(V) over dotO2 on-kinetics in isolated canine muscle in situ during slowed convective O2 delivery

Goodwin ML, Hernandez A, Lai N, Cabrera ME, Gladden LB. VO2 on-kinetics in isolated canine muscle in situ during slowed convective O-2 delivery. J Appl Physiol 112: 9-19, 2012. First published October 6, 2011; doi:10.1152/japplphysiol.01480.2010.-The purpose of this study was to examine O-2 uptake (V) over dotO(2)) on-kinetics when the spontaneous blood flow (and therefore O2 delivery) on-response was slowed by 25 and 50 s. The isolated gastrocnemius muscle complex (GS) in situ was studied in six anesthetized dogs during transitions from rest to a submaximal metabolic rate (approximate to 50-70% of peak (V) over dotO(2)). Four trials were performed: 1) a pretrial in which resting and steady-state blood flows were established, 2) a control trial in which the blood flow on-kinetics mean response time (MRT) was set at 20 s (CT20), 3) an experimental trial in which the blood flow on-kinetics MRT was set at 45 s (EX45), and 4) an experimental trial in which the blood flow on-kinetics MRT was set at 70 s (EX70). Slowing O-2 delivery via slowing blood flow on-kinetics resulted in a linear slowing of the (V) over dotO(2) on-kinetics response (R = 0.96). Average MRT values for CT20, EX45, and EX70 (V) over dotO(2) on-kinetics were (means +/- SD) 17 +/- 2, 23 +/- 4, and 26 +/- 3 s, respectively (P < 0.05 among all). During these transitions, slowing blood flow resulted in greater muscle deoxygenation (as indicated by near-infrared spectroscopy), suggesting that lower intracellular PO2 values were reached. In this oxidative muscle, (V) over dotO(2) and O-2 delivery were closely matched during the transition period from rest to steady-state contractions. In conjunction with our previous work showing that speeding O-2 delivery did not alter (V) over dotO(2) on-kinetics under similar conditions, it appears that spontaneously perfused skeletal muscle operates at the nexus of sufficient and insufficient O-2 delivery in the transition from rest to contractions.