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Biomedical subjects

S Krafczyk

Publications and source records attributed to S Krafczyk.

At least 19 recordsLinked to original sources
PubMed2004

[The electrical stimulation bicycle: a neuroprosthesis for the everyday use of paraplegic patients].

Until recently, few patients with complete paraplegia could walk or stand with the help of functional electrical stimulation (FES) of the leg muscles regularly at home. In comparison, FES cycling with an adapted tricycle is easy to put into practice because the legs remain connected to the pedals and through the use of a tricycle or stationary bicycle, the balancing problems of the patient recedes into the background. In the first German feasibility studies for paraplegic cycling, eleven completely paraplegic patients have been tested so far. The goal is to make FES cycling a daily activity in the lives of as many patients as possible.

Bicycling↗
PubMed2004

[Paraplegic cycling using functional electrical stimulation. Experimental and model-based study of power output].

Cycling using functional electrical stimulation offers paraplegics the possibility of muscle and cardiovascular training as well as the chance for independent locomotion. To investigate whether this method might be suitable for a large group of paraplegics, the first German feasibility study of functional electrical stimulation (FES) cycling with seven paraplegic patients was started at the beginning of 2003. Even at the beginning of the study, and without training, these patients were able to drive distances of 0.5-1.6 km. To stimulate cardiovascular adaptation processes in the case of FES ergometer training or to cover useful distances in the case of FES cycling, a minimum amount of generated mechanical output power is required, which as a rule cannot be achieved yet. In this study, we point out two particular aspects of FES cycling, which impair power output: prolonged fatigue mode and viscous joint friction of the paraplegic FES cyclist. We discuss current possibilities for increasing output power and endurance.

Adult↗
PubMed2003

Treatment of downbeat nystagmus with 3,4-diaminopyridine: a placebo-controlled study.

BACKGROUND: Several drugs that primarily act on gamma-aminobutyrate or muscarinic receptors have been used to treat downbeat nystagmus (DBN) syndrome despite their having only moderate success and causing several side effects that limit their effectiveness. These drugs were tested under the assumption that DBN was caused by a disinhibition of a physiologic inhibitory cerebellar input on vestibular nuclei. OBJECTIVE: To evaluate the effects of a single dose of the potassium channel blocker 3,4-diaminopyridine (3,4-DAP), which is known to increase the excitability of Purkinje cells, on DBN in a prospective, placebo-controlled, double-blind study with a crossover design. METHODS: Seventeen patients with DBN due to cerebellar atrophy (5), infarction (3), Arnold-Chiari malformation (1), or unknown etiology (8) were included in the study (1 of 18 patients had to be excluded). Mean peak slow-phase velocity (PSPV) was measured before and 30 minutes after randomized ingestion of 20 mg of 3,4-DAP or placebo orally; at least 1 week later, the treatments were switched. RESULTS: 3,4-DAP reduced mean PSPV of DBN from 7.2 +/- 4.2 degrees /s (mean +/- SD) before treatment to 3.1 +/- 2.5 degrees/s 30 minutes after ingestion of the 3,4-DAP (p < 0.001, two-way analysis of variance). Placebo had no measurable effect. In 10 of 17 subjects, the mean PSPV decreased by >50% and in 12 of 17 by >40%. In parallel, the subjects had less oscillopsia and felt more stable while standing and walking. Nine of the subjects continued to take the drug with success. Except for transient minor perioral or digital paresthesia reported by three subjects and nausea and headache reported by one, no other side effects were observed. CONCLUSIONS: In this study, the authors demonstrated that a single dose of 3,4-DAP significantly improved DBN. In view of animal studies reporting that micromolar concentrations of 4-aminopyridine increased the excitability of Purkinje cells, it is suggested that the efficacy of 3,4-DAP may be due to an increase of the physiologic inhibitory influence of the vestibulocerebellum on the vestibular nuclei.

4-Aminopyridine↗
PubMed2001

Postural reflexes evoked by tapping forehead and chest.

We investigated whether a tap with a reflex hammer to the forehead can elicit responses in the leg muscles and whether vestibular stimulation is the crucial prerequisite for eliciting these responses. We also measured the postural changes caused by the tap and by the compensatory, presumably reflex-like reactions of the subject. Tap-evoked activity of leg muscles was easily elicited during upright stance in normal subjects and was also seen in two subjects without vestibular function. The pattern of muscle activation clearly showed a counteraction to the tap-evoked perturbation of stance. Taps applied to the chest elicited similar reflexes. Since these two conditions imply a different activation of the vestibular apparatus, the vestibular input alone cannot account for the observed leg muscle reflexes. We suggest that multisensory reflex pathways that integrate vestibular and proprioceptive inputs account for these reflexes.

