Biomedical subjects

D F Stegeman

Publications and source records attributed to D F Stegeman.

At least 73 records · Page 4Linked to original sources

PubMed1993

Variability and interrelationships of surface EMG parameters during local muscle fatigue.

The inter- and intraindividual variability of the frequency power density spectral and surface EMG amplitude parameters and of the muscle fiber conduction velocity (MFCV) is studied in 26 healthy volunteers during fatiguing isometric ischemic intermittent exercise of the m. biceps brachii at 80% of the maximal voluntary contraction level, with a contraction rate of 30/min. No significant age effects were found. Males were significantly stronger compared with females. The higher initial SEMG amplitude and the stronger shift of the frequency power density spectrum (PDS) to lower frequencies appear to be significantly correlated with males. Fatigue induces an almost proportional compression of the SEMG frequency content. The muscle fiber conduction velocity has the highest intraindividual reproducibility (r = 0.81). Despite the definite and strong influence of the MFCV on the PDS, the shift of the PDS can not be explained by a change of MFCV alone.

Adult↗

PubMed1993

A statistical approach to fiber diameter distribution in human sural nerve.

Fifty-one normal sural nerve biopsies were obtained from 800 diagnostic biopsies. The external diameter distribution of myelinated fibers was described using the sum of two beta probability density functions, describing the thin as well as the thick fiber group. A cross-sectional study using these distribution functions showed increasing values of the peak of the larger fiber group, the diameter of the thickest fibers, and the separation between the smaller and the larger groups until the beginning of adult life. The transition from a uni- into a bimodal histogram occurred gradually between 7 and 13 months. Total transverse fascicular area increased with age, whereas fiber density decreased significantly with age. The number of fibers remained stable over age. The relative proportion of the numbers of fibers in both groups described by one of the beta distributions remained constant over age. This occurred despite a marked decrease in the number of small fibers with a diameter less than, e.g., 6.5 microns. The results indicated an outgrowth of especially the larger myelinated fibers with age. This process continues with decreasing intensity into adult life.

Adolescent↗

PubMed1993

Evoked potential measures of auditory cortical function and auditory comprehension in aphasia.

This study investigated the relation between severity of auditory comprehension impairment in aphasia and the functional integrity of the posterior superior temporal region as evaluated by middle- and long-latency auditory evoked potentials and dipole source analysis. AEPs were studied in 20 stroke patients and in age-matched controls. AEPs and language data were collected 1 year or more post onset, and were compared to performance early after onset. Patients were differentiated in a group with severe and a group with moderate to recovered auditory comprehension impairment. Significant asymmetries of auditory evoked dipole source potentials were more frequent in the severely impaired group. However, a severe auditory comprehension deficit was not incompatible with normal AEPs. The results confirm the importance of the posterior superior temporal region for auditory language comprehension, but the correlation between AEP asymmetry and auditory comprehension seems due to the close spatial relation of AEP generating substrate and posterior language area rather than to partial overlap. Dipole source analysis of AEPs proved to be a valuable method for the assessment of interhemispheric asymmetries, enhancing the sensitivity of AEPs to unilateral damage of auditory cortex.

Aged↗

PubMed1993

Phonological effects on the auditory N400 event-related brain potential.

We report 3 experiments exploring the responsiveness of the auditory N400 event-related potential to the phonological relations between word or non-word targets and preceding prime words. When subjects had to decide whether primes and targets rhymed, non-rhyming words produced greater negativity in the N400 time range than rhyming words. The same effect was obtained when these targets were spoken by another voice than the prime words, suggesting that the effect is determined by phonological factors, and not merely by a physical-acoustic mismatch (Experiment 1). In the rhyming task, the differential N400 for non-rhyming vs. rhyming words was equally pronounced for non-rhyming vs. rhyming non-words (Experiment 2). In a lexical decision task on the same stimuli, a difference between non-rhyming and rhyming targets was obtained for words, but not for non-words (Experiment 3). The results show that the auditory N400 is sensitive to phonological variables. It is further proposed that phonological effects on the auditory N400 are not manifestations unique to phonological processes that demand conscious attention, but may also reflect operations that are performed automatically during auditory word recognition.

Acoustic Stimulation↗

PubMed1992

A study of motor unit structure by means of scanning EMG.

