Journal of Applied Physiology, Vol 65, Issue 5 2075-2079, Copyright © 1988 by American Physiological Society
Multiple gas washout during jet ventilation
G. G. Berdine, J. L. Lehr and P. J. Strollo
Department of Medicine, University of Texas Health Sciences Center, Audie L. Murphy Memorial Veterans Hospital, San Antonio.
Simultaneous washouts of He, N2, and SF6 were monitored during jet
ventilation with tidal volumes of 50-200 ml and rates of 1-2 Hz. Gas
concentrations were measured from the trachea and from a lower lobe
bronchus in six baboons by mass spectrometry. Washouts using large tidal
volumes approximated single exponential decays with the relative
exponential rates of decay being He fastest, SF4 slowest, and N2
intermediate. Washouts using smaller tidal volumes demonstrated a two-phase
exponential decay pattern. During the fast phase, the relative exponential
rates of decay were He slowest, SF6 fastest, and N2 intermediate, the
reverse order seen during large-volume washouts. During the slow phase, the
relative exponential rates of decay were He fastest, SF4 slowest, and N2
intermediate, the same order seen during large-volume washouts. The
magnitude of the first phase observed from the lower lobe bronchus was less
than that observed from the trachea. These data are consistent with a
serial two-compartment transport model incorporating a limitation of
molecular diffusion between the peripheral and proximal compartments. The
more rapid clearance of less diffusible gases from the central airways
during the first phase of washout was due to slower transport from the
alveoli to the central airways rather than faster transport from the
central airways to the airway opening.
