Regional expansion of oleic acid-injured lungs

It has been suggested that dependent regions of an injured lung are collaps ed and subject to cyclic reopening and collapse during mechanical ventilati on. To test this hypothesis, we measured both temporal and spatial heteroge neity of lobar expansion in oleic acid (OA)-injured dogs. Regional volumes were measured in nine dogs (seven supine and two prone) during closed loop sinusoidal oscillations of the lungs before and after OA injury using the p arenchymal marker technique. In contrast to computer tomography, the parenc hymal marker technique provides absolute measures of regional tissue dimens ions as opposed to relative measures of regional air to liquid content. The experiments generated three major findings: (1) OA injury did not lead to the collapse of dependent lung units at FRC, (2) OA injury did not steepen the vertical gradient in regional lung volumes at FRC, and (3) during sinus oidal oscillation of the OA-injured lungs from FRC, dependent regions did n ot undergo cyclic reopening and collapse. On the basis of these results, we propose an alternative mechanism for the topographic variability in region al impedances and lung expansion after injury, namely liquid and foam in co nducting airways.