Faster adjustment of O2 delivery does not affect V(O2) on-kinetics in isolated in situ canine muscle.
The mechanism(s) limiting muscle O2 uptake (VO2) kinetics was investigated in isolated canine gastrocnemius muscles (n = 7) during transitions from rest to 3 min of electrically stimulated isometric tetanic contractions (200-ms trains, 50 Hz; 1 contraction/2 s; 60-70% of peak V(O2)). Two conditions were mainly compared: 1) spontaneous adjustment of blood flow (Q) [control, spontaneous Q (C Spont)]; and 2) pump-perfused Q, adjusted approximately 15 s before contractions at a constant level corresponding to the steady-state value during contractions in C Spont [faster adjustment of O2 delivery (Fast O2 Delivery)]. During Fast O2 Delivery, 1-2 ml/min of 10(-2) M adenosine were infused intra-arterially to prevent inordinate pressure increases with the elevated Q. The purpose of the study was to determine whether a faster adjustment of O2 delivery would affect V(O2) kinetics. Q was measured continuously; arterial (Ca(O2)) and popliteal venous (Cv(O2)) O2 contents were determined at rest and at 5- to 7-s intervals during contractions; O2 delivery was calculated as Q x Ca(O2), and V(O2) was calculated as Q x arteriovenous O2 content difference. Times to reach 63% of the difference between baseline and steady-state VO2 during contractions were 23.8 +/- 2.0 (SE) s in C Spont and 21.8 +/- 0.9 s in Fast O2 Delivery (not significant). In the present experimental model, elimination of any delay in O2 delivery during the rest-to-contraction transition did not affect muscle V(O2) kinetics, which suggests that this kinetics was mainly set by an intrinsic inertia of oxidative metabolism.
Grassi
B
B
Department of Medicine, University of California, San Diego, La Jolla, California 92093-0623, USA. grassi@itba.mi.cnr.it
Gladden
L B
LB
Samaja
M
M
Stary
C M
CM
Hogan
M C
MC
D000818:Animals; D001794:Blood Pressure; D002245:Carbon Dioxide / Q000097:blood; D004285:Dogs; D004558:Electric Stimulation; D005260:Female; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D018763:Muscle Fatigue; D018482:Muscle, Skeletal / Q000098:blood supply / Q000502:physiology*; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption / Q000502:physiology*; D010477:Perfusion; D012039:Regional Blood Flow; D014655:Vascular Resistance
D002245:Carbon Dioxide; D010100:Oxygen