Biomedical subjects

U Fietzek

Publications and source records attributed to U Fietzek.

7 recordsLinked to original sources

PubMed2004

Tremor analysis in two normal cohorts.

OBJECTIVE: Quantitative tremor analyses using almost identical methods were compared between two independent large normal cohorts, to separate robust measures that may readily be used diagnostically from more critical ones needing lab-specific normalization. METHODS: Hand accelerometry and surface EMG from forearm flexors and extensors were recorded with (500 and 1000 g) and without weight loading under postural conditions in 117 and 67 normal volunteers in two different specialty centers for movement disorders in Germany. RESULTS: Tremor amplitude (total power) and frequency fell within a similar range but differed significantly. A significant reduction of tremor frequency under 1000 g weight load (>1 Hz), and a lack of rhythmic EMG activity at the tremor frequency in around 85-90% of the recordings were robust findings in both centers. CONCLUSIONS: The differences in frequency and total power indicate that these measures critically depend on the details of the recording conditions being slightly different between the two centers. Thus each lab needs to establish its own normative data. We estimate that at least 25 normal subjects have to be recorded to obtain normal values. The reduction of tremor frequency under load and lacking tremor-related EMG activity were well reproducible allowing a differentiation of physiological from low amplitude pathological tremor. SIGNIFICANCE: This study provides a framework for more standardized tremor analyses in clinical neurophysiology.

Adult↗

PubMed2003

Deep brain stimulation of the subthalamic nucleus in Parkinson's disease: evaluation of active electrode contacts.

BACKGROUND: The subthalamic nucleus is the preferred target for deep brain stimulation in patients with advanced Parkinson's disease. The site of permanent stimulation is the subject of ongoing debate, as stimulation both within and adjacent to the subthalamic nucleus may be effective. OBJECTIVE: To assess the position of active electrode contacts in relation to the dorsal margin of the subthalamic nucleus as determined by intraoperative microrecordings and magnetic resonance imaging (MRI). METHODS: In 25 patients suffering from severe levodopa sensitive parkinsonism, deep brain stimulating electrodes (n = 49) were implanted following mapping of the subthalamic nucleus by microrecording and microstimulation along five parallel tracks. Postoperative stereotactic radiography and fusion of pre- and postoperative MRI studies were used to determine the stereotactic position relative to the midcommissural point of the most effective electrode contacts selected for permanent stimulation (n = 49). Intraoperative microrecordings were analysed retrospectively to define the dorsal margin of the subthalamic nucleus. In cases where the dorsal margin could be defined in at least three microrecording tracks (n = 37) it was correlated with the position of the active contact using an algorithm developed for direct three dimensional comparisons. RESULTS: Stimulation of the subthalamic nucleus resulted in marked improvement in levodopa sensitive parkinsonian symptoms and levodopa induced dyskinesias, with significant improvement in UPDRS III scores. In several instances, projection of the electrode artefacts onto the T2 weighted MRI visualised subthalamic nucleus of individual patients suggested that the electrodes had passed through the subthalamic nucleus. When the actual position of active electrode contacts (n = 35) was correlated with the dorsal margin of the subthalamic nucleus as defined neurophysiologically, most contacts were located either in proximity (+/- 1.0 mm) to the dorsal border of the subthalamic nucleus (32.4%) or further dorsal within the subthalamic region (37.8%). The other active contacts (29.7%) were detected within the dorsal (sensorimotor) subthalamic nucleus. The average position of all active contacts (n = 49) was 12.8 mm (+/- 1.0) lateral, 1.9 mm (+/- 1.4) posterior, and 1.6 mm (+/- 2.1) ventral to the midcommissural point. CONCLUSIONS: Subthalamic nucleus stimulation appears to be most effective in the border area between the upper subthalamic nucleus (sensorimotor part) and the subthalamic area containing the zona incerta, fields of Forel, and subthalamic nucleus projections.

Aged↗

PubMed2003

Subthalamic nucleus stimulation in Parkinson's disease: correlation of active electrode contacts with intraoperative microrecordings.

