Effect of [hemoglobin] on blood flow distribution and o2 transport
in maximally working skeletal muscle.
Kurdak, S. Sadi, Bruno Grassi, Peter D. Wagner, and Michael C. Hogan.
Division of Physiology, Department of Medicine, University of
California, San Diego, La Jolla, CA 92093-0623
APStracts 2:0279A, 1995.
We investigated whether the reduction in calculated muscle diffusion
capacity for O2 (DmO2) previously shown to occur with lowered [Hb]
perfusion of maximally working muscle is related to changes in the
blood flow distribution. If blood flow distribution is altered during
low [Hb] conditions, the reduction in the calculated DmO2 may in fact
be due to increasing heterogeneity and not to some other hemoglobin
-related factor. Color-stained (15 [mu]m-diameter) microspheres were
injected into the artery supplying maximally working, isolated in
situ dog gastrocnemius muscle (n=6) while being perfused (flow
controlled by pump-perfusion) with whole blood at three different
levels of [Hb] (14.1+/-0.5, 8.9+/-0.4, and 5.7+/-0.4 g/100 ml;
mean+/-SE) in a blocked order design. Muscle blood flow and arterial
PO2 were not changed as [Hb] was altered. Maximal O2 uptake (O2max;
11.8+/-1.3, 8.2+/-0.8, and 6.0+/-0.9 ml.100 g-1.min-1 for those [Hb]
values respectively) and the associated estimate of DmO2 (0.25+/
-0.03, 0.18+/-0.03, and 0.15+/-0.03 ml.100 g-1.min-1.Torr-1) declined
significantly (p<0.05) with [Hb]. However, the dispersion of the
blood flow distribution did not change significantly, and if anything
indicated less heterogeneity at lower [Hb] (coefficient of
variation=0.52+/-0.06, 0.46+/-0.05, and 0.43+/-0.03). These results
suggest that in maximally working canine muscle in situ, when O2
delivery is reduced by lowering [Hb] (at constant blood flow),
changes in blood flow distribution play no significant role in the
reduction of O2max and calculated DmO2. The apparent increase in the
resistance to O2 diffusion (i.e. reduction in the DmO2) during anemia
may therefore be a result of increased red blood cell spacing in the
capillary, slow chemical off-loading kinetics of O2 from Hb, or some
other effect that remains to be determined.
Received 12 September 1994; accepted in final form 21 June 1995.
APS Manuscript Number A954-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 11 July 1995.