Oxygen consumption and mechanical performance of dog gastrocnemius muscle with artificially increased blood flow

Summary In dogs anesthetized with morphine, chloralose and urethane O₂ consumption, lactic acid production and mechanical performance of the gastrocnemius muscle were measured during supramaximal stimulation to rhythmic isotonic tetanic contractions of varied force and duration. The muscle was artificially perfused with arterial blood at flow rates higher by a factor of 2 to 4 than those obtained with intact blood supply and normal arterial blood pressure.It was attempted to subdivide the total net O₂ consumption into two components attributable to shortening (dynamic work) and to maintenance of contraction (static work), respectively. The O₂ consumption attributable to maintenance of contraction turned out to be nearly independent of the load (2 to 8 kg), averaging 260 ml/kg muscle and minute of stimulation With 8 kg load the O₂ consumed for one shortening was equal to the O₂ consumed for maintenance of a contraction during 0.40 seconds; with 2 kg load the corresponding time was 0.24 seconds.Comparison with measurements performed with normal blood supply showed that for the same load and stimulation parameters the mechanical performance was about equal whereas the O₂ uptake was considerably higher in the overperfused muscle. Lactic acid formation rate was small in all cases and energetically rather insignificant. Possible mechanisms underlying the observed dependency of O₂ uptake upon blood flow are discussed.