Affiliation:
1. Department of Medicine, University of California, San Diego, La Jolla, California 92093-0623; Istituto di Tecnologie Biomediche Avanzate, Consiglio Nazionale delle Ricerche, I-20090 Segrate (MI), Italy; and Department of Health and Human Performance, Auburn University, Auburn, Alabama 36849-5323
Abstract
To test the hypothesis that muscle O2 uptake (V˙o 2) on-kinetics is limited, at least in part, by peripheral O2 diffusion, we determined theV˙o 2 on-kinetics in 1) normoxia (Control); 2) hyperoxic gas breathing (Hyperoxia); and 3) hyperoxia and the administration of a drug (RSR-13, Allos Therapeutics), which right-shifts the Hb-O2dissociation curve (Hyperoxia+RSR-13). The study was conducted in isolated canine gastrocnemius muscles ( n = 5) during transitions from rest to 3 min of electrically stimulated isometric tetanic contractions (200-ms trains, 50 Hz; 1 contraction/2 s; 60–70% peakV˙o 2). In all conditions, before and during contractions, muscle was pump perfused with constantly elevated blood flow (Q˙), at a level measured at steady state during contractions in preliminary trials with spontaneous Q˙. Adenosine was infused intra-arterially to prevent inordinate pressure increases with the elevated Q˙. Q˙ was measured continuously, arterial and popliteal venous O2 concentrations were determined at rest and at 5- to 7-s intervals during contractions, andV˙o 2 was calculated asQ˙ ⋅ arteriovenous O2 content difference.[Formula: see text] at 50% Hbo 2saturation (P50) was calculated. Mean capillary [Formula: see text](P [Formula: see text]) was estimated by numerical integration. P50 was higher in Hyperoxia+RSR-13 [40 ± 1 (SE) Torr] than in Control and in Hyperoxia (31 ± 1 Torr). After 15 s of contractions,P [Formula: see text]was higher in Hyperoxia (97 ± 9 Torr) vs. Control (53 ± 3 Torr) and in Hyperoxia+RSR-13 (197 ± 39 Torr) vs. Hyperoxia. The time to reach 63% of the difference between baseline and steady-stateV˙o 2 during contractions was 24.7 ± 2.7 s in Control, 26.3 ± 0.8 s in Hyperoxia, and 24.7 ± 1.1 s in Hyperoxia+RSR-13 (not significant). Enhancement of peripheral O2 diffusion (obtained by increasedP [Formula: see text]at constant O2 delivery) during the rest-to-contraction (60–70% of peakV˙o 2) transition did not affect muscle V˙o 2on-kinetics.
Publisher
American Physiological Society
Subject
Physiology (medical),Physiology
Cited by
140 articles.
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