Adult↗
PubMed2000

Patients with somatoform phobic postural vertigo: the more difficult the balance task, the better the balance performance.

The objective was to test, whether the increased body sway activity, shown in patients with phobic postural vertigo (PPV) in a previous posturographic study, impairs postural balance during demanding balance tasks. In 17 patients with PPV and 15 normal subjects body sway was analyzed for two standing positions on a foam rubber-padded posturographic platform with the eyes open or closed: (a) normal upright stance, (b) tandem stance. During normal upright stance patients showed an increase in body sway activity between 0.1 and 19 Hz and in sway path values for lateral and fore/aft directions. During the most difficult balance task, i.e. tandem stance with the eyes closed, body sway activity and sway path values did not differ between patients and controls. Objective balance skills were not impaired in patients with PPV during balance tasks at the limits of postural control.

Adult↗
PubMed1999

Increased body sway at 3.5-8 Hz in patients with phobic postural vertigo.

Postural sway during upright stance was analyzed in 12 patients with phobic postural vertigo (PPV) and in 12 age-matched healthy volunteers. Recordings were made under different conditions (with the eyes open or closed): when standing on a foam rubber pad with the head upright, turned 30 degrees to the right or left, or during 1 Hz horizontal head oscillations. Sway analysis included calculation of sway path, of root mean square values of sway and of the power spectrum of sway in fore/aft and lateral directions. There was a significant increase in sway activity in the 3.53-8 Hz frequency band in patients with PPV. This did not impair objective postural stability. Increase in higher frequency sway activity may simply reflect a change in postural strategy rather than a sensorimotor dysfunction. The patients' conscious control of stance may augment co-activation of anti-gravity muscles, a strategy applied by normal subjects when performing demanding balancing tasks.

Adult↗
PubMed1995

Postural stability differentiates "lower body" from idiopathic parkinsonism.

INTRODUCTION: Patients with an akinetic Parkinson syndrome of the lower extremities and a poor response to L-DOPA have been described as "lower body Parkinsonism" (LBP). These patients are characterized by frequent fallings and poor balance. METHODS: We have studied body sway with static (force platform) and dynamic (Equitest) posturography in 11 LBP patients, 6 of them revealing deep white matter lesions on MRI and 10 patients with advanced Parkinson's disease (PD) and compared performance with 30 age-matched controls. RESULTS: When standing on a fixed support the postural performance of both patient groups lay within the normal range. The balance of LBP patients worsened in the static testing in the conditions "eyes open on foam" (p < 0.05) and "eyes closed on foam" (p < 0.0006, of 11 patients falling), whereas the balance of PD patients deteriorated only with "eyes closed on foam" (p < 0.05). Dynamic posturography confirmed these results in 6 different sensory conditions, clearly distinguishing the more unstable LBP patients from PD patients during "standing, eyes closed, foot support sway referenced" (p < 0.005). CONCLUSION: We conclude, that postural adjustments in LBP patients are more disturbed than those in PD patients and posturography can be an additional tool for the differential diagnosis of Parkinson syndromes with gait disorders.

Aged↗
PubMed1994

Dependence of visual stabilization of postural sway on the cortical magnification factor of restricted visual fields.

Monocular visual stabilization of fore-aft and lateral body sway was tested posturographically in normal subjects (wearing visual field blinds) as a function of visual field size and location of the visual field on the central or peripheral retina. Body sway applied to a force- measuring platform is less with central (foveal) vision when central and peripheral visual fields have the same area. If, however, the peripheral field size is corrected by the cortical magnification factor of the retina in the primary cortex, body sway is stabilized by the peripheral retina to the same extent. Thus, there is no functional specialization of central and peripheral retina with respect to balance control. Visual stabilization of upright stance is a function of field size and cortical representation of the retina. The central and the peripheral retina have different thresholds to detect motion; this was surprisingly not reflected in measurements of normal fore-aft and lateral body sway.

Adult↗
PubMed1992

Postural imbalance: an early sign in HIV-1 infected patients.

We have recorded postural performance in 50 HIV-infected patients in different stages of the disease (Walter Reed (WR) stages I-VI) by means of a force measuring platform. The results were compared with 50 age-matched controls. A significant instability was particularly evident when standing on an unstable foot support. In patients standing with "eyes closed", postural sway was significantly higher in every patient group (WR I-II: P less than 0.02, WR III-V: P less than 0.001, WR VI: P less than 0.001). Patients in stage WR I-II showed no relevant neurological abnormalities. In agreement with other neurophysiological data in the literature we suggest that postural imbalance could be an early sign of central nervous system penetration of HIV. No correlation with electromyographic or cerebrospinal fluid findings could be found.

