Journal of Applied Physiology, Vol 66, Issue 5 2462-2467, Copyright © 1989 by American Physiological Society
High-frequency ventilation-induced apnea: interaction of frequency, volume, FRC, and CO2
P. W. Davenport and D. J. Dalziel
Department of Physiological Sciences, University of Florida, Gainesville 32610.
Apnea is often observed during high-frequency oscillatory ventilation
(HFOV). This study on anesthetized dogs varied the oscillator frequency (f)
and determined the stroke volume (SV) at which apnea occurred. Relaxation
functional residual capacity (FRC) and the eupneic breathing end-tidal CO2
level were held constant. Airway pressure and CO2 were measured from a side
port of the tracheostomy cannula. An arterial cannula was inserted for
blood gas analysis. Diaphragm electromyogram (EMG) was recorded with
bipolar electrodes. Apnea was defined as the absence of phasic diaphragm
EMG activity for a minimum of 60 s. During HFOV, SV was increased at each f
(5-40 Hz) until apnea occurred. The apnea inducing SV decreased as f
increased. SV was minimal at 25-30 Hz. Frequencies greater than 30 Hz
required increased SV to produce apnea. The f-SV curve was defined as the
apneic threshold. Increased FRC resulted in a downward shift (less SV at
the same f) in the apneic threshold. Elevated CO2 caused an upward shift
(more SV at the same f) in the apneic threshold. These results demonstrate
that the apnea elicited by HFOV is dependent on the interaction of
oscillator f and SV, the FRC, and CO2.
