Search PubMed⌕ Search

Biomedical subjects

C Marquardt

Publications and source records attributed to C Marquardt.

At least 19 recordsLinked to original sources
PubMed2000

Moving weightless objects. Grip force control during microgravity.

When we move grasped objects, our grip force precisely anticipates gravitational and inertial loads. We analysed the control of grip forces during very substantial load changes induced by parabolic flights. During these flight manoeuvres, the gravity varies between hypergravity associated with a doubling of normal terrestrial gravity and a 20-s period of microgravity. Accordingly, the contribution of the object's weight to the load changed from being twice the normal value to being absent. Two subjects continuously performed vertical and horizontal movements of an object equipped with grip force and acceleration sensors. Whereas, during vertical movements performed under normal and hypergravity, a load force maximum occurred at the lower turning point and a minimum at the upper turning point, the load force pattern was completely changed under microgravity. In particular, the upper turning point was also associated with a load force maximum. Analysis of the grip forces produced by the two subjects revealed that the grip forces underwent the same characteristic changes as the load forces. Thus, subjects were able to adjust grip forces in anticipation of arm movement-induced fluctuations in load force under different and novel load conditions. Adaptation to changing levels of gravity was also obvious when the vertical and horizontal movements were compared: grip forces depended heavily on movement direction during normal and hypergravity but not during microgravity. The predictive coupling of grip force and load force was observed even during transitions between gravity levels, indicating rapid adaptation to changing load conditions. To account for the striking preservation of the normal characteristics of grip force control, we suggest that a highly automatized, extremely flexible sensorimotor mechanism firmly implemented within the central nervous system can cope with even massive changes in the environmental conditions.

Adaptation, Physiological↗
PubMed1999

Visual background motion reduces size distortion in spatial neglect.

Patients with visual neglect show deficits in horizontal size perception in their neglected hemispace, as previously reported. The present study examined whether this size distortion can be modulated by visual background motion to the left or right while the patient performs a visual size judgment task. Six neglect patients and six normal subjects were investigated with a psychophysical size judgment task. All neglect patients showed a significant perceptual underestimation of horizontal bars in their left hemispace expressed as an overestimation of horizontal object size in the baseline (no motion) condition. Slow visual motion of background stimuli towards the right, ipsilesional side aggravated the deficit slightly, but not significantly, whereas leftward background motion completely normalized the size distortion (in four cases) or even led to an overcompensation (in two cases). This facilitatory effect was specific as it was obvious for the constant errors in the size judgments, but not in their accuracy as reflected by unchanged difference thresholds. These results suggest that coherent background motion restores temporarily the disturbed perception and representation of horizontal object size in spatial neglect.

Adult↗
PubMed1999

[Biosurgery - maggots, are they really the better surgeons?].

Between 1 October 1996 and 31 December 1998 123 patients (74 men, 43 women) suffering from acute (n = 17) and chronic (n = 21) infections and chronic wounds (n = 85) were treated with sterile maggots (Lucilia sericata). In most patients the indication for the use of maggots was a failure to respond to standard therapy. Healing occurred in all patients with acute infections, and chronic infections showed excellent short-term results. In chronic wounds disturbances of healing in diabetics responded best to maggot therapy, the etiologically inhomogeneous group of leg ulcers asked for a polypragmatic approach, and the worst results were seen in chronic arterial occlusive disease (stage 4). Our limited experience with "biosurgery", biased selection of patients, and lack of late results reduce the significance of our data; nevertheless, sterile maggots seem to be an astonishingly workable tool for solving problems in surgical wound treatment.

Acute Disease↗
PubMed1999

Grip forces exerted against stationary held objects during gravity changes.

In the present study, grip forces exerted against a stationary held object were recorded during parabolic flights. Such flight maneuvers induce changes of gravity with two periods of hypergravity, associated with a doubling of normal terrestrial gravity, and a 20 s period of microgravity. Accordingly, the object's weight changed from being twice as heavy as normally experienced and weightless. Grip-force recordings demonstrated that force control was seriously disturbed only during the first experience of hyper- and microgravity, with the grip forces being exceedingly high and yielding irregular fluctuations. Thereafter, however, grip force traces were smooth, the force level was scaled to the object's weight under normal and high-G conditions, and the grip force changed in parallel with the weight during the transitions between hyper- and microgravity. In addition, during weightlessness, when virtually no force was necessary to stabilize the object, a low force was established, which obviously represented a reasonable safety margin for preventing possible perturbations. Thus, all relevant aspects of grip-force control observed under normal gravity conditions were preserved during gravity changes induced by parabolic flights. Hence, grip-force control mechanisms were able to cope with hyper- and microgravity, either by incorporating relevant receptor signals, such as those originating from cutaneous mechanoreceptors, or by adequately including perceived gravity signals into control programs. However, the adaptation to the uncommon gravity conditions was not complete following the first experience; finer tuning of the control system to both hyper- and microgravity continued over the measurement interval, presumably with a longer observation period being necessary before a stable performance can be reached.

