Journal of Applied Physiology, Vol 56, Issue 2 506-512, Copyright © 1984 by American Physiological Society
Lung compliance changes on high-frequency ventilation in normal dogs
G. G. Weinmann, B. A. Simon and W. Mitzner
To test the hypothesis that high-frequency ventilation (HFV) promotes lung
stability we compared the temporal course of dynamic lung compliance
changes after two inflations on HFV with those occurring on conventional
mechanical ventilation (CMV) at two different lung volumes, specifically
with and without 5 cmH2O positive end-expiratory pressure (PEEP). In our
first set of experiments we ventilated six anesthetized paralyzed dogs
first with CMV, then with HFV, then again with CMV using tidal volumes of
15 ml/kg at rates of 16-18 times/min for CMV and less than 90 ml and a rate
of 15 Hz for HFV. In our second set of experiments we ventilated six dogs
for 4 h, the 1st h with CMV at 0 cmH2O end-expiratory pressure, the 2nd h
with CMV with 5 cmH2O PEEP, the 3rd h with HFV at the same mean pleural
pressure, and the 4th h again with CMV with 5 cmH2O PEEP. We found the
decreases in dynamic compliance with time following hyperinflations were
similar on HFV and CMV (P greater than 0.5) at both lung volumes. With the
lower lung volume the initial dynamic compliance following hyperinflation
also tended to fall progressively from one hour to the next despite the
inflations. However, with PEEP the initial dynamic compliance over
successive hours tended to rise from one hour to the next. We found that
changes in dynamic compliance were not necessarily reflected in the venous
admixture or alveolar to arterial O2 partial pressure gradients. We thus
conclude that lung stability in normal dogs is not improved during HFV, and
blood gases cannot be used to predict compliance changes.
