Journal of Applied Physiology, Vol 58, Issue 4 1360-1371, Copyright © 1985 by American Physiological Society
Adaptation to reflex effects of prolonged lung inflation
M. A. Grippi, A. I. Pack, R. O. Davies and A. P. Fishman
Adaptation to the reflex effects of sustained changes in lung volume on
inspiratory duration (TI), expiratory duration (TE), and the phrenic
neurogram was examined. Test inflations in gallamine-paralyzed dogs
anesthetized with pentobarbital sodium were made during a 6-min trial while
the animal was not ventilated: 2 min at functional residual capacity (FRC),
2 min at elevated airway pressure, and 2 min back at FRC. The dogs were
hyperoxygenated and arterial PCO2 was kept constant by an infusion of tris
(hydroxymethyl) aminomethane. The maintained inflations produced minimal
changes in TI. On return to FRC, TI was prolonged in proportion to the
magnitude of the prior inflation. In contrast, inflation produced marked
prolongation of TE, which then adapted back toward preinflation values. On
return to FRC, TE shortened initially to values below control. This
shortening increased with greater prior lung inflations. The times to
reestablish steady-state values upon return to FRC differed for TI (14.8
+/- 4.6 s) and TE (33.8 +/- 12.7 s). The magnitude of the phrenic neurogram
at a fixed time from onset of inspiration and its slope were unchanged with
inflation. These results indicate that respiratory phase durations are
influenced not only by pulmonary afferent input within each respiratory
cycle but also by prior vagal afferent activity that engages central
processes with long, although different, time constants. Afferent input to
the slow central process controlling TI is not gated to only one phase of
the respiratory cycle.
