Journal of Applied Physiology, Vol 66, Issue 2 755-758, Copyright © 1989 by American Physiological Society
Influence of muscle activity on the elastance of the upper airway of rabbits
L. G. Olson, L. G. Ulmer and N. A. Saunders
Faculty of Medicine, University of Newcastle, New South Wales, Australia.
This study sought to assess the effect of variations in upper airway muscle
activity on upper airway pressure-volume properties. Upper airway
elastance, closing pressure, and reserve volume were measured in the
isolated upper airways of anesthetized rabbits under control conditions and
after administration of gallamine (2 mg/kg iv) or after 10 min of
spontaneous respiration of 7% CO2 in O2. Administration of gallamine to
seven animals was associated with a fall in reserve volume from 0.94 +/-
0.24 to 0.69 +/- 0.17 (95% confidence interval) ml (P less than 0.01) and
of closing pressure from -7.53 +/- 0.23 to -5.75 +/- 1.05 cmH2O (P less
than 0.01), but airway elastance did not change significantly. Hypercapnia
in seven animals was associated with a rise in elastance from 7.06 +/- 0.91
to 7.67 +/- 0.86 cmH2O/ml (P less than 0.001) and in reserve volume from
0.68 +/- 0.06 to 0.86 +/- 0.13 ml (P less than 0.05). Closing pressure also
changed from -5.88 +/- 0.94 to -7.92 +/- 1.85 cmH2O. This change was
correlated with the change in reserve volume but not with the change in
elastance. In three animals exposed to hypercapnia, return to room air
breathing was associated with return of elastance, reserve volume, and
closing pressure to control levels. It is concluded that muscle activity in
the upper airway affects both the size and elastance of the airway, but the
dominant mechanism by which upper airway muscles increase the resistance of
the upper airway to collapse is by increasing airway volume.
