Biomedical subjects

J H Blok

Publications and source records attributed to J H Blok.

6 recordsLinked to original sources

PubMed2006

Heart rate changes are insensitive for detecting postasphyxial seizures in neonates.

We studied heart rate (HR) changes during 169 seizures (mean 12 per patient, range 8 to 18) in 14 neonates with severe birth asphyxia. HR changes were found in 21 seizures (12.4%) in eight patients (HR increases in four, decreases in one, and both patterns in three patients), suggesting the existence of neonatal cerebral hemispheric connections with brainstem autonomic regulatory centers. HR monitoring appears to be insensitive for detecting postasphyxial neonatal seizures.

Arrhythmias, Cardiac↗

PubMed2002

Three-layer volume conductor model and software package for applications in surface electromyography.

On comparing multichannel surface electromyographic measurements of the m. biceps brachii with simulations performed with a previously developed two-layer volume conduction model, we found substantial discrepancies. To incorporate an apparent distorting effect of the skin tissue, the model was extended to three layers. This new model describes the potential resulting from an eccentric bioelectric source in a finite, cylindrical, and anisotropic volume conductor consisting of three layers, representing muscle, subcutaneous fat, and skin tissue. This contribution presents the governing mathematical equations of the three-layer volume conductor model as well as our approach to their solution. A comparison of various models shows that the three-layer model best describes measured potential distributions. Furthermore, we present the "ANVOLCON" (analytical volume conductor) software package. This package has been developed to facilitate the use of the model for scientific and educational purposes and is freely available from http://www.mbfys.kun.nl/knf

Action Potentials↗

PubMed2001

Propagation disturbance of motor unit action potentials during transient paresis in generalized myotonia: a high-density surface EMG study.

Patients with autosomal recessive generalized myotonia, or Becker's disease, often suffer from a peculiar transient paresis. As yet, the relationship between this transient paresis and the defect in the gene encoding for a voltage gated Cl- channel protein in the muscle membrane of these patients is unclear. In order to gain a better understanding of the electrophysiological properties of the muscle fibre membrane in these generalized myotonia patients, we have studied transient paresis with a novel high-density surface EMG (sEMG) technique. We conclude that the transient paresis is explained by a deteriorating muscle membrane function, ending in conduction block and paresis. Multi-channel sEMG during the period of force decline in transient paresis shows a decrease in peak-peak amplitude of the motor unit action potentials from endplate towards tendon. This disturbance increases with time and place, indicating a deteriorating membrane function, and ends in a complete blocking of propagation within seconds. Spatiotemporally, this leads to a V-shaped sEMG pattern. In a more general sense, this contribution shows how spatiotemporal information, available through non-invasive high-density sEMG, may provide novel insights into electrophysiological aspects of membrane dysfunction.

Action Potentials↗

PubMed2000

Magnetic stimulation-induced modulations of motor unit firings extracted from multi-channel surface EMG.

The noninvasive assessment of motor unit (MU) firing patterns on the basis of topographical information from 128-channel high-density surface electromyography (SEMG) is reported. First, multi-channel MU action potential (MUAP) templates are obtained by clustering detected firing events according to the surface topography of the MUAP. Second, a template-matching algorithm is used to find all firings of a MU, including the superimpositions of MUAPs. From a single recording, the firing pattern of up to five MUs could be derived. The modulation of MU firing by transcranial magnetic stimulation was analyzed in peri-stimulus time histograms. The results are similar to previous results of transcranial magnetic stimulation (TMS) obtained by needle electromyographic (EMG) recordings. The method can be used to investigate MU firing patterns in patients with central motor disorders. An additional advantage of the technique, apart from its noninvasiveness, is the structural and functional information that it provides on the MUs, which is not obtained by needle EMG.

Action Potentials↗

PubMed2000

Surface EMG models: properties and applications.

After a general introduction on the kind of models and the use of models in the natural sciences, the main body of this paper reviews potential properties of structure based surface EMG (sEMG) models. The specific peculiarities of the categories (i) source description, (ii) motor unit structure, (iii) volume conduction, (iv) recording configurations and (v) recruitment and firing behaviour are discussed. For a specific goal, not all aspects conceivable have to be part of a model description. Therefore, finally an attempt is made to integrate the 'question level' and the 'model property level' in a matrix providing direction to the development and application of sEMG models with different characteristics and varying complexity. From this overview it appears that the least complex are models describing how the morphological muscle features are reflected in multi-channel EMG measurements. The most challenging questions in terms of model complexity are related to supporting the diagnosis of neuromuscular disorders.

Electromyography↗

PubMed1978

The incidence of sudden infant death syndrome in North Carolina's cities and counties: 1972--1974.

Between January 1, 1972 and December 31, 1974, 534 Sudden Infant Death Syndrome cases were reported in North Carolina. All but the out-of-state cases were mapped by county and city locations to determine if urban or rural cases predominated. The mapping was also undertaken to see if significant spatial variabilities could be detected between the county and city populations of infants at risk. The state had an overall SIDS rate of 2.06 per thousand live births. The mapping revealed that counties had a range from zero to a high of 6.6 and that cities with populations of over 10,000 had SIDS rates which ranged from zero to a high of 10.6. The proportions of SIDS cases occurring in either urban or rural locations roughly approximated the distribution of the state's population, with neither location accounting for disproportionately more cases. The larger cities, however, reported more cases than did their suburbs and the immediately surrounding rural areas. The largest and smallest cities, when grouped accordingly, had the lowest urban SIDS rates. The summary SIDS rates for whites was 1.23 per thousant live births, for blacks it was 3.75, and for Indians it was 6.56 per thousand live births.

Autopsy↗