Journal of Applied Physiology, Vol 71, Issue 5 1774-1779, Copyright © 1991 by American Physiological Society
Occlusion pressure response to inspiratory flow-resistive loading in anesthetized swine
B. S. Segal, J. G. Inman and I. R. Moss
Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas 75235-9063.
Conscious animals subjected to inspiratory flow-resistive loading augment
respiratory drive [as measured by airway occlusion pressure (P100)]
independently of changes in chemical drive. Past studies of anesthetized
subjects, however, have failed to demonstrate this response, and
investigators have concluded that its presence depends on a state of
consciousness. We tested the hypothesis that respiratory depression due to
anesthesia or endogenous opioids rather than unconsciousness per se was
responsible for this observation. Miniature piglets were anesthetized with
ketamine and xylazine and subjected to hyperoxic CO2 rebreathing trials
with and without added inspiratory resistance, before and after treatment
with the opioid antagonist naltrexone. Before naltrexone there was a
parallel leftward shift in the occlusion pressure vs. PCO2 relationship
without a change in slope (delta P100/delta PCO2). After naltrexone there
was a 45.5 +/- 15% increase in slope with loading. Addition of incremental
doses of pentobarbital markedly reduced this increase in slope. We conclude
that anesthetized animals can demonstrate flow-resistive load compensation
in the form of augmented neuromuscular output not due to increased chemical
drive. Failure to observe this response in past studies may reflect
respiratory depression due to the anesthetic agents employed.
