Role of convective O2 delivery in determiningV˙o 2 on-kinetics in canine muscle contracting at peak V˙o 2

Publisher Website
Google Scholar
Abstract
A previous study (Grassi B, Gladden LB, Samaja M, Stary CM, and Hogan MC, J Appl Physiol 85: 1394–1403, 1998) showed that convective O2 delivery to muscle did not limit O2 uptake (V˙o 2) on-kinetics during transitions from rest to contractions at ∼60% of peakV˙o 2. The present study aimed to determine whether this finding is also true for transitions involving contractions of higher metabolic intensities.V˙o 2 on-kinetics were determined in isolated canine gastrocnemius muscles in situ ( n = 5) during transitions from rest to 4 min of electrically stimulated isometric tetanic contractions corresponding to the muscle peakV˙o 2. Two conditions were compared: 1) spontaneous adjustment of muscle blood flow (Q˙) (Control) and 2) pump-perfused Q˙, adjusted ∼15–30 s before contractions at a constant level corresponding to the steady-state value during contractions in Control (Fast O2 Delivery). In Fast O2 Delivery, adenosine was infused intra-arterially. Q˙ was measured continuously in the popliteal vein; arterial and popliteal venous O2 contents were measured at rest and at 5- to 7-s intervals during the transition. Muscle V˙o 2 was determined as Q˙times the arteriovenous blood O2 content difference. The time to reach 63% of the V˙o 2 difference between resting baseline and steady-state values during contractions was 24.9 ± 1.6 (SE) s in Control and 18.5 ± 1.8 s in Fast O2 Delivery ( P < 0.05). FasterV˙o 2 on-kinetics in Fast O2Delivery was associated with an ∼30% reduction in the calculated O2 deficit and with less muscle fatigue. During transitions involving contractions at peak V˙o 2, convective O2 delivery to muscle, together with an inertia of oxidative metabolism, contributes in determining theV˙o 2 on-kinetics.