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Biomedical subjects

J Gorecki

Publications and source records attributed to J Gorecki.

15 recordsLinked to original sources
PubMed2006

Multiargument logical operations performed with excitable chemical medium.

Assuming that a pulse of excitation corresponds to the logical "true" state one can use a chemical medium for information processing and construct devices that execute the basic binary logical operations. Here we discuss direct chemical realizations of four argument logical functions equivalent to special types of McCulloch-Pitts neuron. We demonstrate that if a proper geometrical arrangement of excitable and nonexcitable areas is used then the construction of the considered devices can be much simpler than in the case where they are composed of chemical binary logical gates.

Journal Article↗
PubMed2005

Derivation of a quantitative minimal model from a detailed elementary-step mechanism supported by mathematical coupling analysis.

Accurate experimental data increasingly allow the development of detailed elementary-step mechanisms for complex chemical and biochemical reaction systems. Model reduction techniques are widely applied to obtain representations in lower-dimensional phase space which are more suitable for mathematical analysis, efficient numerical simulation, and model-based control tasks. Here, we exploit a recently implemented numerical algorithm for error-controlled computation of the minimum dimension required for a still accurate reduced mechanism based on automatic time scale decomposition and relaxation of fast modes. We determine species contributions to the active (slow) dynamical modes of the reaction system and exploit this information in combination with quasi-steady-state and partial-equilibrium approximations for explicit model reduction of a novel detailed chemical mechanism for the Ru-catalyzed light-sensitive Belousov-Zhabotinsky reaction. The existence of a minimum dimension of seven is demonstrated to be mandatory for the reduced model to show good quantitative consistency with the full model in numerical simulations. We derive such a maximally reduced seven-variable model from the detailed elementary-step mechanism and demonstrate that it reproduces quantitatively accurately the dynamical features of the full model within a given accuracy tolerance.

Journal Article↗
PubMed2005

Sensing the distance to a source of periodic oscillations in a nonlinear chemical medium with the output information coded in frequency of excitation pulses.

A spatially distributed excitable chemical medium can collect and process information coded in the propagating pulses of excitation. We consider the problem of distance sensing with the use of a nonlinear chemical medium. We demonstrate that a sensor that can feel the distance separating it from a source of periodic excitations can be constructed by a proper geometrical arrangement of excitable and nonexcitable regions. The sensor returns information about the distance in the frequency of outgoing pulses. The sensor functionality is tested by simulations based on the Rovinsky-Zhabotinsky model. The results are confirmed in experiments performed for a ruthenium-catalyzed Belousov-Zhabotinsky reaction.

Journal Article↗
PubMed2005

On one dimensional chemical diode and frequency generator constructed with an excitable surface reaction.

The oxidation of carbon monoxide on a Pt(110) surface is considered as a medium for chemical information processing in which bits of information are represented by traveling pulses of high oxygen coverage. Using numerical simulations for a model of CO oxidation we demonstrate that in such system one dimensional chemical signal diode can be realized by setting a proper profile of temperature. We also show that a pulse splitting can occur on a temperature inhomogeneity. The phenomenon of pulse splitting can be used to construct one dimensional generator of a train of pulses with adjustable frequency.

Carbon Monoxide↗
PubMed1995

Spontaneous and evoked dysesthesias observed in the rat after spinal cordotomies.

Thirty-six rats have received surgical spinal cord lesions, 7 at a thoracic and 29 at a cervical level. More than 70% of rats with lesions which involved the lateral column (spinothalamic tract) developed spontaneous dysesthesias in the contralateral limb. Only high cervical (C1-C2) lateral column lesions were followed frequently by forelimb signs. Lesions restricted to the dorsal columns were not followed by dysesthesias.

Animals↗
PubMed1990

Correlation of CT and MR with impedance monitoring and histopathology in stereotactic biopsies.

Magnetic Resonance Imaging (MR) and Computer Assisted Tomography (CT) guided stereotaxis combined with intraoperative impedance monitoring and multiple sequential biopsies provides the opportunity to correlate the results of radiologic imaging with impedance and histopathology. The authors present the methods used and preliminary results obtained from 30 stereotactic biopsies with complete correlation in 12 cases. Impedance changes correlate accurately with lesion margins as defined by histology. CT images of enhancing lesions correlate quite closely to the histopathologic lesion margins whereas the appearance of the lesion on MR images is often larger than subsequently identified by either impedance or at pathologic examination. Impedance monitoring is a useful adjunct to stereotactic biopsy as it helps to accurately define lesion margins and can help direct the choice of biopsy sites.

Biopsy↗
PubMed1989

Recordings of abnormal activity in patients with deafferentation and central pain.

