Vj. Abernathy et al., NONINVASIVE MEASUREMENTS OF ALBUMIN FLUX INTO LUNG INTERSTITIUM WITH INCREASED MICROVASCULAR PRESSURE, American journal of physiology. Heart and circulatory physiology, 38(1), 1995, pp. 288-296
The purpose of this study was to determine the effect of increasing le
ft atrial pressure on noninvasive measurements of radiolabeled albumin
normalized slope index (NSI). Using portable gamma scintillation dete
ctors, we monitored radioactivities of I-131-labeled albumin and Cr-51
-labeled red blood cells in the blood and over the lung of six anesthe
tized sheep before and 2 h after a 9- to 14-Torr increase in left atri
al pressure. Measurements of NSI for I-131-albumin decreased > 50% aft
er a step increase in left atrial pressure. We interpreted the data us
ing a model that has been used to successfully describe unsteady-state
lymph flow and protein concentrations after vascular pressure increas
es in sheep. Model predictions strongly suggest that the reduction in
NSI is due to rapid fluid and solute removal from the interstitium via
the lymphatics. The theoretical model was able to predict external sc
an data and lung lymph protein concentrations only when a change in ly
mphatic conductance (L(I)) or initial lymphatic pressure (P-o) was imp
osed at the time of increased pressure. On average, model-predicted in
creases in L(I) were sevenfold, whereas predicted decreases in P-o wer
e four- to fivefold. Imposed changes in L(I) and P-o opposed increases
in interstitial fluid volume after increased pressure. This was consi
stent with normal-to-low postmortem measurements of bloodless wet-to-d
ry lung weight ratios. In summary, these results indicate that changes
in the rate of fluid removal from the interstitium can significantly
alter NSI, and in this case, NSI does not reflect pulmonary microvascu
lar permeability. In sheep, increases in the lymphatics' ability to re
move interstitial fluid may occur with relatively small increases in m
icrovascular pressure.