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Biomedical subjects

F Awiszus

Publications and source records attributed to F Awiszus.

At least 19 recordsLinked to original sources
PubMed1999

Characterisation of paired-pulse transcranial magnetic stimulation conditions yielding intracortical inhibition or I-wave facilitation using a threshold-hunting paradigm.

Short-interval, paired-pulse transcranial magnetic stimulation (TMS) is usually used to demonstrate intracortical inhibition. It was shown recently that with short-interval, paired-pulse TMS a facilitation - called intracortical I-wave facilitation - can also be demonstrated. It was the aim of this study to investigate which stimulus conditions lead to intracortical inhibition and what conditions yield an intracortical I-wave facilitation in a hand muscle of normal subjects. Paired-pulse TMS responses with an interstimulus interval of 1.2 ms were obtained from the abductor digiti minimi muscle of four normal subjects. A threshold-hunting paradigm with hunting through first or second stimulus variation was used to obtain a curve of threshold-pair strengths. All subjects showed two branches of stimulus interaction on this diagram. If the first stimulus of a threshold pair was below approximately 65% of resting motor threshold it modified the response primarily due to the second stimulus through intracortical inhibition. However, if the first stimulus of a threshold pair exceeded approximately 65% of resting motor threshold it became responsible for the spinal action-potential initiation. The subsequent second stimulus served as a "booster" for the ongoing intracortical I-wave activity, making it impossible to observe the intracortical inhibition evoked by the first stimulus.

Action Potentials↗
PubMed1999

Effects of the amplitude threshold on the separability of neuropathic and myopathic from normal EMG using parameters of the turns/amplitude analysis.

OBJECTIVE: In this study, the relationship between the amplitude threshold used for the determination of the turns of the electromyographic (EMG) interference pattern and the parameters of the turns/amplitude analysis was examined. It was investigated whether the discrimination of myopathic and neuropathic from normal muscles could be optimized by an appropriate amplitude threshold. METHODS: The interference patterns of the tibialis anterior muscle of 15 patients with myopathies, 30 patients with neuropathies and 56 controls were recorded, using concentric needle electrodes. A computer program performed the Willison analysis, systematically varying the amplitude threshold between 10 microV and 200 microV. RESULTS: Amplitudes as well as the number of turns per second were non-linearly related to the amplitude threshold. The reduction of the amplitude threshold to 30 microV resulted in a clearly better separation of the distributions of the number of turns of neuropathic, myopathic and normal EMG, compared to the traditional threshold value of 100 microV. The distributions of amplitude values, however, were not affected. The distance between the turns parameter distributions of neuropathic patients and controls and between the distributions of myopathic patients and controls, expressed by the Kolmogoroff-Smirnov distance, had a maximum at 30 microV. CONCLUSIONS: For the turns/amplitude analysis of the tibialis anterior muscle an amplitude threshold of 30 microV should be selected.

Adult↗
PubMed1999

Bilateral deficit of voluntary quadriceps muscle activation after unilateral ACL tear.

PURPOSE: The inability to fully activate the quadriceps femoris muscle voluntarily is known to accompany several different knee-joint pathologies. The extent of a voluntary-activation deficit in patients after isolated rupture of the anterior cruciate ligament (ACL), however, has been reported to be small or nonexistent, making it questionable if a voluntary-activation deficit is a relevant factor for these patients at all. METHODS: In this study the ability to voluntarily activate the quadriceps femoris muscles was quantified in 22 male patients with arthroscopically-proven isolated ACL ruptures using an established highly sensitive twitch-interpolation technique. Furthermore, the maximal voluntary contraction force of the quadriceps muscle was obtained by isometric knee-joint torque measurements. The results were compared with an age-, gender-, and activity-matched control group. RESULTS: There was a moderate but significant mean reduction in maximal voluntary activation (VA) in both the injured (VA: 83.9 +/- 2.3%, mean +/- SEM) and uninjured side (VA: 84.7 +/- 2.2%) in comparison with controls (VA: 91.1 +/- 0.8%). However, of the patients the 23% who presented a considerably reduced voluntary-activation of less than 80% were mainly responsible for the significant mean deficit. CONCLUSIONS: The deficit of isometric muscle strength on the injured side compared with that of controls was explained by the voluntary-activation deficit and a true muscle weakness. On the other hand, the diminished muscle strength of the uninjured side was explained sufficiently by the voluntary-activation deficit alone. Considering the bilateral voluntary-activation deficit, functional muscle tests might not be valid when the uninjured extremity serves as reference.

