[Coefficient of oxygen diffusion in fibers of the skeletal muscles]

The effective coefficient of oxygen diffusion in muscle fibers (DO2eff) calculated from measured values of O2 critical pressure, O2 intake and fiber diameter in different skeletal muscles in vertebrates turned to be equal to (0.9-1.8) x 10(-6) cm2/s, which is 11 to 33 times lower than O2 in water. In mature animals, DO2eff reaches this value after the fiber diameter has grown to the maximum. In embryos and developing species with thinner myofibers DO2eff is significantly lower. Variations in oxidative metabolism in the fiber do not change DO2eff. Temperature drop in the fiber by 10 degrees C reduces DO2eff by approximately 30%. Modeling of the oxygen regimes in skeletal muscles with low DO2eff demonstrated that increase of the size of the O2-rich interstitium from 9 up to 25% reduces the diffusive resistance to O2 on the way from the capillary to mitochondria by approximately 20% (1); in combined muscles hypoxic areas may appear in the center of fibers with a high O2 demand, particularly when diameters of these fibers are comparatively large (2); the volumetric blood flow in the muscle can be infinitely large and O2 pressure in veins can remain high (the so-called functional shunting).