleration, respectively. Compression wave intensity was increased during inotropic stimulation by dobutamine (10-15 microg/kg per min i.v. infusion; +161% +/- 31% mean change in peak value +/- SEM (%), P < 0.05), and was reduced during beta-blockade by propranolol (1 mg/kg i.v. injection; -58% +/- 7%, P < 0.05). Expansion wave intensity was unchanged by dobutamine and propranolol (n = 6). In a separate group of animals (n = 7), expansion wave intensity was reduced during vasodilatation by nitroglycerin (0.5mg i.v. injection and 0.02 microg/kg per min infusion; -32% +/- 12%, P < 0.05), but was unchanged during vasoconstriction by methoxamine (2 mg i.v. injection). However, methoxamine reduced compression wave intensity (-46% +/- 14%, P < 0.05). These results indicate that (1) compression and expansion wavefronts generated by the left ventricle dominate acceleration and deceleration in the ascending aorta, (2) compression wave intensity is related to the inotropic state of the left ventricle, but is reduced during vasoconstriction, and (3) expansion wave intensity is reduced during vasodilatation. This time domain analysis of traveling wavefronts readily provides information concerning the dynamics of the ventriculoarterial interaction.

Adrenergic alpha-Agonists↗
PubMed2003

[Evaluation of abnormal myocardial wall motions in patients with univentricular heart by tissue Doppler echocardiography].

INTRODUCTION: Assessment of systolic and diastolic ventricular function in children and adults with morphologically and functionally univentricular heart is difficult using the conventional echocardiographic methods. Quantitative assessment of systolic and diastolic wall motion by TDE may provide information on abnormal systolic and diastolic ventricular function. Thus, the object of this study was to analyze the patterns of anterior and posterior wall motions in children with univentricular heart after palliative Fontan operation in comparison to normal subjects. PATIENTS AND METHODS: We investigated 21 patients of an average age of 10.1 years (range 4.2 to 32 years) with the primary diagnosis of univentricular heart and tricuspid atresia after a median period of 4.3 (range 1.2 to 8) years after cavo-pulmonary anastomosis (Fontan procedure) and in comparison to a normal collective of children without cardiovascular malformations. For investigation we used the novel tissue Doppler echocardiography (TDE) (EchoPack 6.3.6, Vingmed, Norway). Thereby we chose the standardized apical view and evaluated the left and right annular systolic (S(T)), early diastolic (E(T)) and atrial (A(T)) motion. We also registered the acceleration and deceleration time of each obtained curve. RESULTS: In comparison to the posterior myocardial wall the velocities at the anterior wall of the rudimentary ventricle were significantly reduced in all patients with tricuspid atresia and univentricular heart (p<0.0001). Particularly the annular systolic and diastolic wall motions of the rudimentary ventricle as well as their deceleration and acceleration time in patients with univentricular hearts differed significantly from those in healthy persons. CONCLUSION: Abnormal myocardial wall motion is detectable in children and adults with univentricular heart after palliative cardiac procedures using tissue Doppler echocardiography. The hemodynamic value of the measured abnormal wall motions, however, need further comparative studies.

Adolescent↗
PubMed1999

Injuries from hand grenades in civilian settings.

Four cases of hand grenade detonations in civilian life with homicidal intent are reported. The detonations always occurred in close proximity to the victims but there were only two fatalities out of seven victims directly attributable to the hand grenades. The relatively low mortality rate results from the ballistic characteristics of hand grenade missiles such as low mass and sectional density. This leads to rapid deceleration and thus to a poor penetration capacity of intermediate targets and tissue. Window glass at a distance of 2 m was not perforated in one case and the vast majority of fragment wounds showed a short wound tract of small diameter. The potential for physical activity can be unaffected even after a detonation inside a car. However, body parts almost in contact with the hand grenade, such as in a struggle, suffer large lacerations and comminuted fractures. At a distance, the chance of striking a vulnerable body region is increased by the multiple missiles but the wounding potential clearly decreases with increasing distance due to rapid deceleration and decreasing fragment cloud density. The effective range of detonation shock waves from hand grenades is very short and can only contribute to wounding in close-to-contact detonations. The forensic reconstruction is based on the directed radial character of the forces generated and on the sharply decreasing intensity of these forces with increasing distance from the detonation.

Autopsy↗
PubMed1997

A comparison of the effects of agonist and antagonist muscle fatigue on performance of rapid movements.