Adolescent↗
PubMed1999

Detailed analysis of proprioception in normal and ACL-deficient knees.

We assessed proprioception using threshold levels for the perception of knee movement at slow angular velocities (0.1 degrees/s to 0.85 degrees/s) in 20 patients with unilateral tears of the anterior cruciate ligament (ACL) and 15 age-related control subjects. Failure to detect movement was also analysed. The threshold levels of detection did not differ between the damaged and undamaged knees in the patients or between the patients and the control group. Failure to appreciate movement, however, was significantly greater in knees with ACL loss compared with the undamaged knees of patients and the control group. Our findings show a proprioceptive deficit in the absence of the ACL. Measurements of threshold levels of detection of passive movement alone are not suitable for the evaluation of proprioceptive loss in ACL deficiency; assessment of failure to appreciate movement is essential.

Adult↗
PubMed1998

Characterization of human joint proprioception by means of a threshold hunting paradigm.

A method has been developed to measure the proprioceptive performance of movement detection in human joints, with the threshold hunting paradigm commonly used in other sensory modalities. Methods applied in former studies regarding movement detection were very time consuming (hours), making them not applicable to patients. Using the threshold hunting paradigm, the subject changes the parameter value continuously around the threshold producing a threshold hunting curve, which itself might be valuable for investigation of movement detection performance. The method presented here, is very quick compared to other studies in this field, especially when velocity is hunted and the threshold values are very low. The threshold parameter value is stable since there is a control at any time over the subject's stimulus perception. Furthermore, a Monte Carlo simulation showed that hunting curves can clearly be distinguished from guessing. Also reliability is given. All these points allow to use the method to evaluate the proprioceptive performance of a single individual. Considering the results, the method described may be useful for basic and clinical investigations regarding the proprioceptive performance limits of movement detection aspects.

Adult↗
PubMed1998

[Influence of retropatellar arthrosis on the proprioceptive ability of patients with gonarthrosis].

Degenerative changes of the retropatellar articular surface contribute to a great extent to functional disability in patients with osteoarthritic knees. Therefore, in the present study we examined the influence of retropatellar osteoarthritis (OA) on proprioception in patients with knee OA. Comparison of movement sense determined by threshold levels for the perception of knee motion was performed in 10 patients with severe, in 10 patients with moderate, and in 9 patients with mild retropatellar OA. In addition, detection failures occurring during movement sense measurements were analysed. At correct movement detections, threshold levels did not differ between the three groups of patients regardless the extent of retropatellar OA. In contrast, analysis of detection failures occurring during movement sense measurements revealed significantly higher failure rates with greater severity of retropatellar OA. In conclusion, our study gives evidence for increased proprioceptive deficits with greater severity of retropatellar articular surface damage. Hereby, analysis of detection failures occurring during movement sense measurements proved to be a feasible tool for the assessment of proprioceptive deficits.

Humans↗
PubMed1998

[Measuring knee joint kinesthesis for determining proprioceptive deficits in varus gonarthrosis].

