EFFECT OF INCREASED DURATION OF HIGH PERFUSION-PRESSURE ON STRESS FAILURE OF PULMONARY CAPILLARIES

have previously shown that raising the capillary transmural pressure ( Ptm) in rabbit lung causes disruption of the capillary endothelium, al veolar epithelium, or sometimes all layers of the wall. In those studi es the lungs were perfused with autologous blood (1 min), then saline/ dextran (3 min), followed by glutaraldehyde fixative (10 min), all at the same pressure. The present study was designed to determine whethe r increasing the time of exposure of the capillaries to the increased pressure altered the frequency of stress failure. The procedure was id entical to that of the previous study except that the duration of the blood perfusion was extended from 1 to 10 and 100 min. We chose a Ptm of 32.5 cm H2O because our previous studies showed that this caused on ly a few disruptions per millimeter endothelial and epithelial boundar y length (0.7 +/- 0.4 and 0.9 +/- 0.6 (SE), respectively). Ten New Zea land white rabbit lungs were perfused with autologous blood plus homol ogous blood from additional rabbits for 10 and 100 min. After 100 min of blood perfusion the number of disruptions per millimeter endothelia l and epithelial boundary length (0.66 +/- 0.4 and 0.52 +/- 0.33 (SE), respectively) was not significantly different from the earlier study. Thus, increasing the duration of the increased Ptm during blood perfu sion by 100-fold did not alter the incidence of stress failure. These results indicated that any viscoelastic behavior resulting in further strain and ultimately failure of the capillary walls is insignificant over a wide range of exposure times to increased pressure under the co nditions of this study. (C) 1995 Academic Press, Inc.