Journal of Applied Physiology, Vol 65, Issue 1 179-186, Copyright © 1988 by American Physiological Society
Chemical and mechanical determinants of apnea during high-frequency ventilation
S. L. Thompson-Gorman, R. S. Fitzgerald and W. Mitzner
Division of Environmental Physiology, School of Hygiene and Public Health, Johns Hopkins Medical Institutions, Baltimore, Maryland 21205.
The factors responsible for the apnea observed during high-frequency
ventilation (HFV) were evaluated in 14 pentobarbital sodium-anesthetized
cats. A multiple logistic regression analysis provided an estimate of the
probability of apnea during HFV as a function of four respiratory
variables: mean airway pressure (Paw), tidal volume (VT), frequency, and
arterial PCO2 (PaCO2). When mean Paw was 2 cmH2O, PaCO2, VT, and their
interaction contributed significantly to the probability of apnea during
HFV. At a low value of PaCO2 (25 Torr), the probability of apnea had a
minimum value of 0.19 and gradually increased toward 1.0 as VT increased
from 0.5 to 7 ml/kg. At higher levels of PaCO2 (30 and 35 Torr) the
probability of apnea was zero in the low range of VT but sharply approached
1.0 above a VT of approximately 2.0 ml/kg. However, when Paw was increased
to 6 cmH2O, only PaCO2 was an important determinant of apnea. In this case,
the probability of apnea was 0.51 when PaCO2 was 25 Torr but decreased to
0.22 when PaCO2 was raised to 25 Torr. At neither Paw was the probability
of apnea dependent on frequency. These results suggest that chemoreceptor
inputs, in addition to both static and dynamic lung mechanoreceptor
afferents, are responsible for determining the output of the central
respiratory centers during HFV.
