S. L. H. Notermans

Detectability of auditory evoked response components in preterm infants

In determining the detectability of brainstem, middle latency and cortical auditory evoked responses in preterm newborns, one has to deal with the ongoing maturation of the auditory system. In the preterm period the detectability of evoked responses is closely related to the appearance of the individual evoked response components. The detectability of the individual evoked response components in preterm infants is important, because low detectability rates make the absence of a particular evoked response component irrelevant with respect to the clinical-neurophysiological correlation. In a longitudinal study we determined the detectability and cumulative detectability, i.e. the presence of individual evoked response components in one or more recordings of evoked response components in 37 low risk preterm infants between 30 and 41 weeks conceptional age (CA). On the basis of their detectability it is concluded that evoked response components, determined between 30 and 34 weeks CA, are generally of limited use for clinical application, except for auditory brainstem response (ABR) components I, IIn, V and Vc and middle latency response (MLR) component Na. Our study made clear that improvement can be achieved by performing more than one examination within a period of approximately 4 weeks between the recording sessions. The cumulative detectability rates after two recordings showed improvement for all components involved in this study. The cumulative detectability rates of ABR components I, II, IIN, III, V, IIc, IIINc, Vc, MLR components Na and P0, and auditory cortical response (ACR) components PbP1 and N2p are sufficient to use as measures in the neurophysiological judgement of functional integrity of the central auditory pathway in preterm infants.

The Central Auditory Conduction at Term Date and Three Months After Birth I. Composite Group Averages of Brainstem (ABR), Middle Latency (MLR) and Auditory Cortical Responses (ACR)

We are investigating the maturation of auditory evoked responses, as a potential diagnostic tool for the neurological examination of premature infants at the Intensive Care Unit for Prematures. In this communication we report the group composite averages of the BMC-ARs in a group of 25 mature and healthy newborns with a follow-up at 3 months of age. The ABRs showed a remarkable variability in wave I latency, with a relatively stable I-V central conduction time (CCT) of the brainstem. The ipsilateral II-V CCT does not differ appreciably from the contralateral II-V CCT. The MLR components NoPoNa and Nb, Nc, Nd are easy to identify in the group averages. Voltage asymmetry between stimulated versus non-stimulated side is slight but persistent in the newborn period as well as at 3 months of age. The group averaged ACRs, show an early complex within the latency reach of 100 ms and a slow W-shaped late complex, most distinct at 3 months. The results indicate that the protocol as applied constitutes a tool for the testing of conduction function of the auditory afference in newborns, even beyond the level of the brainstem. Group averaging offers a method to determine the intragroup stability of evoked potentials under investigation.

EEG findings in patients with vascular parkinsonism

Objectives– To investigate whether the conventional and quantitative EEGs of patients with vascular parkinsonism (VP) differ from those of idiopathic Parkinsons disease (PD) patients. Material and methods– The EEGs of 13 patients with vascular parkinsonism and 14 patients with idiopathic Parkinsons disease were scored on a simple scale regarding aspects of conventional EEG variables. Alpha band power asymmetry and EEG slowing (increased delta and theta power) were calculated by the neurometrics method of quantitative EEG data evaluation.

Reliability of Doppler sonography in extracranial cerebro-vascular stenosis

Of our patients who underwent quantitative Doppler sonography (Haemato-Tacho-Graphy), 382 underwent carotid angiography and 61 vertebral artery angiography. The reliability of the method proved to be between 90 and 95 percent for carotid as well as for vertebral arteries. The HTG proved to be a useful addition to angiography in patients with extracranial cerebro-vascular stenosis.

Electromyographic evidence of delayed fatigue-induced sarcolemmal excitability impairment in McArdle's disease

Loss of sarcolemmal excitability is an early sign of fatigue in exercising muscle. This can be determined from a decreasing muscle fibre conduction velocity (MFCV). Underlying causes are still unclear. Three McArdles disease patients and seven healthy controls performed sustained isometric ischaemic biceps brachii exercise until exhaustion. Each subject participated in three tests: at 40%, at 80% and at 100% of the maximal voluntary contraction (MVC). Analysis was done over the period in which the force level was maintained at 40% and 80% MVC, and over the period during loss of force at all three levels. We found that, in contrast to the occurrence of an immediately starting and ongoing decrease of MFCV in controls, a delayed onset of this decrease was observed in patients with McArdles disease. Only during the loss of force phase was the MFCV decrease similar in patients and controls. The early occurrence of an MFCV decrease in controls appears to be related to the accumulation of lactic acid, which is virtually absent in the patient group. During force loss, different (additional) mechanisms must be responsible for the MFCV decrease in patients and, most probably, in controls as well.

The Central Auditory Conduction at Term Date and Three Months After Birth III. Middle Latency Responses (MLRs)

Middle latency responses (MLRs) were obtained in 25 healthy newborns with a follow-up recording at 3 months in all but three. A four-channel recording provided topographic information. Linkage of the ear references reduced the myogenic contamination of the recordings. P0 and Na proved to be the most consistent components in the sinusoidal MLR wave sequence. Topographic differences suggest a generation of P0 and Na contralateral to stimulation. A significant latency decrease was found for P0 and na between term and 3 months. The most important latency and amplitude changes may occur before term date and immediately thereafter. The MLRs are the link between the auditory brainstem responses (ABRs) and the auditory cortical responses (ACRs), and it may be possible to use them for recordings in newborn infants. They provide information about the generation of specific components as well as regarding the auditory afference in the stimulus propagation between the brainstem and the cortical auditory areas.

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.

EEG spectra in children aged 8, 9 and 10 years

SummaryIn a group of normal children aged 8, 9 and 10 years power density spectra of a 100-second EEG period were made over four different brain regions. All children had to undergo medical and psychological examinations prior to this EEG and the criteria for normality were based on these examinations. Reference values of the power density distribution for children between 8 and 10.5 years are given.ZusammenfassungBei einem Kollektiv von Kindern im Alter zwischen 8 und 10 Jahren wurde eine Breitbandfrequenzanalyse des Elektroencephalogramms über eine 100-sec-Periode und in vier verschiedenen Hirnregionen durchgeführt. Diese Kinder wurden aufgrund einer vorausgegangenen ärztlichen und psychologischen Untersuchung als normal betrachtet. Es werden in der vorliegenden Arbeit die Normwerte betreffend die Verteilung der Breitbandfrequenzanalyse für Kinder zwischen 8 und 10 1/2 Jahren dargelegt.