Journal of Applied Physiology, Vol 69, Issue 3 1063-1072, Copyright © 1990 by American Physiological Society
Effect of airway and left atrial pressures on microcirculation of newborn lungs
C. D. Fike and S. J. Lai-Fook
Department of Pediatrics, Baylor College of Medicine, Houston, 77030.
To determine the effect of lung inflation and left atrial pressure on the
hydrostatic pressure gradient for fluid flux across 20- to 60-microns-diam
venules, we isolated and perfused the lungs from newborn rabbits, 7-14 days
old. We used the micropuncture technique to measure venular pressures in
some lungs and perivenular interstitial pressures in other lungs. For all
lungs, we first measured venular or interstitial pressures at a constant
airway pressure of 5 or 15 cmH2O with left atrial pressure greater than
airway pressure (zone 3). For most lungs, we continued to measure venular
or interstitial pressures as we lowered left atrial pressure below airway
pressure (zone 2). Next, we inflated some lungs to whichever airway
pressure had not been previously used, either 5 or 15 cmH2O, and repeated
venular or interstitial pressures under one or both zonal conditions. We
found that at constant blood flow a reduction of left atrial pressure below
airway pressure always resulted in a reduction in venular pressure at both
5 and 15 cmH2O airway pressures. This suggests that the site of flow
limitation in zone 2 was located upstream of venules. When left atrial
pressure was constant relative to airway pressure, the transvascular
gradient (venular-interstitial pressures) was greater at 15 cmH2O airway
pressure than at 5 cmH2O airway pressure. These findings suggest that in
newborn lungs edema formation would increase at high airway pressures only
if left atrial pressure is elevated above airway pressure to maintain zone
3 conditions.
