AJP - Heart and Circulatory Physiology, Vol 248, Issue 4 577-H586, Copyright © 1985 by American Physiological Society
Statistical constraints on microvascular measurements using fluorescent erythrocytes
I. H. Sarelius and S. M. McKinlay
We show that two separate estimators of microvessel hematocrit (H) using
the same fluorescent cell technique are not equally precise. The precision
of H (indicated by the coefficient of variation, CV) depends on in vivo
labeled cell counts (m), the labeled fraction (p), and for time-averaged H
estimates, the mean cell velocity (v). Thus, for length-dependent estimates
of H, CV2(HL) = 1/E(m) + CV2(p) and for time-averaged H estimates, CV2(Ht)
= 1/E(m) + CV2(p) + CV2(v). Because CV(p) can be made small arbitrarily and
independently, the precision of H is principally dependent on the expected
value of m. Practical sampling constraints and minimum sampling intervals
are identified and used to define strategies to minimize CV(H). We show
that Ht is preferable to HL because it is more precise and the useful in
vivo sampling range of m and p is more flexible. In addition, Ht allows
simultaneous determination of cell flux and mean cell velocity.
