PubMed Health⌕ Search

Biomedical subjects

D F Bruley

Publications and source records attributed to D F Bruley.

12 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↗
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↗