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T D Lagerlund

Publications and source records attributed to T D Lagerlund.

28 records · Page 2Linked to original sources
PubMed1993

A data interchange standard for clinical neurophysiology.

A Standard Specification for Transferring Digital Neurophysiological Data Between Independent Computer Systems (Designation E 1467-92) has been developed. The specification defines a common representation of all of the data associated with a complete clinical study, including digitized neurophysiological waveforms, textual annotations and interpretive reports. Patterned after existing, related healthcare data interchange standards, it will facilitate data interchange between neurophysiological instruments, computer systems within the neurophysiology laboratory, other information systems in the hospital, and outside healthcare facilities or research laboratories.

Computer Communication Networks↗
PubMed1991

Axial diffusion and Michaelis-Menten kinetics in oxygen delivery in rat peripheral nerve.

Our simulation of the release, diffusion, and consumption of oxygen in the capillaries and surrounding tissue of peripheral nerve now includes axial diffusion in blood and in surrounding tissue, in addition to bulk flow of blood and radial diffusion of oxygen out of the capillary. Our simulation assumes that the oxygen consumption of nerve tissue obeys Michaelis-Menten kinetics rather than zero-order kinetics as had been assumed in the Krogh model. We can calculate the oxygen tension at all points in the capillary and surrounding tissue as a function of distance from the center of the nearest capillary and distance along the capillary from the arterial to the venous end. Using average measured values for microcirculatory parameters in rat nerve, we calculated a distribution of oxygen tension values that agrees with experimentally measured distributions. The effects of axial diffusion and of Michaelis-Menten kinetics on the oxygen distributions were noticeable under normal conditions, but these effects were much more important in situations in which oxygen delivery was adversely affected.

Animals↗
PubMed1989

Computer simulation of the generation of the electroencephalogram.

We have used a computer program for modeling some features of the scalp electroencephalogram (EEG) in terms of the time- and space-dependent interactions of populations of neurons in different hypothetical brain configurations of increasing levels of complexity. The input of the model consists of: (1) geometric and anatomic data characterizing the brain configuration, including interconnecting fiber pathways between neuronal groups; (2) physiologic characteristics of neurons, such as thresholds, driving potentials and conductances of excitatory and inhibitory synapses, synaptic delay times, and rise and fall times of postsynaptic potentials; and (3) functions describing the time-dependent afferent impulses to the brain configuration under study. The output of the model consists of plots of selected intracellular and extracellular potentials, including electrical potentials measured by an array of electrodes on the surface of the head, as a function of time. The objective was to assess how the characteristic frequencies seen in scalp EEG recordings might be determined by characteristics of local neuronal circuits (such as thalamic 'pacemakers') and by global circuit characteristics (such as cortico-cortical and thalamo-cortical interactions). We find that in our model the basic requirement for rhythmic behavior is the existence of local feedback circuits containing inhibitory neurons and that, when parameters of the model are chosen so that sustained rhythmic oscillations in the alpha frequency range are generated, the characteristic frequencies of these oscillations are primarily determined by the local circuit parameters, especially the duration of the inhibitory postsynaptic potentials, and are relatively independent of global circuit parameters such as the ranges of the long interconnecting axons and the propagation velocity of action potentials in these axons.

Animals↗
PubMed1989

Analysis of H2 clearance curves used to measure blood flow in rat sciatic nerve.

1. By use of the H2 clearance technique, blood flow was measured in the sciatic nerve of healthy, anaesthetized Sprague-Dawley rats at rest, during inferior vena cava occlusion and during 5-hydroxytryptamine infusion. The purpose was to clarify the mechanisms underlying the biexponential curves which are commonly obtained using this technique. 2. An analysis of the frequency distribution of rate constants of 270 nerve and thirty-three arterial samples indicated that H2 clearance rates cluster below 20 ml min-1 100 g-1 and between 70 and 100 ml min-1 100 g-1. This suggests that at least two compartments are present. 3. The contribution of diffusion was studied by recording H2 clearance immediately following circulatory arrest. Slow clearance rates (median = 2.4 ml min-1 100 g-1) were observed, indicating that diffusion is not likely to contribute significantly to nutritive flow under most situations. 4. The contribution of arteriovenous shunts to H2 clearance was assessed by determining H2 clearance during inferior vena cava occlusion and the infusion of 5-hydroxytryptamine. Both manoeuvres caused abolition of, or a significant reduction in the weight of, the fast component which indicates that this compartment is closely related to arteriovenous shunts in nerve. 5. By use of a multi-compartmental model, it was shown that H2 clearance should follow a multi-exponential course, where the weights of the components reflect the relative volumes of each compartment and the exponents represent the relative flow (i.e. flow per unit volume) in each compartment. 6. By use of other mathematical models, estimates were made for the clearance rates attributable to polarographic oxidation of H2 at the tip of the microelectrode (0.2 ml min-1 100 g-1) and to diffusion to air (2 ml min-1 100 g-1). The latter estimate is very close to the measured value of 2.4 ml min-1 100 g-1. 7. These findings indicate that it is possible to separately assess nutritive and non-nutritive flow by application of biexponential analysis to H2 clearance curves. The data suggest that the fast component of a H2 clearance curve is closely associated with arteriovenous shunts, while the slower component is likely to represent capillary flow. Processes such as diffusion to air or oxidation of H2 by the electrode are very slow and therefore are unlikely to distort the assessment of blood flow by using this technique.