Adult↗
PubMed1999

Visual control of automated handwriting movements.

This study provides new insight into the subtle interaction between visual feedback and automated handwriting movements. To separate effects of visual feedback from effects of speed/accuracy trade-off, subjects were trained to perform the tasks with rapid and automated movements. To control the visual feedback the written trace was presented only on a computer screen. In the first experiment the visual feedback of script size was manipulated. Subjects had to write the character combination "ll" onto a pattern of squares. In some trials the script size was unpredictably enlarged by 133% or reduced by 66%. Results showed that the ongoing "l" was not affected by the manipulation, but subjects adapted script size in the following "l" without any change in the kinematic characteristic of the movements. In a second experiment trajectory correction strategies in perturbed writing movements were studied. Two small boxes had to be connected by rapid and single-stroke movements. In some of the trials the position of the target box was changed unpredictably to a new position. Kinematic analysis revealed that the initial movement was not aborted, but rather a second independent movement was added to correct the trajectory to the new target. Thus, this proves that a distortion of visual feedback does not directly slow down open-loop movements to allow control of the motor output in a closed-loop mode. The ballisticity and automation was maintained during movement correction. Our findings fit perfectly well with recent theories of kinematic organization where complex movements are composed by elemental movement strokes.

Adolescent↗
PubMed1999

Prehension with the ipsilesional hand after unilateral brain damage.

Sensorimotor deficits in the hand ipsilateral to a brain lesion have been reported in different motor tasks. We evaluated performance of the ipsilesional hand in 12 patients with either left (LBD) or right brain damage (RBD) by kinematic analysis in order to precisely characterize possible deficits in the two components of prehension (transport and grasp). Both patient groups exhibited performance deficits in the main kinematic parameters, e.g., reduced velocity of the transport component and prolonged movement time. However, while LBD patients showed a more general slowing, RBD patients prolonged in particular the last phase of the movement toward the object. We suggest that relevant visuospatial representations and the adequate mapping of motor processes may be impaired after RBD. In contrast, LBD caused a more unspecific disturbance pattern, supporting the view that the precise parameterization of motor programs is impaired. Maximum grip aperture was normal in both patient groups. However, since aperture could be biased by slowed movement, the notion that the grasp component was preserved remains speculative. The patient's ability to scale the maximum velocity of the transport component to adapt to changes in movement amplitude and to scale the maximum hand aperture of the grasp component to adapt to object size was preserved in both groups. Thus both hemispheres can have competence for this scaling mechanism.

Adult↗
PubMed1999

Comparative analysis of diadochokinetic movements.

Tests of diadochokinesia are an inherent part of a neurological examination. Various quantifying methods have been proposed to increase the objectivity, sensitivity, and reliability of such examinations. The methods used and analyses performed, however, differ substantially between tasks. We used a three-dimensional, ultrasound-based recording device to continuously record joint angles during three diadochokinetic movements, avoiding any external constraints of the movements. Alternate pronation and supination of the forearm, tapping with the whole hand and with the index finger in isolation were analyzed in a sample of 63 healthy control subjects. The most sensitive measure for capturing effects of gender, sex, and active hand was frequency. The right hand was faster than the left in all tasks, tapping performance declined with increasing age, and male subjects were faster than females in forearm diadochokinesia. Other measures that characterize speed of movement such as maximum angular velocities and accelerations did not yield comparable sensitivity in detecting the same statistical effects. However, angular velocity achieved the highest test-retest reliability for forearm diadochokinesia, while frequency was reproduced in the tapping tasks. Additional measures characterizing symmetry of the angular velocity profiles and intraindividual variability were shown to be largely independent of movement speed. Examples in neurological patients showed that the data define a valuable standard against which pathological performance can be precisely evaluated. In addition, the different measures captured dissociable aspects of motor performance that may further help to characterize the deficit and adjust therapy.

