Peripheral O2 diffusion does not affect V(O2)on-kinetics in isolated insitu canine muscle.
To test the hypothesis that muscle O2 uptake (V(O2)) on-kinetics is limited, at least in part, by peripheral O2 diffusion, we determined the V(O2) 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-O2 dissociation 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% peak V(O2)). 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 x Adenosine was infused intra-arterially to prevent inordinate pressure increases with the elevated Q x Q was measured continuously, arterial and popliteal venous O2 concentrations were determined at rest and at 5- to 7-s intervals during contractions, and V(O2) was calculated as Q x arteriovenous O2 content difference. PO2 at 50% HbO2 saturation (P50) was calculated. Mean capillary PO2 (Pc(O2)) 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, Pc(O2) 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-state V(O2) 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 increased PcO2 at constant O2 delivery) during the rest-to-contraction (60-70% of peak V(O2)) transition did not affect muscle V(O2) on- kinetics.
Department of Medicine, University of California, San Diego, La Jolla, California 92093-0623, USA. grassi@itba.mi.cnr.it
B
B
Grassi
L B
LB
Gladden
C M
CM
Stary
P D
PD
Wagner
M C
MC
Hogan
D000818:Animals; D001639:Bicarbonates / Q000097:blood; D001794:Blood Pressure; D002245:Carbon Dioxide / Q000097:blood; D004058:Diffusion; D004285:Dogs; D005260:Female; D018496:Hyperoxia; D007700:Kinetics; D008297:Male; D018763:Muscle Fatigue; D018482:Muscle, Skeletal / Q000098:blood supply / Q000502:physiology*; D010100:Oxygen / Q000097:blood / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D010108:Oxyhemoglobins / Q000378:metabolism*; D010313:Partial Pressure; D014655:Vascular Resistance
D001639:Bicarbonates; D010108:Oxyhemoglobins; D002245:Carbon Dioxide; D010100:Oxygen