Journal of Applied Physiology, Vol 58, Issue 2 605-611, Copyright © 1985 by American Physiological Society
Effect of expiratory loading on glottic dimensions in humans
T. P. Brancatisano, D. S. Dodd, P. W. Collett and L. A. Engel
We examined the effects of external mechanical loading on glottic
dimensions in 13 normal subjects. When flow-resistive loads of 7, 27, and
48 cmH2O X l-1 X s, measured at 0.2 l/s, were applied during expiration,
glottic width at the mid-tidal volume point in expiration (dge) was 2.3 +/-
12, 37.9 +/- 7.5, and 38.3 +/- 8.9% (means +/- SE) less than the control
dge, respectively. Simultaneously, mouth pressure (Pm) increased by 2.5 +/-
4, 3.0 +/- 0.4, and 4.6 +/- 0.6 cmH2O, respectively. When subjects were
switched from a resistance to a positive end-expiratory pressure at
comparable values of Pm, both dge and expiratory flow returned to control
values, whereas the level of hyperinflation remained constant. Glottic
width during inspiration (unloaded) did not change on any of the resistive
loads. There was a slight inverse relationship between the ratio of
expiratory to inspiratory glottic width and the ratio of expiratory to
inspiratory duration. Our results show noncompensatory glottic narrowing
when subjects breathe against an expiratory resistance and suggest that the
glottic dimensions are influenced by the time course of lung emptying
during expiration. We speculate that the glottic constriction is related to
the increased activity of expiratory medullary neurons during loaded
expiration and, by increasing the internal impedance of the respiratory
system, may have a stabilizing function.
