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Biomedical subjects

D F Stegeman

Publications and source records attributed to D F Stegeman.

At least 91 records · Page 5Linked to original sources
PubMed1988

Dermatomal somatosensory evoked potentials of the lumbar and cervical roots. Method and normal values.

We describe a method for obtaining cortical evoked potentials after stimulation of the lumbosacral and cervical dermatomes in healthy volunteers. Such dermatomal evoked potentials are expected to contribute to the diagnosis of lumbar and cervical root entrapment. Normative data are presented for each dermatome including left-right differences. A significant correlation was found between absolute latencies and body length for the lumbosacral segments. This correlation was virtually absent in the cervical segments. The latency difference between the same cervical or lumbosacral dermatome left and right was also independent of body length for all segments.

Adolescent↗
PubMed1988

Abnormal EMG and SSEP in a young child with an ependymoma.

We report our findings on a case of ependymoma in a one-year-old boy. A partial paresis of the left arm was found but the EEG and BAEP were normal. The EMG showed fibrillations and positive sharp waves in the paretic muscles and the SSEP showed a far field negativity. After removal of the cerebral process all neurophysiologic findings normalized. We discuss a hypothesis for the established clinical neurophysiological findings.

Brain Neoplasms↗
PubMed1987

Far-field evoked potential components induced by a propagating generator: computational evidence.

This study validates current hypotheses for the generation of so-called far-field or stationary somatosensory evoked potential (SEP) components. Changes in the volume conductor configuration and changes in the direction of nerve propagation are demonstrated to be capable of generating such components. Results are based on basic aspects of the theory of volume conduction. It is shown that in an essentially restricted volume conductor any disturbance of uniform nerve propagation in a homogeneous extracellular medium will lead to the generation of non-moving field components. A number of illustrative examples are presented in which intermingling of non-moving and propagating potential fields can be observed. These results can be helpful in unravelling complicated wave forms from the nervous system in which both types of potential field can be distinguished. It is shown that realistic changes within the volume conductor can lead to substantial far-field components. This type of volume conductor induced 'virtual generators' or 'secondary sources' is present in the peripheral nervous system and most probably also in the inhomogeneous structures of the brain.

Action Potentials↗
PubMed1987

The maturation of the central auditory conduction in preterm infants until three months post term. III. The middle latency auditory evoked response (MLR).

Middle latency auditory evoked responses (MLRs) were recorded in 64 premature infants; serially in 54 of them. The last recording sessions occurred at 50-52 weeks conceptional age (CA), defined as the gestational age (GA) added to the chronological age. The MLRs were analyzed for the components PO, Na and Pa, and the interpeak latency difference (IPLD) Na-PO. The detectability rate of PO and Na reached 80-90% at about 30 weeks CA. Pa reached the highest rate of about 60% at 52 weeks CA. The degree of prematurity did not result in clear differences with respect to the parameter values. Also, the side of stimulation did not influence the MLR parameter values. The latency values of the MLR components are strongly age dependent. Topographic differences were found between the sides ipsi- and contralateral to stimulation. They are, however, different for PO, Na and Pa. The influence of the state of vigilance on the parameter values could generally only be established at CA levels of about 32 and 52 weeks CA. The amplitude values at 52 weeks CA are especially sensitive for sleep or awake state. The particular pattern of age dependency of the different components and their topographic differences are consistent with a differential generation of bilateral nature. The early appearance of the response supports the generation of an early functioning subcortical structure in the auditory pathway.

Arousal↗
PubMed1987

The maturation of the central auditory conduction in preterm infants until three months post term. IV. Composite group averages of the cortical auditory evoked responses (ACRs).

Composite group averages were constructed from cortical auditory evoked responses (ACRs), which are recorded sequentially at maximally 8 conceptional age levels in 5 groups of 49 preterm infants, with additional inclusion of the records of 16 prematures obtained at different conceptional age levels. The group averages for the 5 gestational age groups showed replicable waveforms at all conceptional age (CA) levels reflecting the intragroup stability of the ACR complex. From the earliest age levels, from 25 weeks CA on, ACR group averages can be obtained, containing relative low voltage fast waves and high voltage slow waves. The most outstanding developmental changes in the ACR complex are the waveform changes. Until about 36 weeks CA a premature waveform is found, followed by a transitional phase with low voltage noisy records. Finally the adult waveform is found in the measurements at three months after term date. The latency values of the group averages are determined by the waveform changes. Persistent amplitude differences are found for the slow late waves between the vertex and the central temporal derivations.

