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Biomedical subjects

C Marquardt

Publications and source records attributed to C Marquardt.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1994

[Standardized analysis of visuospatial perception. Studies of objectivity, reliability and validity].

Retest reliability and validity of a computational method (VS, [19]) for the analysis of visual spatial perception in brain damaged patients was investigated. Retest reliability was tested in 20 patients (retest interval: 1 week; range: 1-3) and varied from r = 0.65-0.95 for the different subtests for the "point of subjective equality" and r = 0.39-0.89 for the "interval of uncertainty". In the several investigations concerning the validity of VS. 234 patients and 10 normal subjects participated. In the first place, we found significant relationships of some of the subtests of VS to similar visual-spatial tests, but no relationship to tests of visual object perception. Secondly, we found significant relationships to certain tasks which approximated daily functioning. In summary, the present results demonstrate the objectivity, retest-reliability and validity of VS in brain damaged patients.

Adolescent↗
PubMed1993

Effects of baroreceptor stimulation on sensorimotor control of the hand.

Finger movements are presumed to be controlled by somatosensory and motor areas of neocortex via the corticospinal tract. Since baroreceptor activation appears to reduce central nervous system activity, an effect on sensorimotor control during precise manual manipulations is expected. To test this hypothesis, motor responses to slow and fast perturbations during grasping of a small object (precision grip) were examined. Baroreceptor activation was manipulated with the phase-related external suction (PRES) technique, which allows the application of baroreceptor stimulation and control conditions in a well-controlled and indiscernible way. Motor reactions following slow perturbations were influenced in the expected way in good-performance subjects. The time to stop slow perturbations was longer and the electromyographic (EMG) activity of the small thumb muscles was lower during baroreceptor stimulation than in the control condition. These effects did not appear in the fast-perturbation task. Fast perturbations were followed by EMG activity onset after about 50 msec, which indicates that a prominent part of the EMG activity must be attributed to a more automatic motor response. EMG activity following slow perturbations began after about 90 msec, and it may be assumed that these motor reactions are primarily under voluntary control. The fact that we found effects of baroreceptor stimulation in slow but not in fast perturbations could have been caused by at least partially different pathways utilized for automatic versus voluntary motor responses, which seem to be differentially vulnerable to baroreceptor activation. An electrocortical sign that precedes voluntary movements is the Bereitschaftspotential, or readiness potential. Since this potential is a slow brain potential, and baroreceptor activation is known to reduce slow brain potentials, it is plausible that baroreceptor activation primarily affects motor responses following slow but not fast perturbations.

Adult↗
PubMed1993

[Standardized analysis of visual spatial perception. Construction of the procedure and applications].

Assessment of visuo-spatial perception (VS) in brain-damaged patients. So far, no comprehensive methods for reliable assessment of visuo-spatial deficits after brain damage have been described. The tests usually applied are subtests of intelligence tests, paper-pencil tests or visual-constructive tests which also require motor and planning abilities. Almost all these methods are unsuitable for measuring therapeutic changes and do not reveal specific impairments. The computational method presented here (VS) is suitable for the quantitative assessment of visuo-spatial functions, e.g. subjective visual vertical and horizontal; orientation, length, distance, form and position discrimination as well as line bisection. It can easily be installed on an IBM compatible PC. A clinical standard examination can be performed within 20-30 minutes including numerical and graphical analysis of the results. The method is sensitive for measuring therapeutic changes. Moreover, it offers a wide range of experimental task manipulations for more sophisticated experimental tests.

Attention↗
PubMed1992

Effect of skin temperature on platelet function in patients undergoing extracorporeal bypass.

Thirty-seven patients undergoing cardiopulmonary bypass operations were studied to assess the effect of skin temperature on platelet function. Differences in skin temperature between the two arms were created during bypass, at the completion of bypass, and at 2 and 24 hours after the completion of bypass. In each of 37 patients the temperature of one arm was increased with a water-filled blanket set at 40 degrees C. In 11 of these patients the other arm was allowed to equilibrate with the environment, and in the other 26 patients the arm was cooled with ice. Except for the differences in local skin temperature between the two arms, all factors known to affect the patient's bleeding time were similar. Measurements were made of bleeding times and the levels of thromboxane B2 and 6-keto-prostaglandin F1 alpha in shed blood obtained at the template bleeding time site. In the 33 patients not treated with aspirin, local hypothermia produced an increased bleeding time and a significant reduction in the thromboxane B2 level at the bleeding time site, but no reduction in 6-keto-prostaglandin F1 alpha level. Local rewarming produced a significant increase in the shed blood thromboxane B2 level. In the four patients treated with aspirin, local hypothermia produced no differences in bleeding times or shed blood levels of thromboxane B2 or 6-keto-prostaglandin F1 alpha. These data show the benefits of rewarming patients with hypothermia who have nonsurgical blood loss to restore to normal both core and peripheral temperatures before resorting to the transfusion of homologous blood products.

6-Ketoprostaglandin F1 alpha↗
PubMed1991

Rat mast cell tryptase.

Rat mast cell tryptase is located largely if not totally in the cell's secretory granules. When the active site reagent [3H]diisopropyl fluorophosphate was used to label tryptase and chymase simultaneously, the ratio of tryptase:chymase active sites was determined to be 0.05. In comparison to chymase and tryptase in other species and chymase in the rat, rat tryptase is poorly bound to the granule matrix as evidenced by (1) its release parallel to histamine on induction of secretion and (2) its appearance in the supernatant when isolated granules were stripped of their membranes with hypotonic medium. Tryptase on release from the granule is moderately stable at a pH of 5.0 but unstable at pH 7.5, the pH that the enzyme encounters on secretion from the cell. These several properties indicate that the role of rat mast cell tryptase extracellularly is likely to differ greatly from that of chymase.

