AN EASY-TO-USE MODEL FOR O-2 SUPPLY TO RED MUSCLE - VALIDITY OF ASSUMPTIONS, SENSITIVITY TO ERRORS IN DATA

An easy-to-use capillary cylinder model of O-2 supply to muscle is pre sented that considers all those factors that are known to be most impo rtant for realistic results: (1) red blood cell (RBC) O-2 unloading al ong the capillary, (2) effects of the particulate nature of blood, (3) free and hemoglobin-facilitated O-2 diffusion and reaction kinetics i nside RBCs, (4) free and myoglobin-facilitated O-2 diffusion inside th e muscle cell, and (5) carrier-free region separating RBC and tissue. In a first approach, a highly simplified yet reasonably accurate treat ment of the complex three-dimensional oxygen diffusion field in and ne xt to capillaries is employed. As an alternative, a more realistic des cription using RBC/capillary diffusing capacity has been included, Mod el development proceeds step by step and is designed to be easily comp rehensible for a broad readership. In spite of the number of features accounted for, the model is simple to apply, even for scientists not s pecialized in the field of modeling. P-O2 distributions calculated by the model are in good qualitative agreement with experimental data and with former modelling results, By means of suitable extensions to the model that are also developed it is shown for a wide range of muscle performances that quite generally the following complication may be ne glected safely. (1) complexity of O-2 diffusion field near capillaries , (2) deviations of capillary domain cross sections from the circular shape, (3) O-2 diffusion parallel to the capillary direction, and (4) P-O2 dependence of O-2 consumption rate. Finally, a sensitivity analys is is performed in which propagation of errors in the input data into the results is investigated. The interpretation of the calculated sens itivities gives insights in the specific dependencies of muscular O-2 supply on the various input parameters. Moreover, basic interrelations governing carrier-facilitated diffusional O-2 transport to muscle bec ome apparent and are discussed.