Studying knee osteoarthrosis proprioceptive deficits play a growing role. However, the methods for the detection of these deficits using joint position sense measurements have been criticized recently. Therefore, we developed a new method for the measurement of knee-joint kinaesthesia. At 5 different angular velocities of passive knee movement both movement and stop detection were tested. Tests were performed both in 25 patients with osteoarthrosis of the knee and in a control group of 20 age related normal subjects. In addition to the measurements of movement detection and stop-detection thresholds, a specific detection-failure analysis was performed in our study. In addition to a significant improvement of proprioceptive abilities with increasing angular velocities, detection failure analysis brought about significant differences between patients with knee osteoarthrosis and normal subjects yielding a significant proprioceptive deficit in osteoarthrosis of the knee. In contrast, in case of correct movement detection or stop-detection there were no significant differences in the detection-threshold values between normal and ostheoarthrotic knees. In conclusion, both the lack of differences in detection thresholds between the arthrosis and the control-groups and the increased detection failure rates in arthrosis patients gave evidence for these proprioceptive differences being a result of central nervous dysregulation in knee osteoarthrosis.

Humans↗
PubMed1998

[Intraoperative monitoring of the function of the peroneal nerve in knee joint operations].

Operations on the knee are known to be associated with postoperative neurological complications. There is no consensus opinion on the causes of these complications. The aim of the present study was to develop a method for the intraoperative monitoring of the function of the common peroneal nerve. This was done as to identify intraoperative factors that might be responsible for reversible and irreversible neurological deficits. Computer-aided neuromonitoring is based on online digitizing of the surface EMG of the anterior tibial muscle. An algorithm continuously modifies the amplitude to determine the motor threshold. The method described has been used in 18 patients undergoing high tibial osteotomy. In 10 of the 18 patients, the nerve is rendered completely non-excitable after an average tourniquet application time of 59 min. This non-excitability was reversed on release of the tourniquet. In the remaining 8 patients, excitability was maintained throughout the ischaemic period, which did not exceed 60 minutes in any of the cases. Our method enables accurate quantification of the neural function throughout the entire operation, and convincingly documents the influence of ischaemia on peripheral nerve block.

Electromyography↗
PubMed1998

[Intraoperative computer-assisted measurement of stimulation threshold of the common peroneal nerve in osteotomy of the head of the tibia].

Using a computer-assisted threshold hunting paradigm the motoric threshold of the common peroneal nerve was monitored in 18 patients during a high tibial osteotomy (HTO). The exposed nerve (lateral approach) was stimulated proximal to the osteotomy area and the surface EMG of the M. tibialis anterior was used to guide a threshold hunting device. Motoric threshold as a sensitive indicator of nerve function was found to be almost unaffected by several surgical steps of HTO. Only forceful rotation of a subperiostal Hohmann device during high peroneal osteotomy evoked a slight threshold shift that was fully reversible with device repositioning. The tourniquet, however, affected the threshold significantly. In 10 of the 18 patients the nerve became completely inexcitable after an average time of 59 min. The inexcitability was reversible after opening of the tourniquet. On the other hand, the eight patients maintaining an excitability throughout the entire ischemic period had tourniquet times that did not exceed 60 min. There are several factors that may be responsible for the observed inexcitability after long ischemic periods and we conclude that tourniquet time minimization appears appropriate to avoid neurological deficits during a high tibial osteotomy.

Adult↗
PubMed1997

Spike train analysis.

Procedures for the analysis of stimulus-correlated spike train data are reviewed. All procedures considered attempt to extract excitability changes evoked by the stimulus at the neuron investigated. The methods covered range from rather simple methods that require very little computational effort (raw spike train displays; peri-stimulus-time histogram (PSTH)) to more sophisticated procedures that attempt to extract all information available in the recorded spike-train data.

Action Potentials↗
PubMed1997

Influence of stimulus cross talk on results of the twitch-interpolation technique at the biceps brachii muscle.

Biceps brachii muscles of five healthy volunteers were tested with a high-resolution twitch-interpolation technique. Parameters of the electrical surface stimulation were varied. It was found that a supramaximal stimulus strength activates both biceps and triceps brachii motor units simultaneously severely affecting twitch-interpolation results. Crosstalk contamination of twitches, however, can be avoided, if submaximal stimuli are used yielding twitch-interpolation results for the biceps-brachii that are similar to those of the quadriceps muscle.

