Biomedical subjects

B R Wienke

Publications and source records attributed to B R Wienke.

7 recordsLinked to original sources

PubMed1992

Numerical phase algorithm for decompression computers and application.

Present generation decompression computers employ a simplified algorithm, limiting dissolved gas build-up in tissue and blood according to a method proposed by Haldane 80 years ago. Such a model works well for single dives, but is usually liberal and theoretically incomplete for multiple exposures within 24 hr spans. Using the critical phase hypothesis in a bubble model, we have extended the classical model of Haldane to multi-exposures. This model is discussed, and a decomputer algorithm described for multi-diving. The focus is permissible bubble excess, not just dissolved gas per se, with phase constraints affecting all tissues, fast and slow, and requiring a systematic lowering of repetitive tissue tensions. Deep repetitive and shallow multi-day exposures are impacted most by the procedure. Within nucleation theory deeper-than-first dives are also treated. A set of multi-diving fractions, xi, accounting for micronuclei excitation and regeneration, reduced bubble elimination in repetitive activity, and coupled effects on tissue tension, are proposed, with xi representing a set of multiplicative factors (less than one) applied to critical tissue tensions for multi-exposures. These factors affect repetitive activity over short time spans, deeper-than-previous and continuous multi-day activities, compared to standard computer software, and are easily encoded into existing decompression meters, potentially extending their range and flexibility over exposure regimes.

Algorithms↗

PubMed1991

Bubble number saturation curve and asymptotics of hypobaric and hyperbaric exposures.

Within bubble number limits of the varying permeability and reduced gradient bubble models, it is shown that a linear form of the saturation curve for hyperbaric exposures and a nearly constant decompression ratio for hypobaric exposures are simultaneously recovered from the phase volume constraint. Both limits are maintained within a single bubble number saturation curve. A bubble term, varying exponentially with inverse pressure, provides closure. Two constants describe the saturation curve, both linked to seed numbers. Limits of other decompression models are also discussed and contrasted for completeness. It is suggested that the bubble number saturation curve thus provides a consistent link between hypobaric and hyperbaric data, a link not established by earlier decompression models.

Atmospheric Pressure↗

PubMed1990

Modeling dissolved and free phase gas dynamics under decompression.

Dissolved and free gases do not behave the same way in tissue under pressure, and their interaction is complex. Differences are highlighted, particularly with respect to time scales, gradients and transport. Impacts of free phases on diving are described, contrasting increased off-gassing pressures, slower ascent rates, safety stops and reduced repetitive exposures as consistent practical measures within Haldane models (limited supersaturation) which can be played off against buildup of dissolved gas. Simple computations illustrate the points.

Algorithms↗

PubMed1990

Reduced gradient bubble model.

An approach to decompression modeling, the reduced gradient bubble model (RGBM), is developed from the critical phase hypothesis. The phase limit is introduced, extended, and applied within bubble-nucleation theory proposed by Yount. Much is different in the RGBM algorithm, on both theoretical and applied sides, with a focus on permissible bubble excesses rather than just dissolved gas buildup, something of a departure from traditional models. Overall, the approach is conservative, with changes in parameter settings affording flexibility. Marginal profiles permitted by tables and meters are restricted by the bubble algorithm. Highlighted features of the conservative algorithm include: (1) reduced no-stop time limits from the varying-permeability model (VPM); (2) short safety stops (or shallow swimming ascents) in the 10-20 feet of sea water (fsw) zone; (3) ascent and descent rates of 60 fsw/min, or slower; (4) restricted repetitive exposures, particularly beyond 100 fsw, based on reduced permissible bubble excess; (5) restricted spike (shallow-to-deep) exposures based on excitation of additional micronuclei; (6) restricted multi-day activity based on regeneration of micronuclei; (7) consistent treatment of altitude diving within model framework; (8) algorithm linked to bubble-nucleation theory and experiment. Coupled to medical reports about the long term effects of breathing pressurized gases and shortcomings in dissolved gas models, conservative modeling seems prudent.

Algorithms↗

PubMed1989

Equivalent multi-tissue and thermodynamic decompression algorithms.

Multi-tissue and thermodynamic decompression algorithms are described and a computational equivalence is established between the two approaches. Eigenvalues and weighted eigenfunctions of the Fick-Fourier equation effectively define response functions from which Haldane half-lives can be extracted from arbitrary exposures, operationally bridging the two approaches. Decompression criteria for the algorithms are also described and coupled. Comparisons of similarities and differences of approaches are given from both theoretical and applied viewpoints. A seven-parameter set, spanning both models, forms the basis of analysis. We find that representative thermodynamic parameters in a perfusion-diffusion model effectively recover Haldane half-lives in a bootstrap and that critical parameters overlap, though ranges differ in the two cases.

Algorithms↗

PubMed1989

Tissue gas exchange models and decompression computations: a review.

Mathematical models for inert gas transport and decompression are summarized. Both semi-infinite and finite media are treated, and resulting analytic expressions are obtained and compared against each other. One-dimensional plane and cylindrical geometries are considered, and limiting forms are explicitly detailed. Models are placed into three categories for discussion--bounded, bulk, and perfusion-diffusion. The intent is to collect treatments and techniques into one source for reference. Staging criteria, where appropriate to a model, are also included in the development. Bounded, bulk, and perfusion-diffusion models are described in supersaturation, statistical, and thermodynamic frameworks. Some strengths and weaknesses of deterministic and statistical models are noted. Today, models can be nested in hi-tech decomputers utilizing precision depth sensors and elapsed timers. The ability to solve equations and check criteria in an essentially continuous time mode imparts new dimensionality, enhancing capability and optimizing performance. However, there are limits on all computational models, both in theory and application, and herein we review range, physical correctness, and history of the algorithm.

Biological Transport, Active↗

PubMed1987

Computational decompression models.

Early computational models for decompression are based on supersaturation assumptions for dissolved gases. Such models, and our understanding of decompression biophysics, have been extended in the past 20 years by analyses of phase separation of gases. Generally termed thermodynamic decompression (or phase equilibration), these studies postulate a continuous exchange of inert gas between tissues and nucleation sites (gas micropockets), consistent with many commonplace phenomena. Postulates lead to decompression schedules and transfer mechanisms that differ from their earlier predecessors. The precise physical and computational bases supporting both viewpoints are described and contrasted.

Decompression↗