Cerebral Cortex↗
PubMed1987

The maturation of the central auditory conduction in preterm infants until three months post term. V. The auditory cortical response (ACR).

Auditory cortical evoked responses (ACRs) were recorded in 65 preterm infants, at least on 3 occasions in 48 of them. The infants were divided into 5 groups according to their gestational age (GA). The recording sessions were performed at 8 conceptional age (CA) levels, defined as the gestational age added to the chronological age. The last recordings were obtained at 50-52 weeks CA. The ACRs were analyzed for the primary complex containing middle latency components (MLR) and the secondary complex, containing the slow late components. The ACR records first appear at about 25 weeks CA, initiating the premature stage followed by a transitional stage around term date and the gradual development into the mature stage, achieved at 50-52 weeks CA. The detectability rate of the various components generally increased with increasing conceptional age, for some of the components, especially N2p and N2, this rate achieved a value of about 80%. The degree of prematurity did not influence appreciably the development of the ACR. The waveforms, and to a lesser extent the latency and amplitude values, are strongly age dependent. Remarkable topographic differences between the ACR parameter latency and more importantly amplitude values are found between the derivations from the vertex and the central temporal areas, supporting the theory of different generation sites for the ACR components. The premature and mature ACR appeared relatively insensitive to changes in the states of vigilance. The ACR in premature infants are useful in developmental studies with respect to the central audition in premature infants and might contribute in the clinical assessment on the quality of the premature central auditory system.

Cerebral Cortex↗
PubMed1987

The maturation of the central auditory conduction in preterm infants until three months post term. I. Composite group averages of brainstem (ABR) and middle latency (MLR) auditory evoked responses.

Brainstem (ABR) and middle latency (MLR) auditory evoked responses were obtained sequentially in 49 preterm infants until three months post term date. In addition, the records of 16 preterm infants, obtained at different conceptional age levels, were included. The recording of these responses was performed successively in one procedure, together with auditory cortical evoked responses. The infants were divided into 5 groups according to their gestational age, i.e. the term at birth. Composite group averages were determined, showing the group stable components of the 5 gestational age groups at 8 different conceptional age levels, i.e. term at the time of the recording. The intra group stable components could thus be determined for further study of developmental trends in the responses. The group averages also serve as a reference in the visual analysis of the individual records. The averaged ABRs showed that with increasing conceptional age increasingly better identifiable waveforms were obtained. These were particularly outstanding for peaks I and V ipsilateral to stimulation, and peaks IIc and Vc contralateral to stimulation. This enabled the measurement of the central conduction times. The MLRs were especially remarkable for their latency changes which occurred in peak PO and the troughs Na and Nb. The results indicated that the conduction of the subcortical auditory afferent signals can be measured successfully in groups of very premature infants with ABRs and MLRs.

Audiometry, Evoked Response↗
PubMed1987

The maturation of the central auditory conduction in preterm infants until three months post term. II. The auditory brainstem responses (ABRs).

Auditory evoked brainstem responses (ABRs) were recorded in 65 preterm infants (serially in 55 of them), divided into 5 groups, according to their gestational age (GA). The recording sessions were performed at 8 conceptional age levels (CA = GA + chronological age), of which the last two were about 40 and 52 weeks CA. The number of recording sessions varied from one to seven. A full set of ABR latency and amplitude parameters was analyzed including peaks I, II, IIN, III, V and IIc, IIINc and Vc as well as some interpeak latency differences (IPLDs), and the amplitude ratios. The detectability of the different components in the ABR tests at 70 dB reached 80-100% at about 32 weeks CA. The side of stimulation nor the state of vigilance influences the detectability. The degree of prematurity in the 5 GA groups did not influence the development of the parameters. Neither the side of stimulation nor generally the state of vigilance give rise to different parameter values. The thresholds show an age dependent decrease, which is also determined by central maturation. The differential development of the latency decrease of the ABR parameters with increasing conceptional age can be associated with morphological maturational processes and may add weight to the arguments in the delineation of the sources of the ABR. The ipsi- and contralateral central conduction V-II and Vc-IIc do not show latency differences at any CA level. The components IIc and Vc, however, lagged behind in absolute latency compared with II and V. It is concluded that the ABR is a powerful instrument for the study of the maturation of the human auditory pathway in the brainstem. In view of the variability, the detectability and the complex changes within the ABR during the preterm period, its application for clinical purposes during this period has a limited value.

