Faster adjustment of O2 delivery does not affect VO2 on-kinetics in isolated in situ canine muscle |
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Authors: | Grassi Bruno; Gladden L Bruce; Samaja Michele; Stary Creed M; Hogan Michael C |
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Abstract: | The mechanism(s)limiting muscle O2 uptake( O2) 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 peak O2). Two conditions weremainly compared: 1) spontaneousadjustment of blood flow ( ) control, spontaneous (C Spont)]; and2) pump-perfused , 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 . The purpose of the study was todetermine whether a faster adjustment ofO2 delivery would affect O2 kinetics. 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 as · CaO2,and O2 was calculated as · arteriovenous O2 content difference. Times toreach 63% of the difference between baseline and steady-state O2 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 muscle O2 kinetics, which suggeststhat this kinetics was mainly set by an intrinsic inertia of oxidativemetabolism. |
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