Journal of Applied Physiology, Vol 55, Issue 4 1154-1159, Copyright © 1983 by American Physiological Society
Pulmonary hemodynamics and gas exchange properties during progressive edema
Y. K. Ngeow and W. Mitzner
In this investigation we have studied the effect of increments of pulmonary
edema on pulmonary hemodynamics, and physiological and hemodynamic shunt in
an isolated lung preparation. Hemodynamic shunt was defined by the slope of
the relationship between pulmonary arterial and airway pressures; when the
slope decreases, there is a greater degree of shunt. Cardiovascular changes
were analyzed using a Starling resistor model of the pulmonary circulation
where the effective downstream pressure to flow as seen from the pulmonary
artery exceeds the pulmonary venous outflow pressure. This effective
downstream pressure is referred to as the critical pressure (Pc), and at
low lung inflation the locus of this critical pressure is in extra-alveolar
vessels. With 3-4 h of progressive edema to an average of 185% initial lobe
weight we found a progressive rise in pulmonary arterial pressure (Ppa)
from 12.1 to 21.5 cmH2O. About one-third of this increase in Ppa resulted
from an increased Pc and the remainder resulted from an increased
resistance upstream from the locus of Pc. These results are consistent with
the hypothesis that the interstitial accumulation of fluid creates enough
of an increase in interstitial pressure to compress extra-alveolar vessels.
There was no significant correlation between the amount of edema and the
measured physiologic shunt, but the hemodynamic shunt showed a highly
significant correlation. The hemodynamic shunt theoretically measures the
extent of obstructed airways and may be a useful index of the degree of
pulmonary edema.
