Journal of Applied Physiology, Vol 55, Issue 2 453-461, Copyright © 1983 by American Physiological Society
Effect of a hydrostatic pleural pressure gradient on mechanical behavior of lung lobes
B. G. Murphy, F. Plante and L. A. Engel
Using 133Xe, the vertical distribution of regional volume (Vr) was measured
in three regions of excised canine lobes both in air and when completely
submerged in saline at 40, 60, 70, and 80% lobar vital capacity (VC). The
estimated pleural pressure gradient, derived from values of Vr, distance
between regions, and the lobar pressure-volume (PV) curve, underestimated
the true gradient by 45%. Conversely, the gradient of Vr was substantially
less than predicted. From the mean depth of each region below the
waterline, pleural, and hence transpulmonary, pressure (PL) was computed.
The values of Vr-PL for each region at 40, 60, and 80% lung volume (VL)
were related to the lobar PV curve. Slopes of lines joining initial VL-PL
points on the lobar PV curve to corresponding Vr-PL points in submerged
lobes represent an effective regional compliance of a lobe undergoing
deformation. With one exception this was less than the corresponding
homogeneous compliance, indicating a stiffening of the lobe during
deformation. Slopes of lines joining Vr-PL points of each region at the
three lobar volumes represent effective regional compliance of a deformed
lobe undergoing volume change. This was not significantly different from
the homogeneous compliance. However, effective compliance can only be an
approximate indicator of the forces required for a given volume change due
to the inadequacy of PL to represent the unequal stress components induced
by lobe deformation.