Animals↗
PubMed1991

Anxiety induced by cardiac perceptions in patients with panic attacks: a field study.

In panic disorder bodily sensations appear to play an important role as a trigger for anxiety. In our psychophysiological model of panic attacks we postulate the following vicious circle: individuals with panic attacks perceive even quite small increases in heart rate and interpret these changes as being catastrophic. This elicits anxiety and a further increase in heart rate. To evaluate this model we conducted a field study of 28 subjects with panic attacks and 20 healthy controls. A 24 hr ambulatory ECG was recorded and the subjects were instructed to report any cardiac perceptions during this period and to rate the anxiety elicited by these perceptions. The incidence of cardiac perceptions was about the same in both groups, but only subjects with panic attacks reported anxiety associated with such perceptions. Analysis of the ECGs revealed that in both groups heart rate accelerations preceded cardiac perceptions. Following cardiac perceptions, the healthy controls showed a heart rate deceleration, whereas the subjects with panic attacks had a further acceleration. This heart rate increase after cardiac perceptions was positively related to the level of anxiety elicited by the perceptions. These results provide clear evidence in support of the vicious circle model of panic attacks.

Adult↗
PubMed1991

Heartbeat and arrhythmia perception in diabetic autonomic neuropathy.

A comparative study of diabetics with autonomic neuropathy (N = 13) as against non-neuropathic diabetics (N = 16) and healthy control persons (N = 20) was carried out with respect to heart rate both at rest and under stress, frequency of cardiac arrhythmias in a 24-h ECG and accuracy of heartbeat and arrhythmia perception. In the subjects with diabetic autonomic neuropathy, the spontaneous variability and stress-induced reactivity of the heart rate as well as the number of tachycardic episodes were reduced, whereas the frequency of ventricular extrasystoles was somewhat increased. Impaired heartbeat perception and a complete loss of perception of arrhythmias as a consequence of neuropathic deafferentation could be demonstrated. Cardiac perception disorders also play a vital role in other clinical problems, e.g. silent myocardial infarction and lack of awareness of hypoglycaemia in diabetes mellitus.

Adult↗
PubMed1991

[Cardiovascular factors of cardiac phobia--a field study].

The interaction between psychological and physiological factors was studied with a field approach in 28 patients with cardiac phobia and 20 healthy controls. A 24-hour ambulatory ECG was recorded, and the subjects were instructed to report their activities and any cardiac perception during this period. Additionally, psychological tests assessing well-being (Bf-S), bodily complaints (B-L), and state and trait anxiety (Stai-S and Stai-T) were administered. The groups did not differ in the mean cardiovascular parameters, however patients with cardiac phobia and healthy controls showed clear differences in the strength and direction of correlations between psychological and physiological variables. The incidence of cardiac perceptions was about the same in both groups, but only patients with cardiac phobia attributed the perceptions to an internal stimulus and associated the perceptions with anxiety. Depending on the anxiety elicited by the cardiac perceptions, the patients with cardiac phobia showed heart rate accelerations, which did not occur in healthy controls. This study confirms a psychosomatic process between psychological and physiological variables, which seems to be able to explain the development and maintenance of cardiac phobia.

Adult↗
PubMed1989

Hypomagnesemia and low alkaline phosphatase activity in patients' serum after cardiac surgery.

Significant decreases in magnesium (Mg) concentration and alkaline phosphatase (ALP, EC 3.1.3.1) activity in serum were seen in patients after cardiac surgery with cardiopulmonary bypass (Group 1), as compared with non-cardiac-surgery patients after general anesthesia (Group 2) or only spinal anesthesia (Group 3). Mean changes for Mg and ALP by the first postoperative day, compared with pre-operative baseline values, were as follows: Group 1: Mg -7.5 mg/L (-38.3%), ALP -46U/L (-48.4%); Group 2: Mg -3.3 mg/L (-17.4%), ALP -17 U/L (-16.5%); and Group 3: Mg -1.9 mg/L (-10.0%), ALP -15 U/L (-14.0%). The decreases in Mg and ALP observed in post-cardiac-surgery patients appear to be a consequence of the cardiac surgery and the cardiopulmonary bypass pump. Measurement of Mg and ALP in a subgroup of 10 cardiac-surgery patients for 10 days postoperatively showed initial decreases, with gradual recovery to near-normal values by the 10th day. That the changes in Mg and ALP seen postoperatively were not attributable to hemodilution alone was confirmed by measuring total-protein concentrations before and after operation. ALP requires Mg ion in vitro for optimal activity, but addition of Mg in the appropriate amounts to sera with low ALP activity did not restore ALP activity. The low ALP activity seen in post-cardiac surgery patients in vivo may perhaps be related to factors other than Mg that were removed by the cardiopulmonary bypass pump.

Alkaline Phosphatase↗
PubMedDate not supplied

Evaluation of precision grip using pneumatically controlled loads.

Precise control of grip force and finger movement is a fundamental aspect of motor tasks in which an object is held and manipulated between the subject's fingers. A new device to measure motor performance which simultaneously records grip force and finger movement is described. The subject holds a small, compressible cylinder between thumb and index finger. The load opposing finger movements is controlled pneumatically and may be altered with computer software. Different types of loads (e.g., constant load, spring load) may be applied. In addition, reactions to perturbing stimuli (e.g., fast changes of load) may be measured. Construction principles and examples of tasks investigating different aspects of hand function are presented in the paper.

Anthropometry↗