Interaction of blood flow and oxygen delivery affects peak VO2 and fatigue in canine muscle in situ

This investigation was designed to examine the interactive effects of blood flow (Q(over dot)) and oxygen delivery (Q(over dot)O-2) on peak oxygen consumption (V(over dot)O-2peak) and fatigue in the gastrocnemius-plantaris dog muscle in situ. Arterial oxygen content (CaO2) was manipulated by varying the fraction of inspired O-2 to create a high- and a low-Q(over dot)O-2 treatment at each of three levels of Q(over dot) (congruent to800, 1100 and 1500 ml(.)kg(-1.)min(-1)). Isometric contraction was achieved by stimulation with one tetanic contraction per second (260 ms at 70 Hz) at supramaximal voltage for 10 min to achieve V(over dot)O-2peak under each condition. Arterial and venous blood were sampled, and Q(over dot) and tension development (T-D) were measured at 1, 5 and 10 min into the contractions. Fatigue was calculated as the percentage (%) change in T-D from min 1 to min 10. While V(over dot)O-2peak was highly correlated to Q(over dot)O-2 (R = 0.97) in both the moderate- and high-Q(over dot) conditions, both low-Q(over dot) conditions had a significantly (P < 0.05) higher V(over dot)O-2peak than predicted by the Q(over dot)O-2-V(over dot)O-2 relationship. In addition, V(over dot)O-2peak was significantly greater in the low-Q(over dot) versus the high-Q(over dot) condition. Fatigue (% decrease in T-D) was significantly different between the two low-Q(over dot) conditions [Low-Q(over dot)O-2 = 38.4 (6.9), Norm Q(over dot)O-2 = 27.9 (1.8)] and the two moderate-Q(over dot) conditions [low-Q(over dot)O-2 = 31.1 (7.3) high Q(over dot)O-2 = 20.9 (4.1)] but not between the two high-Q(over dot) conditions [normal-Q(over dot)O-2 = 10.4 (6.9); high-Q(over dot)O-2 = 11.9 (4.5)]. In the two conditions of equal Q(over dot)O-2, fatigue was significantly less in the high-Q(over dot) condition (10.4%) compared to the low (27.9%). Thus. it seems that there is a unique interaction between and Q(over dot) and Q(over dot)O-2 which determine the V(over dot)O-2peak and rate of fatigue in contracting muscle.