Animals↗
PubMed1988

An electroencephalographic study of glossopharyngeal neuralgia with syncope.

In the case described, electroencephalography (EEG) proved valuable for determining the nature of spells of loss of consciousness with brief clonic jerks associated with ear and throat pain. A 70-year-old woman had a history of episodic brief attacks of pain below the right ear and deep in the neck that had started three years previously. The spells became more severe and progressed to loss of awareness associated with clonic jerks of the extremities. Because of a concern that the spells represented seizures, an EEG was performed, with electrocardiographic monitoring. Multiple spells were recorded; they began with profound bradycardia followed by generalized slow-wave activity and then by suppression of all EEG activity correlating with loss of consciousness and clonic jerking. The spells were thought to represent syncopal attacks associated with glossopharyngeal neuralgia.

Aged↗
PubMed1988

Computer simulation of neuronal circuit models of rhythmic behavior in the electroencephalogram.

A computer program for modeling some features of the electroencephalogram (EEG) recorded by scalp electrodes in terms of the time- and space-dependent interactions of populations of neurons in different hypothetical brain configurations was developed. The input of the model consists of: (1) geometric and anatomic data characterizing the brain configuration; (2) physiologic features characterizing neurons; and (3) functions describing the time-dependent afferent impulses to the brain configuration under study. The output of the model consists of plots of selected intracellular and extracellular potentials as a function of time. In application of the model to various brain configurations, some configurations were sufficiently compact spatially that propagation times of action potentials between elements were either taken to be constant or were nearly independent of distance within the accuracy of the calculations. Other configurations represented cerebral cortex alone or a combined thalamocortical system in which many elements interacted via global interconnections. The basic requirement for rhythmic behavior is the existence of circuits containing inhibitory neurons. The characteristic frequencies of rhythmic oscillations are primarily determined by the local circuit parameters and are relatively independent of global circuit parameters.

Action Potentials↗
PubMed1987

A mathematical simulation of oxygen delivery in rat peripheral nerve.

We have performed a mathematical simulation on a CYBER computer of the release, diffusion, and consumption of oxygen in the capillaries and surrounding tissue of peripheral nerve under steady-state conditions. The Krogh-Erlang equation was used to calculate oxygen tension in tissue, while numerical solution of the differential equation governing oxygen release from hemoglobin and diffusion was used to calculate oxygen tension in the capillary. Using average measured values for the parameters of oxygen solubility, diffusion coefficient, capillary diameter, capillary density, nerve blood flow, oxygen consumption rate, and arterial oxygen tension in rat peripheral nerve, we calculated the endoneurial oxygen tension as a function of distance from the nearest capillary and distance along the capillary from the arterial end to the venous end. The range of calculated values agreed with experimental measurements obtained from the sciatic nerves of rats. Alterations in these parameters produced changes in the calculated oxygen tension distributions. Conditions which adversely affected oxygen delivery include reduced capillary diameter, increased intercapillary distance, reduced blood flow, and reduced arterial oxygen tension. The lower experimentally obtained oxygen tensions in sciatic nerves of diabetic rats could be accounted for reasonably by this model on the basis of a 33% reduction in nerve blood flow (consistent with previously measured flow reduction). However, the measured reduction in oxygen tensions in sciatic nerves of rats with experimental galactose neuropathy were not as marked as those predicted on the basis of a 22% increase in tissue cylinder radius in the model (consistent with experimental observations). This may be due to the fact that the oxygen consumption rate is reduced in hypoxic regions of tissue.

Animals↗
PubMedDate not supplied

Comparison of EEG background frequency analysis, psychologic test scores, short test of mental status, and quantitative SPECT in dementia.

Fourteen patients who had cognitive dysfunction were studied with quantitative electroencephalography (EEG), single-photon emission computed tomography (SPECT), and several tests of intellectual and memory function, including the Wechsler Adult Intelligence Scale (WAIS), the Auditory Verbal Learning Test, and the Short Test of Mental Status, to determine whether EEG background frequency content correlates with degree of dementia and with regional uptake of radioisotope on SPECT. The factors from spectral analysis that correlated best with psychometric data were mean frequency in the 1.5- to 20-Hz range and percentage power in the 13- to 20-Hz band (positive correlation) or the 1.5- to 8-Hz band (negative correlation). The WAIS subtest scores that correlated most with the EEG data were performance IQ and perceptual organization. Correlations between percentage power and amplitude ratio in the EEG frequency bands and regional SPECT counts were found, but most were not statistically significant.

Aged↗