The aim of this study was to investigate the effects of agonist and antagonist muscle fatigue on the performance of rapid, self-terminating movements. Six subjects performed rapid, consecutive elbow flexion and extension movements between two targets prior to and after fatiguing either the elbow flexor or elbow extensor muscles. The experiments demonstrated consistent results. Agonist muscle fatigue was associated with a decrease in peak velocity and peak deceleration, while a decrease in peak acceleration was particularly prominent. Antagonist muscle fatigue, however, was associated with a decrease in peak deceleration, while a decrease in both the peak velocity and peak acceleration was modest and, in some tests, non-significant. The relative acceleration time (i.e. acceleration time as a proportion of the total movement time) increased when agonists were fatigued, but decreased when antagonists were fatigued. Taken together, these results emphasize the mechanical roles of the agonist and antagonist muscles; namely, the fatigue of each muscle group particularly affected the movement phase in which that group accelerated a limb, while changes of the movement kinematics pattern provided more time for action of the fatigued muscles. In addition, the results presented suggest that agonist muscle fatigue affects movement velocity more than antagonist muscle fatigue, even in movements that demonstrate prominently both mechanical and myoelectric activity of the antagonist muscles, such as rapid, self-terminating movements.

Adult↗
PubMed1999

Very long-chain fatty acids in Rett syndrome.

UNLABELLED: Rett syndrome (RS), found exclusively in girls, is characterised by a global deceleration of psychomotor development, loss of acquired speech, loss of manual skills and subsequent deceleration of head growth. The cause of this syndrome is so far unknown. To date there are no biological markers for RS; clinical diagnostic criteria were proposed by the Rett Syndrome Diagnostic Criteria Work Group 1988. The first objective of this study was to assay the levels of very long-chain fatty acids (VLCFA), i.e. C22:0, C24:0, C26:0, by gas chromatography in sera of 30 girls with RS. The VLCFA levels in the studied group were lower than the reference range for healthy children and control group. VLCFA levels were again measured after 2 months of L-carnitine administration in the same groups. VLCFA levels had increased. It is possible that the low VLCFA levels have some relation to the lowered carnitine levels. It may be that low carnitine levels impede transportation to mitochondria, thus the oxidation of long-chain fatty acids is inhibited, and compensated to a certain extent by intensified beta-oxidation of VLCFA in the peroxisomal system. Raising carnitine levels could improve substrate delivery for mitochondrial beta-oxidation of long-chain fatty acids, thus reducing the use of VLCFA as substrates for beta-oxidation. We consider VLCFA to be secondary to the pathogenesis of RS, but the possible abnormalities in their levels may provide an insight into the development of this disease. CONCLUSION: Very long-chain fatty acid and carnitine levels are decreased in Rett syndrome L-Carnitine administration increased very long-chain fatty acid levels in serum.

Administration, Oral↗
PubMed1990

Car driver behavior at flashing light railroad grade crossings.

The behavior of car drivers at two Dutch railroad grade crossings with automatic flashing warning lights was analyzed. Car drivers were videotaped while approaching either the red flashing lights or the white flashing "safe"-signal. Approach speeds, positions, and time intervals were semiautomatically measured from videos of more than 900 drivers: 660 while confronted with the red lights and 272 while passing the white light. Of the latter group, head movements during the approach to the crossing were also registered. Red light compliance was relatively good, as no driver was observed to cross later than 6 seconds after the onset of the red lights, despite train-arrival times of well over 60 seconds. The level of red light compliance was further quantified in terms of both the deceleration and time-to-stopping-line as accepted by drivers. From a comparison with earlier research on red light compliance at signalized road intersections it appeared that red light compliance was better at railroad crossings than at road crossings. It is concluded that faulty red light compliance is not a major cause for car-train accidents and that emphasis should be placed on the ability of the present device to attract attention and to signal unambiguously. The high degree of compliance also causes unexpected driver actions, such as emergency braking and hesitations. A yellow phase may reduce these problems. Some drivers tended to proceed immediately after a train had cleared the road instead of waiting for the end of the red signal (typically some 3 to 5 seconds after the train had passed). This tendency might reveal a major cause of dramatic errors when a second train is approaching. Immediate extinction of the red signal is suggested, or even better, a separate signal to announce the arrival of the second train. Behavior during the white signal phase also showed indications of uncertainty. In some 10% of cases drivers tended to decelerate more strongly than necessary and to make extra head movements. It is recommended that the present white flashing signal be reconsidered.

Accidents, Traffic↗