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Faster adjustment of O2 delivery does not affect VO2 on-kinetics in isolated in situ canine muscle
Authors:Grassi  Bruno; Gladden  L Bruce; Samaja  Michele; Stary  Creed M; Hogan  Michael C
Abstract:The mechanism(s)limiting muscle O2 uptake(VO2) kinetics wasinvestigated in isolated canine gastrocnemius muscles(n = 7) during transitions from restto 3 min of electrically stimulated isometric tetanic contractions(200-ms trains, 50 Hz; 1 contraction/2 s; 60-70% of peakVO2). Two conditions weremainly compared: 1) spontaneousadjustment of blood flow (Q) control, spontaneous Q (C Spont)]; and2) pump-perfusedQ, adjusted ~15 s before contractions at aconstant level corresponding to the steady-state value duringcontractions in C Spont faster adjustment ofO2 delivery (FastO2 Delivery)]. During FastO2 Delivery, 1-2 ml/min of10-2 M adenosine wereinfused intra-arterially to prevent inordinate pressure increases withthe elevated Q. The purpose of the study was todetermine whether a faster adjustment ofO2 delivery would affectVO2 kinetics.Q was measured continuously; arterial(CaO2) and popliteal venous(CvO2)O2 contents were determined atrest and at 5- to 7-s intervals during contractions;O2 delivery was calculated asQ · CaO2,and VO2 was calculated asQ · arteriovenous O2 content difference. Times toreach 63% of the difference between baseline and steady-stateVO2 during contractions were23.8 ± 2.0 (SE) s in C Spont and 21.8 ± 0.9 s in FastO2 Delivery (not significant). Inthe present experimental model, elimination of any delay inO2 delivery during therest-to-contraction transition did not affect muscleVO2 kinetics, which suggeststhat this kinetics was mainly set by an intrinsic inertia of oxidativemetabolism.

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