AJP - Heart and Circulatory Physiology, Vol 256, Issue 2 375-H382, Copyright © 1989 by American Physiological Society
Anatomical determinants of O2 flux density at coronary capillaries
C. R. Honig, J. L. Frierson and T. E. Gayeski
Department of Physiology, School of Medicine and Dentistry, University of Rochester, New York 14642.
Calculations indicate that the PO2 in plasma falls to zero approximately 3
microns from an erythrocyte at O2 consumption (VO2) characteristic of
myocardium (Federspiel, W.A., and A. Popel, Microvasc. Res. 32: 164-189,
1986). We measured distances between individual red cells along capillaries
in rat hearts rapidly frozen in situ. Cell spacing varied widely even in
branches of the same capillary. Plasma gaps between red cells were divided
into two populations, those less than 5 microns and those greater than 5
microns. Mean gap lengths were 2.1 and 16.5 microns, respectively. Although
the number of long plasma gaps was underestimated, gaps greater than 5
microns accounted for one-third of observed capillary length. Frozen
muscles were also viewed in cross section. Because the depth of penetration
of light was approximately equal to 3 microns, counts of red
cell-containing capillary profiles in cross section depend on cell spacing
as well as on number of cell-containing flow paths. Counts varied markedly
with arterial O2 partial pressure, indicating that the capillary surface
area functional for O2 transport changes in response to stress. The
adaptive role of change in O2 flux density (flux per area) is discussed in
light of new knowledge of tissue O2 gradients.
