Muscle blood flow and distribution determine maximal VO2 of contracting muscle.
During repetitive contractions, the VO2 of the dog gastrocnemius-plantaris muscle rose with the contraction frequency up to a maximal value and then decreased as contraction frequency was increased further. PVO2 was constant over most of the contraction frequency range. Reducing perfusion pressure/blood flow reduced VO2max with a constant PVO2. During these maneuvers the diffusion conductance, DCO2 (VO2/PVO2), changed with VO2. Raising the perfusion pressure/flow with a pump increased VO2 with a small rise in PVO2 so that DCO2 also increased. Removing tension from the muscle between contractions elevated VO2 and DCO2 without a change in perfusion pressure. Hypoxemia decreased VO2 with a decrease in PVO2; DCO2 remained constant. A three-compartment mathematical model, based on microsphere measurements of regional flow, was used to illustrate how regional flow variations may exist, and how they are poorly revealed in the mixed whole-muscle venous blood. The model shows VO2.g-1 strongly related to flow. As VO2.g-1 increased as Q.g-1 increased, extraction decreased, and DCO2 increased.
Stainsby
W N
WN
Department of Physiology, College of Medicine, University of Florida, Gainesville 32610.
Brechue
W F
WF
Ameredes
B T
BT
D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D001808:Blood Vessels / Q000502:physiology; D004058:Diffusion; D004285:Dogs; D006454:Hemoglobins / Q000378:metabolism; D000860:Hypoxia / Q000503:physiopathology; D007511:Ischemia / Q000503:physiopathology; D008433:Mathematics; D008863:Microspheres; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology*; D009126:Muscle Relaxation / Q000502:physiology; D018482:Muscle, Skeletal / Q000098:blood supply* / Q000378:metabolism*; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption / Q000502:physiology*; D012039:Regional Blood Flow / Q000502:physiology
D006454:Hemoglobins; D010100:Oxygen