EFFECT OF LIPID ON INERT-GAS KINETICS

A Monte Carlo simulation of inert gas transit through skeletal muscle has been extended to include regions of increased gas solubility to si mulate regions of high lipid content. Position of the regions within t he simulation module was varied, as was the muscle-lipid partition coe fficient (lambda). The volume percentage of the lipid regions (alpha) was varied from 0 to 25% while lambda covered the range from 1 to 50. The effects of <zeta alpha and lambda on mean transit time and on rela tive dispersion (RD; ratio of SD to the mean) were examined for a sing le lipid volume and compared with expected values under the assumption that the tissue is composed of two well-stirred compartments. Mean tr ansit times varied from similar to 0.80 to 1.20 times the values predi cted by a simple parallel two-compartment model, whereas RD varied fro m 0.9 to 3.6. For fixed lambda, RD as a function of lipid fraction pas ses through a maximum that is shifted and was also smaller than expect ed from a simple two-compartment model. For fixed alpha, RD approaches an asymptotic value for large lambda, but the asymptote is smaller th an that expected from the two-compartment model. When lipid is distrib uted in only two regions, RD decreases with increasing separation of t he regions and with increasing surface area of the fat regions. A mode l of two well-stirred compartments that allows mixing between the comp artments yields results similar to those from the simulation.