Non-invasive measurements of radiolabeled albumin flux into the
pulmonary interstitium before and after increased microvascular
pressure.
Abernathy, Valerie J., N. Adrienne Pou, Teresa L. Wilson, Robert J.
Roselli.
Department of Biomedical Engineering, School of Engineering, Center
for Lung Research, School of Medicine, Vanderbilt University,
Nashville, TN 37235
APStracts 2:0018H, 1995.
The purpose of this study was to determine the effect of increasing
left atrial pressure on non-invasive measurements of radiolabeled
albumin normalized slope index (NSI). We monitored radioactivities of
131I albumin and 51Cr red blood cells (RBCs) in the blood and over
the lung of 6 anesthetized sheep before and 2 hours after a 9-14 Torr
increase in left atrial pressure using portable gamma scintillation
detectors. Measurements of normalized slope index (NSI) for 131I
albumin decreased more than 50% following a step increase in left
atrial pressure. We interpreted the data using a model which has
previously been used to successfully describe unsteady state lymph
flow and protein concentrations following vascular pressure increases
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 scan data and lung lymph protein concentrations only when a
change in either lymphatic conductance (LI) or initial lymphatic
pressure (PO) was imposed at the time of increased pressure. On
average model-predicted increases in LI were 7 fold while predicted
decreases in PO were 4 to 5 fold. Imposed changes in LI and PO
opposed increases in interstitial fluid volume following increased
pressure. This was consistent with normal to low postmortem
measurements of bloodless wet to dry 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 microvascular permeability. In sheep,
increases in the lymphatics ability to remove interstitial fluid may
occur with relatively small increases in microvascular pressure.
Received 27 September 1994; accepted in final form 27 January
1995.
APS Manuscript Number H869-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 24 February 1995.