Journal of Applied Physiology, Vol 62, Issue 2 781-784, Copyright © 1987 by American Physiological Society
Micropuncture measurement of alveolar liquid pressure in excised dog lung lobes
J. U. Raj, R. L. Conhaim and J. Bhattacharya
We have investigated the mechanism of alveolar liquid filling in pulmonary
edema. We excised, degassed, and intrabronchially filled 14 dog lung lobes
from nine dogs with 75, 150, 225, or 350 ml of 5% albumin solution, and
then air inflated the lobes to a constant airway pressure of 25 cmH2O. By
use of micropipettes, we punctured subpleural alveoli to measure alveolar
liquid pressure by the servo-null technique. Alveolar liquid pressure was
constant in all lobes despite differences in lobe liquid volume and
averaged 10.6 +/- 1.3 cmH2O. Thus, in all lobes a constant pressure drop of
14.4 cmH2O existed from airway to alveolar liquid across the air-liquid
interface. We attribute this finding, on the basis of the Laplace equation,
to an air-liquid interface of constant radius in all the lobes. In fact, we
calculated from the Laplace equation an air-liquid interface radius which
equalled morphological estimates of alveolar radius. We conclude that in
the steady state, alveoli that contained liquid have a constant radius of
curvature of the air-liquid interface possibly because they are always
completely liquid filled.
