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Decompression sickness (DCS) is the result of bubble formation in the body due to excessive/rapid reduction in the ambient pressure. Existing models relate the decompression stress either to the inert gas load or to the size of a single bubble in a tissue compartment. This paper presents a model that uses the gas exchange equations combined with bubble dissolution physics and population balance equations to produce a new mathematical framework for DCS modeling. This framework, the population balance model for decompression sickness (PBMDS), simulates the number of bubbles with their corresponding size distributions in a compartmental tissue array. The model has a modular structure that enables one to explore different modeling results with respect to key aspects of DCS, such as gas exchange, nucleation, and surface tension. The paper's goal is to present the derivation of PBMDS in detail, however, three simple application case studies are provided. The aim of these case studies is to suggest that PBMDS supplies additional information on bubble distribution while supporting the results from current practice. Index Terms--Bubble equations, bubble simulations, decompression modeling, decompression sickness, population balances.

The metabolism of testosterone-4-14C by hamster skin and flank organ was studied; flank organ metabolized more testostrone than an equal weight of adjacent skin. Androstenedione.† androsterone, androstanedione, dihydrotestosterone (DHT), and 3α-androstanediol were identified by chromatography and reverse isotopic dilution as metabolites formed by flank organ. The metabolites of flank organ and general body skin showed identical chromatographic mobilities. Flank organ produced 4 times as much DHT as an equal weight of adjacent skin. The ratio of total 5α-metabolites formed by both tissues was the same as the DHT ratio, indicating that the greater amount of DHT formed is due to greater formation of 5α-metabolites, in general. In contrast, both tissues produced the same amount of 17-ketosteroids from testosterone and had similar DNA contents, suggesting that the observed difference in 5α-reduction was not due to differences in cellularity but to a greater capacity of the flank organ to reduce testosterone. No 3β-hydroxysteroids, the formation of which has been reported in human skin were found. [ABSTRACT FROM AUTHOR]