Journal of Applied Physiology, Vol 40, Issue 4 525-532, Copyright © 1976 by American Physiological Society
Effect of aerosolized isoproterenol on resting myogenic tone in normals
A. M. Stamm, J. L. Clausen and G. M. Tisi
The effects of aerosolized isoproterenol on expiratory (exp) and
inspiratory (insp) conductance (Gaw), maximal exp and insp flow (VEmax and
VImax), and static elastic recoil pressure (Pst) were measured in 12
normals. Both exp and insp Gaw increased throughout the vital capacity (37%
at 50% VC; P less than 0.01). VEmax increased only at 50% VC (9%; P less
than 0.01). VImax and Pst did not change. Accordingly, a dichotomy existed
between the Gaw and Vmax changes during both exp and insp. We do not
attribute this dichotomy to loss of driving pressure or to
volume-time-dependent behavior of airway tone. We interpret the increased
exp and insp Gaw to indicate isoproterenol deposition within and
bronchodilatation of larger central airways (trachea, main stem, lobar,
segmental). Since insp Gaw increased and VImax did not, we conclude that
the caliber of these central airways is not the exclusive deteminant of
VImax, that the caliber of some more distal airways (subsegmental and
beyond) did not change, and that these airways are important determinants
of VImax. We conclude that non-uniform distribution of isoproterenol could
account for the Gaw-Vmax dichotomy during inspiration, and that such
non-uniform distribution coupled with resultant increased compliance and
compressibility of the downstream segment could account for the Faw-Vmax
dichotomy during expiration.