Adult↗
PubMed1998

Ion-exchange column chromatographic method for assaying purine metabolic pathway enzymes.

High energy phosphate levels fall rapidly during cardiac ischemia and recover slowly (more than one week) during reperfusion. The slow recovery of ATP may reflect a lack of purine metabolic precursors and/or increased activity of purine catabolic enzymes such as 5'-nucleotidase (5'-NT, EC 3.1.3.5) and adenosine deaminase (ADA, EC 3.5.4.4). The activity of enzymes involved in both the catabolism of ATP precursors (5-NT and ADA) and the restoration of ATP from slow synthetic pathways [adenosine kinase (AK, EC 2.7.1.20), adenine phosphoribosyl transferase (APRT, EC 2.4.2.7) and hypoxanthine phosphoribosyl transferase (HPRT, EC 2.4.2.8)] may directly affect the rate of ATP recovery. Strategies to enhance recovery will depend on the relative activity of these enzymes following ischemia. Their activity in different species and their response to ischemia are not well characterized. Hence, rapid assay methods for these enzymes would facilitate detailed time course studies of their activities in postischemic myocardium. We modified a single ion-exchange column chromatographic method using DEAE-Sephadex to determine the products of incubation of 5'-NT, AK, APRT and HPRT with their respective substrates. The uniformity of the final product measurement procedure for all assays permits the activities of the four enzymes to be rapidly determined in a single tissue sample and facilitates the study of a large number of samples. This technique should also be useful for enzymes of the pyrimidine metabolic pathway.

5'-Nucleotidase↗
PubMed1997

Development of a true primary repair for the full spectrum of esophageal atresia.

OBJECTIVE: To determine whether or not a true primary repair, without myotomies and with the gastroesophageal junction below the diaphragm, can be accomplished across the esophageal atresia (EA) spectrum. Our hypothesis is that the esophageal anastomosis can withstand significant tension. The consequences, particularly for those patients with a very long gap atresia, were assessed. SUMMARY OF BACKGROUND DATA: Difficulties arise roughly in proportion to the size of the gap between esophageal segments. Reported surgical complications remain frequent, and particularly at the far end of the EA spectrum, not all children are left with a satisfactorily functioning esophagus or esophageal substitute. METHODS: The outcomes of all infants who had a true primary repair of EA from 1976-1997 were determined. Surgically, the methods used to achieve a reliable true primary repair were expanded to accomplish this, even for a very long gap EA. RESULTS: From 1976-97, 70 infants with or without associated tracheoesophageal fistula (TEF) had primary repairs performed with no surgery-related deaths and 11% later deaths. No interpositions were performed since 1983. There were no discernible anastomotic leaks and one late recurrent TEF related to the early use of balloon dilation. Ten infants had gaps of 5.0-6.8 cm and, among these, four had gaps of 5.5-6.8 cm that could not be pulled together initially. Traction sutures in the esophageal ends, however, produced sufficient lengthening within 6-10 days for a true primary repair. Very long gap repairs produced more reflux (10 of 10 required a fundoplication versus 24 of 70 overall) and more dilations to relieve strictures. Two infants underwent stricture resection with no recurrence. On follow-up, all patients over 2 years of age were eating well or satisfactorily, and none had a gastrostomy tube. CONCLUSIONS: (1) The esophageal anastomosis can withstand considerable tension and allows a reliable true primary repair for the full EA spectrum. (2) Growth is rapid and traction sutures will produce significant esophageal lengthening within days. (3) With increasing tension, gastroesophageal reflux (GER) and strictures are more common; however, both are treatable. Follow-up reveals the benefits of true primary repair over other solutions.

Esophageal Atresia↗
PubMed1996

Computational analysis of open loop handwriting movements in Parkinson's disease: a rapid method to detect dopamimetic effects.