We have performed a single-unit analysis of the spontaneous activity of cells in 9 patients with central and deafferentation pain and 4 patients without pain. These studies have concentrated on the analysis of cells firing in bursts, which are particularly prevalent in pain patients. These cells were found to fire typically at interspike intervals of 1-2 ms and interburst intervals of 50 ms. Such cells occurred throughout nucleus ventralis caudalis, nucleus ventrocaudalis parvocellularis and possibly nucleus ventralis intermedius and are different in terms of firing characteristics and locations from bursting cells found in non-pain patients.

Afferent Pathways↗
PubMed1989

Thalamic stimulation and recording in patients with deafferentation and central pain.

Thalamic exploration was carried out in 39 patients with central or deafferentation pain. Several patients were explored more than once or bilaterally; therefore, 52 explorations were carried out. In 16 cases, microelectrode recording and microstimulation were employed. In the deafferented thalamus, a phenomenon of central allodynia was identified, in which patients with hyperpathia experience pain on stimulation rather than the usual sensations. With microrecording, a distinct unit firing in bursts can be identified and classified into three types. In several patients, the thalamic somatotopic map is found to be altered, and this reorganization can be classified into four types.

Afferent Pathways↗
PubMed1987

Microelectrode techniques in localization of stereotactic targets.

Although physiological corroboration of the target is essential in functional stereotactic surgery, the collected data can also be used for the offline study of normal and abnormal brain function. Such studies have the advantage of being made in actual clinical states with the unique opportunity of communicating with the patient. Correlations were made between microelectrode recordings and microstimulation at the same thalamic site with the same microelectrode in 'normal' patients, in those with tremor and in those with central and deafferentation pain. Human somatosensory organization is similar to that of subhuman primates. Five types of tremor cells have been identified-unresponsive nonsynchronous, unresponsive synchronous, kinaesthetic, voluntary, and voluntary with receptive field. While the last two qualify in latency and connectivity as tremor pacemakers, system analysis suggests an important element of long loop feedback as well. In the pain patients, five features were identified-somatotopic reorganization, altered firing in reorganized cells, bursting cells induction of burning widespread in thalamus and reproduction of the patient's pain by microstimulation-possibly a 'central allodynia' found in deafferented somatosensory thalamus particularly in patients with allodynia or hyperpathia. All but the latter effects may be merely the consequence of deafferentation and were seen in a 'control' stroke patient with dystonia, sensory loss but no pain.

Brain Mapping↗
PubMed1987

Thalamic microelectrode recording and microstimulation in central and deafferentation pain.

Microelectrode recording and microstimulation (in 1 case macrostimulation) were used to localize stereotactic targets in 8 patients with central and deafferentation pain and 1 'deafferented control' patient without pain. Off-line study revealed two features commonly proposed as potential physiological factors for such pain, but they were present in both pain and control patients--somatotopographic reorganization and the presence of bursting cells. In all patients in whom stimulation induced pain referred to deafferented parts of the contralateral body, hyperpathia or allodynia were present instead of normal paraesthetic, sensorimotor or thermal responses.

Electric Stimulation↗
PubMed1984

New intraventricular catheter for volume pressure response measurements.

Measurements of the volume-pressure response (VPR) to determine the relative position of a patient on the graphic volume-pressure curve have been used to derive clinically useful information. One reason that these measurements have not been used more frequently has been the fear of introducing infection into the ventricular system. We have designed an intraventricular catheter that allows repeated VPR measurements and reduces the risk of infection.

Catheterization↗
PubMedDate not supplied

Do-not-resuscitate practices in the chronically critically ill.

OBJECTIVES: To determine the frequency of do-not-resuscitate (DNR) orders in the chronically critically ill; to identify the differences in clinical and demographic characteristics of chronically critically ill patients who have DNR orders and those who do not; to identify the differences in the cost of care between patients with and without DNR orders; and to identify the differences in DNR practices between an experimental special care unit and the traditional intensive care unit (ICU). DESIGN: Randomized, prospective design with a block randomization scheme. SUBJECTS: Two hundred twenty patients who met the following eligibility criteria for enrollment in a parent study of the special care unit: an ICU stay of at least 5 days, an absence of pulmonary artery monitoring, an absence of frequent titration of intravenous vasopressors, an Acute Physiology and Chronic Health Evaluation II score of less than 18, and a Therapeutic Intervention Scoring System score of less than 39. SETTING: A large, urban academic medical center. MEASURES: Clinical and demographic variables describing the study populations, mental status, and timing of DNR orders, mortality rates, and cost of hospitalization. RESULTS: There was no difference in the frequency of DNR orders between the special care unit versus the intensive care unit--although patients in the special care unit had a longer interval between hospital admission and initiation of the DNR order. DNR patients differed from non-DNR in that they were older, less likely to be married, and had a higher Acute Physiology and Chronic Health Evaluation II score on admission to the study. The mortality rate in the DNR group was 71% versus 6% in the non-DNR group. There was no difference in total costs. DNR patients were also more likely to have an impaired mental status on admission, and more likely to have deterioration in mental status by the time of discharge than the non-DNR patients.

Aged↗