Obligatory anaerobiosis resulting from oxygen uptake-to-blood flow ratio dispersion in skeletal muscle: a model.

We constructed a computer model whereby the dispersion of the oxygen uptake-to-blood flow ratio (VO2/Q) in working muscle could be altered around its mean level during simulated exercise. The model incorporated standard values for the cardiac output and whole-body O2 uptake responses to incremental exercise in humans. Dispersion of the VO2/Q ratio was induced by distributing Q in a Gaussian fashion around its appropriate mean value with a standard deviation (sigma). By increasing sigma, more regions of the muscle became "anaerobic" as the corresponding local muscle venous blood O2 content fell to zero; these regions thus required proportionally greater rates of lactate production to sustain the required energy transfer. The model yielded a relatively high mixed-muscle venous partial pressure of O2, suggesting that the latter may not be a sufficient indicator of whether or not there may be diffusional limitation to muscle O2 transfer during exercise or whether or not there may be anaerobic production of lactate in certain regions of exercising muscle.