We used the scanning EMG technique to investigate the structure of human quadriceps muscle motor units. A group of healthy volunteers and 2 groups of patients with proven neurogenic or myogenic neuromuscular pathology have been studied. In total, 86 scans were obtained. An estimate of the motor unit territory (S) separates the 2 patient groups: the majority of territories of myogenic patients are smaller than 4 mm, whereas almost all motor unit territories of neurogenic patients are larger. However, the sizes of the pathologic units only occasionally exceed the upper and lower limits of normal units (2 to 8 mm). The myogenic scans show, on average, a much larger temporal dispersion (T) between the MUAPs within a motor unit than the normal scans. These findings are in accordance with observations with the same technique by others. For the neuropathic scans, there is a significant positive correlation between S and T, which is completely absent in myopathic scans. These observations are confronted with current morphometrical knowledge on motor unit physiology and anatomy.

Action Potentials↗

PubMed1992

Attenuation of dipoles modelled from SEP due to a lacunar infarct or altered stimulus rate.

In normal subjects and patients with sensory, sensorimotor or motor deficit, due to a unilateral infarct affecting the thalamocortical radiation, SEPs to median nerve stimulation were analyzed by a spatiotemporal dipole model which describes an evoked potential by a limited number of stationary dipoles with time varying amplitudes. In the normal subjects the SEPs were explained by one dipole in the brainstem and two dipoles in the cortical hand area contralateral to stimulation, all with different time courses. Increasing the stimulus rate to 6.2 Hz yielded a reduction of the moment of both cortical dipoles but hardly affected brainstem dipole moment. In the five patients with sensory or sensorimotor deficit the strength of one or both cortical dipoles was reduced on the side of the lesion. In the patients with pure motor deficit cortical dipole activity was normal. The brainstem dipole was preserved in all patients.

Adolescent↗

PubMed1992

On the possibility of independent activation of bilateral mismatch negativity (MMN) generators.

Event-related potential (ERP) studies on auditory selective attention have suggested that the neuronal traces underlying the mismatch negativity (MMN) develop separately for left and right ear inputs. We investigated whether this feature of the MMN could be exploited to activate the MMN generators in each hemisphere independently. Given the location of the MMN sources, this would allow separate assessment of left and right hemisphere auditory cortical structures. The MMN was elicited in a dichotic oddball paradigm using stimuli and conditions of stimulation that should optimize transmission of left and right ear stimuli to the contralateral auditory cortices. The MMN demonstrated no interhemispheric asymmetries, indicating that the bilateral MMN generators were symmetrically involved. The results of a supplementary experiment provide evidence for the simultaneous existence of multiple traces for MMN generation.

Acoustic Stimulation↗

PubMed1992

The effect of preterm birth on brainstem, middle latency and cortical auditory evoked responses (BMC AERs).

Recent studies on the maturation of auditory brainstem evoked responses (ABRs) present conflicting results, whereas only sparse reports exist with respect to the maturation of middle latency auditory evoked responses (MLRs) and auditory cortical evoked responses (ACRs). The present study reports the effect of preterm birth on the maturation of auditory evoked responses in low risk preterm infants (27-34 weeks conceptional age). The ABRs indicate a consistent trend towards longer latencies for all individual ABR components and towards longer interpeak latencies in preterm infants. The MLR shows longer latencies for early component P0 in preterm infants. The ACRs show a remarkable difference between preterm and term infants. At 40 weeks CA the latencies of ACR components Na and P2 are significantly longer in term infants, whereas at 52 weeks CA the latencies of the same ACR components are shorter in term infants. The results support the hypothesis that retarded myelination of the central auditory pathway is partially responsible for differences found between preterm infants and term infants with respect to late ABR components and early MLR component P0. Furthermore, mild conductive hearing loss in preterm infants may also play its role. A more complex mechanism is implicated to account for the findings noted with respect to MLR component Na and ACR components Na and P2.

Evoked Potentials, Auditory↗

PubMed1991

Fatigue in type I fiber predominance: a muscle force and surface EMG study on the relative role of type I and type II muscle fibers.

