Journal of Applied Physiology, Vol 74, Issue 5 2112-2120, Copyright © 1993 by American Physiological Society
Effect of airway and left atrial pressures on microvascular and interstitial pressures in adult lungs
C. D. Fike and M. R. Kaplowitz
Department of Pediatrics, University of Utah Medical Center, Salt Lake City 84132.
The purpose of this study was to determine the effect of lung inflation and
left atrial pressure on the hydrostatic pressure gradient for fluid flux
across 20- to 80-microns-diam arterioles and venules in isolated perfused
lungs of adult rabbits. We used the micropuncture technique and measured
microvascular or interstitial pressures at constant airway pressures of 5
and 15 cmH2O with left atrial pressure adjusted above (zone 3 conditions)
or below (zone 2 conditions) airway pressure. Only in lungs inflated to the
higher airway pressure did a reduction in left atrial pressure below airway
pressure result in concomitant reductions in venular pressure. This
suggests that the site of flow limitation in zone 2 shifted from venules
> 80 microns diam toward vessels <20 microns diam with inflation from
5 to 15 cmH2O. With the lungs under zone 3 conditions, both transarteriolar
and transvenular gradients (microvascular-interstitial pressures) were
greater at the higher compared with the lower airway pressure. In contrast,
transarteriolar and transvenular gradients changed in opposite directions
when compared at the two inflation pressures under zone 2 conditions.
Counteracting changes in transmicrovascular gradients make it difficult to
predict the effect on fluid filtration from lung inflation under zone 2
conditions. When zone 3 conditions are maintained during inflation, the
tendency for edema formation should increase.
