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Biomedical subjects

D F Bruley

Publications and source records attributed to D F Bruley.

At least 37 records · Page 2Linked 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↗
PubMed1984

Mathematical analysis of transport and consumption of molecules in heterogeneous brain tissue (methodology).

A computer model of metabolite transport and consumption in heterogeneous brain tissue, using a combination of probabilistic and deterministic techniques is being developed. The metabolites are put into two separate classes: (I) those that have reached a membrane for the first time during a small time step, delta t, and (II) those that have not yet reached a cell membrane for the first time during that time step. The time dependent spatial distribution of class (I) molecules is determined using random walk theory, which takes into account the actual paths of the molecules. The variation of the spatial distribution of class (II) molecules with time is determined using the time dependent diffusion equation with a boundary condition of zero concentration on the enclosing membrane boundaries.

Biological Transport, Active↗
PubMed1984

Approximate-analytical solution of the diffusion, convection and reaction problem in homogeneous media.

In convex homogeneous domains, the diffusion, convection and reaction (DCR) problem may be solved by applying Green's function solution technique. When this technique is applied, the solution to the DCR problem consists of the sum of a set of integrals whose integrands involve the Green's function. The Green's function is singular at the upper limit of the time integral and is nonuniformly convergent at the boundaries of the domain. Due to this behaviour, numerical evaluation of the integrals is prohibitively expensive and in some cases, the integrals are incorrectly evaluated. The method presented in this work circumvents all the difficulties inherent with the numerical quadrature of the intergrals and in preliminary case studies (in rectangular coordinates) has reduced the required computation time by up to five orders of magnitude while increasing the accuracy of the results by as much as eight orders of magnitude. The method involves transforming the function in the integrand, which multiplies the Green's function, into a series of Legendre polynomials. The integral of the product of the Green's function and Legendre polynomials can be evaluated analytically. This produces both a rapid and accurate evaluation of the integral and subsequently the solution to the DCR problem.

Biological Transport, Active↗
PubMed1984

Changes in tumor tissue oxygenation during microwave hyperthermia: clinical relevance.

As previously described (Bicher 1981) TpO2 and blood flow increase in tumor as temperature increases until 41 degrees C and decrease thereafter (microcirculation "breaking point"). In the present clinical study using O2 microelectrodes this response was reproduced in over 54 treatment sessions. However, it was found that as treatment progresses (patients are treated for one hour 10 times, twice weekly, and concomitantly receive 4000 rads of ionizing radiation) the initial increase of blood flow and TpO2 is reduced and there is immediate decrease in tissue oxygenation. A correlation between microvascular tumor physiological changes and tumor treatment responses is being developed.

Hot Temperature↗
PubMed1983

The transport of oxygen, glucose, carbon dioxide and lactic acid in the human brain: mathematical models.

Mathematical models of the transport of oxygen, glucose, carbon dioxide and lactic acid in the human brain have been developed and solved for both steady-state and dynamic cases which include normal conditions, arterial and venous hypoxia, reduced flow and hematocrit, hypocapnia, reduced glucose and transient arterial upsets. Results indicate that local concentration deficits of oxygen and/or glucose and excesses of lactic acid can exist within the system described by the models and therefore possibly could exist in the tissues of the human brain under similar conditions.

Biological Transport, Active↗
PubMed1983

Changes in tissue oxygenation and acidity induced by localized microwave hyperthermia and hematoporphyrin phototherapy, an update.

Changes in tumor tissue oxygenation and acidity were determined using ultramicroelectrodes, and presented in histogram fashion. The effect of Hyperthermia and Hpd photo-therapy were tested. It was found that both modalities affect tumor microcirculation, causing a marked drop in oxygen availability. Tissue pH is decreased by Hyperthermia, but not by phototherapy. These effects are long lasting, at least for 24 hours after treatment.

Acid-Base Equilibrium↗
PubMed1982

Identification of viable regions in "in vitro" spheroidal tumors: a mathematical investigation.

In the treatment of solid tumors by hyperthermia, a major question is how to obtain an a priori knowledge of which tumors can be effectively treated with this modality. The key question is; given a solid tumor, what parameters in the various regions of the tumor, need to be measured so that a tumor-tissue model can provide a meaningful real time simulation of the hyperthermic treatment. This paper addresses the former question as a mathematical investigation, and the latter as a consequence of the former.

Animals↗
PubMed1982

Computer modeling of tumor hyperthermia (a dynamic lumped parameter model).

The thermal behavior of normal and neoplastic tissue is modeled by a set of coupled ordinary differential equations. The equations lump the tissue and tumor into individual compartments, so that the equations are time dependent. These equations represent an initial step in the development of a comprehensive model which may be used in studying the dynamics and control of the system under normo- and hyperthermic conditions.

Computers↗
PubMed1980

Probabilistic modeling of oxygen transport in brain tissue.

A three-dimensional model of a subregion of the microcirculation was developed. The model employed parallel probabilistic distributions of reaction and convection of oxygen. A Green's function solution to oxygen transport in this system was derived and applied in a series of dynamic solutions on a minicomputer. Results include the transient response of oxygen tension at grid points throughout the system and a correlation of the oxygen demand and surplus supply. Results clearly represent anticipated oxygen partial pressure behavior trends of a countercurrent flow system and in pertinent ways compared favorably with the results obtained by previous investigators. The technique is conservative and employs from 2,000 to 3,600 time steps to achieve precision of seven significant figures. Excellent stability was observed as well. The simulation provides a reliable means to represent the transient response of oxygen partial pressure in a three-dimensional system. Case studies show effects of changing arterial oxygen partial pressure as well as the importance in this system of the convection of dissolved oxygen. It is concluded that the system adequately simulates the anticipated broad profiles of a probabilistically distributed system and provides a rather original insight into neuronal viability through a correlation of oxygen supply and demand. Adaptation of such a complex, dynamic, three-dimensional stimulation to a minicomputer is a step toward simulation of more sophisticated geometries.

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↗