The relative proportions of fiber types within muscle and the characteristics of these fiber types are important determinants of the surface electromyogram (SEMG) during fatigue. In this study, patients suffering from congenital myopathy characterized by a strong type I fiber predominance were studied. Six patients with 95-100% type I fibers, 2 patients with 80% type I fibers, and 12 healthy volunteers participated in an ischemic, isomeric, intermittent exercise test of m. quadriceps femoris at 80% MVC. Considering the results of the morphometric analysis of muscle biopsy specimen and of the anthropometric estimated muscle-bone volume, it was found that type I muscle fibers had a lower force generating capacity than type II fibers. The initial conduction velocity along the muscle fiber membrane (MFCV) was low in patients with 95-100% type I fibers. During the ischemic exercise test, the 95-100% type I fibers showed less fatigability than type II fibers, which was reflected by a nearby absent decrease of the muscle membrane excitability as measured by the MFCV, and only a slight increase of the SEMG amplitude compared with patients having 80% type I fibers and controls. The absence of a definite MFCV decrease was related to the nearby lacking lactate formation in 95-100% type I fibers.

Adolescent↗

PubMed1991

Finite limb dimensions and finite muscle length in a model for the generation of electromyographic signals.

A volume conductor model is presented in which the aspects of finite volume conductor dimensions and finite muscle fiber length are combined. The effects of these aspects on single muscle fiber action potentials (SFAPs) and on motor unit action potentials (MUAPs) are shown and verified with surface recorded motor unit action potentials. It is demonstrated that the influence of the fiber length being finite is enhanced significantly by the finite limb dimensions of the volume conductor model, for single fiber action potentials as well as for motor unit action potentials. The model described is found to be capable of generating surface MUAPs which show a very good resemblance with measured surface MUAPs. Recorded MUAPs illustrate clearly the effects caused by finite muscle fiber length. The effect of finite limb dimensions in simulated intramuscular MUAPs was evidently less dominant than in simulated surface MUAPs.

Action Potentials↗

PubMed1991

Hereditary motor and sensory neuropathy of neuronal type with onset in early childhood.

Eighteen cases of a chronic progressive motor and sensory neuropathy of neuronal type with early onset are described. Based on the presented data and literature reports a condition is distinguished, which is in clinical, genetic and morphological aspects different from autosomal dominant HMSN type II. The condition corresponds to that described by Ouvrier et al. (1981). It shows a congenital or early childhood onset and causes a severe disability usually with wheelchair dependency already in puberty or later in adult life. The condition is probably transmitted by an autosomal recessive gene. Morphological features of biopsied nerves are an extensive loss of large diameter fibres with a shift to smaller diameters in the histogram. Regenerative features are almost absent in contrast to the distinct cluster formation in autosomal dominant HMSN type II. A maturation disturbance of peripheral motor and sensory neurons with a concomitant or secondary process of chronic neuronal degeneration is suggested. One dominantly inherited case in our group with an infantile onset exhibits clinical and morphological features consistent with an autosomal dominant HMSN type II.

Electrophysiology↗

PubMed1991

Force and fatigue in human type I muscle fibres. A surface EMG study in patients with congenital myopathy and type I fibre predominance.

An isometric ischaemic intermittent m.biceps brachii exercise test is performed by 4 patients suffering from congenital myopathies which are characterized by a 100% type I fibre predominance, and by 26 healthy volunteers. Thirty contractions per minute are made at an 80% of maximal voluntary contraction level. It is found that type I muscle fibres have a fourfold lower force-generating capacity than type II muscle fibres. The EMG amplitude shows that more EMG voltage is needed per unit force in the patients with 100% type I fibres compared with controls. Under standardized fatiguing circumstances the power density frequency spectrum shows a weaker shift to lower frequencies in patients with 100% type I muscle fibres compared with controls. The muscle fibre conduction velocity (MFCV) of type I muscle fibres shows no decline during ischaemic exercise indicating an unimpaired muscle membrane excitability.

Adult↗

PubMed1991

Models and analysis of compound nerve action potentials.

Upon electrical stimulation of a peripheral nerve, a compound action potential (CAP) can be recorded, a procedure that is widely used to study the functional condition of a nerve. The CAP provides relevant information about such parameters as the number of active myelinated fibers and their propagation velocities. This paper reviews methods of model-based CAP analysis that have emerged during the last decade. First, the basic model formulation for the CAP as resulting from a linear summation of the underlying single fiber action potentials (SFAPs) is discussed. Subsequently, a survey is given of volume conductor model approaches for the prediction of the SFAPs. Attention is then concentrated on the "inverse" problem of extracting relevant nerve parameters from experimentally recorded CAPs. Finally, the applicability of such methods is discussed and a direction for future developments is outlined.

