Biomedical subjects

Joleen H Blok

Publications and source records attributed to Joleen H Blok.

7 recordsLinked to original sources

PubMed2006

Conduction velocity distribution in neurologically well-recovered but fatigued Guillain-Barré syndrome patients.

Many patients with Guillain-Barré syndrome (GBS) and chronic inflammatory demyelinating polyneuropathy (CIDP) suffer from excessive fatigue. To assess whether this fatigue might be related to changes in slow-conducting nerve fibers, we determined the conduction velocity distribution (CVD) in the median nerve. Thirteen fatigued but neurologically well-recovered GBS patients, 2 fatigued and stable CIDP patients, and 19 healthy controls participated in this study. Conventional maximal nerve conduction velocities (NCVs) did not show differences between GBS patients and healthy controls. However, in both GBS and CIDP patients the CVD was altered, showing significant narrowing of the velocity distribution with loss of the fastest- and slowest-conducting fibers. These changes were most pronounced in the subgroup of patients with the lowest fatigue scores. We therefore conclude that the observed CVD changes in patients are not likely to contribute to persisting complaints of fatigue after GBS.

Action Potentials↗

PubMed2006

Recovery of neurophysiological features with time after rat sciatic nerve repair: a magneto-neurographic study.

Experimental assessment of peripheral nerve regeneration in rats by electrophysiology is controversial due to low reproducibility of electrophysiological indicators and diminished quantitative evaluation in conventional experimental set-ups. Magnetoneurography (MNG) counteracts these drawbacks by magnetically recording electrophysiological signals ex vivo, thereby providing accurate and quantitative data. In 50 rats, sciatic nerve transection was followed by direct repair. MNG outcome parameters, footprints [static toe spread factor (TSF); function] and muscle weight (MW) were studied for their recovery pattern from 2 to 24 weeks. By using MNG, we showed that the regeneration process still continues when functional recovery (static TSF) becomes stagnant. With regression analysis, MNG parameters amplitude, amplitude area and conduction velocity (CV) demonstrated moderate significant correlation with MW, whereas CV was not significantly associated with static TSF. No significant association exists between MW and static TSF. A Kaplan-Meier survival curve revealed that autotomy/contracture of rat hind paws was not related to decreased MNG outcome values. In conclusion, this study highlights and discusses the dissimilarities between direct (MNG) and indirect (static TSF and MW) assessment techniques of the regeneration process. We emphasise the significance of MNG as a direct derivative of axon regeneration in experimental rat studies. Additionally, we stress the must for right-left ratios, as neurophysiological indicators vary with age, and we confute possible bias in footprint analysis caused by exclusion of autotomy/contracture animals.

Age Factors↗

PubMed2006

Ictal nystagmus in a newborn baby after birth asphyxia.

Ictal nystagmus (IN) is an uncommon phenomenon characterized by rhythmic saccadic eye movements occurring during epileptic seizures. We report a newborn baby with severe birth asphyxia, undergoing long-term video EEG monitoring with electro-oculogram (EOG), who showed irregular IN when eye movements crossed the midline from left to right and vice versa, resulting in large amplitude of the nystagmoid movements. The nystagmus was followed 15 to 29 seconds later by ictal discharges in the occipital regions. MRI of the brain showed features suggestive of periventricular leukomalacia. This interesting combination of findings suggests a complex mechanism for IN of cortical or subcortical ictal rhythms, which results in (a) the generation of subcortical electrical discharges in the pons and midbrain, causing nystagmoid eye movements, and (b) subsequent occipital spiking. We conclude that this clinical manifestation supports the existence of functioning cortical-subcortical connections between the brainstem ocular motor centers and the occipital cortex at birth.

Asphyxia Neonatorum↗

PubMed2005

Statistical motor number estimation assuming a binomial distribution.

