AJP - Regulatory, Integrative and Comparative Physiology, Vol 245, Issue 4 534-R540, Copyright © 1983 by American Physiological Society
Transient solutions of equations for countercurrent capillary exchange
L. D. Homer and P. K. Weathersby
A model for passive countercurrent capillary exchange is presented, and
solutions for transient responses are obtained. The model is applied to an
analysis of hydrogen gas exchange in the renal medulla. Estimates of
medullary flow per gram tissue are in reasonable agreement with estimates
obtained with vascular tracers and similar to the values for whole kidney.
Semilog plots of tissue washout curves appear nearly linear but will
overestimate flow if the countercurrent process is inefficient and will
underestimate flow if the countercurrent exchange is efficient. Analysis of
the countercurrent process also provides some insights into the importance
of tracer exchange between capillaries in vascular beds not arranged in
orderly countercurrent networks. Capillaries in other vascular beds that
are close enough together to permit considerable exchange of inert gas
tracers may simulate countercurrent effects if some of the adjacent
capillaries are in countercurrent or staggered cocurrent arrangements.