Action Potentials↗

PubMed1990

Dantrolene sodium does influence the second-wind phenomenon in McArdle's disease. Electrophysiological evidence during exercise in a double-blind placebo-controlled, cross-over study in 5 patients.

Five patients with McArdle's disease entered a double-blind, placebo-controlled, cross-over study of dantrolene sodium. None of the patients experienced beneficial effect of dantrolene sodium medication. Each patient performed 2 exercise tests. Surface EMG during exercise tests without medication showed a temporary increase in EMG activity during the adaptation phase. Quite unexpectedly however, in view of the negative clinical results, this electrophysiological manifestation of muscle fatigue during the adaptation phase diminished or disappeared in all patients investigated when dantrolene sodium was used.

Adult↗

PubMed1990

The equivalent source description representing the extinction of an action potential at a muscle fiber ending.

Extracellular potential waveforms resulting from the termination of the propagation of the transmembrane potential at the end of an active muscle fiber are studied. The transmembrane potential along the muscle fiber is calculated from Hodgkin-Huxley-like equations with axially varying parameters under the condition of increasing axial resistance, decreasing ionic conductances, or decreasing radius at the muscle fiber end. The extracellular potential distribution is calculated using the derived transmembrane current as a line source in an unbounded volume conductor. Potential waveforms with constant latency at extracellular points far from the fiber end are presented and are compared with measurements and simulations from literature. Monophasic waveforms with constant latency are found. The polarity and the amplitude as a function of axial and radial position relative to the fiber end indicate that an equivalent dipole source adequately represents the propagation stop at the fiber end. An expression for the dipole moment in terms of fiber radius, intracellular conductivity, and transmembrane potential is derived.

Action Potentials↗

PubMed1990

Congenital demyelinating motor and sensory neuropathy with focally folded myelin sheaths.

Six patients (5 index cases and 1 sib) with a congenital motor and sensory neuropathy are described. The clinical, genetic and electrophysiological features resembled Dejerine-Sottas disease or hereditary motor and sensory neuropathy (HMSN) type III. Sural nerve biopsy of 5 patients revealed segmental demyelination and remyelination with hypertrophic changes, although onion bulbs were not as ubiquitous as in classical HMSN type III. A striking discriminating feature from HMSN type III was an abundance of focal myelin thickenings (tomacula) present in nearly all teased fibres. Possible pathogenic implications are discussed. These cases corroborate the heterogeneity of congenital motor and sensory neuropathies.

Adolescent↗

PubMed1990

Muscle fatigue in McArdle's disease. Muscle fibre conduction velocity and surface EMG frequency spectrum during ischaemic exercise.

The origin of fatigue in McArdle's disease is still a matter of debate. Both a reduction of muscle membrane excitability and failure of excitation-contraction (E-C) coupling have been suggested as causes. We performed intermittent isometric biceps brachii contractions (80% maximal voluntary contraction, rate 30/min) under local ischaemia in 5 McArdle's disease patients and 26 healthy controls. Our results show that in McArdle's disease the exerted force is less, the surface EMG (SEMG) amplitude steadily increases, and that the power density spectrum (PDS) shifts to lower frequencies, the latter without significant differences when compared with normals. The most important finding is that muscle membrane excitability remains unimpaired during ischaemic exercise, establishing a dominant role for intramuscular lactic acid formation in the reduction of muscle fibre conduction velocity seen in normal subjects. As is indicated by the shift of the PDS towards lower frequencies, as well as by the increase in SEMG amplitude, it can be concluded that during ischaemic exercise in patients with myophosphorylase deficiency, fatigue occurs without alterations in muscle membrane excitability and is due to a failure of E-C coupling.

Adolescent↗

PubMed1989

Increase in median power frequency of the myoelectric signal in pathological fatigue.

During bicycle ergometry, surface EMG analysis was performed on the m. vastus lateralis in a patient with pathological fatigue (due to skeletal muscle carnitine deficiency). With prolonged, submaximal, exercise (30% VO2 max, 2 h) the median frequency of the power density spectrum increased, despite fatigue and lactate production. This observation questions the general validity of the present concepts on myoelectric aspects of fatigue.

Adult↗