Journal of Applied Physiology, Vol 64, Issue 4 1561-1566, Copyright © 1988 by American Physiological Society
Noninvasive measurement of regional interstitial lung volume in sheep
A. B. Gorin
Department of Internal Medicine, Houston Veterans Administration Medical Center, Baylor College of Medicine, Texas 77211.
The noninvasive external radioflux detection method (ERD) measures net
transvascular flux of tracer protein into and out of the lung extravascular
compartment (EV) and time to zero flux between compartments. With this
information we can now estimate regional interstitial volume in the field
of the external probe (VIs). Dividing the mass of EV tracer by VIs, we
obtain interstitial concentration ([Is]). Directly sampling plasma
concentration of the tracer, we can construct plasma-interstitium
equilibration curves that are analogous to plasma-lymph equilibration
curves without invasive surgery. We completed 46 ERD studies in 21 sheep
with chronic lung lymph fistulas. Sheep were studied under baseline
conditions (n = 30) and after elevating left atrial pressure by mitral
obstruction (n = 7), or intravascular volume infusion (n = 8), and
increasing lung vascular permeability (n = 1). In each study we compared
the slope of the regression through plasma-lymph concentration of tracer
protein over time ([P]-[L], measured directly) with that through values of
plasma-interstitial concentration ([P]-[Is], assessed noninvasively), an
index of vascular permeability. For this correlation, r = 0.94, and the
regression line approximates identity. Mean [Is] appears to approximate [L]
in sheep.
