Effect of chronic resistive loading on hypoxic ventilatory
responsiveness.
Greenberg, Harly E., Rammohan S. Rao, Anthony L. Sica, Steven M.
Scharf.
Division of Pulmonary & Critical Care Medicine and Division of
Pediatric Research, Long Island Jewish Medical Center, Long Island
Campus for the Albert Einstein College of Medicine, New Hyde Park,
N.Y. 11040
APStracts 3:0496A, 1996.
Depression of ventilation mediated by endogenous opioids has been
observed acutely after resistive airway loading. We evaluated the
effects of chronically increased airway resistance on hypoxic
ventilatory responsiveness shortly after load imposition and 6 weeks
later. A circumferential tracheal band was placed in 200g rats
tripling tracheal resistance. Sham surgery was performed in controls.
Ventilation and the ventilatory response to hypoxia were measured
using barometric plethysmography at 2 days and 6 weeks post-surgery
in unanesthetized rats during room air and 12% O2, 5 % CO2 balance N2
exposure. Trials were performed with and without naloxone (1 mg/kg,
IP). Room air arterial blood gases demonstrated hypercapnia with
normoxia in obstructed rats at 2 days and 6 weeks post-surgery.
During hypoxia a 30 mmHg fall in PO2 occurred with no change in PCO2.
Hypoxic ventilatory responsiveness was suppressed in obstructed rats
at 2 days post-loading. Naloxone partially reversed this suppression.
However, at 6 weeks hypoxic responsiveness was not different from
control levels. Naloxone had a small effect on ventilatory pattern at
this time with no overall effect on hypoxic responsiveness. This was
in contrast to previously demonstrated long term suppression of CO2
sensitivity in this model which was partially reversible by naloxone
only during the immediate period after load imposition. Endogenous
opioids apparently modulate ventilatory control acutely after load
imposition. Their effect wanes with time despite persistence of
depressed CO2 sensitivity.
Received 11 December 1995; accepted in final form 26 September
1996.
APS Manuscript Number A1298-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 November 1996