MUSCLE BLOOD-FLOW AND DISTRIBUTION DETERMINE MAXIMAL VO2 OF CONTRACTING MUSCLE

During repetitive contractions, the VO2 of the dog gastrocnemius-plant aris muscle rose with the contraction frequency up to a maximal value and then decreased as contraction frequency was increased further. PVO 2 was constant over most of the contraction frequency range. Reducing perfusion pressure/blood flow reduced VO2max with a constant PVO2. Dur ing these maneuvers the diffusion conductance, DCO2 (VO2/PVO2), change d with VO2. Raising the perfusion pressure/flow with a pump increased VO2 with a small rise in PVO2 so that DCO2 also increased. Removing te nsion from the muscle between contractions elevated VO2 and DCO2 witho ut a change in perfusion pressure. Hypoxemia decreased VO2 with a decr ease in PVO2; DCO2 remained constant. A three-compartment mathematical model, based on microsphere measurements of regional flow, was used t o illustrate how regional flow variations may exist, and how they are poorly revealed in the mixed whole-muscle venous blood. The model show s VO2.g(-1) strongly related to flow. As VO2.g(-1) increased as Q.g(-1 ) increased, extraction decreased, and DCO2 increased.