Analysis of Variance↗
PubMed1986

The second wind phenomenon in McArdle's disease.

Three patients with McArdle's disease exercised for 2 h at 30% VO2max. During exercise two phases occurred. During the first 15 min they experienced progressive fatigue and weakness of exercised muscles, with a rapid and complete recovery (adaptation phase). Following this, all 3 patients were able to continue exercise without difficulty ('second wind' phase). During the adaptation phase, patients have to cope with their inability to use muscle glycogen as a fuel. Processes occurring during this phase are as follows. An increase in cardiac output. This might be expected to increase muscle blood flow in order to supply exercising muscle with substrates that can substitute for muscle glycogen (free fatty acids (FFA), bloodborne glucose). Changes in the metabolic pathways. These cause a sufficient amount of hexose phosphates to be present to overcome the first 2.5 min of exercise, and FFA and bloodborne glucose to play a major role in energy supply at an earlier stage in exercise than in control subjects. An increase in EMG activity. This is most probably caused by the recruitment of more motor units to compensate for a failure of force generation in the muscle fibres. Central command seems to play an important role in the regulation of cardiovascular processes during the adaptation phase. Despite these compensatory mechanisms, metabolic stress occurs during the adaptation phase. During the 'second wind' phase there are no important differences between the metabolism of exercising muscle of patients with McArdle's disease and that of control subjects.

Adaptation, Physiological↗
PubMed1983

Modelling compound action potentials of peripheral nerves in situ. III. Nerve propagation in the refractory period.

Compound nerve action potentials (CAPs) of sural nerves of healthy persons were measured in the relative refractory period of the fibres. Double stimuli were used with interstimulus intervals ranging from 0.7 to 4.0 msec. The CAP latency increase, its amplitude decrease and its wave shape alterations with decreasing interstimulus interval are discussed, using a model description. Recovery functions for the single fibre action potential in the relative refractory period are defined. These recovery functions, however, cannot sufficiently explain the CAP amplitude diminutions actually measured. Apparently in the relative refractory period an increasing number of fibres ceases to propagate an action potential when the stimulus interval is shortened. This effect, which is caused by subthreshold stimulation, predominantly involves the slower fibres. The usual derivation of refractory period parameters in clinical practice is reviewed.

Action Potentials↗
PubMed1982

Modelling compound action potentials of peripheral nerves in situ. II. A study of the influence of temperature.

Compound nerve action potentials of sural nerves of healthy volunteers have been measured at different temperatures. In the range from 21 to 39 degrees C a linear temperature dependence of the propagation velocity, related to the fastest fibres, is found (slope 1.9 m/sec/degree C). The causes of amplitude and shape alterations in the compounds action potentials (CAPs) with changing temperature are analysed with the help of a model. It appears that the changes in the measured CAPs are well explained by known temperature effects on the single fibre level. Both the considerable increase in CAP duration after cooling and the relative constancy of the CAP amplitude were reproduced by the model. Close fits to the actually measured CAPs can be obtained when some crucial parameter values are optimized. The results of this procedure are presented.

Action Potentials↗
PubMed1982

Modelling compound action potentials of peripheral nerves in situ. I. Model description: evidence for a non-linear relation between fibre diameter and velocity.

Compound sensory nerve action potentials of sural nerves of healthy volunteers have been measured at 7 different distances between the site of stimulation and the site of recording. The results are used to adjust a model description for the generation of compound nerve action potentials. A fairly good agreement between experiment and model is obtained when a weak non-linear, S-shaped relation between external fibre diameter and propagation velocity of the single fibre action potential is assumed. This result corresponds surprisingly well with findings in "classical' reconstruction attempts reported in the literature.

Action Potentials↗