Journal of Applied Physiology, Vol 56, Issue 1 187-195, Copyright © 1984 by American Physiological Society
High-frequency ventilation in lung edema: effects on gas exchange and perfusion
P. H. Breen, J. Ali and L. D. Wood
In six open-chest dogs, unilobar pulmonary edema was induced by injection
of oleic acid into a lower lobe pulmonary arterial branch. Two hours later,
intermittent positive-pressure ventilation (IPPV) and high-frequency
oscillatory ventilation (HFOV) at matched mean alveolar pressures (MAP)
were compared at 30-min intervals. The edematous lobar venous admixture
(Qva/QT) increased by 0.14 (P less than 0.1) and its relative perfusion
(QL/QT) decreased by 0.03. (P less than 0.1) during HFOV compared with
IPPV. In another six dogs the MAP was increased by 1.5 cmH2O during HFOV;
now the edematous lobar Qva/QT decreased by 0.15 (P less than 0.03) and
QL/QT increased by 0.03 (P less than 0.03) during HFOV compared with IPPV.
Greater MAP during HFOV also improved the edematous lobar ventilation
(lobar venous PCO2) during HFOV compared with IPPV. Conceivably, the
increase in MAP inflated collapsed, flooded regions, and thereby increased
their O2 transfer, perfusion, and ventilation. Whole-lung Qva/QT was
similar during IPPV and HFOV in both groups because of the opposing effects
of lobar Qva/QT and QL/QT. We conclude that HFOV supports
cardiovascular-respiratory function in open-chest unilobar pulmonary edema
compared with IPPV at similar MAP; gas exchange and perfusion of edematous
units may be sensitive to small changes in MAP, and we detected no
intrinsic effects of HFOV on these variables. We speculate that similar
beneficial effects in diffuse pulmonary edema may be effected by small
variations in MAP during HFOV without the barotrauma side effects sometimes
observed when MAP is increased during IPPV.