We used a computational analysis of open loop handwriting movements and a clinical rating scale for monitoring the effect of apomorphine in 16 patients with early untreated parkinsonism [subsequently L-DOPA responsive, probable Parkinson's disease (PD)], six patients with long-standing PD with L-DOPA associated motor fluctuations, and seven patients with known L-DOPA unresponsive parkinsonism. Subjects were instructed to write fluently concentric circles of approximately 12 mm in diameter. Movements were recorded for two periods of 3 s each, using a digitizing tablet. Mean peak velocity (Vmax) and mean peak acceleration (Amax) were determined. In addition, two sensitive indices describing the degree of automation of handwriting were derived: (a) NCV, calculated as the mean Number of Changes in direction of Velocity per half circle, and (b) NCA, the mean Number of Changes in the direction of Acceleration. Clinical rating was performed according to the Unified Parkinson's Disease Rating Scale part III (UPDRS III). After apomorphine injection, the patients with early untreated probable PD showed significant improvement of Vmax, Amax, NCV, NCA, and UPDRS III scores. Likewise, the patients with long-standing PD improved significantly in all kinematic parameters and UPDRS III scores. Patients with L-DOPA unresponsive parkinsonism failed to change significantly in any of the parameters tested. These observations suggest that the computer-assisted analysis of automated handwriting movements can be used as an objective quick method for quantifying dopamimetic effects on the kinematics of handwriting movements in parkinsonian patients.

Adult↗
PubMed1996

[Closure of defect wounds by combined vacuum sealing with instrumental skin expansion].

Between 1.6.1995 and 31.12.1995, 17 trauma defect wounds were closed by suturing in 12 patients with a median of age of 35 (11-65) years, a new type of instrument for skin stretching being used in combination with a vacuum sealing procedure. According to clinical experience, closure of the skin defect would have required skin grafting in all patients. After secondary suturing 15 wounds healed without problems, while in the case of 1 wound there was a small skin defect, which healed spontaneously. In another sutured wound a partial dehiscence occurred over the medial malleolus on the 10th postoperative day; this also healed spontaneously without further surgical measures. There were no wound infections or necroses of the wound edges. This procedure is recommended for the closure of defect wounds, as it reduces the risk of wound infections, shortens the period of treatment and avoids cosmetically and functionally inadequate skin grafts.

Adolescent↗
PubMed1996

Kinematic analysis of movement imitation in apraxia.

Accuracy of the final position and kinematics of movement were analysed during the imitation of meaningless gestures in patients with unilateral brain lesions who performed with the hand ipsilateral to the lesion and in control subjects. Controls imitated the gestures virtually without spatial errors. The kinematics of their movements was characterized by single-peaked and approximately bell-shaped velocity profiles of the transport phase combined with no or only minor corrective movements in the final phase. Patients with right brain damage (RBD) performed as well as control subjects with respect to both spatial accuracy of final hand-positions and kinematic parameters of the movement trajectories. Patients with left brain damage (LBD) committed spatial parapraxias and had a much higher frequency of kinematic abnormalities. However, there was no correlation between kinematic abnormalities and apraxic errors. There were kinematically abnormal movements which reached a correct final position as well as kinematically normal movements leading to apraxic errors. One possible explanation for the combined occurrence of kinematic abnormalities and parapraxias in LBD patients would be that they are independent sequels of left hemisphere lesions. An alternative account is that the associations and dissociations result from an interaction between one common basic deficit and strategies to cope with this deficit. The basic deficit may concern the mental representation of the target position. The LBD patients may react to the absence of an appropriate representation of the target by one of two alternative strategies; they may switch to a strategy of slowed, on-line controlled movements to find the required final position, or they may move their hand smoothly at normal speed to a roughly specified location without taking note of their deficiency. Depending on whether these strategies are successful or not they would lead to the observed associations and dissociations between kinematic abnormalities and spatial parapraxias.

Adult↗
PubMed1995

Persistent mirror movements: force and timing of "mirroring" are task-dependent.

A simple isometric motor task was used to quantify intended and unintended finger movements in two subjects (father and son) with persistent mirror movements. One hand voluntarily changed grip force between thumb and index finger at different amplitudes and frequencies, while the other hand was to maintain a constant force. During all experimental conditions the "steady" hand showed insuppressible, highly cross-correlated contractions, compatible with bilateral distribution of a single motor command to the spinal cord. However, these associated movements were not strictly mirror images, nor did they show a fixed relationship to the voluntary movements across experimental conditions. The ratio of mirror to voluntary movement ranged from 1.4 to 19.1% and from 3.4 to 78.4% in the two subjects and was directly related to voluntary strength and speed. At maximum speed, mirror activity tended to precede voluntary activity, while it was delayed in slow force changes. Comparable time lags were not found in control subjects instructed to simulate mirror movements. We conclude that neuronal mechanisms in addition to bilateral corticomotoneuronal connections are at work in persistent mirror movements.

Adult↗
PubMed1995

VS--a new computer program for detailed offline analysis of visual-spatial perception.