BACKGROUND/AIMS: The most effective site for subthalamic nucleus (STN) stimulation has remained unclear. The position of active contacts relative to the dorsal margin of the STN was determined. METHODS: Electrodes (n = 49) were implanted following STN mapping by microrecording and microstimulation along five tracks (n = 25 patients). The stereotactic position of active contacts was determined and correlated with microrecordings using an algorithm for direct three-dimensional comparisons (n = 37). RESULTS: Most active contacts were detected within +/-1.0 mm from the dorsal margin of the STN as defined by microrecording (32.4%) or farther dorsal in the subthalamic area (37.8%), and only 29.7% were localized to the STN proper. This was consistent with the average stereotactic coordinates of the active contacts in these three groups. CONCLUSION: Our data suggest that the dorsal border area of the STN is the most effective target. Besides the dorsolateral STN (sensorimotor part) this may include projections from/to STN, the zona incerta, and pallidofugal projections in the fields of Forel.

Electric Stimulation Therapy↗

PubMed2001

Inhibitory conditioning stimulus in transcranial magnetic stimulation reduces the number of excited spinal motor neurons.

OBJECTIVE: To study the mechanisms of amplitude attenuation caused by a transcranial magnetic conditioning stimulus. Both conventional MEPs and the recently described triple stimulation technique (TST) were applied; the latter to improve the quantification of the response size decrease. METHODS: TST uses a peripheral collision method to eliminate the effects of desynchronization of the transcranial magnetic stimulation (TMS) induced spinal motor neuron discharges. The attenuation of motor evoked potentials (MEPs) and responses to TST was studied in 10 healthy volunteers using the conditioning-test paradigm with 2 ms interstimulus intervals. RESULTS: Conventional MEPs and responses to TST demonstrated a marked attenuation by the preceding conditioning stimulus in all subjects. The ratio of MEP to TST amplitudes was the same in conditioned and unconditioned responses. CONCLUSIONS: Our findings suggest that the transcranial conditioning stimulus does not change the degrees of desynchronization of spinal motor neuron discharges, but results in a reduced number of excited alpha motor neurons. This reduction can be estimated by both MEPs and TST.

Adult↗

PubMed1999

Absence of transcallosal inhibition in adolescents with diplegic cerebral palsy.

The role of intracortical organization in the pathophysiology of cerebral palsy (CP) is not clear. We used transcranial magnetic stimulation to investigate the paradigm of transcallosal inhibition (TI) in a group of adolescent patients with diplegic CP (n = 4), hereditary spastic paraplegia (n = 2), and healthy control adolescents (n = 4). None of the patients with CP showed TI, whereas all other subjects had normal TI. These findings indicate a lack of inhibitory control of the motor cortex in CP.

Adolescent↗

PubMed1998

Absence of transcallosal inhibition following focal magnetic stimulation in preschool children.

Focal transcranial magnetic stimulation of the hand-associated motor cortex was used to study normal healthy preschool children (n = 7; mean age, 4.6 years) and adults (n = 7; mean age, 29.4 years) under the conditions of standardized tonic voluntary contraction of small hand muscles. Callosally mediated inhibitory as well as corticospinally mediated inhibitory and excitatory motor effects were investigated. Although children had no detectable transcallosal inhibition, their corticospinally mediated postexcitatory silent period was present (mean, 140.8 +/- 30.2 msec). It was significantly shorter than in adults (mean, 192.5 +/- 32.0 msec). The motor thresholds of the cortically elicited muscle responses, measured as the lowest stimulus intensity, were significantly higher in children (mean, 89 +/- 5%) than in adults (mean, 46 +/- 6%). The corticomuscular latency of transcranially elicited motor responses revealed no difference between children and adults. These observations may reflect maturation processes in the motor system. Maturation of at least some direct corticospinal fibers occurs early in life and is followed by that of intracortical excitatory and inhibitory connections. The maturation of functionally competent callosal connections appears to occur after the age of 5 years.

Adult↗

PubMed1997

Transcranial magnetic stimulation in patients with Rett syndrome: preliminary results.

Transcranial magnetic stimulation was used to investigate Rett patients (n = 31, age 2-38 years). The results were compared to healthy control persons (n = 112, age 1 month-35 years). The peripheral conduction time showed no difference between the patients and control persons. The mean central conduction time, however, was shorter in the younger patients with Rett syndrome, and this is particularly evident in the youngest. This phenomenon could be interpreted as cortical and/or spinal hyperexcitability which occurs during the early stages of Rett syndrome.

Adolescent↗