Adult↗
PubMed1997

[Use of automatic, computer-assisted EEG analysis in clinical practice].

Digital EEG-recorders are being increasingly accepted for clinical routine application, thereby offering the possibility for an automated computerised EEG evaluation. This paper presents the results of a corresponding computer programme developed in our group. Based on 313 clinical routine-EEG we compared the computer reports to the visual EEG-interpretations and obtained the following result: Background activity is reliably detected with a rate comparable to a human interpreter. Similar results were observed with focussed pathological activity. Intermittent activity (Parenrhythmia, dysrhythmia) however lacks a sufficiently high score of correct evaluation and requires further development. Epileptiform potentials, especially spikes, are detected with high sensitivity, however, at the cost of low specificity, and are therefore still in need of further improvement.

Cerebral Cortex↗
PubMed1995

Comparison of single motor unit responses to transcranial magnetic and peroneal nerve stimulation in the tibialis anterior muscle of patients with amyotrophic lateral sclerosis.

Responses of single tibialis anterior motor units to transcranial magnetic stimulation and to a synchronized Ia volley evoked by peripheral nerve electrical stimulation were obtained in amyotrophic lateral sclerosis (ALS) patients and normal controls. Whereas the units of normal subjects exhibited rather stereotyped short-latency spike density peaks in response to both types of stimulus, the responses of ALS patient units were much less uniform. All ALS patient units exhibited a response to the synchronized Ia volley indistinguishable from that of normal subjects, indicating that the investigated spinal motoneurons are capable of normal excitatory responses in ALS patients. More than half of the ALS patient units responded to the transcranial magnetic stimulus with prolonged spike-density peaks appearing at a latency consistent with the notion that these pathological peaks are evoked by some relatively hyperexcitable structures presynaptic to the corticomotoneurons.

Adult↗
PubMed1994

Repetitive activity of a branched Hodgkin-Huxley axon with multiple encoding sites.

Afferent activity in a receptor afferent fiber with several encoding sites is generally believed to represent the activity of the fastest pacemaker that resets all more slowly encoding sites. Alternatively, some impulse mixing as well as some nonlinear summation of receptor current to a single encoder have been considered. In this article the repetitive firing activity of a Hodgkin-Huxley axon consisting of two branches that join into a single stem axon was investigated. The model axon was stimulated by constant-current injection into either the right or the left or both branches. It was found that the model axon generated an (infinite) train of action potentials if the input current was large enough. The discharge frequency found was constant, and on combined stimulation of both branches with different current, the site of impulse initiation was always in the branch receiving the higher input current, excluding a simple impulse mixing. On the other hand, the combined stimulation of both branches evoked repetitive firing with a higher frequency than expected by the pacemaker-resetting hypothesis. Moreover, a stimulus that is subthreshold for repetitive firing if injected into one branch yields repetitive firing when it is injected into both branches, a behavior inconsistent with impulse mixing and pacemaker resetting. On the other hand, current injection into one branch allowed repetitive activity only within a rather limited range of firing frequencies. Using distributed current injection into both branches, however, allowed many more different firing frequencies. Such behavior is inconsistent with both pacemaker resetting and (nonlinear) input current summation. Consequently, the repetitive firing behavior of a branched Hodgkin-Huxley axon with multiple encoding sites appears to be more complex than postulated in the simple hypotheses.

Action Potentials↗
PubMed1994

Correlations between size parameters and the amplitude of the excitatory postsynaptic potential evoked by magnetic brain stimulation in human hand muscle motoneurons.