The statistical method of motor unit number estimation (MUNE) uses the natural stochastic variation in a muscle's compound response to electrical stimulation to obtain an estimate of the number of recruitable motor units. The current method assumes that this variation follows a Poisson distribution. We present an alternative that instead assumes a binomial distribution. Results of computer simulations and of a pilot study on 19 healthy subjects showed that the binomial MUNE values are considerably higher than those of the Poisson method, and in better agreement with the results of other MUNE techniques. In addition, simulation results predict that the performance in patients with severe motor unit loss will be better for the binomial than Poisson method. The adapted method remains closer to physiology, because it can accommodate the increase in activation probability that results from rising stimulus intensity. It does not need recording windows as used with the Poisson method, and is therefore less user-dependent and more objective and quicker in its operation. For these reasons, we believe that the proposed modifications may lead to significant improvements in the statistical MUNE technique.

Adult↗

PubMed2005

Motor unit action potential topography and its use in motor unit number estimation.

High-density multichannel electromyography (EMG) recordings add spatial information to the temporal information content of the surface EMG (sEMG) signal. This study explores the potential value of such multichannel information at a single motor unit level, in particular for the improvement of motor unit number estimation (MUNE) techniques. It is shown that multichannel recordings make it easier to distinguish motor unit action potentials (MUAPs) and that MUAP combinations can be better resolved. Furthermore, the spatiotemporal information allows a quantitative assessment of the representativity of the mean of the recorded MUAPs in relation to the maximum CMAP, i.e., for the muscle as a whole. In general, this is practically impossible on the basis of temporal information alone. For these reasons, we expect that high-density sEMG has the potential to address several methodological limitations of single channel surface EMG recordings. This is specifically illustrated in this study for one of the MUNE techniques in use, the F-response method.

Action Potentials↗

PubMed2005

Ultrasound imaging of the rabbit peroneal nerve.

Ultrasound imaging of peripheral nerves is increasingly used in the clinic for a wide range of applications. Although yet unapplied for experimental neuroscience, it also has potential value in this research area. This study explores the feasibility, possibilities and limitations of this technique in rabbits, with special focus on peripheral nerve regeneration after trauma. The peroneal nerve of 25 New Zealand White rabbits was imaged at varying time intervals after a crush lesion. The ultrasonic appearance of the nerve was determined, and recordings were validated with in vivo anatomy. Nerve swelling at the lesion site was estimated from ultrasound images and compared with anatomical parameters. The peroneal nerve could reliably be identified in all animals, and its course and anatomical variations agreed perfectly with anatomy. Nerve diameters from ultrasound were related to in vivo diameters (p < 0.001, R(2) = 77%), although the prediction interval was rather wide. Nerve thickenings could be visualized and preliminary results indicate that ultrasound can differentiate between neuroma formation and external nerve thickening. The value of the technique for experimental neuroscience is discussed. We conclude that ultrasound imaging of the rabbit peroneal nerve is feasible and that it is a promising tool for different research areas within the field of experimental neuroscience.

Animals↗

PubMedDate not supplied

Quantitative EEG monitoring during cerebral air embolism and hyperbaric oxygen treatment in a pig model.

The purpose of this study was to evaluate the contribution of quantitative EEG (qEEG) to an animal model of cerebral air embolism (CAE). In 12 anesthetized pigs, air was injected into the internal carotid artery, and hyperbaric oxygen (HBO) treatment was started either after 3 minutes or after 60 minutes (United States Navy Treatment Table 6). Off-line spectral analysis was used to determine the frequency content of the EEG signal, and factor analysis was performed to determine the frequency ranges that optimally showed the changes in the power spectrum. Factor analysis revealed two factors that represented different and independent spectral changes during embolization: 0.5 to 7.3 Hz (band 1) and 26.4 to 30.3 Hz (band 2). Shortly after embolization, the power in both bands decreased to a minimum, representing an isoelectric EEG in 11 out of the 12 animals. EEG differences between animals were considerable, despite standardized doses of injected air, and qEEG can objectively assess and quantify these differences in immediate impact of air embolism on brain function. Also, qEEG enabled monitoring of the recovery from the initial embolic event and of the response on treatment. The initial recovery was much more protracted in band 2 than in band 1, but even after completing HBO treatment, qEEG values did not return to baseline values in all animals. In addition, two animals did not survive until the end of the HBO treatment, and qEEG proved to be superior to the other measured hemodynamic variables to detect and ensure a deterioration of brain function. This study showed that qEEG monitoring has significant additional value to monitoring HBO treatment.

Animals↗