Journal of Applied Physiology, Vol 66, Issue 4 1789-1799, Copyright © 1989 by American Physiological Society
Pressure-flow behavior of a bronchopleural fistula during mechanical ventilation with positive pressure
J. J. Perez Fontan and A. O. Ray
Department of Pediatrics, Yale University School of Medicine, New Haven, Connecticut 06510.
We examined the mechanical behavior of a bronchopleural fistula created by
sectioning a small subpleural bronchus in seven anesthetized lambs. The
pressure across the fistula was measured as the difference between the
pressure recorded by a retrograde bronchial catheter inserted in the
vicinity of the fistula and the outflow pressure at the fistula exit. The
effective resistance of the fistula (Rf) was computed by dividing this
pressure difference by the gas flow through the fistula measured at the
outlet of an intrapleural tube adjacent to the fistula. Rf increased by 114
+/- 25% (SE) when we inflated the lungs in a stepwise manner from a
tracheal pressure of 2-20 cmH2O. Rf also increased when inflation pressure
varied continuously; this increase, however, was less evident when we
decreased the inflation time from 1.0 to 0.2 s. The relationship between Rf
and lung volume was similar during the stepwise inflations and deflations
but showed marked hysteresis during the continuous inflation-deflation
maneuvers, when Rf was greater during deflation than inflation. Our results
suggest that the fistula behaves as a compliant pathway whose relevant
transmural pressure is the transmural pressure at or near the fistula's
exit. We attribute the increase in Rf during inflation to decreases in
transmural pressure caused by convective and dissipative losses inside the
fistula and by the stress applied by the chest wall on the outer surface of
the fistula.
