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Biomedical subjects

D F Bruley

Publications and source records attributed to D F Bruley.

At least 19 recordsLinked to original sources
PubMed1990

TRIPAS: a triapplicator system with relocatable 'hot spot' at tissue depth.

Solving the problem of heat focusing and standardization of the clinical application of hyperthermia requires a mathematical prediction model. The model should include the medium constitutive parameter, and be able to predict positioning of the microwave applicators to optimize treatment planning and provide for reproducible treatment set-up. We present a configuration of 3 applicators subtended by an equilateral triangle in order to target and relocate a 'hot spot' for improved treatment of deep tumors. A simple geometric analysis is illustrated. The microwave beam absorption profile, from the three power sources, was obtained from phantom studies depicting the radiative heat pattern for the triapplicator system (TRIPAS). A complex mathematical model was developed to demonstrate interaction of the beams in the medium. It was observed empirically that under coherent propagation in the near field electromagnetic (EM) waves tend to add at the center, while varying the propagation axial focal length caused a relocation of the summing focal points. Mathematical prediction correlated very well with the phantom studies. SAR values above 100 W/kg were achieved at 12.5 cm phantom depth, creating a relocatable 'hot spot' at the concentric foci of the 3 air cooled horn microwave applicators operating at 300 MHz.

Computer Simulation↗
PubMed1988

A computer simulation of simultaneous heat and oxygen transport during heterogeneous three dimensional tumor hyperthermia.

Hyperthermia is a developing modelity for the treatment of cancer. This therapy is occasionally used by itself, however, usually it is used as an adjuvate with chemo or radiation therapy. The mechanism for this treatment is based on the fact that cancer cells are heated preferentially by heat application due to lower vascularity in the tumor tissue as compared with the surrounding normal tissue and that, when used with radiation therapy or chemo therapy, higher oxygen partial pressure in the tumor results in increased tumor cell damage. Appropriate mathematical models and their real time prediction of oxygen and temperature profiles could be very helpful in achieving optimal results via hyperthermia and to avoid possible danger which might occur during the treatment. Because of the complexity and the heterogeneous nature of physiological system, it is necessary to include heterogeneous properties in the mathematical models for them to be useful for biomedical calculations. Of course, it is much more difficult to solve mathematically the heterogeneous system than the homogeneous one. In this paper, the importance of the implementation of heterogeneities in the heat and mass transport for biological system mathematical modelling is discussed. Results of a three dimensional computer simulation of mass and heat transfer in tumor tissue with different capillary geometries during hyperthermia are demonstrated. The method used for the computer simulation is a deterministic/probabilistic technique, Williford-Bruley calculational strategy.

Animals↗
PubMed1986

A multicomponent, random walk model of transport and metabolism inside a neuron.

A model of multicomponent transport, consumption, and production of metabolites inside a neuron containing discrete mitochondria and glycolytic enzymes is developed using a random walk model of molecular transport. The ratio of anaerobic to aerobic metabolism which maximizes ATP production under normal, ischemic, and anoxic conditions is calculated. The ratio of the number of mitochondria to glycolytic enzymes which maximizes ATP under normal conditions is also calculated. Because the volume of the neuron is fixed, the sum of the number of mitochondria and glycolytic enzymes is fixed. This constraint is incorporated in the optimization process as an interior penalty function. Some of the advantages of employing the random walk technique are simple stoichiometry can be used to model consumption and production of metabolites, the geometry of the enzyme system and their active sites can be easily included in the model, and saturation of enzymes can be more easily modeled.

Animals↗
PubMed1986

A mathematical model applying the random-walk method to the environment of a neuron.

A mathematical model describing the supply and demand relationships existing in the environment of a brain cell (neuron of the cerebral cortex) was developed. The stochastic random-walk technique was applied to the representation and solution of the system which consisted of a neuron being supplied with nutrients by an adjoining capillary. The random-walk method incorporated a uniformly generated random number which was weighted by the normal distribution curve to determine the random walk of a molecule. The resultant weighted value was designated as defining the motion of any particular species in space. The distribution curve was a function of diffusivity and time. The method allowed the tracking of individual molecules as they proceeded through the metabolic reactions in the cell. Oxygen, glucose, carbon dioxide and lactate were selected as the primary components of study, since they represent the major input and output parameters of metabolism inside the cell. The consumption and/or production of these components were dependent on probability values assigned to each metabolic reaction into which they entered. The solution of the model was based on the number of molecules existing in the tissue as a function of PO2, (partial pressure of oxygen), glucose level, etc. The model was very sensitive to perturbations of metabolic scheme parameters and to PO2 levels in the capillary. The model predicted an excess of O2, (oxygen) in the tissue. The effects of edema on intercapillary distances as well as changes in the size and number of mitochondria within the neuron were examined using the model.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1979

Local oxygen tension and its relationship to unit activity during penicillin interictal discharges in the bullfrog hippocampus.

Simultaneous measurements of extracellular unit activity and pO2 were made with single polarographic microelectrodes in penicillin foci of the bullfrog hippocampus. Individual penicillin-induced ECoG interictal discharges were often associated with both a burst of extracellular unit activity and a simultaneous transient decrease in pO2. The bursts of unit activity lasted up to 1500 msec and were followed by longer periods of inhibition. Transient decreases in pO2 began within 150 msec of the onsets of the bursts but outlasted the bursts by many seconds. The durations of the pO2 transients ranged from 10 to 90 sec, depending upon the frequency of interictal discharges. When the frequency of interictal discharges increased, the pO2 transients summated such that pO2 approached 0 mm Hg. The magnitude of the pO2 decrease was related to both the baseline pO2 and the intensity of the associated burst of action potentials. The transient decrease in pO2 most likely represents increased local tissue O2 consumption. These measurements provide, for the first time, a means of assessing the relationship between local neuronal activity and local oxygen utilization in seizures.

Action Potentials↗
PubMed1976

A stochastic model for the transport of oxygen to brain tissue.

Material balances around a small, but finite volume element have formed the basis for previous mathematical models describing the transport of oxygen in the brain microcirculation. Seeking a model which would be both simple and versatile, a stochastic model was proposed based on the assumption that oxygenation of the brain can be described quantitatively by simulating the activity of only one erythrocyte and the oxygen molecules surrounding it. Compared with existing deterministic models, the capillary space-average oxygen partial pressure profiles were in close agreement. Tissue tensions were decidedly different.

Blood Flow Velocity↗
PubMed1976

Autonomic and pharmacological control of oxygen autoregulation mechanisms in brain tissue.

The effect of several agents active on autonomic nervous system functions was tested on brain oxygen autoregulation parameters. It was found that atropine, propranolol and isproterenol had no influence on the measured parameters. Phenoxybenzamine, tolazoline and dibenamine all suppress autoregulation. In an additional experimental series, a phenoxybenzamine infusion was given during O2 breathing. The infusion induced a marked rise in TpO2. It is concluded that an alpha-adrenergic mechanism is part of the autoregulation process, and its pharmacological blockade could be used to raise TpO2 levels in brain with O2 breathing at normal atmospheric pressure. Also, the increase in brain TpO2 induced by 95% O2 - 5% CO2 breathing seems to be blocked by alpha-adrenolytic drugs.

Animals↗