A new IBM-AT-compatible software program, VS, for the analysis of visual-spatial (VS) perception in humans, especially brain-damaged patients, is described. VS is suitable for analysis of the following visual-spatial tests: (1) subjective visual vertical (SVV), (2) subjective visual horizontal (SVH), and (3) orientation, length, distance, form and position discrimination, as well as line/bar bisection. The program allows manipulation of a wide range of experimental tasks by varying relevant parameters, e.g., length, width, color, movement direction, step width, and position on screen of the stimuli. Psychophysical parameters are computed (methods of limits) and stored in dBASE files which can be retrieved for further data analysis with commercial statistics or graphics software. VS has a versatile text editor, with two macro languages which enables the user to define their own experimental configurations and realize individual graphic plots on screen or laser printer. VS incorporates two standard examinations together with normative data of control subjects and standard plots of the subject's performance. The results of separate investigations show highly stable results in normal control subjects in repeated examinations as well as good retest-reliability of these standard examinations in brain-damaged patients (rtt = 0.77). Representative case reports of a patient with left-sided visual neglect, a patient with Balint's syndrome as well as a patient with visual-spatial deficits subsequent to a left parietal brain lesion demonstrate the sensitivity and specificity of the program.

Adult↗
PubMed1995

Feedback-based training of grip force control in patients with brain damage.

OBJECTIVE: Feedback-based training of grip force control in patients with various brain lesions was evaluated. DESIGN: Patients were instructed to hold a force transducer in a precision grip and to track with their grip force a moving target, which was presented together with the feedback signal on a monitor. Training performance was evaluated during a maximum of 10 sessions. Before and after the training, performance in two transfer tasks, which differed in target characteristics from the training task, was examined. PATIENTS: Ten patients with impaired grip force control, after brain lesions of different origin, were selected on the basis of a clinical examination of hand function. MAIN OUTCOME MEASURES: Tracking accuracy in training tasks and transfer tasks was evaluated by calculating the conventional root-mean-square error. RESULTS: Nine out of the 10 patients reduced their tracking error considerably during a maximum of 10 subsequent sessions (t test, p < 0.05), and most of them reached normal or near-normal performance. In addition, they improved in both transfer tasks (t test, p < 0.05). Detailed analysis showed that impaired initial performance and improvement was not uniform among patients and could be attributed to individual aspects of force control. CONCLUSIONS: In view of these results, a feedback-based training of grip force may be a useful enrichment of motor therapy.

Adult↗
PubMed1994

Perturbation of precision grip in Friedreich's ataxia and late-onset cerebellar ataxia.

Perturbations of precision grip were tested in 7 patients with Friedreich's ataxia (FA) and 11 patients with late-onset cerebellar ataxia (CA). Subjects were instructed to hold a small compressible manipulandum between thumb and index finger and to resist any perturbation of maintained finger position. A sudden increase of load induced a displacement of fingers until this was stopped by subjects' active intervention. The amount of initial displacement emerged as a highly sensitive parameter to differentiate the clinical subgroups: Responses in FA patients were missing or massively delayed, whereas displacements in CA patients were normal or only moderately abnormal. This discrimination of impaired hand function in FA and CA patients has not been possible by using only tasks of isometric grip force control. We concluded that our task relies more on intact sensory afferents, which are known to be impaired in FA, than on cerebellar function. In a second task the stiffness of the maintained grip was determined. On the average, preresponse stiffness was lower in FA patients as compared with CA patients and normal controls. However, stiffness appeared to be an independent parameter that did not influence the amount of displacement in the perturbation task.

Adolescent↗
PubMed1994

A computational procedure for movement analysis in handwriting.

Validity of handwriting movement data recorded with digitizing tablets is poorly reflected by manufacturer's specifications. Actual errors of positional data are in fact in a critical range, in particular when time derivatives are calculated. Because differentiation magnifies errors in the displacement data, data smoothing becomes crucial. A new method for smoothing and differentiating noisy handwriting movement data is proposed. Non-parametric estimation of regression functions using kernel estimates generally offers simple application and extremely fast calculation. Assessing simulation data the efficiency of the procedure was investigated and compared with butterworth filters and finite impulse response (FIR) filters. Kernel estimates show a slightly elevated bias, but strongly reduced residual variance in the velocity and acceleration signals. The overall smoothing behaviour of kernel estimates is better than butterworth filters and very similar to FIR filters, if their transition band is chosen appropriately.

Electronic Data Processing↗