Adult↗
PubMed1991

Influence of magnetic resonance imaging on evoked potentials and nerve conduction velocities in humans.

The authors investigated the influence of a 1.0-T magnetic field of a magnetic resonance (MR) imaging device, as well as the possible effects of the changing magnetic field and the RF field, on somatosensory, visual, and auditory evoked potentials and on peripheral nerve conduction velocities. The neural potentials outside and inside the static magnetic field were recorded before and after MR imaging. The measured latencies before and after MR imaging were within the normal range for healthy volunteers. The magnetic field did not significantly alter central or peripheral conduction velocities.

Adult↗
PubMed1989

Differential effects of retinal target displacement, changing size and changing disparity in the control of anterior/posterior and lateral body sway.

When visual information is provided in addition to input from other sensory systems, normal body sway can be attenuated by about 50%. The essential visual cue is retinal target displacement, which increases as eye-target distance is reduced. As a result, both lateral and anterior/posterior (A-P) sway decrease as eye/target distance decreases. We have investigated the geometrical basis of lateral and fore-aft sway detection by vision, the latter provided by detection of change in disparity of the visual axis of both eyes and change in target size. Using known movement detection thresholds the largest possible distance for visual stabilization of posture can be calculated to be 34 m for lateral sway, and for fore-aft sway 1.50 m for change in disparity and 3.20 m for change in size. Visual stimuli were designed to selectively stabilize fore-aft sway either by change in size or by change in disparity. The experiments revealed that the theoretical prediction overestimates the efficacy of visual stabilization of lateral sway and underestimates the efficacy of fore-aft sway stabilization. It is proposed that microoscillations of the eye increase the threshold for detection of retinal target displacements, leading to less efficient lateral sway stabilization than expected, and that the threshold for detection of self motion in the A-P direction is lower than the threshold for object motion detection used in the calculations, leading to more efficient stabilization of A-P sway.

Form Perception↗
PubMed1989

Postural sway during retinal image stabilisation.

Posturographic measurements using a piezoelectric platform were made in normal subjects while wearing a combination of spectacle and contact lens providing partial stabilisation of the retinal image (RIS). The amount of postural sway seen while wearing the device at rest is intermediate between the "normal vision" and "eyes closed" conditions, and increases with increasing amounts of RIS. However, when large active head-and-eye movements are performed, postural sway is dramatically increased when using RIS, and is then worse than while performing the same task in the "eyes closed" condition. It is concluded that patients who use the partial-RIS device for the treatment of severe oscillopsia may benefit only when performing tasks in which the head is relatively still, such as reading, writing or watching TV. It is also proposed that the partial-RIS device can serve as a model in normal free-standing subjects for the postural effects of oculomotor disorders.

Adult↗
PubMed1988

[Effect of in vivo nuclear magnetic resonance tomography on somatosensory and visual evoked potentials in the human].

By means of registration of somatosensory (SSEP) and visual (VEP) evoked potentials under the influence of different magnetic and electromagnetic fields of Magnetic Resonance we investigated the influence of Magnetic Resonance Imaging (MRI) on human nervous system (all measurements with an 1.0 T MR imager are performed outside and inside the static magnetic field, before and after MR imaging). In vivo experiments on 20 healthy volunteers show in SSEP registrations as well as in VEP-registrations no measurable influence on nerve conduction. The measured latencies before and after MR imaging are found inside the standard values which are valid for healthy volunteers. In vivo experiments at field-strengthens up to 1.0 Tesla show no significant changes of the central and peripheral conduction velocity with human beings.

Adult↗
PubMed1987

Object-motion detection affected by concurrent self-motion perception: applied aspects for vehicle guidance.

Thresholds and response times for object-motion detection are significantly raised during concurrent real or visually induced self-motion perception. This was demonstrated by standardized laboratory experiments in which subjects had to react to a suprathreshold visual stimulus (1 degree-light spot moving with 5 degrees/s speed) under different stimulus conditions of simultaneously perceived self-motion. Elevated response times (mean elevation factor: 3.27) were also obtained for the detection of changes in inter-vehicle distance (headway) under real road conditions with the simultaneous involvement of self- and object-motion perception compared to a corresponding (object-motion perception) simulation in the laboratory without any self-motion. With regard to vehicle guidance, existing concepts of safe stopping distances, which depend upon adequate detection of a collision course and the corresponding reaction times, have to be recalculated.

Adult↗