According to the size principle for motoneurons one would expect that an excitatory stimulus given to a motoneuronal pool should evoke small excitatory postsynaptic potentials (EPSPs) in large and large EPSPs in small motoneurons of the pool. In this study this expectation was tested for the motoneuron pool of the first dorsal interosseus muscle of man excited by a magnetic stimulus given to the contralateral motor cortex. In total, 60 first dorsal interosseus motor units from three healthy volunteers were investigated. For each unit the EPSP size induced by the magnetic brain stimulus was assessed indirectly through a cross correlation of magnetic brain stimuli with motor unit discharges during a slight voluntary contraction. In addition to the indirect measurement of EPSP size, three indicators of motoneuronal size were obtained for each unit: the area the macroelectromyogram (Macro EMG) of the unit encloses with the baseline, the peak-to-peak amplitude of the Macro EMG, and the "true" latency from the magnetic stimulus to the motor unit which in turn provides an indirect estimate for the conduction velocity of the motoneuronal axon. It was found that all three measures of motoneuron size were significantly negatively correlated with the estimates of EPSP amplitude. Such significant negative correlations were found not only in the pooled data but also in the data from each subject individually. These correlations reveal that a magnetic brain stimulus induces small EPSPs in large and large EPSPs in small motoneurons of the first dorsal interosseus muscle of man.

Adult↗
PubMed1994

Quantification of D- and I-wave effects evoked by transcranial magnetic brain stimulation on the tibialis anterior motoneuron pool in man.

Transcranial stimulation in man evokes multiple descending volleys in the spinal cord giving rise to multiple subpeaks in a peri-stimulus-time histogram (PSTH) obtained from a cross-correlation of motor unit discharges with transcranial stimuli. The first volley is termed the D wave, as it is assumed to be evoked by direct excitation of pyramidal tract neurons, whereas the subsequent I waves appear to be generated by indirect excitation of the pyramidal tract neurons via cortical interneurons. It was the aim of this study to obtain an estimate of the effect induced by multiple volleys evoked by transcranial magnetic stimulation on the entire motoneuron pool of the tibialis anterior in awake subjects. A considerable part of a particular motoneuron pool was investigated by sampling responses of a large number (at least 19) from each muscle investigated. In total, three tibialis anterior muscles from three normal volunteers were studied. From each of the 63 units included in this study, a PSTH to 100 transcranial magnetic stimuli and a PSTH to 100 electrical stimuli given to the peroneal nerve were compiled. From the motor unit response to the peripheral nerve stimulation, the latency of the single-unit H reflex peak was obtained. This yielded, the timing of the subpeaks in response to the magnetic stimulation relative to the timing of the H reflex of the same unit, thus eliminating the influence of the peripheral conduction time from the motoneuron to the recording electrode. It was found that 50 (79%) of the motor units exhibited at least two subpeaks in response to the cortical stimulus.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Subdivision of primary afferents from passive cat muscle spindles based on a single slow-adaptation parameter.

38 primary afferents originating from de-efferented cat tibialis anterior muscle spindles were investigated. Ramp-and-hold stretches of the host muscle were performed with a varying amount of muscle pre-stretch while recording the primary afferent discharges. From the discharge responses an interspike interval function was estimated. This revealed a slow adaptation during the hold phase of stretch which could be approximated quite well by a power function. The slow-adaptation power function exponent (SAE) was found to be rather independent of the amount of pre-stretch applied to the host muscle and grouped around a value characteristic for each afferent. These 'characteristic SAEs' showed a clearly bimodal distribution within the population of primaries studied. Moreover, the distribution around both modes was narrow enough to justify the subdivision of the primary afferents according to their characteristic SAE as either high-SAE (10 afferents; 26%) or low-SAE (28 afferents; 74%) afferents. The most likely explanation for this bimodality of slow-adaptation behavior in primary afferents is given by the assumption that the afferent discharge of the passive spindle is mainly provided from a branch innervating either the bag1 (for high-SAE units) or the bag2 and chain (for low-SAE units) intrafusal fibers.

Action Potentials↗